// Copyright Epic Games, Inc. All Rights Reserved.

#include "cachedisklayer.h"

#include <zencore/compactbinary.h>
#include <zencore/compactbinarybuilder.h>
#include <zencore/compactbinaryvalidation.h>
#include <zencore/compress.h>
#include <zencore/except.h>
#include <zencore/fmtutils.h>
#include <zencore/jobqueue.h>
#include <zencore/logging.h>
#include <zencore/scopeguard.h>
#include <zencore/trace.h>
#include <zencore/workthreadpool.h>
#include <zencore/xxhash.h>

#include <future>

//////////////////////////////////////////////////////////////////////////

namespace zen {
namespace {

#pragma pack(push)
#pragma pack(1)

	struct CacheBucketIndexHeader
	{
		static constexpr uint32_t ExpectedMagic	 = 0x75696478;	// 'uidx';
		static constexpr uint32_t Version2		 = 2;
		static constexpr uint32_t CurrentVersion = Version2;

		uint32_t Magic			  = ExpectedMagic;
		uint32_t Version		  = CurrentVersion;
		uint64_t EntryCount		  = 0;
		uint64_t LogPosition	  = 0;
		uint32_t PayloadAlignment = 0;
		uint32_t Checksum		  = 0;

		static uint32_t ComputeChecksum(const CacheBucketIndexHeader& Header)
		{
			return XXH32(&Header.Magic, sizeof(CacheBucketIndexHeader) - sizeof(uint32_t), 0xC0C0'BABA);
		}

		bool IsValid() const
		{
			if (Magic != ExpectedMagic)
			{
				return false;
			}

			if (Checksum != ComputeChecksum(*this))
			{
				return false;
			}

			if (PayloadAlignment == 0)
			{
				return false;
			}

			return true;
		}
	};

	static_assert(sizeof(CacheBucketIndexHeader) == 32);

	struct BucketMetaHeader
	{
		static constexpr uint32_t ExpectedMagic	 = 0x61'74'65'6d;  // 'meta';
		static constexpr uint32_t Version1		 = 1;
		static constexpr uint32_t CurrentVersion = Version1;

		uint32_t Magic		 = ExpectedMagic;
		uint32_t Version	 = CurrentVersion;
		uint64_t EntryCount	 = 0;
		uint64_t LogPosition = 0;
		uint32_t Padding	 = 0;
		uint32_t Checksum	 = 0;

		static uint32_t ComputeChecksum(const BucketMetaHeader& Header)
		{
			return XXH32(&Header.Magic, sizeof(BucketMetaHeader) - sizeof(uint32_t), 0xC0C0'BABA);
		}

		bool IsValid() const
		{
			if (Magic != ExpectedMagic)
			{
				return false;
			}

			if (Checksum != ComputeChecksum(*this))
			{
				return false;
			}

			if (Padding != 0)
			{
				return false;
			}

			return true;
		}
	};

	static_assert(sizeof(BucketMetaHeader) == 32);

#pragma pack(pop)

	//////////////////////////////////////////////////////////////////////////

	template<typename T>
	void Reset(T& V)
	{
		T Tmp;
		V.swap(Tmp);
	}

	const char* IndexExtension = ".uidx";
	const char* LogExtension   = ".slog";
	const char* MetaExtension  = ".meta";

	std::filesystem::path GetIndexPath(const std::filesystem::path& BucketDir, const std::string& BucketName)
	{
		return BucketDir / (BucketName + IndexExtension);
	}

	std::filesystem::path GetMetaPath(const std::filesystem::path& BucketDir, const std::string& BucketName)
	{
		return BucketDir / (BucketName + MetaExtension);
	}

	std::filesystem::path GetLogPath(const std::filesystem::path& BucketDir, const std::string& BucketName)
	{
		return BucketDir / (BucketName + LogExtension);
	}

	std::filesystem::path GetManifestPath(const std::filesystem::path& BucketDir, const std::string& BucketName)
	{
		ZEN_UNUSED(BucketName);
		return BucketDir / "zen_manifest";
	}

	bool ValidateCacheBucketIndexEntry(const DiskIndexEntry& Entry, std::string& OutReason)
	{
		if (Entry.Key == IoHash::Zero)
		{
			OutReason = fmt::format("Invalid hash key {}", Entry.Key.ToHexString());
			return false;
		}
		if (Entry.Location.Reserved != 0)
		{
			OutReason = fmt::format("Reserved field non-zero ({}) for entry {}", Entry.Location.Reserved, Entry.Key.ToHexString());
			return false;
		}
		if (Entry.Location.GetFlags() &
			~(DiskLocation::kStandaloneFile | DiskLocation::kStructured | DiskLocation::kTombStone | DiskLocation::kCompressed))
		{
			OutReason = fmt::format("Invalid flags {} for entry {}", Entry.Location.GetFlags(), Entry.Key.ToHexString());
			return false;
		}
		if (Entry.Location.IsFlagSet(DiskLocation::kTombStone))
		{
			return true;
		}
		if (Entry.Location.Reserved != 0)
		{
			OutReason = fmt::format("Invalid reserved field {} for entry {}", Entry.Location.Reserved, Entry.Key.ToHexString());
			return false;
		}
		uint64_t Size = Entry.Location.Size();
		if (Size == 0)
		{
			OutReason = fmt::format("Invalid size {} for entry {}", Size, Entry.Key.ToHexString());
			return false;
		}
		return true;
	}

	bool MoveAndDeleteDirectory(const std::filesystem::path& Dir)
	{
		int DropIndex = 0;
		do
		{
			if (!std::filesystem::exists(Dir))
			{
				return false;
			}

			std::string			  DroppedName		= fmt::format("[dropped]{}({})", Dir.filename().string(), DropIndex);
			std::filesystem::path DroppedBucketPath = Dir.parent_path() / DroppedName;
			if (std::filesystem::exists(DroppedBucketPath))
			{
				DropIndex++;
				continue;
			}

			std::error_code Ec;
			std::filesystem::rename(Dir, DroppedBucketPath, Ec);
			if (!Ec)
			{
				DeleteDirectories(DroppedBucketPath);
				return true;
			}
			// TODO: Do we need to bail at some point?
			zen::Sleep(100);
		} while (true);
	}
}  // namespace

namespace fs = std::filesystem;
using namespace std::literals;

class BucketManifestSerializer
{
	using MetaDataIndex	 = ZenCacheDiskLayer::CacheBucket::MetaDataIndex;
	using BucketMetaData = ZenCacheDiskLayer::CacheBucket::BucketMetaData;

	using PayloadIndex	= ZenCacheDiskLayer::CacheBucket::PayloadIndex;
	using BucketPayload = ZenCacheDiskLayer::CacheBucket::BucketPayload;

public:
	// We use this to indicate if a on disk bucket needs wiping
	// In version 0.2.5 -> 0.2.11 there was a GC corruption bug that would scramble the references
	// to block items.
	// See: https://github.com/EpicGames/zen/pull/299
	static inline const uint32_t CurrentDiskBucketVersion = 1;

	bool Open(std::filesystem::path ManifestPath)
	{
		Manifest = LoadCompactBinaryObject(ManifestPath);
		return !!Manifest;
	}

	Oid GetBucketId() const { return Manifest["BucketId"sv].AsObjectId(); }

	bool IsCurrentVersion(uint32_t& OutVersion) const
	{
		OutVersion = Manifest["Version"sv].AsUInt32(0);
		return OutVersion == CurrentDiskBucketVersion;
	}

	void ParseManifest(ZenCacheDiskLayer::CacheBucket&							   Bucket,
					   std::filesystem::path									   ManifestPath,
					   ZenCacheDiskLayer::CacheBucket::IndexMap&				   Index,
					   std::vector<AccessTime>&									   AccessTimes,
					   std::vector<ZenCacheDiskLayer::CacheBucket::BucketPayload>& Payloads);

	Oid GenerateNewManifest(std::filesystem::path ManifestPath);

	IoBuffer MakeSidecarManifest(const Oid& BucketId, uint64_t EntryCount);
	uint64_t GetSidecarSize() const { return m_ManifestEntryCount * sizeof(ManifestData); }
	void	 WriteSidecarFile(const std::filesystem::path&										 SidecarPath,
							  uint64_t															 SnapshotLogPosition,
							  ZenCacheDiskLayer::CacheBucket::IndexMap&&						 Index,
							  std::vector<AccessTime>&&											 AccessTimes,
							  const std::vector<ZenCacheDiskLayer::CacheBucket::BucketPayload>&	 Payloads,
							  const std::vector<ZenCacheDiskLayer::CacheBucket::BucketMetaData>& MetaDatas);
	bool	 ReadSidecarFile(ZenCacheDiskLayer::CacheBucket&							 Bucket,
							 std::filesystem::path										 SidecarPath,
							 ZenCacheDiskLayer::CacheBucket::IndexMap&					 Index,
							 std::vector<AccessTime>&									 AccessTimes,
							 std::vector<ZenCacheDiskLayer::CacheBucket::BucketPayload>& Payloads);

	IoBuffer MakeManifest(const Oid&														 BucketId,
						  ZenCacheDiskLayer::CacheBucket::IndexMap&&						 Index,
						  std::vector<AccessTime>&&											 AccessTimes,
						  const std::vector<ZenCacheDiskLayer::CacheBucket::BucketPayload>&	 Payloads,
						  const std::vector<ZenCacheDiskLayer::CacheBucket::BucketMetaData>& MetaDatas);

	CbObject Manifest;

private:
	CbObject LoadCompactBinaryObject(const fs::path& Path)
	{
		FileContents Result = ReadFile(Path);

		if (!Result.ErrorCode)
		{
			IoBuffer Buffer = Result.Flatten();
			if (CbValidateError Error = ValidateCompactBinary(Buffer, CbValidateMode::All); Error == CbValidateError::None)
			{
				return zen::LoadCompactBinaryObject(Buffer);
			}
		}

		return CbObject();
	}

	uint64_t m_ManifestEntryCount = 0;

	struct ManifestData
	{
		IoHash	   Key;		   // 20
		AccessTime Timestamp;  // 4
		IoHash	   RawHash;	   // 20
		uint32_t   Padding_0;  // 4
		size_t	   RawSize;	   // 8
		uint64_t   Padding_1;  // 8
	};

	static_assert(sizeof(ManifestData) == 64);
};

void
BucketManifestSerializer::ParseManifest(ZenCacheDiskLayer::CacheBucket&								Bucket,
										std::filesystem::path										ManifestPath,
										ZenCacheDiskLayer::CacheBucket::IndexMap&					Index,
										std::vector<AccessTime>&									AccessTimes,
										std::vector<ZenCacheDiskLayer::CacheBucket::BucketPayload>& Payloads)
{
	if (Manifest["UsingMetaFile"sv].AsBool())
	{
		ReadSidecarFile(Bucket, GetMetaPath(Bucket.m_BucketDir, Bucket.m_BucketName), Index, AccessTimes, Payloads);

		return;
	}

	ZEN_TRACE_CPU("Z$::ParseManifest");

	Stopwatch  Timer;
	const auto _ = MakeGuard([&] { ZEN_INFO("parsed store manifest '{}' in {}", ManifestPath, NiceTimeSpanMs(Timer.GetElapsedTimeMs())); });

	const uint64_t			  Count = Manifest["Count"sv].AsUInt64(0);
	std::vector<PayloadIndex> KeysIndexes;
	KeysIndexes.reserve(Count);

	CbArrayView KeyArray = Manifest["Keys"sv].AsArrayView();
	for (CbFieldView& KeyView : KeyArray)
	{
		if (auto It = Index.find(KeyView.AsHash()); It != Index.end())
		{
			KeysIndexes.push_back(It.value());
		}
		else
		{
			KeysIndexes.push_back(PayloadIndex());
		}
	}

	size_t		KeyIndexOffset = 0;
	CbArrayView TimeStampArray = Manifest["Timestamps"].AsArrayView();
	for (CbFieldView& TimeStampView : TimeStampArray)
	{
		const PayloadIndex KeyIndex = KeysIndexes[KeyIndexOffset++];
		if (KeyIndex)
		{
			AccessTimes[KeyIndex] = TimeStampView.AsInt64();
		}
	}

	KeyIndexOffset			 = 0;
	CbArrayView RawHashArray = Manifest["RawHash"].AsArrayView();
	CbArrayView RawSizeArray = Manifest["RawSize"].AsArrayView();
	if (RawHashArray.Num() == RawSizeArray.Num())
	{
		auto RawHashIt = RawHashArray.CreateViewIterator();
		auto RawSizeIt = RawSizeArray.CreateViewIterator();
		while (RawHashIt != CbFieldViewIterator())
		{
			const PayloadIndex KeyIndex = KeysIndexes[KeyIndexOffset++];

			if (KeyIndex)
			{
				uint64_t RawSize = RawSizeIt.AsUInt64();
				IoHash	 RawHash = RawHashIt.AsHash();
				if (RawSize != 0 || RawHash != IoHash::Zero)
				{
					BucketPayload& Payload = Payloads[KeyIndex];
					Bucket.SetMetaData(Payload, BucketMetaData{.RawSize = RawSize, .RawHash = RawHash});
				}
			}

			RawHashIt++;
			RawSizeIt++;
		}
	}
	else
	{
		ZEN_WARN("Mismatch in size between 'RawHash' and 'RawSize' arrays in {}, skipping meta data", ManifestPath);
	}
}

Oid
BucketManifestSerializer::GenerateNewManifest(std::filesystem::path ManifestPath)
{
	const Oid BucketId = Oid::NewOid();

	CbObjectWriter Writer;
	Writer << "BucketId"sv << BucketId;
	Writer << "Version"sv << CurrentDiskBucketVersion;
	Manifest = Writer.Save();
	WriteFile(ManifestPath, Manifest.GetBuffer().AsIoBuffer());

	return BucketId;
}

IoBuffer
BucketManifestSerializer::MakeManifest(const Oid&														  BucketId,
									   ZenCacheDiskLayer::CacheBucket::IndexMap&&						  Index,
									   std::vector<AccessTime>&&										  AccessTimes,
									   const std::vector<ZenCacheDiskLayer::CacheBucket::BucketPayload>&  Payloads,
									   const std::vector<ZenCacheDiskLayer::CacheBucket::BucketMetaData>& MetaDatas)
{
	using namespace std::literals;

	ZEN_TRACE_CPU("Z$::MakeManifest");

	size_t ItemCount = Index.size();

	// This tends to overestimate a little bit but it is still way more accurate than what we get with exponential growth
	// And we don't need to reallocate the underlying buffer in almost every case
	const size_t   EstimatedSizePerItem = 54u;
	const size_t   ReserveSize			= ItemCount == 0 ? 48u : RoundUp(32u + (ItemCount * EstimatedSizePerItem), 128);
	CbObjectWriter Writer(ReserveSize);

	Writer << "BucketId"sv << BucketId;
	Writer << "Version"sv << CurrentDiskBucketVersion;

	if (!Index.empty())
	{
		Writer.AddInteger("Count"sv, gsl::narrow<std::uint64_t>(Index.size()));
		Writer.BeginArray("Keys"sv);
		for (auto& Kv : Index)
		{
			const IoHash& Key = Kv.first;
			Writer.AddHash(Key);
		}
		Writer.EndArray();

		Writer.BeginArray("Timestamps"sv);
		for (auto& Kv : Index)
		{
			GcClock::Tick AccessTime = AccessTimes[Kv.second];
			Writer.AddInteger(AccessTime);
		}
		Writer.EndArray();

		if (!MetaDatas.empty())
		{
			Writer.BeginArray("RawHash"sv);
			for (auto& Kv : Index)
			{
				const ZenCacheDiskLayer::CacheBucket::BucketPayload& Payload = Payloads[Kv.second];
				if (Payload.MetaData)
				{
					Writer.AddHash(MetaDatas[Payload.MetaData].RawHash);
				}
				else
				{
					Writer.AddHash(IoHash::Zero);
				}
			}
			Writer.EndArray();

			Writer.BeginArray("RawSize"sv);
			for (auto& Kv : Index)
			{
				const ZenCacheDiskLayer::CacheBucket::BucketPayload& Payload = Payloads[Kv.second];
				if (Payload.MetaData)
				{
					Writer.AddInteger(MetaDatas[Payload.MetaData].RawSize);
				}
				else
				{
					Writer.AddInteger(0);
				}
			}
			Writer.EndArray();
		}
	}

	Manifest = Writer.Save();
	return Manifest.GetBuffer().AsIoBuffer();
}

IoBuffer
BucketManifestSerializer::MakeSidecarManifest(const Oid& BucketId, uint64_t EntryCount)
{
	m_ManifestEntryCount = EntryCount;

	CbObjectWriter Writer;
	Writer << "BucketId"sv << BucketId;
	Writer << "Version"sv << CurrentDiskBucketVersion;
	Writer << "Count"sv << EntryCount;
	Writer << "UsingMetaFile"sv << true;
	Manifest = Writer.Save();

	return Manifest.GetBuffer().AsIoBuffer();
}

bool
BucketManifestSerializer::ReadSidecarFile(ZenCacheDiskLayer::CacheBucket&							  Bucket,
										  std::filesystem::path										  SidecarPath,
										  ZenCacheDiskLayer::CacheBucket::IndexMap&					  Index,
										  std::vector<AccessTime>&									  AccessTimes,
										  std::vector<ZenCacheDiskLayer::CacheBucket::BucketPayload>& Payloads)
{
	ZEN_ASSERT(AccessTimes.size() == Payloads.size());

	std::error_code Ec;

	BasicFile SidecarFile;
	SidecarFile.Open(SidecarPath, BasicFile::Mode::kRead, Ec);

	if (Ec)
	{
		throw std::system_error(Ec, fmt::format("failed to open sidecar file '{}'", SidecarPath));
	}

	uint64_t FileSize = SidecarFile.FileSize();

	auto InvalidGuard = MakeGuard([&] { ZEN_WARN("skipping invalid sidecar file '{}'", SidecarPath); });

	if (FileSize < sizeof(BucketMetaHeader))
	{
		return false;
	}

	BasicFileBuffer Sidecar(SidecarFile, 128 * 1024);

	BucketMetaHeader Header;
	Sidecar.Read(&Header, sizeof Header, 0);

	if (!Header.IsValid())
	{
		return false;
	}

	if (Header.Version != BucketMetaHeader::Version1)
	{
		return false;
	}

	const uint64_t ExpectedEntryCount = (FileSize - sizeof(sizeof(BucketMetaHeader))) / sizeof(ManifestData);
	if (Header.EntryCount > ExpectedEntryCount)
	{
		return false;
	}

	InvalidGuard.Dismiss();

	uint64_t RemainingEntryCount = ExpectedEntryCount;
	uint64_t EntryCount			 = 0;
	uint64_t CurrentReadOffset	 = sizeof(Header);

	while (RemainingEntryCount--)
	{
		const ManifestData* Entry = Sidecar.MakeView<ManifestData>(CurrentReadOffset);
		CurrentReadOffset += sizeof(ManifestData);

		if (auto It = Index.find(Entry->Key); It != Index.end())
		{
			PayloadIndex PlIndex = It.value();

			ZEN_ASSERT(size_t(PlIndex) <= Payloads.size());

			ZenCacheDiskLayer::CacheBucket::BucketPayload& PayloadEntry = Payloads[PlIndex];

			AccessTimes[PlIndex] = Entry->Timestamp;

			if (Entry->RawSize && Entry->RawHash != IoHash::Zero)
			{
				Bucket.SetMetaData(PayloadEntry, BucketMetaData{.RawSize = Entry->RawSize, .RawHash = Entry->RawHash});
			}
		}

		EntryCount++;
	}

	ZEN_ASSERT(EntryCount == ExpectedEntryCount);

	return true;
}

void
BucketManifestSerializer::WriteSidecarFile(const std::filesystem::path&										  SidecarPath,
										   uint64_t															  SnapshotLogPosition,
										   ZenCacheDiskLayer::CacheBucket::IndexMap&&						  Index,
										   std::vector<AccessTime>&&										  AccessTimes,
										   const std::vector<ZenCacheDiskLayer::CacheBucket::BucketPayload>&  Payloads,
										   const std::vector<ZenCacheDiskLayer::CacheBucket::BucketMetaData>& MetaDatas)
{
	BucketMetaHeader Header;
	Header.EntryCount  = m_ManifestEntryCount;
	Header.LogPosition = SnapshotLogPosition;
	Header.Checksum	   = Header.ComputeChecksum(Header);

	std::error_code Ec;

	TemporaryFile SidecarFile;
	SidecarFile.CreateTemporary(SidecarPath.parent_path(), Ec);

	if (Ec)
	{
		throw std::system_error(Ec, fmt::format("failed creating '{}'", SidecarFile.GetPath()));
	}

	SidecarFile.Write(&Header, sizeof Header, 0);

	// TODO: make this batching for better performance
	{
		uint64_t WriteOffset = sizeof Header;

		BasicFileWriter SidecarWriter(SidecarFile, 128 * 1024);

		for (auto& Kv : Index)
		{
			const IoHash&	   Key	   = Kv.first;
			const PayloadIndex PlIndex = Kv.second;

			IoHash	 RawHash = IoHash::Zero;
			uint64_t RawSize = 0;

			if (const MetaDataIndex MetaIndex = Payloads[PlIndex].MetaData)
			{
				RawHash = MetaDatas[MetaIndex].RawHash;
				RawSize = MetaDatas[MetaIndex].RawSize;
			}

			ManifestData ManifestEntry =
				{.Key = Key, .Timestamp = AccessTimes[PlIndex], .RawHash = RawHash, .Padding_0 = 0, .RawSize = RawSize, .Padding_1 = 0};

			SidecarWriter.Write(&ManifestEntry, sizeof ManifestEntry, WriteOffset);

			WriteOffset += sizeof ManifestEntry;
		}
	}

	SidecarFile.MoveTemporaryIntoPlace(SidecarPath, Ec);

	if (Ec)
	{
		throw std::system_error(Ec, fmt::format("failed to move '{}' into '{}'", SidecarFile.GetPath(), SidecarPath));
	}
}

//////////////////////////////////////////////////////////////////////////

ZenCacheDiskLayer::CacheBucket::CacheBucket(GcManager&				   Gc,
											std::atomic_uint64_t&	   OuterCacheMemoryUsage,
											std::string				   BucketName,
											const BucketConfiguration& Config)
: m_Gc(Gc)
, m_OuterCacheMemoryUsage(OuterCacheMemoryUsage)
, m_BucketName(std::move(BucketName))
, m_Configuration(Config)
, m_BucketId(Oid::Zero)
{
	if (m_BucketName.starts_with(std::string_view("legacy")) || m_BucketName.ends_with(std::string_view("shadermap")))
	{
		const uint64_t LegacyOverrideSize = 16 * 1024 * 1024;

		// This is pretty ad hoc but in order to avoid too many individual files
		// it makes sense to have a different strategy for legacy values
		m_Configuration.LargeObjectThreshold = Max(m_Configuration.LargeObjectThreshold, LegacyOverrideSize);
	}
	m_Gc.AddGcReferencer(*this);
}

ZenCacheDiskLayer::CacheBucket::~CacheBucket()
{
	m_Gc.RemoveGcReferencer(*this);
}

bool
ZenCacheDiskLayer::CacheBucket::OpenOrCreate(std::filesystem::path BucketDir, bool AllowCreate)
{
	using namespace std::literals;

	ZEN_TRACE_CPU("Z$::Disk::Bucket::OpenOrCreate");

	ZEN_LOG_SCOPE("opening cache bucket '{}'", BucketDir);

	m_BlocksBasePath = BucketDir / "blocks";
	m_BucketDir		 = BucketDir;

	CreateDirectories(m_BucketDir);

	std::filesystem::path ManifestPath = GetManifestPath(m_BucketDir, m_BucketName);

	bool IsNew = false;

	BucketManifestSerializer ManifestReader;

	if (ManifestReader.Open(ManifestPath))
	{
		m_BucketId = ManifestReader.GetBucketId();
		if (m_BucketId == Oid::Zero)
		{
			return false;
		}

		uint32_t Version = 0;
		if (ManifestReader.IsCurrentVersion(/* out */ Version) == false)
		{
			ZEN_INFO("Wiping bucket '{}', found version {}, required version {}",
					 BucketDir,
					 Version,
					 BucketManifestSerializer::CurrentDiskBucketVersion);
			IsNew = true;
		}
	}
	else if (AllowCreate)
	{
		m_BucketId = ManifestReader.GenerateNewManifest(ManifestPath);
		IsNew	   = true;
	}
	else
	{
		return false;
	}

	InitializeIndexFromDisk(IsNew);

	if (IsNew)
	{
		return true;
	}

	ManifestReader.ParseManifest(*this, ManifestPath, m_Index, m_AccessTimes, m_Payloads);

	return true;
}

void
ZenCacheDiskLayer::CacheBucket::WriteIndexSnapshot(const std::function<uint64_t()>& ClaimDiskReserveFunc)
{
	ZEN_TRACE_CPU("Z$::Disk::Bucket::WriteIndexSnapshot");

	const uint64_t LogCount = m_SlogFile.GetLogCount();
	if (m_LogFlushPosition == LogCount)
	{
		return;
	}

	ZEN_DEBUG("writing store snapshot for '{}'", m_BucketDir);
	const uint64_t EntryCount = m_Index.size();
	Stopwatch	   Timer;
	const auto	   _ = MakeGuard([&] {
		ZEN_INFO("wrote store snapshot for '{}' containing {} entries in {}",
				 m_BucketDir,
				 EntryCount,
				 NiceTimeSpanMs(Timer.GetElapsedTimeMs()));
	});

	namespace fs = std::filesystem;

	fs::path IndexPath = GetIndexPath(m_BucketDir, m_BucketName);

	try
	{
		const uint64_t	IndexSize = sizeof(CacheBucketIndexHeader) + EntryCount * sizeof(DiskIndexEntry);
		std::error_code Error;
		DiskSpace		Space = DiskSpaceInfo(m_BucketDir, Error);
		if (Error)
		{
			throw std::system_error(Error, fmt::format("get disk space in '{}' FAILED", m_BucketDir));
		}

		bool EnoughSpace = Space.Free >= IndexSize + 1024 * 512;
		if (!EnoughSpace)
		{
			uint64_t ReclaimedSpace = ClaimDiskReserveFunc();
			EnoughSpace				= (Space.Free + ReclaimedSpace) >= IndexSize + 1024 * 512;
		}
		if (!EnoughSpace)
		{
			throw std::runtime_error(
				fmt::format("not enough free disk space in '{}' to save index of size {}", m_BucketDir, NiceBytes(IndexSize)));
		}

		TemporaryFile	ObjectIndexFile;
		std::error_code Ec;
		ObjectIndexFile.CreateTemporary(m_BucketDir, Ec);
		if (Ec)
		{
			throw std::system_error(Ec, fmt::format("failed to create new snapshot file in '{}'", m_BucketDir));
		}

		{
			// This is in a separate scope just to ensure IndexWriter goes out
			// of scope before the file is flushed/closed, in order to ensure
			// all data is written to the file
			BasicFileWriter IndexWriter(ObjectIndexFile, 128 * 1024);

			CacheBucketIndexHeader Header = {.EntryCount	   = EntryCount,
											 .LogPosition	   = LogCount,
											 .PayloadAlignment = gsl::narrow<uint32_t>(m_Configuration.PayloadAlignment)};

			Header.Checksum = CacheBucketIndexHeader::ComputeChecksum(Header);
			IndexWriter.Write(&Header, sizeof(CacheBucketIndexHeader), 0);

			uint64_t IndexWriteOffset = sizeof(CacheBucketIndexHeader);

			for (auto& Entry : m_Index)
			{
				DiskIndexEntry IndexEntry;
				IndexEntry.Key		= Entry.first;
				IndexEntry.Location = m_Payloads[Entry.second].Location;
				IndexWriter.Write(&IndexEntry, sizeof(DiskIndexEntry), IndexWriteOffset);

				IndexWriteOffset += sizeof(DiskIndexEntry);
			}

			IndexWriter.Flush();
		}

		ObjectIndexFile.Flush();
		ObjectIndexFile.MoveTemporaryIntoPlace(IndexPath, Ec);
		if (Ec)
		{
			std::filesystem::path TempFilePath = ObjectIndexFile.GetPath();
			ZEN_WARN("snapshot failed to rename new snapshot '{}' to '{}', reason: '{}'", TempFilePath, IndexPath, Ec.message());

			if (std::filesystem::is_regular_file(TempFilePath))
			{
				if (!std::filesystem::remove(TempFilePath, Ec) || Ec)
				{
					ZEN_WARN("snapshot failed to remove temporary file {}, reason: '{}'", TempFilePath, Ec.message());
				}
			}
		}
		else
		{
			// We must only update the log flush position once the snapshot write succeeds
			m_LogFlushPosition = LogCount;
		}
	}
	catch (std::exception& Err)
	{
		ZEN_WARN("snapshot FAILED, reason: '{}'", Err.what());
	}
}

uint64_t
ZenCacheDiskLayer::CacheBucket::ReadIndexFile(const std::filesystem::path& IndexPath, uint32_t& OutVersion)
{
	ZEN_TRACE_CPU("Z$::Disk::Bucket::ReadIndexFile");

	if (!std::filesystem::is_regular_file(IndexPath))
	{
		return 0;
	}

	auto InvalidGuard = MakeGuard([&] { ZEN_WARN("skipping invalid index file '{}'", IndexPath); });

	BasicFile ObjectIndexFile;
	ObjectIndexFile.Open(IndexPath, BasicFile::Mode::kRead);
	uint64_t FileSize = ObjectIndexFile.FileSize();
	if (FileSize < sizeof(CacheBucketIndexHeader))
	{
		return 0;
	}

	CacheBucketIndexHeader Header;
	ObjectIndexFile.Read(&Header, sizeof(Header), 0);

	if (!Header.IsValid())
	{
		return 0;
	}

	if (Header.Version != CacheBucketIndexHeader::Version2)
	{
		return 0;
	}

	const uint64_t ExpectedEntryCount = (FileSize - sizeof(sizeof(CacheBucketIndexHeader))) / sizeof(DiskIndexEntry);
	if (Header.EntryCount > ExpectedEntryCount)
	{
		return 0;
	}

	InvalidGuard.Dismiss();

	size_t	   EntryCount = 0;
	Stopwatch  Timer;
	const auto _ = MakeGuard([&] {
		ZEN_INFO("read store '{}' index containing {} entries in {}", IndexPath, EntryCount, NiceTimeSpanMs(Timer.GetElapsedTimeMs()));
	});

	m_Configuration.PayloadAlignment = Header.PayloadAlignment;

	m_Payloads.reserve(Header.EntryCount);
	m_Index.reserve(Header.EntryCount);

	BasicFileBuffer FileBuffer(ObjectIndexFile, 128 * 1024);

	uint64_t CurrentReadOffset	 = sizeof(CacheBucketIndexHeader);
	uint64_t RemainingEntryCount = Header.EntryCount;

	std::string InvalidEntryReason;
	while (RemainingEntryCount--)
	{
		const DiskIndexEntry* Entry = FileBuffer.MakeView<DiskIndexEntry>(CurrentReadOffset);
		CurrentReadOffset += sizeof(DiskIndexEntry);

		if (!ValidateCacheBucketIndexEntry(*Entry, InvalidEntryReason))
		{
			ZEN_WARN("skipping invalid entry in '{}', reason: '{}'", IndexPath, InvalidEntryReason);
			continue;
		}

		const PayloadIndex EntryIndex = PayloadIndex(EntryCount);
		m_Payloads.emplace_back(BucketPayload{.Location = Entry->Location});
		m_Index.insert_or_assign(Entry->Key, EntryIndex);

		EntryCount++;
	}

	ZEN_ASSERT(EntryCount == m_Payloads.size());

	m_AccessTimes.resize(EntryCount, AccessTime(GcClock::TickCount()));

	if (m_Configuration.EnableReferenceCaching)
	{
		m_FirstReferenceIndex.resize(EntryCount);
	}

	OutVersion = CacheBucketIndexHeader::Version2;
	return Header.LogPosition;
}

uint64_t
ZenCacheDiskLayer::CacheBucket::ReadLog(const std::filesystem::path& LogPath, uint64_t SkipEntryCount)
{
	ZEN_TRACE_CPU("Z$::Disk::Bucket::ReadLog");

	if (!std::filesystem::is_regular_file(LogPath))
	{
		return 0;
	}

	uint64_t   LogEntryCount = 0;
	Stopwatch  Timer;
	const auto _ = MakeGuard([&] {
		ZEN_INFO("read store '{}' log containing {} entries in {}", LogPath, LogEntryCount, NiceTimeSpanMs(Timer.GetElapsedTimeMs()));
	});

	TCasLogFile<DiskIndexEntry> CasLog;
	CasLog.Open(LogPath, CasLogFile::Mode::kRead);
	if (!CasLog.Initialize())
	{
		return 0;
	}

	const uint64_t EntryCount = CasLog.GetLogCount();
	if (EntryCount < SkipEntryCount)
	{
		ZEN_WARN("reading full log at '{}', reason: Log position from index snapshot is out of range", LogPath);
		SkipEntryCount = 0;
	}

	LogEntryCount			   = EntryCount - SkipEntryCount;
	uint64_t InvalidEntryCount = 0;

	CasLog.Replay(
		[&](const DiskIndexEntry& Record) {
			std::string InvalidEntryReason;
			if (Record.Location.Flags & DiskLocation::kTombStone)
			{
				// Note: this leaves m_Payloads and other arrays with 'holes' in them
				m_Index.erase(Record.Key);
				return;
			}

			if (!ValidateCacheBucketIndexEntry(Record, InvalidEntryReason))
			{
				ZEN_WARN("skipping invalid entry in '{}', reason: '{}'", LogPath, InvalidEntryReason);
				++InvalidEntryCount;
				return;
			}
			PayloadIndex EntryIndex = PayloadIndex(m_Payloads.size());
			m_Payloads.emplace_back(BucketPayload{.Location = Record.Location});
			m_Index.insert_or_assign(Record.Key, EntryIndex);
		},
		SkipEntryCount);

	m_AccessTimes.resize(m_Payloads.size(), AccessTime(GcClock::TickCount()));

	if (m_Configuration.EnableReferenceCaching)
	{
		m_FirstReferenceIndex.resize(m_Payloads.size());
	}

	if (InvalidEntryCount)
	{
		ZEN_WARN("found {} invalid entries in '{}'", InvalidEntryCount, m_BucketDir);
	}

	return LogEntryCount;
};

void
ZenCacheDiskLayer::CacheBucket::InitializeIndexFromDisk(const bool IsNew)
{
	ZEN_TRACE_CPU("Z$::Disk::Bucket::OpenLog");

	m_StandaloneSize = 0;

	m_Index.clear();
	m_Payloads.clear();
	m_AccessTimes.clear();
	m_MetaDatas.clear();
	m_FreeMetaDatas.clear();
	m_MemCachedPayloads.clear();
	m_FreeMemCachedPayloads.clear();
	m_FirstReferenceIndex.clear();
	m_ReferenceHashes.clear();
	m_NextReferenceHashesIndexes.clear();
	m_ReferenceCount = 0;

	std::filesystem::path LogPath	= GetLogPath(m_BucketDir, m_BucketName);
	std::filesystem::path IndexPath = GetIndexPath(m_BucketDir, m_BucketName);

	if (IsNew)
	{
		fs::remove(LogPath);
		fs::remove(IndexPath);
		fs::remove_all(m_BlocksBasePath);
	}

	CreateDirectories(m_BucketDir);

	m_BlockStore.Initialize(m_BlocksBasePath, m_Configuration.MaxBlockSize, BlockStoreDiskLocation::MaxBlockIndex + 1);

	if (std::filesystem::is_regular_file(IndexPath))
	{
		uint32_t IndexVersion = 0;
		m_LogFlushPosition	  = ReadIndexFile(IndexPath, IndexVersion);
		if (IndexVersion == 0)
		{
			ZEN_WARN("removing invalid index file at '{}'", IndexPath);
			std::filesystem::remove(IndexPath);
		}
	}

	uint64_t LogEntryCount = 0;
	if (std::filesystem::is_regular_file(LogPath))
	{
		if (TCasLogFile<DiskIndexEntry>::IsValid(LogPath))
		{
			LogEntryCount = ReadLog(LogPath, m_LogFlushPosition);
		}
		else if (fs::is_regular_file(LogPath))
		{
			ZEN_WARN("removing invalid log at '{}'", LogPath);
			std::filesystem::remove(LogPath);
		}
	}

	m_SlogFile.Open(LogPath, CasLogFile::Mode::kWrite);

	BlockStore::BlockIndexSet KnownBlocks;
	for (const auto& Entry : m_Index)
	{
		size_t				 EntryIndex = Entry.second;
		const BucketPayload& Payload	= m_Payloads[EntryIndex];
		const DiskLocation&	 Location	= Payload.Location;

		if (Location.IsFlagSet(DiskLocation::kStandaloneFile))
		{
			m_StandaloneSize.fetch_add(Location.Size(), std::memory_order::relaxed);
		}
		else
		{
			const BlockStoreLocation& BlockLocation = Location.GetBlockLocation(m_Configuration.PayloadAlignment);
			KnownBlocks.Add(BlockLocation.BlockIndex);
		}
	}
	m_BlockStore.SyncExistingBlocksOnDisk(KnownBlocks);

	if (IsNew || LogEntryCount > 0)
	{
		WriteIndexSnapshot();
	}
}

void
ZenCacheDiskLayer::CacheBucket::BuildPath(PathBuilderBase& Path, const IoHash& HashKey) const
{
	char HexString[sizeof(HashKey.Hash) * 2];
	ToHexBytes(HashKey.Hash, sizeof HashKey.Hash, HexString);

	Path.Append(m_BucketDir);
	Path.AppendSeparator();
	Path.Append(L"blob");
	Path.AppendSeparator();
	Path.AppendAsciiRange(HexString, HexString + 3);
	Path.AppendSeparator();
	Path.AppendAsciiRange(HexString + 3, HexString + 5);
	Path.AppendSeparator();
	Path.AppendAsciiRange(HexString + 5, HexString + sizeof(HexString));
}

IoBuffer
ZenCacheDiskLayer::CacheBucket::GetInlineCacheValue(const DiskLocation& Loc) const
{
	ZEN_TRACE_CPU("Z$::Disk::Bucket::GetInlineCacheValue");

	BlockStoreLocation Location = Loc.GetBlockLocation(m_Configuration.PayloadAlignment);

	IoBuffer Value = m_BlockStore.TryGetChunk(Location);
	if (Value)
	{
		Value.SetContentType(Loc.GetContentType());
	}

	return Value;
}

IoBuffer
ZenCacheDiskLayer::CacheBucket::GetStandaloneCacheValue(ZenContentType ContentType, const IoHash& HashKey) const
{
	ZEN_TRACE_CPU("Z$::Disk::Bucket::GetStandaloneCacheValue");

	ExtendablePathBuilder<256> DataFilePath;
	BuildPath(DataFilePath, HashKey);

	RwLock::SharedLockScope ValueLock(LockForHash(HashKey));

	if (IoBuffer Data = IoBufferBuilder::MakeFromFile(DataFilePath.ToPath()))
	{
		Data.SetContentType(ContentType);

		return Data;
	}

	return {};
}

bool
ZenCacheDiskLayer::CacheBucket::Get(const IoHash& HashKey, ZenCacheValue& OutValue)
{
	metrics::RequestStats::Scope StatsScope(m_GetOps, 0);

	RwLock::SharedLockScope IndexLock(m_IndexLock);
	auto					It = m_Index.find(HashKey);
	if (It == m_Index.end())
	{
		m_DiskMissCount++;
		if (m_Configuration.MemCacheSizeThreshold > 0)
		{
			m_MemoryMissCount++;
		}
		return false;
	}

	size_t EntryIndex		  = It.value();
	m_AccessTimes[EntryIndex] = GcClock::TickCount();
	DiskLocation Location	  = m_Payloads[EntryIndex].Location;

	bool FillRawHashAndRawSize = (!Location.IsFlagSet(DiskLocation::kStructured)) && (Location.Size() > 0);

	const BucketPayload* Payload = &m_Payloads[EntryIndex];
	if (Payload->MetaData)
	{
		const BucketMetaData& MetaData = m_MetaDatas[Payload->MetaData];
		OutValue.RawHash			   = MetaData.RawHash;
		OutValue.RawSize			   = MetaData.RawSize;
		FillRawHashAndRawSize		   = false;
	}

	if (Payload->MemCached)
	{
		OutValue.Value = m_MemCachedPayloads[Payload->MemCached];
		Payload		   = nullptr;
		IndexLock.ReleaseNow();
		m_MemoryHitCount++;
	}
	else
	{
		Payload = nullptr;
		IndexLock.ReleaseNow();
		if (m_Configuration.MemCacheSizeThreshold > 0)
		{
			m_MemoryMissCount++;
		}
		if (Location.IsFlagSet(DiskLocation::kStandaloneFile))
		{
			OutValue.Value = GetStandaloneCacheValue(Location.GetContentType(), HashKey);
		}
		else
		{
			OutValue.Value = GetInlineCacheValue(Location);
			if (m_Configuration.MemCacheSizeThreshold > 0)
			{
				size_t ValueSize = OutValue.Value.GetSize();
				if (OutValue.Value && ValueSize <= m_Configuration.MemCacheSizeThreshold)
				{
					ZEN_TRACE_CPU("Z$::Disk::Bucket::Get::MemCache");
					OutValue.Value = IoBufferBuilder::ReadFromFileMaybe(OutValue.Value);
					RwLock::ExclusiveLockScope _(m_IndexLock);
					if (auto UpdateIt = m_Index.find(HashKey); UpdateIt != m_Index.end())
					{
						BucketPayload& WritePayload = m_Payloads[EntryIndex];
						// Only update if it has not already been updated by other thread
						if (!WritePayload.MemCached)
						{
							SetMemCachedData(WritePayload, OutValue.Value);
						}
					}
				}
			}
		}
	}

	if (FillRawHashAndRawSize)
	{
		ZEN_TRACE_CPU("Z$::Disk::Bucket::Get::MetaData");
		if (Location.IsFlagSet(DiskLocation::kCompressed))
		{
			if (!CompressedBuffer::ValidateCompressedHeader(OutValue.Value, OutValue.RawHash, OutValue.RawSize))
			{
				OutValue = ZenCacheValue{};
				m_DiskMissCount++;
				return false;
			}
		}
		else
		{
			OutValue.RawHash = IoHash::HashBuffer(OutValue.Value);
			OutValue.RawSize = OutValue.Value.GetSize();
		}
		RwLock::ExclusiveLockScope __(m_IndexLock);
		if (auto WriteIt = m_Index.find(HashKey); WriteIt != m_Index.end())
		{
			BucketPayload& WritePayload = m_Payloads[WriteIt.value()];

			// Only set if no other path has already updated the meta data
			if (!WritePayload.MetaData)
			{
				SetMetaData(WritePayload, {.RawSize = OutValue.RawSize, .RawHash = OutValue.RawHash});
			}
		}
	}
	if (OutValue.Value)
	{
		m_DiskHitCount++;
		StatsScope.SetBytes(OutValue.Value.GetSize());
		return true;
	}
	else
	{
		m_DiskMissCount++;
		return false;
	}
}

void
ZenCacheDiskLayer::CacheBucket::Put(const IoHash& HashKey, const ZenCacheValue& Value, std::span<IoHash> References)
{
	metrics::RequestStats::Scope $(m_PutOps, Value.Value.Size());

	if (Value.Value.Size() >= m_Configuration.LargeObjectThreshold)
	{
		PutStandaloneCacheValue(HashKey, Value, References);
	}
	else
	{
		PutInlineCacheValue(HashKey, Value, References);
	}

	m_DiskWriteCount++;
}

void
ZenCacheDiskLayer::CacheBucket::MemCacheTrim(GcClock::TimePoint ExpireTime)
{
	GcClock::Tick ExpireTicks = ExpireTime.time_since_epoch().count();

	RwLock::ExclusiveLockScope _(m_IndexLock);
	for (const auto& Kv : m_Index)
	{
		if (m_AccessTimes[Kv.second] < ExpireTicks)
		{
			BucketPayload& Payload = m_Payloads[Kv.second];
			RemoveMemCachedData(Payload);
		}
	}
}

void
ZenCacheDiskLayer::CacheBucket::GetUsageByAccess(GcClock::TimePoint		TickStart,
												 GcClock::Duration		SectionLength,
												 std::vector<uint64_t>& InOutUsageSlots)
{
	RwLock::SharedLockScope _(m_IndexLock);
	for (const auto& It : m_Index)
	{
		size_t		   Index   = It.second;
		BucketPayload& Payload = m_Payloads[Index];
		if (!Payload.MemCached)
		{
			continue;
		}
		GcClock::TimePoint ItemAccessTime = GcClock::TimePointFromTick(GcClock::Tick(m_AccessTimes[Index]));
		GcClock::Duration  Age			  = TickStart.time_since_epoch() - ItemAccessTime.time_since_epoch();
		uint64_t		   Slot			  = gsl::narrow<uint64_t>(Age.count() > 0 ? Age.count() / SectionLength.count() : 0);
		if (Slot >= InOutUsageSlots.capacity())
		{
			Slot = InOutUsageSlots.capacity() - 1;
		}
		if (Slot > InOutUsageSlots.size())
		{
			InOutUsageSlots.resize(uint64_t(Slot + 1), 0);
		}
		InOutUsageSlots[Slot] += m_MemCachedPayloads[Payload.MemCached].GetSize();
	}
}

bool
ZenCacheDiskLayer::CacheBucket::Drop()
{
	ZEN_TRACE_CPU("Z$::Disk::Bucket::Drop");

	RwLock::ExclusiveLockScope _(m_IndexLock);

	std::vector<std::unique_ptr<RwLock::ExclusiveLockScope>> ShardLocks;
	ShardLocks.reserve(256);
	for (RwLock& Lock : m_ShardedLocks)
	{
		ShardLocks.push_back(std::make_unique<RwLock::ExclusiveLockScope>(Lock));
	}
	m_BlockStore.Close();
	m_SlogFile.Close();

	bool Deleted = MoveAndDeleteDirectory(m_BucketDir);

	m_Index.clear();
	m_Payloads.clear();
	m_AccessTimes.clear();
	m_MetaDatas.clear();
	m_FreeMetaDatas.clear();
	m_MemCachedPayloads.clear();
	m_FreeMemCachedPayloads.clear();
	m_FirstReferenceIndex.clear();
	m_ReferenceHashes.clear();
	m_NextReferenceHashesIndexes.clear();
	m_ReferenceCount = 0;
	m_StandaloneSize.store(0);
	m_OuterCacheMemoryUsage.fetch_sub(m_MemCachedSize.load());
	m_MemCachedSize.store(0);

	return Deleted;
}

void
ZenCacheDiskLayer::CacheBucket::Flush()
{
	ZEN_TRACE_CPU("Z$::Disk::Bucket::Flush");
	bool Expected = false;
	if (m_IsFlushing || !m_IsFlushing.compare_exchange_strong(Expected, true))
	{
		return;
	}
	auto FlushingGuard = MakeGuard([&] { m_IsFlushing.store(false); });

	ZEN_INFO("Flushing bucket {}", m_BucketDir);

	try
	{
		m_BlockStore.Flush(/*ForceNewBlock*/ false);
		m_SlogFile.Flush();

		SaveSnapshot();
	}
	catch (std::exception& Ex)
	{
		ZEN_WARN("Failed to flush bucket in '{}'. Reason: '{}'", m_BucketDir, Ex.what());
	}
}

void
ZenCacheDiskLayer::CacheBucket::SaveSnapshot(const std::function<uint64_t()>& ClaimDiskReserveFunc)
{
	try
	{
		bool	 UseLegacyScheme = false;
		uint64_t SidecarSize	 = 0;

		IoBuffer				 Buffer;
		BucketManifestSerializer ManifestWriter;

		{
			std::vector<AccessTime>		AccessTimes;
			std::vector<BucketPayload>	Payloads;
			std::vector<BucketMetaData> MetaDatas;
			IndexMap					Index;

			{
				RwLock::SharedLockScope IndexLock(m_IndexLock);
				WriteIndexSnapshot();
				// Note: this copy could be eliminated on shutdown to
				// reduce memory usage and execution time
				Index		= m_Index;
				Payloads	= m_Payloads;
				AccessTimes = m_AccessTimes;
				MetaDatas	= m_MetaDatas;
			}

			if (UseLegacyScheme)
			{
				Buffer = ManifestWriter.MakeManifest(m_BucketId, std::move(Index), std::move(AccessTimes), Payloads, MetaDatas);
			}
			else
			{
				const uint64_t EntryCount = Index.size();
				Buffer					  = ManifestWriter.MakeSidecarManifest(m_BucketId, EntryCount);
				SidecarSize				  = ManifestWriter.GetSidecarSize();
			}

			const uint64_t RequiredSpace = SidecarSize + Buffer.GetSize() + 1024 * 512;

			std::error_code Error;
			DiskSpace		Space = DiskSpaceInfo(m_BucketDir, Error);
			if (Error)
			{
				ZEN_WARN("get disk space in '{}' FAILED, reason: '{}'", m_BucketDir, Error.message());
				return;
			}
			bool EnoughSpace = Space.Free >= RequiredSpace;
			if (!EnoughSpace)
			{
				uint64_t ReclaimedSpace = ClaimDiskReserveFunc();
				EnoughSpace				= (Space.Free + ReclaimedSpace) >= RequiredSpace;
			}
			if (!EnoughSpace)
			{
				ZEN_WARN("not enough free disk space in '{}'. FAILED to save manifest of size {}",
						 m_BucketDir,
						 NiceBytes(Buffer.GetSize()));
				return;
			}

			if (!UseLegacyScheme)
			{
				ManifestWriter.WriteSidecarFile(GetMetaPath(m_BucketDir, m_BucketName),
												m_LogFlushPosition,
												std::move(Index),
												std::move(AccessTimes),
												Payloads,
												MetaDatas);
			}
		}

		std::filesystem::path ManifestPath = GetManifestPath(m_BucketDir, m_BucketName);
		WriteFile(ManifestPath, Buffer);
	}
	catch (std::exception& Err)
	{
		ZEN_WARN("writing manifest in '{}' FAILED, reason: '{}'", m_BucketDir, Err.what());
	}
}

IoHash
HashBuffer(const CompositeBuffer& Buffer)
{
	IoHashStream Hasher;

	for (const SharedBuffer& Segment : Buffer.GetSegments())
	{
		Hasher.Append(Segment.GetView());
	}

	return Hasher.GetHash();
}

bool
ValidateCacheBucketEntryValue(ZenContentType ContentType, IoBuffer Buffer)
{
	ZEN_ASSERT_SLOW(Buffer.GetContentType() == ContentType);

	if (ContentType == ZenContentType::kCbObject)
	{
		CbValidateError Error = ValidateCompactBinary(Buffer, CbValidateMode::All);

		if (Error == CbValidateError::None)
		{
			return true;
		}

		ZEN_SCOPED_ERROR("compact binary validation failed: '{}'", ToString(Error));

		return false;
	}
	else if (ContentType == ZenContentType::kCompressedBinary)
	{
		IoBuffer MemoryBuffer = IoBufferBuilder::ReadFromFileMaybe(Buffer);

		IoHash	 HeaderRawHash;
		uint64_t RawSize = 0;
		if (!CompressedBuffer::ValidateCompressedHeader(MemoryBuffer, /* out */ HeaderRawHash, /* out */ RawSize))
		{
			ZEN_SCOPED_ERROR("compressed buffer header validation failed");

			return false;
		}

		CompressedBuffer Compressed =
			CompressedBuffer::FromCompressed(SharedBuffer(MemoryBuffer), /* out */ HeaderRawHash, /* out */ RawSize);
		CompositeBuffer Decompressed	 = Compressed.DecompressToComposite();
		IoHash			DecompressedHash = HashBuffer(Decompressed);

		if (HeaderRawHash != DecompressedHash)
		{
			ZEN_SCOPED_ERROR("decompressed hash {} differs from header hash {}", DecompressedHash, HeaderRawHash);

			return false;
		}
	}
	else
	{
		// No way to verify this kind of content (what is it exactly?)

		static int Once = [&] {
			ZEN_WARN("ValidateCacheBucketEntryValue called with unknown content type ({})", ToString(ContentType));
			return 42;
		}();
	}

	return true;
};

void
ZenCacheDiskLayer::CacheBucket::ScrubStorage(ScrubContext& Ctx)
{
	ZEN_TRACE_CPU("Z$::Disk::Bucket::Scrub");

	ZEN_INFO("scrubbing '{}'", m_BucketDir);

	Stopwatch Timer;
	uint64_t  ChunkCount		 = 0;
	uint64_t  VerifiedChunkBytes = 0;

	auto LogStats = MakeGuard([&] {
		const uint32_t DurationMs = gsl::narrow<uint32_t>(Timer.GetElapsedTimeMs());

		ZEN_INFO("cache bucket '{}' scrubbed {}B in {} from {} chunks ({})",
				 m_BucketName,
				 NiceBytes(VerifiedChunkBytes),
				 NiceTimeSpanMs(DurationMs),
				 ChunkCount,
				 NiceRate(VerifiedChunkBytes, DurationMs));
	});

	std::vector<IoHash> BadKeys;
	auto				ReportBadKey = [&](const IoHash& Key) { BadKeys.push_back(Key); };

	try
	{
		std::vector<BlockStoreLocation> ChunkLocations;
		std::vector<IoHash>				ChunkIndexToChunkHash;

		RwLock::SharedLockScope _(m_IndexLock);

		const size_t BlockChunkInitialCount = m_Index.size() / 4;
		ChunkLocations.reserve(BlockChunkInitialCount);
		ChunkIndexToChunkHash.reserve(BlockChunkInitialCount);

		// Do a pass over the index and verify any standalone file values straight away
		// all other storage classes are gathered and verified in bulk in order to enable
		// more efficient I/O scheduling

		for (auto& Kv : m_Index)
		{
			const IoHash&		 HashKey = Kv.first;
			const BucketPayload& Payload = m_Payloads[Kv.second];
			const DiskLocation&	 Loc	 = Payload.Location;

			if (Loc.IsFlagSet(DiskLocation::kStandaloneFile))
			{
				Ctx.ThrowIfDeadlineExpired();

				++ChunkCount;
				VerifiedChunkBytes += Loc.Size();

				if (Loc.GetContentType() == ZenContentType::kBinary)
				{
					// Blob cache value, not much we can do about data integrity checking
					// here since there's no hash available
					ExtendablePathBuilder<256> DataFilePath;
					BuildPath(DataFilePath, HashKey);

					RwLock::SharedLockScope ValueLock(LockForHash(HashKey));

					std::error_code Ec;
					uintmax_t		size = std::filesystem::file_size(DataFilePath.ToPath(), Ec);
					if (Ec)
					{
						ReportBadKey(HashKey);
					}
					if (size != Loc.Size())
					{
						ReportBadKey(HashKey);
					}
					continue;
				}
				else
				{
					// Structured cache value
					IoBuffer Buffer = GetStandaloneCacheValue(Loc.GetContentType(), HashKey);
					if (!Buffer)
					{
						ReportBadKey(HashKey);
						continue;
					}
					if (!ValidateCacheBucketEntryValue(Loc.GetContentType(), Buffer))
					{
						ReportBadKey(HashKey);
						continue;
					}
				}
			}
			else
			{
				ChunkLocations.emplace_back(Loc.GetBlockLocation(m_Configuration.PayloadAlignment));
				ChunkIndexToChunkHash.push_back(HashKey);
				continue;
			}
		}

		const auto ValidateSmallChunk = [&](size_t ChunkIndex, const void* Data, uint64_t Size) -> void {
			++ChunkCount;
			VerifiedChunkBytes += Size;
			const IoHash& Hash = ChunkIndexToChunkHash[ChunkIndex];
			if (!Data)
			{
				// ChunkLocation out of range of stored blocks
				ReportBadKey(Hash);
				return;
			}
			if (!Size)
			{
				ReportBadKey(Hash);
				return;
			}
			IoBuffer Buffer(IoBuffer::Wrap, Data, Size);
			if (!Buffer)
			{
				ReportBadKey(Hash);
				return;
			}
			const BucketPayload& Payload	 = m_Payloads[m_Index.at(Hash)];
			ZenContentType		 ContentType = Payload.Location.GetContentType();
			Buffer.SetContentType(ContentType);
			if (!ValidateCacheBucketEntryValue(ContentType, Buffer))
			{
				ReportBadKey(Hash);
				return;
			}
		};

		const auto ValidateLargeChunk = [&](size_t ChunkIndex, BlockStoreFile& File, uint64_t Offset, uint64_t Size) -> void {
			Ctx.ThrowIfDeadlineExpired();

			++ChunkCount;
			VerifiedChunkBytes += Size;
			const IoHash& Hash = ChunkIndexToChunkHash[ChunkIndex];
			IoBuffer	  Buffer(IoBuffer::BorrowedFile, File.GetBasicFile().Handle(), Offset, Size);
			if (!Buffer)
			{
				ReportBadKey(Hash);
				return;
			}
			const BucketPayload& Payload	 = m_Payloads[m_Index.at(Hash)];
			ZenContentType		 ContentType = Payload.Location.GetContentType();
			Buffer.SetContentType(ContentType);
			if (!ValidateCacheBucketEntryValue(ContentType, Buffer))
			{
				ReportBadKey(Hash);
				return;
			}
		};

		m_BlockStore.IterateChunks(ChunkLocations, ValidateSmallChunk, ValidateLargeChunk);
	}
	catch (ScrubDeadlineExpiredException&)
	{
		ZEN_INFO("Scrubbing deadline expired, operation incomplete");
	}

	Ctx.ReportScrubbed(ChunkCount, VerifiedChunkBytes);

	if (!BadKeys.empty())
	{
		ZEN_WARN("Scrubbing found {} bad chunks in '{}'", BadKeys.size(), m_BucketDir);

		if (Ctx.RunRecovery())
		{
			// Deal with bad chunks by removing them from our lookup map

			std::vector<DiskIndexEntry> LogEntries;
			LogEntries.reserve(BadKeys.size());

			{
				RwLock::ExclusiveLockScope IndexLock(m_IndexLock);
				for (const IoHash& BadKey : BadKeys)
				{
					// Log a tombstone and delete the in-memory index for the bad entry
					const auto	   It	   = m_Index.find(BadKey);
					BucketPayload& Payload = m_Payloads[It->second];
					if (m_Configuration.EnableReferenceCaching)
					{
						RemoveReferences(IndexLock, m_FirstReferenceIndex[It->second]);
					}
					DiskLocation Location = Payload.Location;
					if (Location.IsFlagSet(DiskLocation::kStandaloneFile))
					{
						m_StandaloneSize.fetch_sub(Location.Size(), std::memory_order::relaxed);
					}

					RemoveMemCachedData(Payload);
					RemoveMetaData(Payload);

					Location.Flags |= DiskLocation::kTombStone;
					LogEntries.push_back(DiskIndexEntry{.Key = BadKey, .Location = Location});
					m_Index.erase(BadKey);
				}
			}
			for (const DiskIndexEntry& Entry : LogEntries)
			{
				if (Entry.Location.IsFlagSet(DiskLocation::kStandaloneFile))
				{
					ExtendablePathBuilder<256> Path;
					BuildPath(Path, Entry.Key);
					fs::path				   FilePath = Path.ToPath();
					RwLock::ExclusiveLockScope ValueLock(LockForHash(Entry.Key));
					if (fs::is_regular_file(FilePath))
					{
						ZEN_DEBUG("deleting bad standalone cache file '{}'", Path.ToUtf8());
						std::error_code Ec;
						fs::remove(FilePath, Ec);  // We don't care if we fail, we are no longer tracking this file...
					}
				}
			}
			m_SlogFile.Append(LogEntries);

			// Clean up m_AccessTimes and m_Payloads vectors
			{
				std::vector<BucketPayload>	Payloads;
				std::vector<AccessTime>		AccessTimes;
				std::vector<BucketMetaData> MetaDatas;
				std::vector<IoBuffer>		MemCachedPayloads;
				std::vector<ReferenceIndex> FirstReferenceIndex;
				IndexMap					Index;

				{
					RwLock::ExclusiveLockScope IndexLock(m_IndexLock);
					CompactState(Payloads, AccessTimes, MetaDatas, MemCachedPayloads, FirstReferenceIndex, Index, IndexLock);
				}
			}
		}
	}

	// Let whomever it concerns know about the bad chunks. This could
	// be used to invalidate higher level data structures more efficiently
	// than a full validation pass might be able to do
	if (!BadKeys.empty())
	{
		Ctx.ReportBadCidChunks(BadKeys);
	}
}

void
ZenCacheDiskLayer::CacheBucket::GatherReferences(GcContext& GcCtx)
{
	ZEN_TRACE_CPU("Z$::Disk::Bucket::GatherReferences");

#define CALCULATE_BLOCKING_TIME 0

#if CALCULATE_BLOCKING_TIME
	uint64_t WriteBlockTimeUs		 = 0;
	uint64_t WriteBlockLongestTimeUs = 0;
	uint64_t ReadBlockTimeUs		 = 0;
	uint64_t ReadBlockLongestTimeUs	 = 0;
#endif	// CALCULATE_BLOCKING_TIME

	Stopwatch  TotalTimer;
	const auto _ = MakeGuard([&] {
#if CALCULATE_BLOCKING_TIME
		ZEN_DEBUG("gathered references from '{}' in {} write lock: {} ({}), read lock: {} ({})",
				  m_BucketDir,
				  NiceTimeSpanMs(TotalTimer.GetElapsedTimeMs()),
				  NiceLatencyNs(WriteBlockTimeUs),
				  NiceLatencyNs(WriteBlockLongestTimeUs),
				  NiceLatencyNs(ReadBlockTimeUs),
				  NiceLatencyNs(ReadBlockLongestTimeUs));
#else
		ZEN_DEBUG("gathered references from '{}' in {}", m_BucketDir, NiceTimeSpanMs(TotalTimer.GetElapsedTimeMs()));
#endif	// CALCULATE_BLOCKING_TIME
	});

	const GcClock::TimePoint ExpireTime = GcCtx.CacheExpireTime();

	const GcClock::Tick ExpireTicks = ExpireTime.time_since_epoch().count();

	IndexMap					Index;
	std::vector<AccessTime>		AccessTimes;
	std::vector<BucketPayload>	Payloads;
	std::vector<ReferenceIndex> FirstReferenceIndex;
	{
		RwLock::SharedLockScope __(m_IndexLock);
#if CALCULATE_BLOCKING_TIME
		Stopwatch  Timer;
		const auto ___ = MakeGuard([&] {
			uint64_t ElapsedUs = Timer.GetElapsedTimeUs();
			WriteBlockTimeUs += ElapsedUs;
			WriteBlockLongestTimeUs = std::max(ElapsedUs, WriteBlockLongestTimeUs);
		});
#endif	// CALCULATE_BLOCKING_TIME
		Index				= m_Index;
		AccessTimes			= m_AccessTimes;
		Payloads			= m_Payloads;
		FirstReferenceIndex = m_FirstReferenceIndex;
	}

	std::vector<IoHash> ExpiredKeys;
	ExpiredKeys.reserve(1024);

	std::vector<IoHash> Cids;
	if (!GcCtx.SkipCid())
	{
		Cids.reserve(1024);
	}

	std::vector<std::pair<IoHash, size_t>> StructuredItemsWithUnknownAttachments;

	for (const auto& Entry : Index)
	{
		const IoHash& Key		   = Entry.first;
		size_t		  PayloadIndex = Entry.second;
		GcClock::Tick AccessTime   = AccessTimes[PayloadIndex];
		if (AccessTime < ExpireTicks)
		{
			ExpiredKeys.push_back(Key);
			continue;
		}

		if (GcCtx.SkipCid())
		{
			continue;
		}

		BucketPayload&		Payload = Payloads[PayloadIndex];
		const DiskLocation& Loc		= Payload.Location;

		if (!Loc.IsFlagSet(DiskLocation::kStructured))
		{
			continue;
		}
		if (m_Configuration.EnableReferenceCaching)
		{
			if (FirstReferenceIndex.empty() || FirstReferenceIndex[PayloadIndex] == ReferenceIndex::Unknown())
			{
				StructuredItemsWithUnknownAttachments.push_back(Entry);
				continue;
			}

			bool ReferencesAreKnown = false;
			{
				RwLock::SharedLockScope IndexLock(m_IndexLock);
#if CALCULATE_BLOCKING_TIME
				Stopwatch  Timer;
				const auto ___ = MakeGuard([&] {
					uint64_t ElapsedUs = Timer.GetElapsedTimeUs();
					WriteBlockTimeUs += ElapsedUs;
					WriteBlockLongestTimeUs = std::max(ElapsedUs, WriteBlockLongestTimeUs);
				});
#endif	// CALCULATE_BLOCKING_TIME
				if (auto It = m_Index.find(Key); It != m_Index.end())
				{
					ReferencesAreKnown = GetReferences(IndexLock, m_FirstReferenceIndex[It->second], Cids);
				}
			}
			if (ReferencesAreKnown)
			{
				if (Cids.size() >= 1024)
				{
					GcCtx.AddRetainedCids(Cids);
					Cids.clear();
				}
				continue;
			}
		}
		StructuredItemsWithUnknownAttachments.push_back(Entry);
	}

	for (const auto& Entry : StructuredItemsWithUnknownAttachments)
	{
		const IoHash&		Key			 = Entry.first;
		size_t				PayloadIndex = Entry.second;
		BucketPayload&		Payload		 = Payloads[PayloadIndex];
		const DiskLocation& Loc			 = Payload.Location;
		{
			IoBuffer Buffer;
			if (Loc.IsFlagSet(DiskLocation::kStandaloneFile))
			{
				if (Buffer = GetStandaloneCacheValue(Loc.GetContentType(), Key); !Buffer)
				{
					continue;
				}
			}
			else
			{
				RwLock::SharedLockScope IndexLock(m_IndexLock);
#if CALCULATE_BLOCKING_TIME
				Stopwatch  Timer;
				const auto ___ = MakeGuard([&] {
					uint64_t ElapsedUs = Timer.GetElapsedTimeUs();
					WriteBlockTimeUs += ElapsedUs;
					WriteBlockLongestTimeUs = std::max(ElapsedUs, WriteBlockLongestTimeUs);
				});
#endif	// CALCULATE_BLOCKING_TIME
				if (auto It = m_Index.find(Key); It != m_Index.end())
				{
					const BucketPayload& CachedPayload = Payloads[PayloadIndex];
					if (CachedPayload.MemCached)
					{
						Buffer = m_MemCachedPayloads[CachedPayload.MemCached];
						ZEN_ASSERT_SLOW(Buffer);
					}
					else
					{
						DiskLocation Location = m_Payloads[It->second].Location;
						IndexLock.ReleaseNow();
						Buffer = GetInlineCacheValue(Location);
						// Don't memcache items when doing GC
					}
				}
				if (!Buffer)
				{
					continue;
				}
			}

			ZEN_ASSERT(Buffer);
			ZEN_ASSERT(Buffer.GetContentType() == ZenContentType::kCbObject);
			CbObjectView Obj(Buffer.GetData());
			size_t		 CurrentCidCount = Cids.size();
			Obj.IterateAttachments([&Cids](CbFieldView Field) { Cids.push_back(Field.AsAttachment()); });
			if (m_Configuration.EnableReferenceCaching)
			{
				RwLock::ExclusiveLockScope IndexLock(m_IndexLock);
#if CALCULATE_BLOCKING_TIME
				Stopwatch  Timer;
				const auto ___ = MakeGuard([&] {
					uint64_t ElapsedUs = Timer.GetElapsedTimeUs();
					ReadBlockTimeUs += ElapsedUs;
					ReadBlockLongestTimeUs = std::max(ElapsedUs, ReadBlockLongestTimeUs);
				});
#endif	// CALCULATE_BLOCKING_TIME
				if (auto It = m_Index.find(Key); It != m_Index.end())
				{
					if (m_FirstReferenceIndex[It->second] == ReferenceIndex::Unknown())
					{
						SetReferences(IndexLock,
									  m_FirstReferenceIndex[It->second],
									  std::span<IoHash>(Cids.data() + CurrentCidCount, Cids.size() - CurrentCidCount));
					}
					else
					{
						Cids.resize(CurrentCidCount);
						(void)GetReferences(IndexLock, m_FirstReferenceIndex[It->second], Cids);
					}
				}
			}
			if (Cids.size() >= 1024)
			{
				GcCtx.AddRetainedCids(Cids);
				Cids.clear();
			}
		}
	}

	GcCtx.AddRetainedCids(Cids);
	GcCtx.SetExpiredCacheKeys(m_BucketDir.string(), std::move(ExpiredKeys));
}

void
ZenCacheDiskLayer::CacheBucket::CollectGarbage(GcContext& GcCtx)
{
	ZEN_TRACE_CPU("Z$::Disk::Bucket::CollectGarbage");

	ZEN_DEBUG("collecting garbage from '{}'", m_BucketDir);

	Stopwatch	  TotalTimer;
	uint64_t	  WriteBlockTimeUs		  = 0;
	uint64_t	  WriteBlockLongestTimeUs = 0;
	uint64_t	  ReadBlockTimeUs		  = 0;
	uint64_t	  ReadBlockLongestTimeUs  = 0;
	uint64_t	  TotalChunkCount		  = 0;
	uint64_t	  DeletedSize			  = 0;
	GcStorageSize OldTotalSize			  = StorageSize();

	std::unordered_set<IoHash> DeletedChunks;
	uint64_t				   MovedCount = 0;

	const auto _ = MakeGuard([&] {
		ZEN_DEBUG(
			"garbage collect from '{}' DONE after {}, write lock: {} ({}), read lock: {} ({}), collected {} bytes, deleted {} and moved "
			"{} "
			"of {} "
			"entries ({}/{}).",
			m_BucketDir,
			NiceTimeSpanMs(TotalTimer.GetElapsedTimeMs()),
			NiceLatencyNs(WriteBlockTimeUs),
			NiceLatencyNs(WriteBlockLongestTimeUs),
			NiceLatencyNs(ReadBlockTimeUs),
			NiceLatencyNs(ReadBlockLongestTimeUs),
			NiceBytes(DeletedSize),
			DeletedChunks.size(),
			MovedCount,
			TotalChunkCount,
			NiceBytes(OldTotalSize.DiskSize),
			NiceBytes(OldTotalSize.MemorySize));

		bool Expected = false;
		if (m_IsFlushing || !m_IsFlushing.compare_exchange_strong(Expected, true))
		{
			return;
		}
		auto FlushingGuard = MakeGuard([&] { m_IsFlushing.store(false); });

		try
		{
			SaveSnapshot([&]() { return GcCtx.ClaimGCReserve(); });
		}
		catch (std::exception& Ex)
		{
			ZEN_WARN("Failed to write index and manifest after GC in '{}'. Reason: '{}'", m_BucketDir, Ex.what());
		}
	});

	m_SlogFile.Flush();

	auto __ = MakeGuard([&]() {
		if (!DeletedChunks.empty())
		{
			// Clean up m_AccessTimes and m_Payloads vectors
			std::vector<BucketPayload>	Payloads;
			std::vector<AccessTime>		AccessTimes;
			std::vector<BucketMetaData> MetaDatas;
			std::vector<IoBuffer>		MemCachedPayloads;
			std::vector<ReferenceIndex> FirstReferenceIndex;
			IndexMap					Index;
			{
				RwLock::ExclusiveLockScope IndexLock(m_IndexLock);
				Stopwatch				   Timer;
				const auto				   ___ = MakeGuard([&] {
					uint64_t ElapsedUs = Timer.GetElapsedTimeUs();
					WriteBlockTimeUs += ElapsedUs;
					WriteBlockLongestTimeUs = std::max(ElapsedUs, WriteBlockLongestTimeUs);
				});
				CompactState(Payloads, AccessTimes, MetaDatas, MemCachedPayloads, FirstReferenceIndex, Index, IndexLock);
			}
			GcCtx.AddDeletedCids(std::vector<IoHash>(DeletedChunks.begin(), DeletedChunks.end()));
		}
	});

	std::span<const IoHash>					   ExpiredCacheKeySpan = GcCtx.ExpiredCacheKeys(m_BucketDir.string());
	std::unordered_set<IoHash, IoHash::Hasher> ExpiredCacheKeys(ExpiredCacheKeySpan.begin(), ExpiredCacheKeySpan.end());

	std::vector<DiskIndexEntry>		 ExpiredStandaloneEntries;
	IndexMap						 IndexSnapshot;
	std::vector<BucketPayload>		 PayloadsSnapshot;
	BlockStore::ReclaimSnapshotState BlockStoreState;
	{
		bool Expected = false;
		if (m_IsFlushing || !m_IsFlushing.compare_exchange_strong(Expected, true))
		{
			ZEN_DEBUG("garbage collect SKIPPED, for '{}', container is currently flushing", m_BucketDir);
			return;
		}
		auto FlushingGuard = MakeGuard([&] { m_IsFlushing.store(false); });

		{
			ZEN_TRACE_CPU("Z$::Disk::Bucket::CollectGarbage::State");
			RwLock::SharedLockScope IndexLock(m_IndexLock);

			Stopwatch  Timer;
			const auto ____ = MakeGuard([&] {
				uint64_t ElapsedUs = Timer.GetElapsedTimeUs();
				WriteBlockTimeUs += ElapsedUs;
				WriteBlockLongestTimeUs = std::max(ElapsedUs, WriteBlockLongestTimeUs);
			});

			BlockStoreState = m_BlockStore.GetReclaimSnapshotState();

			for (const IoHash& Key : ExpiredCacheKeys)
			{
				if (auto It = m_Index.find(Key); It != m_Index.end())
				{
					const BucketPayload& Payload = m_Payloads[It->second];
					if (Payload.Location.Flags & DiskLocation::kStandaloneFile)
					{
						DiskIndexEntry Entry = {.Key = Key, .Location = Payload.Location};
						Entry.Location.Flags |= DiskLocation::kTombStone;
						ExpiredStandaloneEntries.push_back(Entry);
					}
				}
			}

			PayloadsSnapshot = m_Payloads;
			IndexSnapshot	 = m_Index;

			if (GcCtx.IsDeletionMode())
			{
				IndexLock.ReleaseNow();
				RwLock::ExclusiveLockScope __(m_IndexLock);
				for (const auto& Entry : ExpiredStandaloneEntries)
				{
					if (m_Index.erase(Entry.Key) == 1)
					{
						m_StandaloneSize.fetch_sub(Entry.Location.Size(), std::memory_order::relaxed);
						DeletedChunks.insert(Entry.Key);
					}
				}
				m_SlogFile.Append(ExpiredStandaloneEntries);
			}
		}
	}

	if (GcCtx.IsDeletionMode())
	{
		ZEN_TRACE_CPU("Z$::Disk::Bucket::CollectGarbage::Delete");

		ExtendablePathBuilder<256> Path;

		for (const auto& Entry : ExpiredStandaloneEntries)
		{
			const IoHash& Key = Entry.Key;

			Path.Reset();
			BuildPath(Path, Key);
			fs::path FilePath = Path.ToPath();

			{
				RwLock::SharedLockScope IndexLock(m_IndexLock);
				Stopwatch				Timer;
				const auto				____ = MakeGuard([&] {
					 uint64_t ElapsedUs = Timer.GetElapsedTimeUs();
					 WriteBlockTimeUs += ElapsedUs;
					 WriteBlockLongestTimeUs = std::max(ElapsedUs, WriteBlockLongestTimeUs);
				 });
				if (m_Index.contains(Key))
				{
					// Someone added it back, let the file on disk be
					ZEN_DEBUG("skipping z$ delete standalone of file '{}' FAILED, it has been added back", Path.ToUtf8());
					continue;
				}
				IndexLock.ReleaseNow();

				RwLock::ExclusiveLockScope ValueLock(LockForHash(Key));
				if (fs::is_regular_file(FilePath))
				{
					ZEN_DEBUG("deleting standalone cache file '{}'", Path.ToUtf8());
					std::error_code Ec;
					fs::remove(FilePath, Ec);
					if (Ec)
					{
						ZEN_WARN("delete expired z$ standalone file '{}' FAILED, reason: '{}'", Path.ToUtf8(), Ec.message());
						continue;
					}
				}
			}
			DeletedSize += Entry.Location.Size();
		}
	}

	TotalChunkCount = IndexSnapshot.size();

	std::vector<BlockStoreLocation> ChunkLocations;
	BlockStore::ChunkIndexArray		KeepChunkIndexes;
	std::vector<IoHash>				ChunkIndexToChunkHash;
	ChunkLocations.reserve(TotalChunkCount);
	ChunkLocations.reserve(TotalChunkCount);
	ChunkIndexToChunkHash.reserve(TotalChunkCount);
	{
		TotalChunkCount = 0;
		for (const auto& Entry : IndexSnapshot)
		{
			size_t				EntryIndex	 = Entry.second;
			const DiskLocation& DiskLocation = PayloadsSnapshot[EntryIndex].Location;

			if (DiskLocation.Flags & DiskLocation::kStandaloneFile)
			{
				continue;
			}
			const IoHash&	   Key		  = Entry.first;
			BlockStoreLocation Location	  = DiskLocation.GetBlockLocation(m_Configuration.PayloadAlignment);
			size_t			   ChunkIndex = ChunkLocations.size();
			ChunkLocations.push_back(Location);
			ChunkIndexToChunkHash[ChunkIndex] = Key;
			if (ExpiredCacheKeys.contains(Key))
			{
				continue;
			}
			KeepChunkIndexes.push_back(ChunkIndex);
		}
	}
	TotalChunkCount	   = ChunkLocations.size();
	size_t DeleteCount = TotalChunkCount - KeepChunkIndexes.size();

	const bool PerformDelete = GcCtx.IsDeletionMode() && GcCtx.CollectSmallObjects();
	if (!PerformDelete)
	{
		m_BlockStore.ReclaimSpace(BlockStoreState, ChunkLocations, KeepChunkIndexes, m_Configuration.PayloadAlignment, true);
		GcStorageSize CurrentTotalSize = StorageSize();
		ZEN_DEBUG("garbage collect from '{}' DISABLED, found {} chunks of total {} ({}/{})",
				  m_BucketDir,
				  DeleteCount,
				  TotalChunkCount,
				  NiceBytes(CurrentTotalSize.DiskSize),
				  NiceBytes(CurrentTotalSize.MemorySize));
		return;
	}

	m_BlockStore.ReclaimSpace(
		BlockStoreState,
		ChunkLocations,
		KeepChunkIndexes,
		m_Configuration.PayloadAlignment,
		false,
		[&](const BlockStore::MovedChunksArray& MovedChunks, const BlockStore::ChunkIndexArray& RemovedChunks) {
			std::vector<DiskIndexEntry> LogEntries;
			LogEntries.reserve(MovedChunks.size() + RemovedChunks.size());
			{
				RwLock::ExclusiveLockScope __(m_IndexLock);
				Stopwatch				   Timer;
				const auto				   ____ = MakeGuard([&] {
					uint64_t ElapsedUs = Timer.GetElapsedTimeUs();
					WriteBlockTimeUs += ElapsedUs;
					WriteBlockLongestTimeUs = std::max(ElapsedUs, WriteBlockLongestTimeUs);
				});
				for (const auto& Entry : MovedChunks)
				{
					size_t					  ChunkIndex  = Entry.first;
					const BlockStoreLocation& NewLocation = Entry.second;
					const IoHash&			  ChunkHash	  = ChunkIndexToChunkHash[ChunkIndex];
					size_t					  EntryIndex  = m_Index[ChunkHash];
					BucketPayload&			  Payload	  = m_Payloads[EntryIndex];
					if (PayloadsSnapshot[IndexSnapshot[ChunkHash]].Location != m_Payloads[EntryIndex].Location)
					{
						// Entry has been updated while GC was running, ignore the move
						continue;
					}
					Payload.Location = DiskLocation(NewLocation, m_Configuration.PayloadAlignment, Payload.Location.GetFlags());
					LogEntries.push_back({.Key = ChunkHash, .Location = Payload.Location});
				}
				for (const size_t ChunkIndex : RemovedChunks)
				{
					const IoHash&  ChunkHash  = ChunkIndexToChunkHash[ChunkIndex];
					size_t		   EntryIndex = m_Index[ChunkHash];
					BucketPayload& Payload	  = m_Payloads[EntryIndex];
					if (PayloadsSnapshot[IndexSnapshot[ChunkHash]].Location != Payload.Location)
					{
						// Entry has been updated while GC was running, ignore the delete
						continue;
					}
					const DiskLocation& OldDiskLocation = Payload.Location;
					LogEntries.push_back({.Key		= ChunkHash,
										  .Location = DiskLocation(OldDiskLocation.GetBlockLocation(m_Configuration.PayloadAlignment),
																   m_Configuration.PayloadAlignment,
																   OldDiskLocation.GetFlags() | DiskLocation::kTombStone)});

					RemoveMemCachedData(Payload);
					RemoveMetaData(Payload);

					m_Index.erase(ChunkHash);
					DeletedChunks.insert(ChunkHash);
				}
			}

			m_SlogFile.Append(LogEntries);
			m_SlogFile.Flush();
		},
		[&]() { return GcCtx.ClaimGCReserve(); });
}

ZenCacheDiskLayer::BucketStats
ZenCacheDiskLayer::CacheBucket::Stats()
{
	GcStorageSize Size = StorageSize();
	return ZenCacheDiskLayer::BucketStats{.DiskSize			= Size.DiskSize,
										  .MemorySize		= Size.MemorySize,
										  .DiskHitCount		= m_DiskHitCount,
										  .DiskMissCount	= m_DiskMissCount,
										  .DiskWriteCount	= m_DiskWriteCount,
										  .MemoryHitCount	= m_MemoryHitCount,
										  .MemoryMissCount	= m_MemoryMissCount,
										  .MemoryWriteCount = m_MemoryWriteCount,
										  .PutOps			= m_PutOps.Snapshot(),
										  .GetOps			= m_GetOps.Snapshot()};
}

uint64_t
ZenCacheDiskLayer::CacheBucket::EntryCount() const
{
	RwLock::SharedLockScope _(m_IndexLock);
	return static_cast<uint64_t>(m_Index.size());
}

CacheValueDetails::ValueDetails
ZenCacheDiskLayer::CacheBucket::GetValueDetails(const IoHash& Key, PayloadIndex Index) const
{
	std::vector<IoHash>	 Attachments;
	const BucketPayload& Payload = m_Payloads[Index];
	if (Payload.Location.IsFlagSet(DiskLocation::kStructured))
	{
		IoBuffer	 Value = Payload.Location.IsFlagSet(DiskLocation::kStandaloneFile)
								 ? GetStandaloneCacheValue(Payload.Location.GetContentType(), Key)
								 : GetInlineCacheValue(Payload.Location);
		CbObjectView Obj(Value.GetData());
		Obj.IterateAttachments([&Attachments](CbFieldView Field) { Attachments.emplace_back(Field.AsAttachment()); });
	}
	BucketMetaData MetaData = GetMetaData(Payload);
	return CacheValueDetails::ValueDetails{.Size		= Payload.Location.Size(),
										   .RawSize		= MetaData.RawSize,
										   .RawHash		= MetaData.RawHash,
										   .LastAccess	= m_AccessTimes[Index],
										   .Attachments = std::move(Attachments),
										   .ContentType = Payload.Location.GetContentType()};
}

CacheValueDetails::BucketDetails
ZenCacheDiskLayer::CacheBucket::GetValueDetails(const std::string_view ValueFilter) const
{
	CacheValueDetails::BucketDetails Details;
	RwLock::SharedLockScope			 _(m_IndexLock);
	if (ValueFilter.empty())
	{
		Details.Values.reserve(m_Index.size());
		for (const auto& It : m_Index)
		{
			Details.Values.insert_or_assign(It.first, GetValueDetails(It.first, It.second));
		}
	}
	else
	{
		IoHash Key = IoHash::FromHexString(ValueFilter);
		if (auto It = m_Index.find(Key); It != m_Index.end())
		{
			Details.Values.insert_or_assign(It->first, GetValueDetails(It->first, It->second));
		}
	}
	return Details;
}

void
ZenCacheDiskLayer::CacheBucket::EnumerateBucketContents(
	std::function<void(const IoHash& Key, const CacheValueDetails::ValueDetails& Details)>& Fn) const
{
	RwLock::SharedLockScope _(m_IndexLock);
	for (const auto& It : m_Index)
	{
		CacheValueDetails::ValueDetails Vd = GetValueDetails(It.first, It.second);

		Fn(It.first, Vd);
	}
}

void
ZenCacheDiskLayer::CollectGarbage(GcContext& GcCtx)
{
	ZEN_TRACE_CPU("Z$::Disk::CollectGarbage");

	std::vector<CacheBucket*> Buckets;
	{
		RwLock::SharedLockScope _(m_Lock);
		Buckets.reserve(m_Buckets.size());
		for (auto& Kv : m_Buckets)
		{
			Buckets.push_back(Kv.second.get());
		}
	}
	for (CacheBucket* Bucket : Buckets)
	{
		Bucket->CollectGarbage(GcCtx);
	}
	MemCacheTrim(Buckets, GcCtx.CacheExpireTime());
}

void
ZenCacheDiskLayer::CacheBucket::PutStandaloneCacheValue(const IoHash& HashKey, const ZenCacheValue& Value, std::span<IoHash> References)
{
	ZEN_TRACE_CPU("Z$::Disk::Bucket::PutStandaloneCacheValue");

	uint64_t NewFileSize = Value.Value.Size();

	TemporaryFile DataFile;

	std::error_code Ec;
	DataFile.CreateTemporary(m_BucketDir.c_str(), Ec);
	if (Ec)
	{
		throw std::system_error(Ec, fmt::format("Failed to open temporary file for put in '{}'", m_BucketDir));
	}

	bool CleanUpTempFile = true;
	auto __				 = MakeGuard([&] {
		 if (CleanUpTempFile)
		 {
			 std::error_code Ec;
			 std::filesystem::remove(DataFile.GetPath(), Ec);
			 if (Ec)
			 {
				 ZEN_WARN("Failed to clean up temporary file '{}' for put in '{}', reason '{}'",
						  DataFile.GetPath(),
						  m_BucketDir,
						  Ec.message());
			 }
		 }
	 });

	DataFile.WriteAll(Value.Value, Ec);
	if (Ec)
	{
		throw std::system_error(Ec,
								fmt::format("Failed to write payload ({} bytes) to temporary file '{}' for put in '{}'",
											NiceBytes(NewFileSize),
											DataFile.GetPath().string(),
											m_BucketDir));
	}

	ExtendablePathBuilder<256> DataFilePath;
	BuildPath(DataFilePath, HashKey);
	std::filesystem::path FsPath{DataFilePath.ToPath()};

	RwLock::ExclusiveLockScope ValueLock(LockForHash(HashKey));

	// We do a speculative remove of the file instead of probing with a exists call and check the error code instead
	std::filesystem::remove(FsPath, Ec);
	if (Ec)
	{
		if (Ec.value() != ENOENT)
		{
			ZEN_WARN("Failed to remove file '{}' for put in '{}', reason: '{}', retrying.", FsPath, m_BucketDir, Ec.message());
			Sleep(100);
			Ec.clear();
			std::filesystem::remove(FsPath, Ec);
			if (Ec && Ec.value() != ENOENT)
			{
				throw std::system_error(Ec, fmt::format("Failed to remove file '{}' for put in '{}'", FsPath, m_BucketDir));
			}
		}
	}

	// Assume parent directory exists
	DataFile.MoveTemporaryIntoPlace(FsPath, Ec);
	if (Ec)
	{
		CreateDirectories(FsPath.parent_path());

		// Try again after we or someone else created the directory
		Ec.clear();
		DataFile.MoveTemporaryIntoPlace(FsPath, Ec);

		// Retry if we still fail to handle contention to file system
		uint32_t RetriesLeft = 3;
		while (Ec && RetriesLeft > 0)
		{
			ZEN_WARN("Failed to finalize file '{}', moving from '{}' for put in '{}', reason: '{}', retries left: {}.",
					 FsPath,
					 DataFile.GetPath(),
					 m_BucketDir,
					 Ec.message(),
					 RetriesLeft);
			Sleep(100 - (3 - RetriesLeft) * 100);  // Total 600 ms
			Ec.clear();
			DataFile.MoveTemporaryIntoPlace(FsPath, Ec);
			RetriesLeft--;
		}
		if (Ec)
		{
			throw std::system_error(
				Ec,
				fmt::format("Failed to finalize file '{}', moving from '{}' for put in '{}'", FsPath, DataFile.GetPath(), m_BucketDir));
		}
	}

	// Once we have called MoveTemporaryIntoPlace automatic clean up the temp file
	// will be disabled as the file handle has already been closed
	CleanUpTempFile = false;

	uint8_t EntryFlags = DiskLocation::kStandaloneFile;

	if (Value.Value.GetContentType() == ZenContentType::kCbObject)
	{
		EntryFlags |= DiskLocation::kStructured;
	}
	else if (Value.Value.GetContentType() == ZenContentType::kCompressedBinary)
	{
		EntryFlags |= DiskLocation::kCompressed;
	}

	DiskLocation Loc(NewFileSize, EntryFlags);

	RwLock::ExclusiveLockScope IndexLock(m_IndexLock);
	ValueLock.ReleaseNow();

	PayloadIndex EntryIndex = {};
	if (auto It = m_Index.find(HashKey); It == m_Index.end())
	{
		// Previously unknown object
		EntryIndex = PayloadIndex(m_Payloads.size());
		m_Payloads.emplace_back(BucketPayload{.Location = Loc});
		m_AccessTimes.emplace_back(GcClock::TickCount());
		if (m_Configuration.EnableReferenceCaching)
		{
			m_FirstReferenceIndex.emplace_back(ReferenceIndex{});
			SetReferences(IndexLock, m_FirstReferenceIndex.back(), References);
		}
		m_Index.insert_or_assign(HashKey, EntryIndex);
	}
	else
	{
		EntryIndex = It.value();
		ZEN_ASSERT_SLOW(EntryIndex < PayloadIndex(m_AccessTimes.size()));
		BucketPayload& Payload = m_Payloads[EntryIndex];
		uint64_t	   OldSize = Payload.Location.Size();
		Payload				   = BucketPayload{.Location = Loc};
		if (m_Configuration.EnableReferenceCaching)
		{
			SetReferences(IndexLock, m_FirstReferenceIndex[EntryIndex], References);
		}
		m_AccessTimes[EntryIndex] = GcClock::TickCount();
		RemoveMemCachedData(Payload);
		m_StandaloneSize.fetch_sub(OldSize, std::memory_order::relaxed);
	}
	if (Value.RawSize != 0 || Value.RawHash != IoHash::Zero)
	{
		SetMetaData(m_Payloads[EntryIndex], {.RawSize = Value.RawSize, .RawHash = Value.RawHash});
	}
	else
	{
		RemoveMetaData(m_Payloads[EntryIndex]);
	}

	m_SlogFile.Append({.Key = HashKey, .Location = Loc});
	m_StandaloneSize.fetch_add(NewFileSize, std::memory_order::relaxed);
}

void
ZenCacheDiskLayer::CacheBucket::SetMetaData(BucketPayload& Payload, const ZenCacheDiskLayer::CacheBucket::BucketMetaData& MetaData)
{
	if (Payload.MetaData)
	{
		m_MetaDatas[Payload.MetaData] = MetaData;
	}
	else
	{
		if (m_FreeMetaDatas.empty())
		{
			Payload.MetaData = MetaDataIndex(m_MetaDatas.size());
			m_MetaDatas.emplace_back(MetaData);
		}
		else
		{
			Payload.MetaData = m_FreeMetaDatas.back();
			m_FreeMetaDatas.pop_back();
			m_MetaDatas[Payload.MetaData] = MetaData;
		}
	}
}

void
ZenCacheDiskLayer::CacheBucket::RemoveMetaData(BucketPayload& Payload)
{
	if (Payload.MetaData)
	{
		m_FreeMetaDatas.push_back(Payload.MetaData);
		Payload.MetaData = {};
	}
}

void
ZenCacheDiskLayer::CacheBucket::SetMemCachedData(BucketPayload& Payload, IoBuffer& MemCachedData)
{
	uint64_t PayloadSize = MemCachedData.GetSize();
	ZEN_ASSERT(PayloadSize != 0);
	if (m_FreeMemCachedPayloads.empty())
	{
		if (m_MemCachedPayloads.size() != std::numeric_limits<uint32_t>::max())
		{
			Payload.MemCached = MemCachedIndex(gsl::narrow<uint32_t>(m_MemCachedPayloads.size()));
			m_MemCachedPayloads.push_back(MemCachedData);
			AddMemCacheUsage(PayloadSize);
			m_MemoryWriteCount++;
		}
	}
	else
	{
		Payload.MemCached = m_FreeMemCachedPayloads.back();
		m_FreeMemCachedPayloads.pop_back();
		m_MemCachedPayloads[Payload.MemCached] = MemCachedData;
		AddMemCacheUsage(PayloadSize);
		m_MemoryWriteCount++;
	}
}

size_t
ZenCacheDiskLayer::CacheBucket::RemoveMemCachedData(BucketPayload& Payload)
{
	if (Payload.MemCached)
	{
		size_t PayloadSize = m_MemCachedPayloads[Payload.MemCached].GetSize();
		RemoveMemCacheUsage(PayloadSize);
		m_MemCachedPayloads[Payload.MemCached] = IoBuffer{};
		m_FreeMemCachedPayloads.push_back(Payload.MemCached);
		Payload.MemCached = {};
		return PayloadSize;
	}
	return 0;
}

ZenCacheDiskLayer::CacheBucket::BucketMetaData
ZenCacheDiskLayer::CacheBucket::GetMetaData(const BucketPayload& Payload) const
{
	if (Payload.MetaData)
	{
		return m_MetaDatas[Payload.MetaData];
	}
	return {};
}

void
ZenCacheDiskLayer::CacheBucket::PutInlineCacheValue(const IoHash& HashKey, const ZenCacheValue& Value, std::span<IoHash> References)
{
	ZEN_TRACE_CPU("Z$::Disk::Bucket::PutInlineCacheValue");

	uint8_t EntryFlags = 0;

	if (Value.Value.GetContentType() == ZenContentType::kCbObject)
	{
		EntryFlags |= DiskLocation::kStructured;
	}
	else if (Value.Value.GetContentType() == ZenContentType::kCompressedBinary)
	{
		EntryFlags |= DiskLocation::kCompressed;
	}

	m_BlockStore.WriteChunk(Value.Value.Data(),
							Value.Value.Size(),
							m_Configuration.PayloadAlignment,
							[&](const BlockStoreLocation& BlockStoreLocation) {
								DiskLocation Location(BlockStoreLocation, m_Configuration.PayloadAlignment, EntryFlags);
								m_SlogFile.Append({.Key = HashKey, .Location = Location});

								RwLock::ExclusiveLockScope IndexLock(m_IndexLock);
								if (auto It = m_Index.find(HashKey); It != m_Index.end())
								{
									PayloadIndex EntryIndex = It.value();
									ZEN_ASSERT_SLOW(EntryIndex < PayloadIndex(m_AccessTimes.size()));
									BucketPayload& Payload = m_Payloads[EntryIndex];

									RemoveMemCachedData(Payload);
									RemoveMetaData(Payload);

									Payload					  = (BucketPayload{.Location = Location});
									m_AccessTimes[EntryIndex] = GcClock::TickCount();

									if (m_Configuration.EnableReferenceCaching)
									{
										SetReferences(IndexLock, m_FirstReferenceIndex[EntryIndex], References);
									}
								}
								else
								{
									PayloadIndex EntryIndex = PayloadIndex(m_Payloads.size());
									m_Payloads.emplace_back(BucketPayload{.Location = Location});
									m_AccessTimes.emplace_back(GcClock::TickCount());
									if (m_Configuration.EnableReferenceCaching)
									{
										m_FirstReferenceIndex.emplace_back(ReferenceIndex{});
										SetReferences(IndexLock, m_FirstReferenceIndex.back(), References);
									}
									m_Index.insert_or_assign(HashKey, EntryIndex);
								}
							});
}

std::string
ZenCacheDiskLayer::CacheBucket::GetGcName(GcCtx&)
{
	return fmt::format("cachebucket:'{}'", m_BucketDir.string());
}

class DiskBucketStoreCompactor : public GcStoreCompactor
{
public:
	DiskBucketStoreCompactor(ZenCacheDiskLayer::CacheBucket& Bucket, std::vector<std::pair<IoHash, uint64_t>>&& ExpiredStandaloneKeys)
	: m_Bucket(Bucket)
	, m_ExpiredStandaloneKeys(std::move(ExpiredStandaloneKeys))
	{
		m_ExpiredStandaloneKeys.shrink_to_fit();
	}

	virtual ~DiskBucketStoreCompactor() {}

	virtual void CompactStore(GcCtx& Ctx, GcCompactStoreStats& Stats, const std::function<uint64_t()>& ClaimDiskReserveCallback) override
	{
		Stopwatch  Timer;
		const auto _ = MakeGuard([&] {
			Reset(m_ExpiredStandaloneKeys);
			if (!Ctx.Settings.Verbose)
			{
				return;
			}
			ZEN_INFO("GCV2: cachebucket [COMPACT] '{}': RemovedDisk: {} in {}",
					 m_Bucket.m_BucketDir,
					 NiceBytes(Stats.RemovedDisk),
					 NiceTimeSpanMs(Timer.GetElapsedTimeMs()));
		});

		if (!m_ExpiredStandaloneKeys.empty())
		{
			// Compact standalone items
			size_t					   Skipped = 0;
			ExtendablePathBuilder<256> Path;
			for (const std::pair<IoHash, uint64_t>& ExpiredKey : m_ExpiredStandaloneKeys)
			{
				if (Ctx.IsCancelledFlag.load())
				{
					return;
				}
				Path.Reset();
				m_Bucket.BuildPath(Path, ExpiredKey.first);
				fs::path FilePath = Path.ToPath();

				RwLock::SharedLockScope IndexLock(m_Bucket.m_IndexLock);
				if (m_Bucket.m_Index.contains(ExpiredKey.first))
				{
					// Someone added it back, let the file on disk be
					ZEN_DEBUG("GCV2: cachebucket [COMPACT] '{}': skipping z$ delete standalone of file '{}' FAILED, it has been added back",
							  m_Bucket.m_BucketDir,
							  Path.ToUtf8());
					continue;
				}

				if (Ctx.Settings.IsDeleteMode)
				{
					RwLock::ExclusiveLockScope ValueLock(m_Bucket.LockForHash(ExpiredKey.first));
					IndexLock.ReleaseNow();
					ZEN_DEBUG("GCV2: cachebucket [COMPACT] '{}': deleting standalone cache file '{}'", m_Bucket.m_BucketDir, Path.ToUtf8());

					std::error_code Ec;
					if (!fs::remove(FilePath, Ec))
					{
						continue;
					}
					if (Ec)
					{
						ZEN_WARN("GCV2: cachebucket [COMPACT] '{}': delete expired z$ standalone file '{}' FAILED, reason: '{}'",
								 m_Bucket.m_BucketDir,
								 Path.ToUtf8(),
								 Ec.message());
						continue;
					}
					Stats.RemovedDisk += ExpiredKey.second;
				}
				else
				{
					std::error_code Ec;
					bool			Existed = std::filesystem::is_regular_file(FilePath, Ec);
					if (Ec)
					{
						ZEN_WARN("GCV2: cachebucket [COMPACT] '{}': failed checking cache payload file '{}'. Reason '{}'",
								 m_Bucket.m_BucketDir,
								 FilePath,
								 Ec.message());
						continue;
					}
					if (!Existed)
					{
						continue;
					}
					Skipped++;
				}
			}
			if (Skipped > 0)
			{
				ZEN_DEBUG("GCV2: cachebucket [COMPACT] '{}': skipped deleting of {} eligible files", m_Bucket.m_BucketDir, Skipped);
			}
		}

		if (Ctx.Settings.CollectSmallObjects)
		{
			std::unordered_map<uint32_t, uint64_t> BlockUsage;
			{
				RwLock::SharedLockScope __(m_Bucket.m_IndexLock);
				for (const auto& Entry : m_Bucket.m_Index)
				{
					ZenCacheDiskLayer::CacheBucket::PayloadIndex		 Index	 = Entry.second;
					const ZenCacheDiskLayer::CacheBucket::BucketPayload& Payload = m_Bucket.m_Payloads[Index];
					const DiskLocation&									 Loc	 = Payload.Location;

					if (Loc.IsFlagSet(DiskLocation::kStandaloneFile))
					{
						continue;
					}
					uint32_t BlockIndex = Loc.Location.BlockLocation.GetBlockIndex();
					uint64_t ChunkSize	= RoundUp(Loc.Size(), m_Bucket.m_Configuration.PayloadAlignment);
					auto	 It			= BlockUsage.find(BlockIndex);
					if (It == BlockUsage.end())
					{
						BlockUsage.insert_or_assign(BlockIndex, ChunkSize);
					}
					else
					{
						It->second += ChunkSize;
					}
				}
			}

			{
				BlockStoreCompactState BlockCompactState;
				std::vector<IoHash>	   BlockCompactStateKeys;

				std::vector<uint32_t> BlocksToCompact =
					m_Bucket.m_BlockStore.GetBlocksToCompact(BlockUsage, Ctx.Settings.CompactBlockUsageThresholdPercent);
				BlockCompactState.IncludeBlocks(BlocksToCompact);

				if (BlocksToCompact.size() > 0)
				{
					{
						RwLock::SharedLockScope __(m_Bucket.m_IndexLock);
						for (const auto& Entry : m_Bucket.m_Index)
						{
							ZenCacheDiskLayer::CacheBucket::PayloadIndex		 Index	 = Entry.second;
							const ZenCacheDiskLayer::CacheBucket::BucketPayload& Payload = m_Bucket.m_Payloads[Index];
							const DiskLocation&									 Loc	 = Payload.Location;

							if (Loc.IsFlagSet(DiskLocation::kStandaloneFile))
							{
								continue;
							}
							if (!BlockCompactState.AddKeepLocation(Loc.GetBlockLocation(m_Bucket.m_Configuration.PayloadAlignment)))
							{
								continue;
							}
							BlockCompactStateKeys.push_back(Entry.first);
						}
					}

					if (Ctx.Settings.IsDeleteMode)
					{
						if (Ctx.Settings.Verbose)
						{
							ZEN_INFO("GCV2: cachebucket [COMPACT] '{}': compacting {} blocks",
									 m_Bucket.m_BucketDir,
									 BlocksToCompact.size());
						}

						m_Bucket.m_BlockStore.CompactBlocks(
							BlockCompactState,
							m_Bucket.m_Configuration.PayloadAlignment,
							[&](const BlockStore::MovedChunksArray& MovedArray, uint64_t FreedDiskSpace) {
								std::vector<DiskIndexEntry> MovedEntries;
								RwLock::ExclusiveLockScope	_(m_Bucket.m_IndexLock);
								for (const std::pair<size_t, BlockStoreLocation>& Moved : MovedArray)
								{
									size_t		  ChunkIndex = Moved.first;
									const IoHash& Key		 = BlockCompactStateKeys[ChunkIndex];

									if (auto It = m_Bucket.m_Index.find(Key); It != m_Bucket.m_Index.end())
									{
										ZenCacheDiskLayer::CacheBucket::BucketPayload& Payload = m_Bucket.m_Payloads[It->second];
										const BlockStoreLocation& OldLocation				   = BlockCompactState.GetLocation(ChunkIndex);
										if (Payload.Location.GetBlockLocation(m_Bucket.m_Configuration.PayloadAlignment) != OldLocation)
										{
											// Someone has moved our chunk so lets just skip the new location we were provided, it will be
											// GC:d at a later time
											continue;
										}
										const BlockStoreLocation& NewLocation = Moved.second;

										Payload.Location = DiskLocation(NewLocation,
																		m_Bucket.m_Configuration.PayloadAlignment,
																		Payload.Location.GetFlags());
										MovedEntries.push_back({.Key = Key, .Location = Payload.Location});
									}
								}
								m_Bucket.m_SlogFile.Append(MovedEntries);
								Stats.RemovedDisk += FreedDiskSpace;
								if (Ctx.IsCancelledFlag.load())
								{
									return false;
								}
								return true;
							},
							ClaimDiskReserveCallback);
					}
					else
					{
						if (Ctx.Settings.Verbose)
						{
							ZEN_INFO("GCV2: cachebucket [COMPACT] '{}': skipped compacting of {} eligible blocks",
									 m_Bucket.m_BucketDir,
									 BlocksToCompact.size());
						}
					}
				}
			}
		}
	}

private:
	ZenCacheDiskLayer::CacheBucket&			 m_Bucket;
	std::vector<std::pair<IoHash, uint64_t>> m_ExpiredStandaloneKeys;
};

GcStoreCompactor*
ZenCacheDiskLayer::CacheBucket::RemoveExpiredData(GcCtx& Ctx, GcStats& Stats)
{
	size_t TotalEntries = 0;

	Stopwatch  Timer;
	const auto _ = MakeGuard([&] {
		if (!Ctx.Settings.Verbose)
		{
			return;
		}
		ZEN_INFO("GCV2: cachebucket [REMOVE EXPIRED] '{}': Count: {}, Expired: {}, Deleted: {}, FreedMemory: {} in {}",
				 m_BucketDir,
				 Stats.CheckedCount,
				 Stats.FoundCount,
				 Stats.DeletedCount,
				 NiceBytes(Stats.FreedMemory),
				 NiceTimeSpanMs(Timer.GetElapsedTimeMs()));
	});

	const GcClock::Tick ExpireTicks = Ctx.Settings.CacheExpireTime.time_since_epoch().count();

	std::vector<DiskIndexEntry>				 ExpiredEntries;
	std::vector<std::pair<IoHash, uint64_t>> ExpiredStandaloneKeys;
	uint64_t								 RemovedStandaloneSize = 0;
	{
		RwLock::ExclusiveLockScope IndexLock(m_IndexLock);
		if (Ctx.IsCancelledFlag.load())
		{
			return nullptr;
		}

		TotalEntries = m_Index.size();

		// Find out expired keys
		for (const auto& Entry : m_Index)
		{
			const IoHash&								 Key		= Entry.first;
			ZenCacheDiskLayer::CacheBucket::PayloadIndex EntryIndex = Entry.second;
			GcClock::Tick								 AccessTime = m_AccessTimes[EntryIndex];
			if (AccessTime >= ExpireTicks)
			{
				continue;
			}

			const BucketPayload& Payload	  = m_Payloads[EntryIndex];
			DiskIndexEntry		 ExpiredEntry = {.Key = Key, .Location = Payload.Location};
			ExpiredEntry.Location.Flags |= DiskLocation::kTombStone;

			if (Payload.Location.Flags & DiskLocation::kStandaloneFile)
			{
				ExpiredStandaloneKeys.push_back({Key, Payload.Location.Size()});
				RemovedStandaloneSize += Payload.Location.Size();
				ExpiredEntries.push_back(ExpiredEntry);
			}
			else if (Ctx.Settings.CollectSmallObjects)
			{
				ExpiredEntries.push_back(ExpiredEntry);
			}
		}

		Stats.CheckedCount += TotalEntries;
		Stats.FoundCount += ExpiredEntries.size();

		if (Ctx.IsCancelledFlag.load())
		{
			return nullptr;
		}

		if (Ctx.Settings.IsDeleteMode)
		{
			for (const DiskIndexEntry& Entry : ExpiredEntries)
			{
				auto It = m_Index.find(Entry.Key);
				ZEN_ASSERT(It != m_Index.end());
				BucketPayload& Payload = m_Payloads[It->second];
				RemoveMetaData(Payload);
				Stats.FreedMemory += RemoveMemCachedData(Payload);
				m_Index.erase(It);
				Stats.DeletedCount++;
			}
			m_SlogFile.Append(ExpiredEntries);
			m_StandaloneSize.fetch_sub(RemovedStandaloneSize, std::memory_order::relaxed);
		}
	}

	if (!ExpiredEntries.empty())
	{
		std::vector<BucketPayload>	Payloads;
		std::vector<AccessTime>		AccessTimes;
		std::vector<BucketMetaData> MetaDatas;
		std::vector<IoBuffer>		MemCachedPayloads;
		std::vector<ReferenceIndex> FirstReferenceIndex;
		IndexMap					Index;
		{
			RwLock::ExclusiveLockScope IndexLock(m_IndexLock);
			CompactState(Payloads, AccessTimes, MetaDatas, MemCachedPayloads, FirstReferenceIndex, Index, IndexLock);
		}
	}

	if (Ctx.IsCancelledFlag.load())
	{
		return nullptr;
	}

	return new DiskBucketStoreCompactor(*this, std::move(ExpiredStandaloneKeys));
}

class DiskBucketReferenceChecker : public GcReferenceChecker
{
public:
	DiskBucketReferenceChecker(ZenCacheDiskLayer::CacheBucket& Owner) : m_CacheBucket(Owner) {}

	virtual ~DiskBucketReferenceChecker()
	{
		m_IndexLock.reset();
		if (!m_CacheBucket.m_Configuration.EnableReferenceCaching)
		{
			// If reference caching is not enabled, we temporarily used the data structure for reference caching, lets reset it
			m_CacheBucket.ClearReferenceCache();
		}
	}

	virtual void LockState(GcCtx& Ctx) override
	{
		Stopwatch  Timer;
		const auto _ = MakeGuard([&] {
			if (!Ctx.Settings.Verbose)
			{
				return;
			}
			ZEN_INFO("GCV2: cachebucket [LOCKSTATE] '{}': found {} references in {}",
					 m_CacheBucket.m_BucketDir,
					 m_CacheBucket.m_ReferenceCount + m_UncachedReferences.size(),
					 NiceTimeSpanMs(Timer.GetElapsedTimeMs()));
		});

		m_IndexLock = std::make_unique<RwLock::SharedLockScope>(m_CacheBucket.m_IndexLock);
		if (Ctx.IsCancelledFlag.load())
		{
			m_UncachedReferences.clear();
			m_IndexLock.reset();
			return;
		}

		// Rescan to see if any cache items needs refreshing since last pass when we had the lock
		for (const auto& Entry : m_CacheBucket.m_Index)
		{
			if (Ctx.IsCancelledFlag.load())
			{
				m_UncachedReferences.clear();
				m_IndexLock.reset();
				return;
			}

			size_t												 PayloadIndex = Entry.second;
			const ZenCacheDiskLayer::CacheBucket::BucketPayload& Payload	  = m_CacheBucket.m_Payloads[PayloadIndex];
			const DiskLocation&									 Loc		  = Payload.Location;

			if (!Loc.IsFlagSet(DiskLocation::kStructured))
			{
				continue;
			}
			ZEN_ASSERT(!m_CacheBucket.m_FirstReferenceIndex.empty());
			const IoHash& Key = Entry.first;
			if (m_CacheBucket.m_FirstReferenceIndex[PayloadIndex] == ZenCacheDiskLayer::CacheBucket::ReferenceIndex::Unknown())
			{
				IoBuffer Buffer;
				if (Loc.IsFlagSet(DiskLocation::kStandaloneFile))
				{
					Buffer = m_CacheBucket.GetStandaloneCacheValue(Loc.GetContentType(), Key);
				}
				else
				{
					Buffer = m_CacheBucket.GetInlineCacheValue(Loc);
				}

				if (Buffer)
				{
					ZEN_ASSERT(Buffer.GetContentType() == ZenContentType::kCbObject);
					CbObjectView Obj(Buffer.GetData());
					Obj.IterateAttachments([this](CbFieldView Field) { m_UncachedReferences.insert(Field.AsAttachment()); });
				}
			}
		}
	}

	virtual void RemoveUsedReferencesFromSet(GcCtx& Ctx, HashSet& IoCids) override
	{
		ZEN_ASSERT(m_IndexLock);
		size_t	   InitialCount = IoCids.size();
		Stopwatch  Timer;
		const auto _ = MakeGuard([&] {
			if (!Ctx.Settings.Verbose)
			{
				return;
			}
			ZEN_INFO("GCV2: cachebucket [FILTER REFERENCES] '{}': filtered out {} used references out of {} in {}",
					 m_CacheBucket.m_BucketDir,
					 InitialCount - IoCids.size(),
					 InitialCount,
					 NiceTimeSpanMs(Timer.GetElapsedTimeMs()));
		});

		for (const IoHash& ReferenceHash : m_CacheBucket.m_ReferenceHashes)
		{
			IoCids.erase(ReferenceHash);
		}

		for (const IoHash& ReferenceHash : m_UncachedReferences)
		{
			IoCids.erase(ReferenceHash);
		}
	}
	ZenCacheDiskLayer::CacheBucket&			 m_CacheBucket;
	std::unique_ptr<RwLock::SharedLockScope> m_IndexLock;
	HashSet									 m_UncachedReferences;
};

std::vector<GcReferenceChecker*>
ZenCacheDiskLayer::CacheBucket::CreateReferenceCheckers(GcCtx& Ctx)
{
	Stopwatch  Timer;
	const auto _ = MakeGuard([&] {
		if (!Ctx.Settings.Verbose)
		{
			return;
		}
		ZEN_INFO("GCV2: cachebucket [CREATE CHECKERS] '{}': found {} references in {}",
				 m_BucketDir,
				 m_ReferenceCount,
				 NiceTimeSpanMs(Timer.GetElapsedTimeMs()));
	});

	std::vector<IoHash> UpdateKeys;
	std::vector<IoHash> StandaloneKeys;
	std::vector<size_t> ReferenceCounts;
	std::vector<IoHash> References;

	// Refresh cache
	{
		RwLock::SharedLockScope IndexLock(m_IndexLock);
		for (const auto& Entry : m_Index)
		{
			if (Ctx.IsCancelledFlag.load())
			{
				return {};
			}

			size_t												 PayloadIndex = Entry.second;
			const ZenCacheDiskLayer::CacheBucket::BucketPayload& Payload	  = m_Payloads[PayloadIndex];
			const DiskLocation&									 Loc		  = Payload.Location;

			if (!Loc.IsFlagSet(DiskLocation::kStructured))
			{
				continue;
			}
			if (m_Configuration.EnableReferenceCaching &&
				m_FirstReferenceIndex[PayloadIndex] != ZenCacheDiskLayer::CacheBucket::ReferenceIndex::Unknown())
			{
				continue;
			}
			const IoHash& Key = Entry.first;
			if (Loc.IsFlagSet(DiskLocation::kStandaloneFile))
			{
				StandaloneKeys.push_back(Key);
				continue;
			}
			IoBuffer Buffer = GetInlineCacheValue(Loc);
			if (!Buffer)
			{
				UpdateKeys.push_back(Key);
				ReferenceCounts.push_back(0);
				continue;
			}
			size_t CurrentReferenceCount = References.size();
			{
				CbObjectView Obj(Buffer.GetData());
				Obj.IterateAttachments([&References](CbFieldView Field) { References.emplace_back(Field.AsAttachment()); });
				Buffer = {};
			}
			UpdateKeys.push_back(Key);
			ReferenceCounts.push_back(References.size() - CurrentReferenceCount);
		}
	}
	{
		for (const IoHash& Key : StandaloneKeys)
		{
			if (Ctx.IsCancelledFlag.load())
			{
				return {};
			}

			IoBuffer Buffer = GetStandaloneCacheValue(ZenContentType::kCbObject, Key);
			if (!Buffer)
			{
				continue;
			}

			size_t CurrentReferenceCount = References.size();
			{
				CbObjectView Obj(Buffer.GetData());
				Obj.IterateAttachments([&References](CbFieldView Field) { References.emplace_back(Field.AsAttachment()); });
				Buffer = {};
			}
			UpdateKeys.push_back(Key);
			ReferenceCounts.push_back(References.size() - CurrentReferenceCount);
		}
	}

	{
		size_t					   ReferenceOffset = 0;
		RwLock::ExclusiveLockScope IndexLock(m_IndexLock);
		if (!m_Configuration.EnableReferenceCaching)
		{
			ZEN_ASSERT(m_FirstReferenceIndex.empty());
			ZEN_ASSERT(m_ReferenceHashes.empty());
			ZEN_ASSERT(m_NextReferenceHashesIndexes.empty());
			ZEN_ASSERT(m_ReferenceCount == 0);
			// If reference caching is not enabled, we will resize and use the data structure in place for reference caching when
			// we figure out what this bucket references. This will be reset once the DiskBucketReferenceChecker is deleted.
			m_FirstReferenceIndex.resize(m_Payloads.size());
		}
		for (size_t Index = 0; Index < UpdateKeys.size(); Index++)
		{
			const IoHash& Key			 = UpdateKeys[Index];
			size_t		  ReferenceCount = ReferenceCounts[Index];
			auto		  It			 = m_Index.find(Key);
			if (It == m_Index.end())
			{
				ReferenceOffset += ReferenceCount;
				continue;
			}
			if (m_FirstReferenceIndex[It->second] != ReferenceIndex::Unknown())
			{
				continue;
			}
			SetReferences(IndexLock,
						  m_FirstReferenceIndex[It->second],
						  std::span<IoHash>{References.data() + ReferenceOffset, ReferenceCount});
			ReferenceOffset += ReferenceCount;
		}
		if (m_Configuration.EnableReferenceCaching)
		{
			CompactReferences(IndexLock);
		}
	}

	return {new DiskBucketReferenceChecker(*this)};
}

void
ZenCacheDiskLayer::CacheBucket::CompactReferences(RwLock::ExclusiveLockScope&)
{
	std::vector<ReferenceIndex> FirstReferenceIndex;
	std::vector<IoHash>			NewReferenceHashes;
	std::vector<ReferenceIndex> NewNextReferenceHashesIndexes;

	FirstReferenceIndex.reserve(m_ReferenceCount);
	NewReferenceHashes.reserve(m_ReferenceCount);
	NewNextReferenceHashesIndexes.reserve(m_ReferenceCount);

	for (const auto& It : m_Index)
	{
		ReferenceIndex SourceIndex = m_FirstReferenceIndex[It.second];
		if (SourceIndex == ReferenceIndex::Unknown())
		{
			FirstReferenceIndex.push_back(ReferenceIndex{});
			continue;
		}
		if (SourceIndex == ReferenceIndex::None())
		{
			FirstReferenceIndex.push_back(ReferenceIndex::None());
			continue;
		}
		FirstReferenceIndex.push_back(ReferenceIndex{NewNextReferenceHashesIndexes.size()});
		NewReferenceHashes.push_back(m_ReferenceHashes[SourceIndex]);
		NewNextReferenceHashesIndexes.push_back(ReferenceIndex::None());

		SourceIndex = m_NextReferenceHashesIndexes[SourceIndex];
		while (SourceIndex != ReferenceIndex::None())
		{
			NewNextReferenceHashesIndexes.back() = ReferenceIndex{NewReferenceHashes.size()};
			NewReferenceHashes.push_back(m_ReferenceHashes[SourceIndex]);
			NewNextReferenceHashesIndexes.push_back(ReferenceIndex::None());
			SourceIndex = m_NextReferenceHashesIndexes[SourceIndex];
		}
	}
	m_FirstReferenceIndex.swap(FirstReferenceIndex);
	m_ReferenceHashes.swap(NewReferenceHashes);
	m_ReferenceHashes.shrink_to_fit();
	m_NextReferenceHashesIndexes.swap(NewNextReferenceHashesIndexes);
	m_NextReferenceHashesIndexes.shrink_to_fit();
	m_ReferenceCount = m_ReferenceHashes.size();
}

ZenCacheDiskLayer::CacheBucket::ReferenceIndex
ZenCacheDiskLayer::CacheBucket::AllocateReferenceEntry(RwLock::ExclusiveLockScope&, const IoHash& Key)
{
	ReferenceIndex NewIndex = ReferenceIndex{m_ReferenceHashes.size()};
	m_ReferenceHashes.push_back(Key);
	m_NextReferenceHashesIndexes.emplace_back(ReferenceIndex::None());
	m_ReferenceCount++;
	return NewIndex;
}

void
ZenCacheDiskLayer::CacheBucket::SetReferences(RwLock::ExclusiveLockScope& Lock,
											  ReferenceIndex&			  FirstReferenceIndex,
											  std::span<IoHash>			  References)
{
	auto ReferenceIt = References.begin();

	if (FirstReferenceIndex == ReferenceIndex::Unknown())
	{
		FirstReferenceIndex = ReferenceIndex::None();
	}

	ReferenceIndex CurrentIndex = FirstReferenceIndex;
	if (CurrentIndex != ReferenceIndex::None())
	{
		if (ReferenceIt != References.end())
		{
			ZEN_ASSERT_SLOW(*ReferenceIt != IoHash::Zero);
			if (CurrentIndex == ReferenceIndex::None())
			{
				CurrentIndex		= AllocateReferenceEntry(Lock, *ReferenceIt);
				FirstReferenceIndex = CurrentIndex;
			}
			else
			{
				m_ReferenceHashes[CurrentIndex] = *ReferenceIt;
			}
			ReferenceIt++;
		}
	}
	else
	{
		if (ReferenceIt != References.end())
		{
			ZEN_ASSERT_SLOW(*ReferenceIt != IoHash::Zero);
			CurrentIndex = AllocateReferenceEntry(Lock, *ReferenceIt);
			ReferenceIt++;
		}
		FirstReferenceIndex = CurrentIndex;
	}

	while (ReferenceIt != References.end())
	{
		ZEN_ASSERT(CurrentIndex != ReferenceIndex::None());
		ZEN_ASSERT_SLOW(*ReferenceIt != IoHash::Zero);
		ReferenceIndex NextReferenceIndex = m_NextReferenceHashesIndexes[CurrentIndex];
		if (NextReferenceIndex == ReferenceIndex::None())
		{
			NextReferenceIndex						   = AllocateReferenceEntry(Lock, *ReferenceIt);
			m_NextReferenceHashesIndexes[CurrentIndex] = NextReferenceIndex;
		}
		else
		{
			m_ReferenceHashes[NextReferenceIndex] = *ReferenceIt;
		}
		CurrentIndex = NextReferenceIndex;
		ReferenceIt++;
	}

	while (CurrentIndex != ReferenceIndex::None())
	{
		ReferenceIndex NextIndex = m_NextReferenceHashesIndexes[CurrentIndex];
		if (NextIndex != ReferenceIndex::None())
		{
			m_ReferenceHashes[CurrentIndex] = IoHash::Zero;
			ZEN_ASSERT(m_ReferenceCount > 0);
			m_ReferenceCount--;
			m_NextReferenceHashesIndexes[CurrentIndex] = ReferenceIndex::None();
		}
		CurrentIndex = NextIndex;
	}
}

void
ZenCacheDiskLayer::CacheBucket::RemoveReferences(RwLock::ExclusiveLockScope&, ReferenceIndex& FirstReferenceIndex)
{
	if (FirstReferenceIndex == ReferenceIndex::Unknown())
	{
		return;
	}
	ReferenceIndex CurrentIndex = FirstReferenceIndex;
	while (CurrentIndex == ReferenceIndex::None())
	{
		m_ReferenceHashes[CurrentIndex] = IoHash::Zero;
		ZEN_ASSERT(m_ReferenceCount > 0);
		m_ReferenceCount--;
		CurrentIndex = m_NextReferenceHashesIndexes[CurrentIndex];
	}
	FirstReferenceIndex = {};
}

bool
ZenCacheDiskLayer::CacheBucket::LockedGetReferences(ReferenceIndex FirstReferenceIndex, std::vector<IoHash>& OutReferences) const
{
	if (FirstReferenceIndex == ReferenceIndex::Unknown())
	{
		return false;
	}

	ReferenceIndex CurrentIndex = FirstReferenceIndex;
	while (CurrentIndex != ReferenceIndex::None())
	{
		ZEN_ASSERT_SLOW(m_ReferenceHashes[CurrentIndex] != IoHash::Zero);
		OutReferences.push_back(m_ReferenceHashes[CurrentIndex]);
		CurrentIndex = m_NextReferenceHashesIndexes[CurrentIndex];
	}
	return true;
}

void
ZenCacheDiskLayer::CacheBucket::ClearReferenceCache()
{
	RwLock::ExclusiveLockScope IndexLock(m_IndexLock);
	Reset(m_FirstReferenceIndex);
	Reset(m_ReferenceHashes);
	Reset(m_NextReferenceHashesIndexes);
	m_ReferenceCount = 0;
}

void
ZenCacheDiskLayer::CacheBucket::CompactState(std::vector<BucketPayload>&  Payloads,
											 std::vector<AccessTime>&	  AccessTimes,
											 std::vector<BucketMetaData>& MetaDatas,
											 std::vector<IoBuffer>&		  MemCachedPayloads,
											 std::vector<ReferenceIndex>& FirstReferenceIndex,
											 IndexMap&					  Index,
											 RwLock::ExclusiveLockScope&  IndexLock)
{
	size_t EntryCount = m_Index.size();
	Payloads.reserve(EntryCount);
	AccessTimes.reserve(EntryCount);
	if (m_Configuration.EnableReferenceCaching)
	{
		FirstReferenceIndex.reserve(EntryCount);
	}
	Index.reserve(EntryCount);
	for (auto It : m_Index)
	{
		PayloadIndex EntryIndex = PayloadIndex(Payloads.size());
		Payloads.push_back(m_Payloads[It.second]);
		BucketPayload& Payload = Payloads.back();
		AccessTimes.push_back(m_AccessTimes[It.second]);
		if (Payload.MetaData)
		{
			MetaDatas.push_back(m_MetaDatas[Payload.MetaData]);
			Payload.MetaData = MetaDataIndex(MetaDatas.size() - 1);
		}
		if (Payload.MemCached)
		{
			MemCachedPayloads.push_back(std::move(m_MemCachedPayloads[Payload.MemCached]));
			Payload.MemCached = MemCachedIndex(gsl::narrow<uint32_t>(MemCachedPayloads.size() - 1));
		}
		if (m_Configuration.EnableReferenceCaching)
		{
			FirstReferenceIndex.push_back(m_FirstReferenceIndex[It.second]);
		}
		Index.insert({It.first, EntryIndex});
	}
	m_Index.swap(Index);
	m_Payloads.swap(Payloads);
	m_AccessTimes.swap(AccessTimes);
	m_MetaDatas.swap(MetaDatas);
	Reset(m_FreeMetaDatas);
	m_MemCachedPayloads.swap(MemCachedPayloads);
	Reset(m_FreeMemCachedPayloads);
	if (m_Configuration.EnableReferenceCaching)
	{
		m_FirstReferenceIndex.swap(FirstReferenceIndex);
		CompactReferences(IndexLock);
	}
}

#if ZEN_WITH_TESTS
void
ZenCacheDiskLayer::CacheBucket::SetAccessTime(const IoHash& HashKey, GcClock::TimePoint Time)
{
	GcClock::Tick			TimeTick = Time.time_since_epoch().count();
	RwLock::SharedLockScope IndexLock(m_IndexLock);
	if (auto It = m_Index.find(HashKey); It != m_Index.end())
	{
		size_t EntryIndex = It.value();
		ZEN_ASSERT_SLOW(EntryIndex < m_AccessTimes.size());
		m_AccessTimes[EntryIndex] = TimeTick;
	}
}
#endif	// ZEN_WITH_TESTS

//////////////////////////////////////////////////////////////////////////

ZenCacheDiskLayer::ZenCacheDiskLayer(GcManager& Gc, JobQueue& JobQueue, const std::filesystem::path& RootDir, const Configuration& Config)
: m_Gc(Gc)
, m_JobQueue(JobQueue)
, m_RootDir(RootDir)
, m_Configuration(Config)
{
}

ZenCacheDiskLayer::~ZenCacheDiskLayer()
{
}

bool
ZenCacheDiskLayer::Get(std::string_view InBucket, const IoHash& HashKey, ZenCacheValue& OutValue)
{
	ZEN_TRACE_CPU("Z$::Disk::Get");

	const auto	 BucketName = std::string(InBucket);
	CacheBucket* Bucket		= nullptr;

	{
		RwLock::SharedLockScope _(m_Lock);

		auto It = m_Buckets.find(BucketName);

		if (It != m_Buckets.end())
		{
			Bucket = It->second.get();
		}
	}

	if (Bucket == nullptr)
	{
		// Bucket needs to be opened/created

		RwLock::ExclusiveLockScope _(m_Lock);

		if (auto It = m_Buckets.find(BucketName); It != m_Buckets.end())
		{
			Bucket = It->second.get();
		}
		else
		{
			auto InsertResult =
				m_Buckets.emplace(BucketName,
								  std::make_unique<CacheBucket>(m_Gc, m_TotalMemCachedSize, BucketName, m_Configuration.BucketConfig));
			Bucket = InsertResult.first->second.get();

			std::filesystem::path BucketPath = m_RootDir;
			BucketPath /= BucketName;

			if (!Bucket->OpenOrCreate(BucketPath))
			{
				m_Buckets.erase(InsertResult.first);
				return false;
			}
		}
	}

	ZEN_ASSERT(Bucket != nullptr);
	if (Bucket->Get(HashKey, OutValue))
	{
		TryMemCacheTrim();
		return true;
	}
	return false;
}

void
ZenCacheDiskLayer::Put(std::string_view InBucket, const IoHash& HashKey, const ZenCacheValue& Value, std::span<IoHash> References)
{
	ZEN_TRACE_CPU("Z$::Disk::Put");

	const auto	 BucketName = std::string(InBucket);
	CacheBucket* Bucket		= nullptr;

	{
		RwLock::SharedLockScope _(m_Lock);

		auto It = m_Buckets.find(BucketName);

		if (It != m_Buckets.end())
		{
			Bucket = It->second.get();
		}
	}

	if (Bucket == nullptr)
	{
		// New bucket needs to be created

		RwLock::ExclusiveLockScope _(m_Lock);

		if (auto It = m_Buckets.find(BucketName); It != m_Buckets.end())
		{
			Bucket = It->second.get();
		}
		else
		{
			auto InsertResult =
				m_Buckets.emplace(BucketName,
								  std::make_unique<CacheBucket>(m_Gc, m_TotalMemCachedSize, BucketName, m_Configuration.BucketConfig));
			Bucket = InsertResult.first->second.get();

			std::filesystem::path BucketPath = m_RootDir;
			BucketPath /= BucketName;

			try
			{
				if (!Bucket->OpenOrCreate(BucketPath))
				{
					ZEN_WARN("Found directory '{}' in our base directory '{}' but it is not a valid bucket", BucketName, m_RootDir);
					m_Buckets.erase(InsertResult.first);
					return;
				}
			}
			catch (const std::exception& Err)
			{
				ZEN_WARN("creating bucket '{}' in '{}' FAILED, reason: '{}'", BucketName, BucketPath, Err.what());
				throw;
			}
		}
	}

	ZEN_ASSERT(Bucket != nullptr);

	Bucket->Put(HashKey, Value, References);
	TryMemCacheTrim();
}

void
ZenCacheDiskLayer::DiscoverBuckets()
{
	DirectoryContent DirContent;
	GetDirectoryContent(m_RootDir, DirectoryContent::IncludeDirsFlag, DirContent);

	// Initialize buckets

	std::vector<std::filesystem::path> BadBucketDirectories;
	std::vector<std::filesystem::path> FoundBucketDirectories;

	RwLock::ExclusiveLockScope _(m_Lock);

	for (const std::filesystem::path& BucketPath : DirContent.Directories)
	{
		const std::string BucketName = PathToUtf8(BucketPath.stem());

		if (auto It = m_Buckets.find(BucketName); It != m_Buckets.end())
		{
			continue;
		}

		if (IsKnownBadBucketName(BucketName))
		{
			BadBucketDirectories.push_back(BucketPath);

			continue;
		}

		FoundBucketDirectories.push_back(BucketPath);
		ZEN_INFO("Discovered bucket '{}'", BucketName);
	}

	for (const std::filesystem::path& BadBucketPath : BadBucketDirectories)
	{
		bool IsOk = false;

		try
		{
			IsOk = DeleteDirectories(BadBucketPath);
		}
		catch (std::exception&)
		{
		}

		if (IsOk)
		{
			ZEN_INFO("found bad bucket at '{}', deleted contents", BadBucketPath);
		}
		else
		{
			ZEN_WARN("bad bucket delete failed for '{}'", BadBucketPath);
		}
	}

	RwLock SyncLock;

	const size_t MaxHwTreadUse		   = std::thread::hardware_concurrency();
	const int	 WorkerThreadPoolCount = gsl::narrow<int>(Min(MaxHwTreadUse, FoundBucketDirectories.size()));

	WorkerThreadPool Pool(WorkerThreadPoolCount, "CacheBucket::OpenOrCreate");
	Latch			 WorkLatch(1);
	for (auto& BucketPath : FoundBucketDirectories)
	{
		WorkLatch.AddCount(1);
		Pool.ScheduleWork([&]() {
			auto _ = MakeGuard([&]() { WorkLatch.CountDown(); });

			const std::string BucketName = PathToUtf8(BucketPath.stem());
			try
			{
				std::unique_ptr<CacheBucket> NewBucket =
					std::make_unique<CacheBucket>(m_Gc, m_TotalMemCachedSize, BucketName, m_Configuration.BucketConfig);

				CacheBucket* Bucket = nullptr;
				{
					RwLock::ExclusiveLockScope __(SyncLock);
					auto					   InsertResult = m_Buckets.emplace(BucketName, std::move(NewBucket));
					Bucket									= InsertResult.first->second.get();
				}
				ZEN_ASSERT(Bucket);

				if (!Bucket->OpenOrCreate(BucketPath, /* AllowCreate */ false))
				{
					ZEN_WARN("Found directory '{}' in our base directory '{}' but it is not a valid bucket", BucketName, m_RootDir);

					{
						RwLock::ExclusiveLockScope __(SyncLock);
						m_Buckets.erase(BucketName);
					}
				}
			}
			catch (const std::exception& Err)
			{
				ZEN_ERROR("Opening bucket '{}' in '{}' FAILED, reason: '{}'", BucketName, BucketPath, Err.what());
				return;
			}
		});
	}
	WorkLatch.CountDown();
	WorkLatch.Wait();
}

bool
ZenCacheDiskLayer::DropBucket(std::string_view InBucket)
{
	RwLock::ExclusiveLockScope _(m_Lock);

	auto It = m_Buckets.find(std::string(InBucket));

	if (It != m_Buckets.end())
	{
		CacheBucket& Bucket = *It->second;
		m_DroppedBuckets.push_back(std::move(It->second));
		m_Buckets.erase(It);

		return Bucket.Drop();
	}

	// Make sure we remove the folder even if we don't know about the bucket
	std::filesystem::path BucketPath = m_RootDir;
	BucketPath /= std::string(InBucket);
	return MoveAndDeleteDirectory(BucketPath);
}

bool
ZenCacheDiskLayer::Drop()
{
	RwLock::ExclusiveLockScope _(m_Lock);

	std::vector<std::unique_ptr<CacheBucket>> Buckets;
	Buckets.reserve(m_Buckets.size());
	while (!m_Buckets.empty())
	{
		const auto&	 It		= m_Buckets.begin();
		CacheBucket& Bucket = *It->second;
		m_DroppedBuckets.push_back(std::move(It->second));
		m_Buckets.erase(It->first);
		if (!Bucket.Drop())
		{
			return false;
		}
	}
	return MoveAndDeleteDirectory(m_RootDir);
}

void
ZenCacheDiskLayer::Flush()
{
	std::vector<CacheBucket*> Buckets;
	Stopwatch				  Timer;
	const auto				  _ = MakeGuard([&] {
		   if (Buckets.empty())
		   {
			   return;
		   }
		   ZEN_INFO("Flushed {} buckets at '{}' in {}", Buckets.size(), m_RootDir, NiceTimeSpanMs(Timer.GetElapsedTimeMs()));
	   });

	{
		RwLock::SharedLockScope __(m_Lock);
		if (m_Buckets.empty())
		{
			return;
		}
		Buckets.reserve(m_Buckets.size());
		for (auto& Kv : m_Buckets)
		{
			CacheBucket* Bucket = Kv.second.get();
			Buckets.push_back(Bucket);
		}
	}
	{
		const size_t MaxHwTreadUse		   = Max((std::thread::hardware_concurrency() / 4u), 1u);
		const int	 WorkerThreadPoolCount = gsl::narrow<int>(Min(MaxHwTreadUse, Buckets.size()));

		WorkerThreadPool Pool(WorkerThreadPoolCount, "CacheBucket::Flush");
		Latch			 WorkLatch(1);
		for (auto& Bucket : Buckets)
		{
			WorkLatch.AddCount(1);
			Pool.ScheduleWork([&]() {
				auto _ = MakeGuard([&]() { WorkLatch.CountDown(); });
				Bucket->Flush();
			});
		}
		WorkLatch.CountDown();
		while (!WorkLatch.Wait(1000))
		{
			ZEN_DEBUG("Waiting for {} buckets at '{}' to flush", WorkLatch.Remaining(), m_RootDir);
		}
	}
}

void
ZenCacheDiskLayer::ScrubStorage(ScrubContext& Ctx)
{
	RwLock::SharedLockScope _(m_Lock);

	{
		std::vector<std::future<void>> Results;
		Results.reserve(m_Buckets.size());

		for (auto& Kv : m_Buckets)
		{
#if 1
			Results.push_back(Ctx.ThreadPool().EnqueueTask(
				std::packaged_task<void()>{[this, Bucket = Kv.second.get(), &Ctx] { Bucket->ScrubStorage(Ctx); }}));
#else
			CacheBucket& Bucket = *Kv.second;
			Bucket.ScrubStorage(Ctx);
#endif
		}

		for (auto& Result : Results)
		{
			Result.get();
		}
	}
}

void
ZenCacheDiskLayer::GatherReferences(GcContext& GcCtx)
{
	ZEN_TRACE_CPU("Z$::Disk::GatherReferences");

	std::vector<CacheBucket*> Buckets;
	{
		RwLock::SharedLockScope _(m_Lock);
		Buckets.reserve(m_Buckets.size());
		for (auto& Kv : m_Buckets)
		{
			Buckets.push_back(Kv.second.get());
		}
	}
	for (CacheBucket* Bucket : Buckets)
	{
		Bucket->GatherReferences(GcCtx);
	}
}

GcStorageSize
ZenCacheDiskLayer::StorageSize() const
{
	GcStorageSize StorageSize{};

	RwLock::SharedLockScope _(m_Lock);
	for (auto& Kv : m_Buckets)
	{
		GcStorageSize BucketSize = Kv.second->StorageSize();
		StorageSize.DiskSize += BucketSize.DiskSize;
		StorageSize.MemorySize += BucketSize.MemorySize;
	}

	return StorageSize;
}

ZenCacheDiskLayer::DiskStats
ZenCacheDiskLayer::Stats() const
{
	GcStorageSize				 Size  = StorageSize();
	ZenCacheDiskLayer::DiskStats Stats = {.DiskSize = Size.DiskSize, .MemorySize = Size.MemorySize};
	{
		RwLock::SharedLockScope _(m_Lock);
		Stats.BucketStats.reserve(m_Buckets.size());
		for (auto& Kv : m_Buckets)
		{
			Stats.BucketStats.emplace_back(NamedBucketStats{.BucketName = Kv.first, .Stats = Kv.second->Stats()});
		}
	}
	return Stats;
}

ZenCacheDiskLayer::Info
ZenCacheDiskLayer::GetInfo() const
{
	ZenCacheDiskLayer::Info Info = {.RootDir = m_RootDir, .Config = m_Configuration};
	{
		RwLock::SharedLockScope _(m_Lock);
		Info.BucketNames.reserve(m_Buckets.size());
		for (auto& Kv : m_Buckets)
		{
			Info.BucketNames.push_back(Kv.first);
			Info.EntryCount += Kv.second->EntryCount();
			GcStorageSize BucketSize = Kv.second->StorageSize();
			Info.StorageSize.DiskSize += BucketSize.DiskSize;
			Info.StorageSize.MemorySize += BucketSize.MemorySize;
		}
	}
	return Info;
}

std::optional<ZenCacheDiskLayer::BucketInfo>
ZenCacheDiskLayer::GetBucketInfo(std::string_view Bucket) const
{
	RwLock::SharedLockScope _(m_Lock);

	if (auto It = m_Buckets.find(std::string(Bucket)); It != m_Buckets.end())
	{
		return ZenCacheDiskLayer::BucketInfo{.EntryCount = It->second->EntryCount(), .StorageSize = It->second->StorageSize()};
	}
	return {};
}

void
ZenCacheDiskLayer::EnumerateBucketContents(std::string_view																		   Bucket,
										   std::function<void(const IoHash& Key, const CacheValueDetails::ValueDetails& Details)>& Fn) const
{
	RwLock::SharedLockScope _(m_Lock);

	if (auto It = m_Buckets.find(std::string(Bucket)); It != m_Buckets.end())
	{
		It->second->EnumerateBucketContents(Fn);
	}
}

CacheValueDetails::NamespaceDetails
ZenCacheDiskLayer::GetValueDetails(const std::string_view BucketFilter, const std::string_view ValueFilter) const
{
	RwLock::SharedLockScope				_(m_Lock);
	CacheValueDetails::NamespaceDetails Details;
	if (BucketFilter.empty())
	{
		Details.Buckets.reserve(BucketFilter.empty() ? m_Buckets.size() : 1);
		for (auto& Kv : m_Buckets)
		{
			Details.Buckets[Kv.first] = Kv.second->GetValueDetails(ValueFilter);
		}
	}
	else if (auto It = m_Buckets.find(std::string(BucketFilter)); It != m_Buckets.end())
	{
		Details.Buckets[It->first] = It->second->GetValueDetails(ValueFilter);
	}
	return Details;
}

void
ZenCacheDiskLayer::MemCacheTrim()
{
	ZEN_TRACE_CPU("Z$::Disk::MemCacheTrim");

	ZEN_ASSERT(m_Configuration.MemCacheTargetFootprintBytes != 0);

	const GcClock::TimePoint Now = GcClock::Now();

	const GcClock::Tick		   NowTick			   = Now.time_since_epoch().count();
	const std::chrono::seconds TrimInterval		   = std::chrono::seconds(m_Configuration.MemCacheTrimIntervalSeconds);
	GcClock::Tick			   LastTrimTick		   = m_LastTickMemCacheTrim;
	const GcClock::Tick		   NextAllowedTrimTick = LastTrimTick + GcClock::Duration(TrimInterval).count();
	if (NowTick < NextAllowedTrimTick)
	{
		return;
	}

	bool Expected = false;
	if (!m_IsMemCacheTrimming.compare_exchange_strong(Expected, true))
	{
		return;
	}

	// Bump time forward so we don't keep trying to do m_IsTrimming.compare_exchange_strong
	const GcClock::Tick NextTrimTick = NowTick + GcClock::Duration(TrimInterval).count();
	m_LastTickMemCacheTrim.store(NextTrimTick);

	m_JobQueue.QueueJob("ZenCacheDiskLayer::MemCacheTrim", [this, Now, TrimInterval](JobContext&) {
		ZEN_TRACE_CPU("Z$::ZenCacheDiskLayer::MemCacheTrim [Async]");

		uint64_t   StartSize = m_TotalMemCachedSize.load();
		Stopwatch  Timer;
		const auto Guard = MakeGuard([&] {
			uint64_t EndSize = m_TotalMemCachedSize.load();
			ZEN_INFO("trimmed {} (remaining {}), from memory cache in {}",
					 NiceBytes(StartSize > EndSize ? StartSize - EndSize : 0),
					 NiceBytes(m_TotalMemCachedSize),
					 NiceTimeSpanMs(Timer.GetElapsedTimeMs()));
			m_IsMemCacheTrimming.store(false);
		});

		const std::chrono::seconds MaxAge = std::chrono::seconds(m_Configuration.MemCacheMaxAgeSeconds);

		std::vector<uint64_t> UsageSlots;
		UsageSlots.reserve(std::chrono::seconds(MaxAge / TrimInterval).count());

		std::vector<CacheBucket*> Buckets;
		{
			RwLock::SharedLockScope __(m_Lock);
			Buckets.reserve(m_Buckets.size());
			for (auto& Kv : m_Buckets)
			{
				Buckets.push_back(Kv.second.get());
			}
		}
		for (CacheBucket* Bucket : Buckets)
		{
			Bucket->GetUsageByAccess(Now, GcClock::Duration(TrimInterval), UsageSlots);
		}

		uint64_t TotalSize = 0;
		for (size_t Index = 0; Index < UsageSlots.size(); ++Index)
		{
			TotalSize += UsageSlots[Index];
			if (TotalSize >= m_Configuration.MemCacheTargetFootprintBytes)
			{
				GcClock::TimePoint ExpireTime = Now - (TrimInterval * Index);
				MemCacheTrim(Buckets, ExpireTime);
				break;
			}
		}
	});
}

void
ZenCacheDiskLayer::MemCacheTrim(std::vector<CacheBucket*>& Buckets, GcClock::TimePoint ExpireTime)
{
	if (m_Configuration.MemCacheTargetFootprintBytes == 0)
	{
		return;
	}
	RwLock::SharedLockScope __(m_Lock);
	for (CacheBucket* Bucket : Buckets)
	{
		Bucket->MemCacheTrim(ExpireTime);
	}
	const GcClock::TimePoint   Now				   = GcClock::Now();
	const GcClock::Tick		   NowTick			   = Now.time_since_epoch().count();
	const std::chrono::seconds TrimInterval		   = std::chrono::seconds(m_Configuration.MemCacheTrimIntervalSeconds);
	GcClock::Tick			   LastTrimTick		   = m_LastTickMemCacheTrim;
	const GcClock::Tick		   NextAllowedTrimTick = NowTick + GcClock::Duration(TrimInterval).count();
	m_LastTickMemCacheTrim.compare_exchange_strong(LastTrimTick, NextAllowedTrimTick);
}

#if ZEN_WITH_TESTS
void
ZenCacheDiskLayer::SetAccessTime(std::string_view InBucket, const IoHash& HashKey, GcClock::TimePoint Time)
{
	const auto	 BucketName = std::string(InBucket);
	CacheBucket* Bucket		= nullptr;

	{
		RwLock::SharedLockScope _(m_Lock);

		auto It = m_Buckets.find(BucketName);

		if (It != m_Buckets.end())
		{
			Bucket = It->second.get();
		}
	}

	if (Bucket == nullptr)
	{
		return;
	}
	Bucket->SetAccessTime(HashKey, Time);
}
#endif	// ZEN_WITH_TESTS

}  // namespace zen