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

#include <zencore/compactbinarybuilder.h>
#include <zencore/filesystem.h>
#include <zencore/fmtutils.h>
#include <zencore/logging.h>
#include <zencore/session.h>
#include <zencore/system.h>
#include <zencore/testing.h>
#include <zencore/testutils.h>
#include <zenutil/basicfile.h>
#include <zenutil/cache/rpcrecording.h>

ZEN_THIRD_PARTY_INCLUDES_START
#include <fmt/format.h>
#include <gsl/gsl-lite.hpp>
ZEN_THIRD_PARTY_INCLUDES_END

#include <deque>
#include <thread>

namespace zen::cache {

const RecordedRequestInfo RecordedRequestInfo::NullRequest = {.ContentType = ZenContentType::kUnknownContentType,
															  .AcceptType  = ZenContentType::kUnknownContentType,
															  .SessionId   = Oid::Zero};

}

namespace zen::cache::v1 {

struct RecordedRequest
{
	uint64_t	   Offset;
	uint64_t	   Length;
	ZenContentType ContentType;
	ZenContentType AcceptType;
};

const uint64_t RecordedRequestBlockSize	   = 1ull << 31u;
const uint64_t StandaloneFileSizeThreshold = 1 * 1024 * 1024ull;

struct RecordedRequestsWriter
{
	void BeginWrite(const std::filesystem::path& BasePath)
	{
		m_BasePath = BasePath;
		std::filesystem::create_directories(m_BasePath);
	}

	void EndWrite()
	{
		RwLock::ExclusiveLockScope _(m_Lock);
		m_BlockFiles.clear();

		try
		{
			// Emit some metadata alongside the recording

			DateTime EndTime = DateTime::Now();
			TimeSpan Duration{EndTime.GetTicks() - m_StartTime.GetTicks()};

			CbObjectWriter Cbo;
			Cbo << "time_start" << m_StartTime << "time_end" << EndTime << "duration" << Duration;
			Cbo << "entry_count" << m_Entries.size() << "entry_size" << sizeof(RecordedRequest);
			Cbo << "block_size" << RecordedRequestBlockSize << "standalone_threshold" << StandaloneFileSizeThreshold;

			Cbo.BeginObject("system_info");
			Cbo << "host" << GetMachineName() << "os" << GetOperatingSystemName() << "cpu" << GetCpuName();
			Describe(GetSystemMetrics(), Cbo);
			Cbo.EndObject();
			CbObject Metadata = Cbo.Save();

			WriteFile(m_BasePath / "rpc_recording_metadata.zcb", Metadata.GetBuffer().AsIoBuffer());
		}
		catch (const std::exception& Ex)
		{
			ZEN_WARN("caught exception while generating metadata for RPC recording: {}", Ex.what());
		}

		IoBuffer  IndexBuffer(IoBuffer::Wrap, m_Entries.data(), m_Entries.size() * sizeof(RecordedRequest));
		BasicFile IndexFile;
		IndexFile.Open(m_BasePath / "index.bin", BasicFile::Mode::kTruncate);
		std::error_code Ec;
		IndexFile.WriteAll(IndexBuffer, Ec);
		IndexFile.Close();
		m_Entries.clear();
	}

	void WriteRequest(const RecordedRequestInfo& RequestInfo, const IoBuffer& RequestBuffer)
	{
		RwLock::ExclusiveLockScope Lock(m_Lock);
		uint64_t				   RequestIndex = m_Entries.size();
		RecordedRequest&		   Entry		= m_Entries.emplace_back(RecordedRequest{.Offset	  = ~0ull,
																						 .Length	  = RequestBuffer.Size(),
																						 .ContentType = RequestInfo.ContentType,
																						 .AcceptType  = RequestInfo.AcceptType});

		if (Entry.Length < StandaloneFileSizeThreshold)
		{
			const uint32_t BlockIndex = gsl::narrow<uint32_t>((m_ChunkOffset + Entry.Length) / RecordedRequestBlockSize);
			if (BlockIndex == m_BlockFiles.size())
			{
				std::unique_ptr<BasicFile>& NewBlockFile = m_BlockFiles.emplace_back(std::make_unique<BasicFile>());
				NewBlockFile->Open(m_BasePath / fmt::format("chunks{}.bin", BlockIndex), BasicFile::Mode::kTruncate);
				m_ChunkOffset = BlockIndex * RecordedRequestBlockSize;
			}
			ZEN_ASSERT(BlockIndex < m_BlockFiles.size());
			BasicFile* BlockFile = m_BlockFiles[BlockIndex].get();
			ZEN_ASSERT(BlockFile != nullptr);

			Entry.Offset  = m_ChunkOffset;
			m_ChunkOffset = RoundUp(m_ChunkOffset + Entry.Length, 1u << 4u);
			Lock.ReleaseNow();

			std::error_code Ec;
			BlockFile->Write(RequestBuffer.Data(), RequestBuffer.Size(), Entry.Offset - BlockIndex * RecordedRequestBlockSize, Ec);
			if (Ec)
			{
				Entry.Length = 0;
			}
		}
		else
		{
			Lock.ReleaseNow();

			BasicFile RequestFile;
			RequestFile.Open(m_BasePath / fmt::format("request{}.bin", RequestIndex), BasicFile::Mode::kTruncate);
			std::error_code Ec;
			RequestFile.WriteAll(RequestBuffer, Ec);
			if (Ec)
			{
				Entry.Length = 0;
			}
		}
	}

	std::filesystem::path					m_BasePath;
	mutable RwLock							m_Lock;
	std::vector<RecordedRequest>			m_Entries;
	std::vector<std::unique_ptr<BasicFile>> m_BlockFiles;
	uint64_t								m_ChunkOffset;
	zen::DateTime							m_StartTime = DateTime::Now();
};

struct RecordedRequestsReader
{
	uint64_t BeginRead(const std::filesystem::path& BasePath, bool InMemory)
	{
		m_BasePath = BasePath;
		BasicFile IndexFile;
		IndexFile.Open(m_BasePath / "index.bin", BasicFile::Mode::kRead);
		m_Entries.resize(IndexFile.FileSize() / sizeof(RecordedRequest));
		IndexFile.Read(m_Entries.data(), IndexFile.FileSize(), 0);
		uint64_t MaxChunkPosition = 0;
		for (const RecordedRequest& R : m_Entries)
		{
			if (R.Offset != ~0ull)
			{
				MaxChunkPosition = Max(MaxChunkPosition, R.Offset + R.Length);
			}
		}
		uint32_t BlockCount = gsl::narrow<uint32_t>(MaxChunkPosition / RecordedRequestBlockSize) + 1;
		m_BlockFiles.resize(BlockCount);
		for (uint32_t BlockIndex = 0; BlockIndex < BlockCount; ++BlockIndex)
		{
			if (InMemory)
			{
				BasicFile Chunk;
				Chunk.Open(m_BasePath / fmt::format("chunks{}.bin", BlockIndex), BasicFile::Mode::kRead);
				m_BlockFiles[BlockIndex] = Chunk.ReadAll();
				continue;
			}
			m_BlockFiles[BlockIndex] = IoBufferBuilder::MakeFromFile(m_BasePath / fmt::format("chunks{}.bin", BlockIndex));
		}
		return m_Entries.size();
	}
	void EndRead() { m_BlockFiles.clear(); }

	RecordedRequestInfo ReadRequest(uint64_t RequestIndex, IoBuffer& OutBuffer) const
	{
		if (RequestIndex >= m_Entries.size())
		{
			return RecordedRequestInfo::NullRequest;
		}

		const RecordedRequest& Entry = m_Entries[RequestIndex];
		if (Entry.Length == 0)
		{
			return RecordedRequestInfo::NullRequest;
		}

		if (Entry.Offset != ~0ull)
		{
			uint32_t BlockIndex	 = gsl::narrow<uint32_t>((Entry.Offset + Entry.Length) / RecordedRequestBlockSize);
			uint64_t ChunkOffset = Entry.Offset - (BlockIndex * RecordedRequestBlockSize);
			OutBuffer			 = IoBuffer(m_BlockFiles[BlockIndex], ChunkOffset, Entry.Length);
		}
		else
		{
			OutBuffer = IoBufferBuilder::MakeFromFile(m_BasePath / fmt::format("request{}.bin", RequestIndex));
		}

		return {.ContentType = Entry.ContentType, .AcceptType = Entry.AcceptType, .SessionId = Oid::Zero};
	}

	std::filesystem::path		 m_BasePath;
	std::vector<RecordedRequest> m_Entries;
	std::vector<IoBuffer>		 m_BlockFiles;
};

class DiskRequestRecorder : public IRpcRequestRecorder
{
public:
	DiskRequestRecorder(const std::filesystem::path& BasePath) { m_RecordedRequests.BeginWrite(BasePath); }
	virtual ~DiskRequestRecorder() { m_RecordedRequests.EndWrite(); }

private:
	virtual void RecordRequest(const RecordedRequestInfo& RequestInfo, const IoBuffer& RequestBuffer) override
	{
		m_RecordedRequests.WriteRequest(RequestInfo, RequestBuffer);
	}

	RecordedRequestsWriter m_RecordedRequests;
};

class DiskRequestReplayer : public IRpcRequestReplayer
{
public:
	DiskRequestReplayer(const std::filesystem::path& BasePath, bool InMemory)
	{
		m_RequestCount = m_RequestBuffer.BeginRead(BasePath, InMemory);
	}
	virtual ~DiskRequestReplayer() { m_RequestBuffer.EndRead(); }

	virtual uint64_t GetRequestCount() const override { return m_RequestCount; }

	virtual RecordedRequestInfo GetRequest(uint64_t RequestIndex, IoBuffer& OutBuffer) override
	{
		return m_RequestBuffer.ReadRequest(RequestIndex, OutBuffer);
	}

private:
	std::uint64_t		   m_RequestCount;
	RecordedRequestsReader m_RequestBuffer;
};

}  // namespace zen::cache::v1

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

namespace zen::cache::v2 {

using namespace std::literals;

struct RecordedRequest
{
	uint32_t	   Offset;		 // 4 bytes
	uint32_t	   Length;		 // 4 bytes
	ZenContentType ContentType;	 // 1 byte
	ZenContentType AcceptType;	 // 1 byte
	uint8_t		   OffsetHigh;	 // 1 byte
	uint8_t		   Padding2;	 // 1 byte
	Oid			   SessionId;	 // 12 bytes

	inline uint64_t GetOffset() const { return uint64_t(Offset) + (uint64_t(OffsetHigh) << 32); }
	inline void		SetOffset(uint64_t NewOffset)
	{
		Offset	   = gsl::narrow_cast<uint32_t>(NewOffset & 0xffff'ffff);
		OffsetHigh = gsl::narrow_cast<uint8_t>(NewOffset >> 32);
	}
};

static_assert(sizeof(RecordedRequest) == 24);

const uint64_t RecordedRequestBlockSize	   = 1 * 1024 * 1024 * 1024;  // 1GiB
const uint64_t StandaloneFileSizeThreshold = 16 * 1024 * 1024ull;	  // 16MiB
const uint64_t SegmentRequestCount		   = 10 * 1000 * 1000;
const uint64_t LooseFileThreshold		   = 5000;	// Somewhat arbitrary, but we try to keep the
													// number of files in a directory below this level
													// for performance
const uint64_t SegmentByteThreshold = 16ull * 1024 * 1024 * 1024;
const TimeSpan SegmentTimeThreshold{/* hours */ 1, /* minutes */ 0, /* seconds */ 0};
const int64_t  MaximumBacklogCount = 2000;

std::string
MakeSegmentPath(uint64_t SegmentIndex)
{
	return fmt::format("segment_{:06}", SegmentIndex);
}

struct RecordedRequestsSegmentWriter
{
	RecordedRequestsSegmentWriter()	 = default;
	~RecordedRequestsSegmentWriter() = default;

	RecordedRequestsSegmentWriter(const RecordedRequestsSegmentWriter&) = delete;
	RecordedRequestsSegmentWriter& operator=(const RecordedRequestsSegmentWriter&) = delete;

	void BeginWrite(const std::filesystem::path& BasePath, uint64_t SegmentIndex, uint64_t RequestBaseIndex);
	void WriteRequest(const RecordedRequestInfo& RequestInfo, const IoBuffer& RequestBuffer);
	void EndWrite();

	inline uint64_t GetRequestCount() const
	{
		if (m_RequestCount)
		{
			return m_RequestCount;
		}

		RwLock::SharedLockScope _(m_Lock);
		return m_Entries.size();
	}
	inline uint64_t GetBaseRequestIndex() const { return m_RequestBaseIndex; }
	inline uint64_t GetSegmentIndex() const { return m_SegmentIndex; }
	inline uint64_t GetFileCount() const { return m_FileCount; }
	inline uint64_t GetRequestsByteCount() const { return m_RequestsByteCount; }
	inline DateTime GetStartTime() const { return m_StartTime; }
	inline DateTime GetEndTime() const { return m_EndTime; }

private:
	std::filesystem::path					m_BasePath;
	uint64_t								m_SegmentIndex	   = 0;
	uint64_t								m_RequestBaseIndex = 0;
	uint64_t								m_RequestCount	   = 0;
	std::atomic_uint64_t					m_FileCount{};
	std::atomic_uint64_t					m_RequestsByteCount{};
	mutable RwLock							m_Lock;
	std::vector<RecordedRequest>			m_Entries;
	std::vector<std::unique_ptr<BasicFile>> m_BlockFiles;
	uint64_t								m_ChunkOffset;
	DateTime								m_StartTime = DateTime::Now();
	DateTime								m_EndTime	= DateTime::Now();
};

struct RecordedRequestsWriter
{
	RecordedRequestsWriter();
	~RecordedRequestsWriter();

	void BeginWrite(const std::filesystem::path& BasePath);
	void EndWrite();
	void WriteRequest(const RecordedRequestInfo& RequestInfo, const IoBuffer& RequestBuffer);

private:
	std::filesystem::path m_BasePath;
	zen::DateTime		  m_StartTime = DateTime::Now();

	mutable RwLock												m_Lock;
	std::unique_ptr<RecordedRequestsSegmentWriter>				m_CurrentWriter;
	std::vector<std::unique_ptr<RecordedRequestsSegmentWriter>> m_FinishedSegments;
	std::vector<uint64_t>										m_SegmentBaseIndex;
	uint64_t													m_NextSegmentBaseIndex = 0;

	RecordedRequestsSegmentWriter& EnsureCurrentSegment();
	void						   CommitCurrentSegment(RwLock::ExclusiveLockScope&);
	void						   WriteRecordingMetadata();

	// I/O thread state

	struct QueuedRequest
	{
		RecordedRequestInfo RequestInfo;
		IoBuffer			RequestBuffer;
	};

	std::unique_ptr<std::thread> m_WriterThread;
	std::atomic_bool			 m_IsActive{false};
	std::atomic_int64_t			 m_PendingRequests{0};
	RwLock						 m_RequestQueueLock;
	std::deque<QueuedRequest>	 m_RequestQueue;

	void WriterThreadMain();
};

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

struct RecordedRequestsSegmentReader
{
	RecordedRequestsSegmentReader() = default;

	RecordedRequestsSegmentReader(const RecordedRequestsSegmentReader&) = delete;
	RecordedRequestsSegmentReader& operator=(const RecordedRequestsSegmentReader&) = delete;

	uint64_t			BeginRead(const std::filesystem::path& BasePath, bool InMemory);
	void				EndRead();
	RecordedRequestInfo ReadRequest(uint64_t RequestIndex, IoBuffer& OutBuffer) const;

private:
	std::filesystem::path		 m_BasePath;
	std::vector<RecordedRequest> m_Entries;
	std::vector<IoBuffer>		 m_BlockFiles;
};

struct RecordedRequestsReader
{
	uint64_t			BeginRead(const std::filesystem::path& BasePath, bool InMemory);
	void				EndRead();
	RecordedRequestInfo ReadRequest(uint64_t RequestIndex, IoBuffer& OutBuffer) const;

private:
	struct SegmentInfo
	{
		uint64_t SegmentIndex;
		uint64_t BaseRequestIndex;
		uint64_t RequestCount;
		uint64_t RequestBytes;
		DateTime StartTime{0};
		DateTime EndTime{0};
	};

	bool					 m_InMemory = false;
	std::filesystem::path	 m_BasePath;
	std::vector<SegmentInfo> m_KnownSegments;

	mutable RwLock														m_SegmentLock;
	mutable std::vector<std::unique_ptr<RecordedRequestsSegmentReader>> m_SegmentReaders;
};

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

void
RecordedRequestsSegmentWriter::BeginWrite(const std::filesystem::path& BasePath, uint64_t SegmentIndex, uint64_t RequestBaseIndex)
{
	m_BasePath		   = BasePath;
	m_SegmentIndex	   = SegmentIndex;
	m_RequestBaseIndex = RequestBaseIndex;
	std::filesystem::create_directories(m_BasePath);
}

void
RecordedRequestsSegmentWriter::EndWrite()
{
	RwLock::ExclusiveLockScope _(m_Lock);
	m_RequestCount = m_Entries.size();
	m_BlockFiles.clear();

	// Emit some metadata alongside the recording

	try
	{
		m_EndTime = DateTime::Now();
		TimeSpan Duration{m_EndTime.GetTicks() - m_StartTime.GetTicks()};

		CbObjectWriter Cbo;
		Cbo << "time_start" << m_StartTime << "time_end" << m_EndTime << "duration" << Duration;
		Cbo << "segment_index" << m_SegmentIndex;
		Cbo << "entry_count" << m_RequestCount << "entry_size" << sizeof(RecordedRequest);
		Cbo << "block_size" << RecordedRequestBlockSize << "standalone_threshold" << StandaloneFileSizeThreshold;

		Cbo.BeginObject("system_info");
		Cbo << "host" << GetMachineName() << "os" << GetOperatingSystemName() << "cpu" << GetCpuName();
		Cbo.EndObject();
		CbObject Metadata = Cbo.Save();

		WriteFile(m_BasePath / "rpc_segment_info.zcb", Metadata.GetBuffer().AsIoBuffer());
	}
	catch (const std::exception& Ex)
	{
		ZEN_WARN("caught exception while writing segment metadata for RPC recording: {}", Ex.what());
	}

	IoBuffer  IndexBuffer(IoBuffer::Wrap, m_Entries.data(), m_Entries.size() * sizeof(RecordedRequest));
	BasicFile IndexFile;
	IndexFile.Open(m_BasePath / "index.bin", BasicFile::Mode::kTruncate);
	std::error_code Ec;
	IndexFile.WriteAll(IndexBuffer, Ec);
	IndexFile.Close();

	// note that simply calling `.reset()` here will *not* release backing memory
	// and it's important that we do because on high traffic servers this will use
	// a lot of memory otherwise
	std::vector<RecordedRequest> EmptyEntries;
	swap(m_Entries, EmptyEntries);
}

void
RecordedRequestsSegmentWriter::WriteRequest(const RecordedRequestInfo& RequestInfo, const IoBuffer& RequestBuffer)
{
	const uint64_t RequestBufferSize = RequestBuffer.GetSize();
	uint64_t	   RequestIndex		 = ~0ull;

	{
		RwLock::ExclusiveLockScope Lock(m_Lock);
		RequestIndex		   = m_Entries.size();
		RecordedRequest& Entry = m_Entries.emplace_back(RecordedRequest{.Offset		 = ~0u,
																		.Length		 = uint32_t(RequestBufferSize & 0xffffFFFFu),
																		.ContentType = RequestInfo.ContentType,
																		.AcceptType	 = RequestInfo.AcceptType,
																		.OffsetHigh	 = 0,
																		.Padding2	 = 0,
																		.SessionId	 = RequestInfo.SessionId});

		if (Entry.Length < StandaloneFileSizeThreshold)
		{
			const uint32_t BlockIndex = gsl::narrow<uint32_t>((m_ChunkOffset + Entry.Length) / RecordedRequestBlockSize);

			if (BlockIndex == m_BlockFiles.size())
			{
				std::unique_ptr<BasicFile>& NewBlockFile = m_BlockFiles.emplace_back(std::make_unique<BasicFile>());
				NewBlockFile->Open(m_BasePath / fmt::format("chunks{}.bin", BlockIndex), BasicFile::Mode::kTruncate);
				m_ChunkOffset = BlockIndex * RecordedRequestBlockSize;
				++m_FileCount;
			}

			ZEN_ASSERT(BlockIndex < m_BlockFiles.size());
			BasicFile* BlockFile = m_BlockFiles[BlockIndex].get();
			ZEN_ASSERT(BlockFile != nullptr);

			// Note that this is the overall logical offset, not the offset within a single file
			const uint64_t ChunkWriteOffset = m_ChunkOffset;
			m_ChunkOffset					= RoundUp(ChunkWriteOffset + Entry.Length, 1u << 4u);
			Entry.SetOffset(ChunkWriteOffset);
			Lock.ReleaseNow();

			std::error_code Ec;
			BlockFile->Write(RequestBuffer.Data(), RequestBuffer.Size(), ChunkWriteOffset - (BlockIndex * RecordedRequestBlockSize), Ec);
			if (Ec)
			{
				// We cannot simply use `Entry` here because the vector may
				// have been reallocated causing the entry to be in a different
				// location
				RwLock::ExclusiveLockScope _(m_Lock);
				m_Entries[RequestIndex].Length = 0;
				return;
			}

			m_RequestsByteCount.fetch_add(RequestBuffer.GetSize());

			return;
		}
	}

	// Write request data to standalone file

	try
	{
		BasicFile RequestFile;
		RequestFile.Open(m_BasePath / fmt::format("request{}.bin", RequestIndex), BasicFile::Mode::kTruncate);

		if (RequestBufferSize > std::numeric_limits<uint32_t>::max())
		{
			// The exact value of the entry is not important, we will use
			// the size of the standalone file regardless when performing
			// the read
			RwLock::ExclusiveLockScope _(m_Lock);
			m_Entries[RequestIndex].Length = std::numeric_limits<uint32_t>::max();
		}

		++m_FileCount;

		std::error_code Ec;
		RequestFile.WriteAll(RequestBuffer, Ec);

		if (Ec)
		{
			RwLock::ExclusiveLockScope _(m_Lock);
			m_Entries[RequestIndex].Length = 0;
		}
		else
		{
			m_RequestsByteCount.fetch_add(RequestBuffer.GetSize());
		}
	}
	catch (const std::exception&)
	{
		RwLock::ExclusiveLockScope _(m_Lock);
		m_Entries[RequestIndex].Length = 0;
	}
}

uint64_t
RecordedRequestsSegmentReader::BeginRead(const std::filesystem::path& BasePath, bool InMemory)
{
	m_BasePath = BasePath;
	BasicFile IndexFile;
	IndexFile.Open(m_BasePath / "index.bin", BasicFile::Mode::kRead);
	m_Entries.resize(IndexFile.FileSize() / sizeof(RecordedRequest));
	IndexFile.Read(m_Entries.data(), IndexFile.FileSize(), 0);
	uint64_t MaxChunkPosition = 0;
	for (const RecordedRequest& R : m_Entries)
	{
		if (R.Offset != ~0u)
		{
			MaxChunkPosition = Max(MaxChunkPosition, R.GetOffset() + R.Length);
		}
	}
	uint32_t BlockCount = gsl::narrow<uint32_t>(MaxChunkPosition / RecordedRequestBlockSize) + 1;
	m_BlockFiles.resize(BlockCount);
	for (uint32_t BlockIndex = 0; BlockIndex < BlockCount; ++BlockIndex)
	{
		if (InMemory)
		{
			BasicFile Chunk;
			Chunk.Open(m_BasePath / fmt::format("chunks{}.bin", BlockIndex), BasicFile::Mode::kRead);
			m_BlockFiles[BlockIndex] = Chunk.ReadAll();
			continue;
		}
		m_BlockFiles[BlockIndex] = IoBufferBuilder::MakeFromFile(m_BasePath / fmt::format("chunks{}.bin", BlockIndex));
	}
	return m_Entries.size();
}

void
RecordedRequestsSegmentReader::EndRead()
{
	m_BlockFiles.clear();
}

RecordedRequestInfo
RecordedRequestsSegmentReader::ReadRequest(uint64_t RequestIndex, IoBuffer& OutBuffer) const
{
	if (RequestIndex >= m_Entries.size())
	{
		return RecordedRequestInfo::NullRequest;
	}
	const RecordedRequest& Entry = m_Entries[RequestIndex];
	if (Entry.Length == 0)
	{
		return RecordedRequestInfo::NullRequest;
	}

	RecordedRequestInfo RequestInfo = {.ContentType = Entry.ContentType, .AcceptType = Entry.AcceptType, .SessionId = Entry.SessionId};

	if (Entry.Offset != ~0u)
	{
		// Inline in block file
		const uint64_t EntryOffset = Entry.GetOffset();
		const uint32_t BlockIndex  = gsl::narrow<uint32_t>((EntryOffset + Entry.Length) / RecordedRequestBlockSize);
		const uint64_t ChunkOffset = EntryOffset - (BlockIndex * RecordedRequestBlockSize);
		OutBuffer				   = IoBuffer(m_BlockFiles[BlockIndex], ChunkOffset, Entry.Length);

		return RequestInfo;
	}

	// Standalone file
	OutBuffer = IoBufferBuilder::MakeFromFile(m_BasePath / fmt::format("request{}.bin", RequestIndex));

	return RequestInfo;
}

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

RecordedRequestsWriter::RecordedRequestsWriter()
{
}

RecordedRequestsWriter::~RecordedRequestsWriter()
{
	EndWrite();
}

void
RecordedRequestsWriter::BeginWrite(const std::filesystem::path& BasePath)
{
	m_BasePath = BasePath;
	m_IsActive = true;

	m_WriterThread.reset(new std::thread(&RecordedRequestsWriter::WriterThreadMain, this));
}

void
RecordedRequestsWriter::EndWrite()
{
	if (m_WriterThread)
	{
		m_IsActive				   = false;
		const int64_t PendingCount = m_PendingRequests.fetch_add(1);
		m_PendingRequests.notify_all();

		if (PendingCount)
		{
			ZEN_INFO("waiting for RPC recorder writing thread to drain {} pending items", PendingCount);
		}

		if (m_WriterThread->joinable())
		{
			m_WriterThread->join();
		}

		m_WriterThread.reset();
	}
}

void
RecordedRequestsWriter::WriteRequest(const RecordedRequestInfo& RequestInfo, const IoBuffer& RequestBuffer)
{
	if (m_IsActive)
	{
		IoBuffer OwnedRequest = RequestBuffer;
		OwnedRequest.MakeOwned();

		{
			RwLock::ExclusiveLockScope _(m_RequestQueueLock);
			m_RequestQueue.push_back(QueuedRequest{RequestInfo, std::move(OwnedRequest)});
			m_PendingRequests.fetch_add(1);
		}

		m_PendingRequests.notify_all();
	}
}

void
RecordedRequestsWriter::WriterThreadMain()
{
	SetCurrentThreadName("rpc_writer");
	EnsureCurrentSegment();

	while (m_IsActive)
	{
		m_PendingRequests.wait(0);

		while (m_PendingRequests)
		{
			RwLock::ExclusiveLockScope _(m_RequestQueueLock);
			if (!m_RequestQueue.empty())
			{
				bool DrainBacklog = false;

				do
				{
					QueuedRequest Request = m_RequestQueue.front();

					m_RequestQueue.pop_front();
					m_PendingRequests.fetch_sub(1);

					// For a sufficiently large backlog, keep blocking queueing operations
					// until we get below the threshold
					DrainBacklog = m_RequestQueue.size() >= MaximumBacklogCount;

					if (!DrainBacklog)
					{
						_.ReleaseNow();
					}

					try
					{
						RecordedRequestsSegmentWriter& Writer = EnsureCurrentSegment();
						Writer.WriteRequest(Request.RequestInfo, Request.RequestBuffer);
					}
					catch (const std::exception&)
					{
						// TODO: what's the right behaviour here? The most likely cause would
						// be some I/O error and we probably ought to just shut down recording
						// at that point
					}
				} while (DrainBacklog);
			}
			else
			{
				// shutdown increments this counter so we need to decrement it
				// here even though we didn't process any request
				m_PendingRequests.fetch_sub(1);
			}
		}
	}

	RwLock::ExclusiveLockScope _(m_Lock);
	CommitCurrentSegment(_);
	WriteRecordingMetadata();
}

RecordedRequestsSegmentWriter&
RecordedRequestsWriter::EnsureCurrentSegment()
{
	RwLock::ExclusiveLockScope _(m_Lock);

	if (m_CurrentWriter)
	{
		bool StartNewSegment = false;

		TimeSpan SegmentAge(DateTime::NowTicks() - m_CurrentWriter->GetStartTime().GetTicks());

		if (m_CurrentWriter->GetRequestCount() >= SegmentRequestCount)
		{
			ZEN_DEBUG("starting new RPC recording segment due to request count >= {}", SegmentRequestCount);
			StartNewSegment = true;
		}
		else if (m_CurrentWriter->GetFileCount() >= LooseFileThreshold)
		{
			ZEN_DEBUG("starting new RPC recording segment due to file count >= {}", LooseFileThreshold);
			StartNewSegment = true;
		}
		else if (m_CurrentWriter->GetRequestsByteCount() >= SegmentByteThreshold)
		{
			ZEN_DEBUG("starting new RPC recording segment due to footprint >= {} bytes", SegmentByteThreshold);
			StartNewSegment = true;
		}
		else if (SegmentAge >= SegmentTimeThreshold)
		{
			ZEN_DEBUG("starting new RPC recording segment due to age >= {}",
					  NiceTimeSpanMs(SegmentTimeThreshold.GetTicks() / TimeSpan::TicksPerMillisecond));
			StartNewSegment = true;
		}

		if (StartNewSegment)
		{
			CommitCurrentSegment(_);
		}
	}

	if (!m_CurrentWriter)
	{
		const uint64_t SegmentIndex = m_FinishedSegments.size();
		m_CurrentWriter				= std::make_unique<RecordedRequestsSegmentWriter>();

		m_CurrentWriter->BeginWrite(m_BasePath / MakeSegmentPath(SegmentIndex), SegmentIndex, m_NextSegmentBaseIndex);
	}

	return *m_CurrentWriter;
}

void
RecordedRequestsWriter::CommitCurrentSegment(RwLock::ExclusiveLockScope&)
{
	if (m_CurrentWriter)
	{
		RecordedRequestsSegmentWriter& Writer = *m_CurrentWriter;
		m_FinishedSegments.push_back(std::move(m_CurrentWriter));
		m_SegmentBaseIndex.push_back(m_NextSegmentBaseIndex);
		m_NextSegmentBaseIndex += Writer.GetRequestCount();

		Writer.EndWrite();
	}
}

void
RecordedRequestsWriter::WriteRecordingMetadata()
{
	try
	{
		DateTime EndTime = DateTime::Now();
		TimeSpan Duration{EndTime.GetTicks() - m_StartTime.GetTicks()};

		CbObjectWriter Cbo;
		Cbo << "time_start" << m_StartTime << "time_end" << EndTime << "duration" << Duration << "format_version" << 2;

		Cbo.BeginObject("system_info");
		Cbo << "host" << GetMachineName() << "os" << GetOperatingSystemName() << "cpu" << GetCpuName();
		Cbo << "segment_count" << m_FinishedSegments.size();
		Cbo << "block_size" << RecordedRequestBlockSize;
		Cbo << "standalone_threshold" << StandaloneFileSizeThreshold;
		Cbo << "segment_request_count" << SegmentRequestCount;
		Cbo << "segment_file_threshold" << LooseFileThreshold;
		Cbo << "segment_byte_threshold" << SegmentByteThreshold;

		Describe(GetSystemMetrics(), Cbo);
		Cbo.EndObject();

		Cbo.BeginArray("segments");

		for (auto& Segment : m_FinishedSegments)
		{
			Cbo.BeginObject();
			Cbo << "segment" << Segment->GetSegmentIndex();
			Cbo << "base_index" << Segment->GetBaseRequestIndex();
			Cbo << "request_count" << Segment->GetRequestCount();
			Cbo << "request_bytes" << Segment->GetRequestsByteCount();
			Cbo << "start_time" << Segment->GetStartTime();
			Cbo << "end_time" << Segment->GetEndTime();
			Cbo.EndObject();
		}

		Cbo.EndArray();

		CbObject Metadata = Cbo.Save();

		WriteFile(m_BasePath / "rpc_recording_info.zcb", Metadata.GetBuffer().AsIoBuffer());
	}
	catch (const std::exception& Ex)
	{
		ZEN_WARN("caught exception while writing metadata for RPC recording: {}", Ex.what());
	}
}

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

uint64_t
RecordedRequestsReader::BeginRead(const std::filesystem::path& BasePath, bool InMemory)
{
	m_InMemory = InMemory;
	m_BasePath = BasePath;

	std::error_code Ec;
	BasicFile		InfoFile;
	InfoFile.Open(m_BasePath / "rpc_recording_info.zcb", BasicFile::Mode::kRead, Ec);

	if (!Ec)
	{
		try
		{
			CbObject CbInfo = LoadCompactBinaryObject(InfoFile.ReadAll());

			uint64_t TotalRequestCount = 0;
			uint64_t MaxSegmentIndex   = 0;

			for (auto SegmentElement : CbInfo["segments"])
			{
				CbObjectView Segment = SegmentElement.AsObjectView();

				const SegmentInfo& Info = m_KnownSegments.emplace_back(SegmentInfo{.SegmentIndex	 = Segment["segment"sv].AsUInt64(),
																				   .BaseRequestIndex = Segment["base_index"sv].AsUInt64(),
																				   .RequestCount = Segment["request_count"sv].AsUInt64(),
																				   .RequestBytes = Segment["request_bytes"sv].AsUInt64(),
																				   .StartTime	 = Segment["start_time"sv].AsDateTime(),
																				   .EndTime		 = Segment["end_time"sv].AsDateTime()});

				TotalRequestCount += Info.RequestCount;
				MaxSegmentIndex = Max(MaxSegmentIndex, Info.SegmentIndex);
			}

			m_SegmentReaders.resize(MaxSegmentIndex + 1);

			return TotalRequestCount;
		}
		catch (const std::exception& Ex)
		{
			ZEN_WARN("could not read metadata file: {}", Ex.what());
		}
	}

	ZEN_INFO("recovering segment info for '{}'", BasePath);

	uint64_t TotalRequestCount = 0;
	uint64_t MaxSegmentIndex   = 0;

	try
	{
		for (int SegmentIndex = 0;; ++SegmentIndex)
		{
			const std::filesystem::path ZcbPath = BasePath / MakeSegmentPath(SegmentIndex) / "rpc_segment_info.zcb";
			FileContents				Fc		= ReadFile(ZcbPath);

			if (Fc.ErrorCode)
				break;

			if (IoBuffer SegmentInfoBuffer = Fc.Flatten())
			{
				CbObject Segment = LoadCompactBinaryObject(SegmentInfoBuffer);

				const SegmentInfo& Info = m_KnownSegments.emplace_back(SegmentInfo{.SegmentIndex = Segment["segment_index"sv].AsUInt64(),
																				   .BaseRequestIndex = 0,
																				   .RequestCount	 = Segment["entry_count"sv].AsUInt64(),
																				   .RequestBytes	 = 0,
																				   .StartTime		 = Segment["time_start"sv].AsDateTime(),
																				   .EndTime			 = Segment["time_end"sv].AsDateTime()});

				TotalRequestCount += Info.RequestCount;
				MaxSegmentIndex = Max(MaxSegmentIndex, Info.SegmentIndex);
			}
		}
	}
	catch (const std::exception&)
	{
	}

	std::sort(begin(m_KnownSegments), end(m_KnownSegments), [](const auto& Lhs, const auto& Rhs) {
		return Lhs.SegmentIndex < Rhs.SegmentIndex;
	});

	uint64_t SegmentRequestOffset = 0;

	for (SegmentInfo& Info : m_KnownSegments)
	{
		Info.BaseRequestIndex = SegmentRequestOffset;
		SegmentRequestOffset += Info.RequestCount;
	}

	m_SegmentReaders.resize(MaxSegmentIndex + 1);

	return TotalRequestCount;
}

void
RecordedRequestsReader::EndRead()
{
	RwLock::ExclusiveLockScope _(m_SegmentLock);
	m_KnownSegments.clear();
	m_SegmentReaders.clear();
	m_BasePath.clear();
}

RecordedRequestInfo
RecordedRequestsReader::ReadRequest(uint64_t RequestIndex, IoBuffer& OutBuffer) const
{
	auto EnsureSegment = [&](uint64_t SegmentIndex) -> const RecordedRequestsSegmentReader& {
		{
			RwLock::SharedLockScope _(m_SegmentLock);

			if (auto SegmentReaderPtr = m_SegmentReaders[SegmentIndex].get())
			{
				return *SegmentReaderPtr;
			}
		}

		RwLock::ExclusiveLockScope _(m_SegmentLock);

		auto& SegmentReaderPtr = m_SegmentReaders[SegmentIndex];

		if (!SegmentReaderPtr)
		{
			RecordedRequestsSegmentReader* NewSegment = new RecordedRequestsSegmentReader;
			NewSegment->BeginRead(m_BasePath / MakeSegmentPath(SegmentIndex), m_InMemory);
			SegmentReaderPtr.reset(NewSegment);
		}

		return *(SegmentReaderPtr.get());
	};

	for (auto& Segment : m_KnownSegments)
	{
		if (Segment.RequestCount > RequestIndex)
		{
			return EnsureSegment(Segment.SegmentIndex).ReadRequest(RequestIndex, OutBuffer);
		}
		else
		{
			RequestIndex -= Segment.RequestCount;
		}
	}

	return RecordedRequestInfo::NullRequest;
}

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

class DiskRequestRecorder : public IRpcRequestRecorder
{
public:
	DiskRequestRecorder(const std::filesystem::path& BasePath) { m_RecordedRequests.BeginWrite(BasePath); }
	virtual ~DiskRequestRecorder() { m_RecordedRequests.EndWrite(); }

	virtual void RecordRequest(const RecordedRequestInfo& RequestInfo, const IoBuffer& RequestBuffer) override
	{
		m_RecordedRequests.WriteRequest(RequestInfo, RequestBuffer);
	}

private:
	RecordedRequestsWriter m_RecordedRequests;
};

class DiskRequestReplayer : public IRpcRequestReplayer
{
public:
	DiskRequestReplayer(const std::filesystem::path& BasePath, bool InMemory)
	{
		m_RequestCount = m_RequestReader.BeginRead(BasePath, InMemory);
	}
	virtual ~DiskRequestReplayer() { m_RequestReader.EndRead(); }

	static bool IsCompatible(const std::filesystem::path& BasePath)
	{
		if (std::filesystem::exists(BasePath / "rpc_recording_info.zcb"))
		{
			return true;
		}

		const std::filesystem::path SegmentZero = BasePath / MakeSegmentPath(0);

		if (std::filesystem::exists(SegmentZero / "rpc_segment_info.zcb") && std::filesystem::exists(SegmentZero / "index.bin"))
		{
			// top-level metadata is missing, possibly because of premature exit
			// on the recording side

			return true;
		}

		return false;
	}

	virtual uint64_t GetRequestCount() const override { return m_RequestCount; }

	virtual RecordedRequestInfo GetRequest(uint64_t RequestIndex, IoBuffer& OutBuffer) override
	{
		return m_RequestReader.ReadRequest(RequestIndex, OutBuffer);
	}

private:
	std::uint64_t		   m_RequestCount;
	RecordedRequestsReader m_RequestReader;
};

}  // namespace zen::cache::v2

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

namespace zen::cache {

std::unique_ptr<cache::IRpcRequestRecorder>
MakeDiskRequestRecorder(const std::filesystem::path& BasePath)
{
	return std::make_unique<v2::DiskRequestRecorder>(BasePath);
}

std::unique_ptr<cache::IRpcRequestReplayer>
MakeDiskRequestReplayer(const std::filesystem::path& BasePath, bool InMemory)
{
	if (v2::DiskRequestReplayer::IsCompatible(BasePath))
	{
		return std::make_unique<v2::DiskRequestReplayer>(BasePath, InMemory);
	}
	else
	{
		return std::make_unique<v1::DiskRequestReplayer>(BasePath, InMemory);
	}
}

#if ZEN_WITH_TESTS

void
rpcrecord_forcelink()
{
}

TEST_SUITE_BEGIN("rpc.recording");

TEST_CASE("rpc.record")
{
	ScopedTemporaryDirectory TempDir;
	auto					 Path = TempDir.Path();

	const Oid SessionId = GetSessionId();

	using namespace std::literals;

	{
		cache::v2::DiskRequestRecorder Recorder{Path};

		for (int i = 0; i < 1000; ++i)
		{
			RecordedRequestInfo RequestInfo{.ContentType = ZenContentType::kCbObject,
											.AcceptType	 = ZenContentType::kCbObject,
											.SessionId	 = SessionId};

			CbObjectWriter RequestPayload;
			RequestPayload << "test"sv << true;
			RequestPayload << "index"sv << i;
			CbObject Req		   = RequestPayload.Save();
			IoBuffer RequestBuffer = Req.GetBuffer().AsIoBuffer();

			Recorder.RecordRequest(RequestInfo, RequestBuffer);
		}
	}

	{
		cache::v2::DiskRequestReplayer Replayer{Path, false};

		for (int i = 0; i < 1000; ++i)
		{
			IoBuffer			RequestBuffer;
			RecordedRequestInfo RequestInfo = Replayer.GetRequest(i, RequestBuffer);

			CHECK(RequestInfo.AcceptType == ZenContentType::kCbObject);
			CHECK(RequestInfo.ContentType == ZenContentType::kCbObject);
			CHECK(RequestInfo.SessionId == SessionId);

			CbObject Req = LoadCompactBinaryObject(RequestBuffer);
			CHECK_EQ(Req["index"sv].AsInt32(), i);
			CHECK_EQ(Req["test"sv].AsBool(), true);
		}
	}
}

TEST_SUITE_END();

#endif

}  // namespace zen::cache