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

#include "symbol_resolver.h"

#include <zencore/filesystem.h>
#include <zencore/fmtutils.h>
#include <zencore/logging.h>
#include <zencore/process.h>
#include <zencore/string.h>
#include <zenhttp/httpclient.h>

#include <algorithm>
#include <filesystem>
#include <mutex>
#include <unordered_map>
#include <vector>

#if !ZEN_PLATFORM_WINDOWS
#	include <cerrno>
#	include <unistd.h>
#endif

#if ZEN_PLATFORM_WINDOWS

ZEN_THIRD_PARTY_INCLUDES_START
#	include <Foundation/PDB_PointerUtil.h>
#	include <PDB.h>
#	include <PDB_CoalescedMSFStream.h>
#	include <PDB_DBIStream.h>
#	include <PDB_ImageSectionStream.h>
#	include <PDB_InfoStream.h>
#	include <PDB_ModuleInfoStream.h>
#	include <PDB_ModuleLineStream.h>
#	include <PDB_ModuleSymbolStream.h>
#	include <PDB_PublicSymbolStream.h>
#	include <PDB_RawFile.h>
ZEN_THIRD_PARTY_INCLUDES_END

#	include <zencore/windows.h>

ZEN_THIRD_PARTY_INCLUDES_START
#	include <DbgHelp.h>
ZEN_THIRD_PARTY_INCLUDES_END

#endif	// ZEN_PLATFORM_WINDOWS

namespace zen::trace_detail {

//////////////////////////////////////////////////////////////////////////////
// Null resolver (used when symbolication is off or unsupported)

class NullSymbolResolver final : public SymbolResolver
{
public:
	void		LoadModule(const ModuleInfo&) override {}
	std::string Resolve(uint64_t) const override { return {}; }
};

#if ZEN_PLATFORM_WINDOWS

//////////////////////////////////////////////////////////////////////////////
// Helpers shared by Windows backends

static std::string
FormatSymbol(std::string_view Name, uint64_t Displacement)
{
	if (Displacement == 0)
	{
		return std::string(Name);
	}
	return fmt::format("{} + 0x{:X}", Name, Displacement);
}

//////////////////////////////////////////////////////////////////////////////
// Memory-mapped file helper

namespace {

	struct MappedFile
	{
		const void* Data		  = nullptr;
		size_t		Size		  = 0;
		HANDLE		FileHandle	  = INVALID_HANDLE_VALUE;
		HANDLE		MappingHandle = nullptr;

		MappedFile() = default;
		~MappedFile() { Close(); }

		bool Open(const std::filesystem::path& Path)
		{
			FileHandle = CreateFileW(Path.c_str(), GENERIC_READ, FILE_SHARE_READ, nullptr, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, nullptr);
			if (FileHandle == INVALID_HANDLE_VALUE)
			{
				return false;
			}

			LARGE_INTEGER FileSize;
			if (!GetFileSizeEx(FileHandle, &FileSize) || FileSize.QuadPart == 0)
			{
				Close();
				return false;
			}

			MappingHandle = CreateFileMappingW(FileHandle, nullptr, PAGE_READONLY, 0, 0, nullptr);
			if (MappingHandle == nullptr)
			{
				Close();
				return false;
			}

			Data = MapViewOfFile(MappingHandle, FILE_MAP_READ, 0, 0, 0);
			if (Data == nullptr)
			{
				Close();
				return false;
			}

			Size = size_t(FileSize.QuadPart);
			return true;
		}

		void Close()
		{
			if (Data != nullptr)
			{
				UnmapViewOfFile(Data);
				Data = nullptr;
			}
			if (MappingHandle != nullptr)
			{
				CloseHandle(MappingHandle);
				MappingHandle = nullptr;
			}
			if (FileHandle != INVALID_HANDLE_VALUE)
			{
				CloseHandle(FileHandle);
				FileHandle = INVALID_HANDLE_VALUE;
			}
			Size = 0;
		}

		MappedFile(const MappedFile&) = delete;
		MappedFile& operator=(const MappedFile&) = delete;
	};

	// Format an ImageId (16-byte GUID + 4-byte Age) as the hex key used in
	// symbol server URLs: <GUID_no_dashes><Age_hex>, e.g. "A1B2C3...1".
	std::string FormatImageIdKey(const eastl::vector<uint8_t>& ImageId)
	{
		if (ImageId.size() < 20)
		{
			return {};
		}

		// GUID bytes are stored as {Data1 LE, Data2 LE, Data3 LE, Data4[8]}.
		// The symbol server key encodes Data1/2/3 as big-endian hex.
		const uint8_t* G = ImageId.data();

		uint32_t Data1;
		uint16_t Data2;
		uint16_t Data3;
		memcpy(&Data1, G + 0, 4);
		memcpy(&Data2, G + 4, 2);
		memcpy(&Data3, G + 6, 2);

		uint32_t Age;
		memcpy(&Age, ImageId.data() + 16, 4);

		return fmt::format("{:08X}{:04X}{:04X}{:02X}{:02X}{:02X}{:02X}{:02X}{:02X}{:02X}{:02X}{:x}",
						   Data1,
						   Data2,
						   Data3,
						   G[8],
						   G[9],
						   G[10],
						   G[11],
						   G[12],
						   G[13],
						   G[14],
						   G[15],
						   Age);
	}

	// PdbName originates from module metadata in an untrusted trace file and is used
	// to build both a filesystem path and an HTTP request path. Restrict it to a safe
	// subset so a malicious trace cannot traverse out of the cache dir, inject URL
	// syntax, or trip cross-platform path parsing quirks (e.g. `\` is a separator on
	// Windows but not POSIX, so filename() doesn't always strip it).
	bool IsSafePdbName(std::string_view Name)
	{
		constexpr AsciiSet SafeChars(
			"abcdefghijklmnopqrstuvwxyz"
			"ABCDEFGHIJKLMNOPQRSTUVWXYZ"
			"0123456789"
			"._-+");

		if (Name.empty() || Name.size() > 255 || Name == "." || Name == "..")
		{
			return false;
		}
		return AsciiSet::HasOnly(Name, SafeChars);
	}

	const std::filesystem::path& GetSymbolCacheDir()
	{
		// Use %TEMP%/zen-symbols as the default cache location.
		static const std::filesystem::path s_CacheDir = [] {
			std::filesystem::path TempDir = std::filesystem::temp_directory_path();
			return TempDir / "zen-symbols";
		}();
		return s_CacheDir;
	}

	// Try to download a PDB from a symbol server URL.
	// Returns the local cache path on success, empty path on failure.
	std::filesystem::path DownloadPdb(std::string_view			   ServerUrl,
									  std::string_view			   PdbName,
									  const std::string&		   ImageIdKey,
									  const std::filesystem::path& CacheDir)
	{
		// Cache path mirrors the server structure
		std::filesystem::path CachePath = CacheDir / PdbName / ImageIdKey / PdbName;

		// Already cached?
		std::error_code Ec;
		if (std::filesystem::exists(CachePath, Ec))
		{
			return CachePath;
		}

		ZEN_INFO("Downloading {} from symbol server...", PdbName);

		try
		{
			std::string RequestPath = fmt::format("/{}/{}/{}", PdbName, ImageIdKey, PdbName);

			zen::HttpClientSettings Settings;
			Settings.Timeout			= std::chrono::milliseconds(30000);
			Settings.ConnectTimeout		= std::chrono::milliseconds(5000);
			Settings.FollowRedirects	= true;
			Settings.ExpectedErrorCodes = {zen::HttpResponseCode::NotFound};

			zen::HttpClient Http(ServerUrl, Settings);

			zen::HttpClient::Response Response = Http.Get(RequestPath);

			if (!Response)
			{
				ZEN_DEBUG("Symbol server: {} not found (HTTP {})", PdbName, int(Response.StatusCode));
				return {};
			}

			// Write to cache using zencore file I/O
			std::filesystem::create_directories(CachePath.parent_path(), Ec);
			zen::WriteFile(CachePath, Response.ResponsePayload);

			ZEN_INFO("Cached {} ({})", PdbName, zen::NiceBytes(Response.ResponsePayload.GetSize()));
			return CachePath;
		}
		catch (const std::exception& Ex)
		{
			ZEN_WARN("Symbol server download failed for {}: {}", PdbName, Ex.what());
			return {};
		}
	}

	// Parse _NT_SYMBOL_PATH to extract symbol server URLs.
	// Format: "srv*<cache>*<url>" or "symsrv*symsrv.dll*<cache>*<url>" or just a URL.
	// Returns a list of server URLs to try.
	const std::vector<std::string>& ParseSymbolPath()
	{
		static const std::vector<std::string> s_Servers = [] {
			std::vector<std::string> Servers;

			const char* EnvPath = std::getenv("_NT_SYMBOL_PATH");
			if (EnvPath == nullptr || EnvPath[0] == '\0')
			{
				// Default to Microsoft public symbol server
				Servers.push_back("https://msdl.microsoft.com/download/symbols");
				return Servers;
			}

			std::string_view Path(EnvPath);

			// Split on ';' for multiple entries
			while (!Path.empty())
			{
				size_t			 Semi  = Path.find(';');
				std::string_view Entry = (Semi != std::string_view::npos) ? Path.substr(0, Semi) : Path;
				Path				   = (Semi != std::string_view::npos) ? Path.substr(Semi + 1) : std::string_view{};

				// Look for srv* or symsrv* prefix — the last '*'-delimited token is the server URL.
				if (Entry.substr(0, 4) == "srv*" || Entry.substr(0, 7) == "symsrv*")
				{
					size_t LastStar = Entry.rfind('*');
					if (LastStar != std::string_view::npos && LastStar + 1 < Entry.size())
					{
						std::string_view Url = Entry.substr(LastStar + 1);
						if (Url.substr(0, 4) == "http")
						{
							Servers.emplace_back(Url);
						}
					}
				}
			}

			if (Servers.empty())
			{
				Servers.push_back("https://msdl.microsoft.com/download/symbols");
			}

			return Servers;
		}();
		return s_Servers;
	}

	// Copy a local PDB into the symbol cache so that future analysis of traces
	// from this build succeeds even after the binary is recompiled.
	void CacheLocalPdb(const std::filesystem::path& PdbPath,
					   std::string_view				PdbName,
					   const std::string&			ImageIdKey,
					   const std::filesystem::path& CacheDir)
	{
		std::filesystem::path CachePath = CacheDir / PdbName / ImageIdKey / PdbName;
		std::error_code		  Ec;
		if (std::filesystem::exists(CachePath, Ec))
		{
			return;
		}

		std::filesystem::create_directories(CachePath.parent_path(), Ec);
		if (Ec)
		{
			return;
		}

		std::filesystem::copy_file(PdbPath, CachePath, std::filesystem::copy_options::skip_existing, Ec);
		if (!Ec)
		{
			uint64_t Size = std::filesystem::file_size(PdbPath, Ec);
			ZEN_INFO("Cached local PDB {} ({})", PdbName, zen::NiceBytes(Size));
		}
	}

	// Look for a PDB in the local symbol cache or download from symbol servers.
	// Returns the cache path on success, empty path on failure.
	std::filesystem::path FindPdbInCacheOrServer(std::string_view			  PdbName,
												 const std::string&			  ImageIdKey,
												 const std::filesystem::path& CacheDir)
	{
		if (ImageIdKey.empty())
		{
			return {};
		}

		// Check local cache first (includes previously cached local PDBs and
		// earlier symbol server downloads).
		std::filesystem::path CachePath = CacheDir / PdbName / ImageIdKey / PdbName;
		std::error_code		  Ec;
		if (std::filesystem::exists(CachePath, Ec))
		{
			return CachePath;
		}

		// Try symbol servers
		const std::vector<std::string>& Servers = ParseSymbolPath();
		for (const std::string& Server : Servers)
		{
			std::filesystem::path Downloaded = DownloadPdb(Server, PdbName, ImageIdKey, CacheDir);
			if (!Downloaded.empty())
			{
				return Downloaded;
			}
		}

		return {};
	}

}  // namespace

//////////////////////////////////////////////////////////////////////////////
// RawPdb backend — reads PDB files directly

class PdbSymbolResolver final : public SymbolResolver
{
public:
	void		LoadModule(const ModuleInfo& Module) override;
	std::string Resolve(uint64_t Address) const override;

private:
	struct FunctionEntry
	{
		uint64_t	Address;
		uint32_t	Size;
		std::string Name;
	};

	struct LineEntry
	{
		uint64_t	Address;
		uint32_t	CodeSize;
		uint32_t	Line;
		std::string File;  // shortened: basename only
	};

	std::vector<FunctionEntry> m_Functions;
	std::vector<LineEntry>	   m_Lines;
};

void
PdbSymbolResolver::LoadModule(const ModuleInfo& Module)
{
	if (Module.FullPath.empty() || Module.Base == 0)
	{
		return;
	}

	std::string					 ImageIdKey = FormatImageIdKey(Module.ImageId);
	std::string					 PdbName	= std::filesystem::path(Module.FullPath).filename().replace_extension(".pdb").string();
	const std::filesystem::path& CacheDir	= GetSymbolCacheDir();

	if (!IsSafePdbName(PdbName))
	{
		ZEN_WARN("Rejecting unsafe PDB name from trace: '{}'", PdbName);
		return;
	}

	// Try local PDB first (next to the binary)
	std::filesystem::path PdbPath(Module.FullPath);
	PdbPath.replace_extension(".pdb");

	std::error_code Ec;
	bool			FromLocal = false;

	if (std::filesystem::exists(PdbPath, Ec))
	{
		FromLocal = true;
	}
	else
	{
		// Try symbol cache / symbol server download
		PdbPath = FindPdbInCacheOrServer(PdbName, ImageIdKey, CacheDir);
		if (PdbPath.empty())
		{
			ZEN_DEBUG("PDB not found locally or on symbol server: {}", PdbName);
			return;
		}
	}

	MappedFile File;
	if (!File.Open(PdbPath))
	{
		ZEN_DEBUG("Failed to open PDB: {}", PdbPath.string());
		return;
	}

	if (PDB::ValidateFile(File.Data, File.Size) != PDB::ErrorCode::Success)
	{
		ZEN_DEBUG("Invalid PDB file: {}", PdbPath.string());
		return;
	}

	PDB::RawFile	RawFile = PDB::CreateRawFile(File.Data);
	PDB::InfoStream PdbInfoStream(RawFile);

	// Verify the PDB matches the traced module by comparing GUID + Age.
	// The trace stores ImageId as 16 bytes GUID followed by 4 bytes Age.
	if (Module.ImageId.size() >= 20)
	{
		const PDB::Header* PdbHeader = PdbInfoStream.GetHeader();

		// Only compare the GUID, not the age. The symbol server may return a
		// PDB with a higher age (from incremental linking) which is compatible.
		if (memcmp(&PdbHeader->guid, Module.ImageId.data(), 16) != 0)
		{
			if (FromLocal)
			{
				// The local PDB no longer matches — the binary was recompiled
				// since the trace was taken. Try the symbol cache / servers for
				// the original PDB.
				File.Close();
				PdbPath = FindPdbInCacheOrServer(PdbName, ImageIdKey, CacheDir);
				if (PdbPath.empty())
				{
					ZEN_WARN("PDB mismatch for {} — binary was recompiled and no cached symbols available", Module.Name);
					return;
				}

				FromLocal = false;

				if (!File.Open(PdbPath))
				{
					ZEN_DEBUG("Failed to open cached PDB: {}", PdbPath.string());
					return;
				}

				if (PDB::ValidateFile(File.Data, File.Size) != PDB::ErrorCode::Success)
				{
					ZEN_DEBUG("Invalid cached PDB: {}", PdbPath.string());
					return;
				}

				RawFile		  = PDB::CreateRawFile(File.Data);
				PdbInfoStream = PDB::InfoStream(RawFile);

				const PDB::Header* CachedHeader = PdbInfoStream.GetHeader();
				if (memcmp(&CachedHeader->guid, Module.ImageId.data(), 16) != 0)
				{
					ZEN_WARN("PDB GUID mismatch for {} — skipping", Module.Name);
					return;
				}
			}
			else
			{
				ZEN_WARN("PDB GUID mismatch for {} — skipping", Module.Name);
				return;
			}
		}
	}

	// Cache the local PDB so that future analysis of traces from this build
	// succeeds even after the binary is recompiled.
	if (FromLocal && !ImageIdKey.empty())
	{
		CacheLocalPdb(PdbPath, PdbName, ImageIdKey, CacheDir);
	}

	if (PDB::HasValidDBIStream(RawFile) != PDB::ErrorCode::Success)
	{
		return;
	}

	const PDB::DBIStream DbiStream = PDB::CreateDBIStream(RawFile);
	if (DbiStream.HasValidImageSectionStream(RawFile) != PDB::ErrorCode::Success)
	{
		return;
	}

	const PDB::ImageSectionStream ImageSections					   = DbiStream.CreateImageSectionStream(RawFile);
	uint64_t					  ModuleBase					   = Module.Base;
	uint32_t					  SkippedModules				   = 0;
	size_t						  FunctionCountBeforeModuleSymbols = m_Functions.size();

	// Collect functions from module symbol streams (S_GPROC32 / S_LPROC32)
	{
		const PDB::ModuleInfoStream							ModInfoStream = DbiStream.CreateModuleInfoStream(RawFile);
		const PDB::ArrayView<PDB::ModuleInfoStream::Module> Modules		  = ModInfoStream.GetModules();
		for (const PDB::ModuleInfoStream::Module& Mod : Modules)
		{
			if (!Mod.HasSymbolStream())
			{
				++SkippedModules;
				continue;
			}

			const PDB::ModuleSymbolStream SymStream = Mod.CreateSymbolStream(RawFile);

			SymStream.ForEachSymbol([&](const PDB::CodeView::DBI::Record* Record) {
				using Kind		 = PDB::CodeView::DBI::SymbolRecordKind;
				const Kind	K	 = Record->header.kind;
				const auto& Data = Record->data;

				if (K == Kind::S_GPROC32 || K == Kind::S_LPROC32 || K == Kind::S_GPROC32_ID || K == Kind::S_LPROC32_ID)
				{
					uint32_t Rva = ImageSections.ConvertSectionOffsetToRVA(Data.S_GPROC32.section, Data.S_GPROC32.offset);
					if (Rva != 0)
					{
						m_Functions.push_back({ModuleBase + Rva, Data.S_GPROC32.codeSize, Data.S_GPROC32.name});
					}
				}
			});
		}
	}

	// Public symbols as fallback only when module symbol streams did not yield any
	// functions. Building the coalesced symbol-record stream is expensive and can
	// allocate tens of megabytes for large PDBs.
	if (FunctionCountBeforeModuleSymbols == m_Functions.size() && DbiStream.HasValidPublicSymbolStream(RawFile) == PDB::ErrorCode::Success)
	{
		const PDB::PublicSymbolStream PubStream	 = DbiStream.CreatePublicSymbolStream(RawFile);
		const PDB::CoalescedMSFStream SymRecords = DbiStream.CreateSymbolRecordStream(RawFile);

		for (const PDB::HashRecord& Hash : PubStream.GetRecords())
		{
			const PDB::CodeView::DBI::Record* Record = SymRecords.GetDataAtOffset<PDB::CodeView::DBI::Record>(Hash.offset);
			if (Record->header.kind == PDB::CodeView::DBI::SymbolRecordKind::S_PUB32)
			{
				uint32_t Rva = ImageSections.ConvertSectionOffsetToRVA(Record->data.S_PUB32.section, Record->data.S_PUB32.offset);
				if (Rva != 0)
				{
					m_Functions.push_back({ModuleBase + Rva, 0, Record->data.S_PUB32.name});
				}
			}
		}
	}

	// Collect line information from module line streams
	if (PdbInfoStream.HasNamesStream())
	{
		const PDB::NamesStream		NamesStream	   = PdbInfoStream.CreateNamesStream(RawFile);
		const PDB::ModuleInfoStream ModInfoStream2 = DbiStream.CreateModuleInfoStream(RawFile);

		for (const PDB::ModuleInfoStream::Module& Mod : ModInfoStream2.GetModules())
		{
			if (!Mod.HasLineStream())
			{
				continue;
			}

			const PDB::ModuleLineStream LineStream = Mod.CreateLineStream(RawFile);

			// Two passes: first find the checksums section, then process lines.
			const PDB::CodeView::DBI::FileChecksumHeader* ModuleChecksumBase = nullptr;

			LineStream.ForEachSection([&](const PDB::CodeView::DBI::LineSection* Section) {
				if (Section->header.kind == PDB::CodeView::DBI::DebugSubsectionKind::S_FILECHECKSUMS)
				{
					ModuleChecksumBase = &Section->checksumHeader;
				}
			});

			if (ModuleChecksumBase == nullptr)
			{
				continue;
			}

			LineStream.ForEachSection([&](const PDB::CodeView::DBI::LineSection* Section) {
				if (Section->header.kind != PDB::CodeView::DBI::DebugSubsectionKind::S_LINES)
				{
					return;
				}

				uint16_t SecIdx = Section->linesHeader.sectionIndex;
				uint32_t SecOff = Section->linesHeader.sectionOffset;

				LineStream.ForEachLinesBlock(Section,
											 [&](const PDB::CodeView::DBI::LinesFileBlockHeader* Block,
												 const PDB::CodeView::DBI::Line*				 Lines,
												 const PDB::CodeView::DBI::Column*) {
												 if (Block->numLines == 0)
												 {
													 return;
												 }

												 // Resolve filename for this block
												 const auto* Checksum = PDB::Pointer::Offset<const PDB::CodeView::DBI::FileChecksumHeader*>(
													 ModuleChecksumBase,
													 Block->fileChecksumOffset);
												 const char* FullFile = NamesStream.GetFilename(Checksum->filenameOffset);

												 // Extract basename
												 std::string_view FileView(FullFile);
												 size_t			  Cut = FileView.find_last_of("\\/");
												 std::string Basename(Cut != std::string_view::npos ? FileView.substr(Cut + 1) : FileView);

												 for (uint32_t I = 0; I < Block->numLines; ++I)
												 {
													 uint32_t Rva =
														 ImageSections.ConvertSectionOffsetToRVA(SecIdx, SecOff + Lines[I].offset);
													 if (Rva == 0)
													 {
														 continue;
													 }

													 uint32_t CodeSize = 0;
													 if (I + 1 < Block->numLines)
													 {
														 CodeSize = Lines[I + 1].offset - Lines[I].offset;
													 }
													 else
													 {
														 CodeSize = Section->linesHeader.codeSize - Lines[I].offset;
													 }

													 m_Lines.push_back({ModuleBase + Rva, CodeSize, Lines[I].linenumStart, Basename});
												 }
											 });
			});
		}
	}

	std::sort(m_Functions.begin(), m_Functions.end(), [](const FunctionEntry& A, const FunctionEntry& B) { return A.Address < B.Address; });

	std::sort(m_Lines.begin(), m_Lines.end(), [](const LineEntry& A, const LineEntry& B) { return A.Address < B.Address; });

	if (SkippedModules > 0)
	{
		ZEN_INFO("Loaded {} symbols, {} line records from {} ({} modules without embedded debug info)",
				 m_Functions.size(),
				 m_Lines.size(),
				 Module.Name,
				 SkippedModules);
	}
	else
	{
		ZEN_INFO("Loaded {} symbols, {} line records from {}", m_Functions.size(), m_Lines.size(), Module.Name);
	}
}

std::string
PdbSymbolResolver::Resolve(uint64_t Address) const
{
	if (m_Functions.empty())
	{
		return {};
	}

	// Resolve function name
	auto FnIt = std::upper_bound(m_Functions.begin(), m_Functions.end(), Address, [](uint64_t Addr, const FunctionEntry& E) {
		return Addr < E.Address;
	});

	if (FnIt == m_Functions.begin())
	{
		return {};
	}

	--FnIt;

	if (FnIt->Size > 0 && Address >= FnIt->Address + FnIt->Size)
	{
		return {};
	}

	std::string Result = FormatSymbol(FnIt->Name, Address - FnIt->Address);

	// Resolve file:line
	if (!m_Lines.empty())
	{
		auto LineIt =
			std::upper_bound(m_Lines.begin(), m_Lines.end(), Address, [](uint64_t Addr, const LineEntry& E) { return Addr < E.Address; });

		if (LineIt != m_Lines.begin())
		{
			--LineIt;
			if (LineIt->CodeSize == 0 || Address < LineIt->Address + LineIt->CodeSize)
			{
				Result += fmt::format(" [{}:{}]", LineIt->File, LineIt->Line);
			}
		}
	}

	return Result;
}

//////////////////////////////////////////////////////////////////////////////
// DbgHelp backend — uses Windows symbol API, supports _NT_SYMBOL_PATH

class DbgHelpSymbolResolver final : public SymbolResolver
{
public:
	DbgHelpSymbolResolver();
	~DbgHelpSymbolResolver() override;

	void		LoadModule(const ModuleInfo& Module) override;
	std::string Resolve(uint64_t Address) const override;

private:
	// Map trace addresses to DbgHelp addresses when the loaded base differs.
	struct ModuleMapping
	{
		uint64_t TraceBase;
		uint64_t TraceEnd;
		int64_t	 Delta;	 // DbgHelpBase - TraceBase
	};

	HANDLE					   m_Process = nullptr;
	std::vector<ModuleMapping> m_Mappings;
	// DbgHelp is not thread-safe; its API functions require serialized access. This
	// mutex covers every DbgHelp call (SymInitialize/SymLoadModuleExW/SymFromAddr/
	// SymGetLineFromAddr64) and therefore serializes all parallel symbol lookups in
	// trace_analyze. For workloads where lookup throughput matters, prefer
	// PdbSymbolResolver, which parses PDBs directly and is lock-free per-module.
	mutable std::mutex m_Mutex;
};

DbgHelpSymbolResolver::DbgHelpSymbolResolver()
{
	std::lock_guard Lock(m_Mutex);

	// Use a unique pseudo-handle so we don't conflict with the runtime
	// symbol handler used by callstack.cpp / crashhandler.cpp.
	m_Process = reinterpret_cast<HANDLE>(static_cast<uintptr_t>(0xDEAD0042));

	// NULL search path lets DbgHelp use _NT_SYMBOL_PATH and its defaults.
	if (!SymInitialize(m_Process, nullptr, FALSE))
	{
		ZEN_WARN("DbgHelp: SymInitialize failed (error {})", GetLastError());
		m_Process = nullptr;
	}
}

DbgHelpSymbolResolver::~DbgHelpSymbolResolver()
{
	std::lock_guard Lock(m_Mutex);

	if (m_Process != nullptr)
	{
		SymCleanup(m_Process);
	}
}

void
DbgHelpSymbolResolver::LoadModule(const ModuleInfo& Module)
{
	std::lock_guard Lock(m_Mutex);

	if (m_Process == nullptr || Module.FullPath.empty() || Module.Base == 0)
	{
		return;
	}

	std::filesystem::path ModulePath(Module.FullPath);
	std::wstring		  WidePath = ModulePath.wstring();

	DWORD64 LoadedBase = SymLoadModuleExW(m_Process, nullptr, WidePath.c_str(), nullptr, Module.Base, Module.Size, nullptr, 0);

	if (LoadedBase == 0)
	{
		DWORD Err = GetLastError();
		if (Err != ERROR_SUCCESS)
		{
			ZEN_DEBUG("DbgHelp: failed to load {}: error {}", Module.Name, Err);
		}
		return;
	}

	int64_t Delta = int64_t(LoadedBase) - int64_t(Module.Base);
	if (Delta != 0)
	{
		ZEN_DEBUG("DbgHelp: {} loaded at 0x{:X} (trace base 0x{:X}, delta {:+})", Module.Name, LoadedBase, Module.Base, Delta);
	}

	uint64_t TraceEnd = Module.Base + (Module.Size > 0 ? Module.Size : 0x1000000);
	m_Mappings.push_back({Module.Base, TraceEnd, Delta});

	ZEN_INFO("DbgHelp: loaded symbols for {}", Module.Name);
}

std::string
DbgHelpSymbolResolver::Resolve(uint64_t Address) const
{
	std::lock_guard Lock(m_Mutex);

	if (m_Process == nullptr)
	{
		return {};
	}

	// Translate the trace address to the DbgHelp address space
	uint64_t DbgAddr = Address;
	for (const ModuleMapping& M : m_Mappings)
	{
		if (Address >= M.TraceBase && Address < M.TraceEnd)
		{
			DbgAddr = uint64_t(int64_t(Address) + M.Delta);
			break;
		}
	}

	alignas(SYMBOL_INFO) char Buffer[sizeof(SYMBOL_INFO) + MAX_SYM_NAME];
	SYMBOL_INFO*			  SymInfo = reinterpret_cast<SYMBOL_INFO*>(Buffer);
	SymInfo->SizeOfStruct			  = sizeof(SYMBOL_INFO);
	SymInfo->MaxNameLen				  = MAX_SYM_NAME;

	DWORD64 Displacement = 0;
	if (!SymFromAddr(m_Process, DbgAddr, &Displacement, SymInfo))
	{
		return {};
	}

	std::string Result = FormatSymbol(std::string_view(SymInfo->Name, SymInfo->NameLen), Displacement);

	IMAGEHLP_LINE64 LineInfo = {};
	LineInfo.SizeOfStruct	 = sizeof(IMAGEHLP_LINE64);
	DWORD LineDisplacement	 = 0;
	if (SymGetLineFromAddr64(m_Process, DbgAddr, &LineDisplacement, &LineInfo))
	{
		std::string_view FileView(LineInfo.FileName);
		size_t			 Cut	  = FileView.find_last_of("\\/");
		std::string_view Basename = (Cut != std::string_view::npos) ? FileView.substr(Cut + 1) : FileView;
		Result += fmt::format(" [{}:{}]", Basename, LineInfo.LineNumber);
	}

	return Result;
}

#endif	// ZEN_PLATFORM_WINDOWS

//////////////////////////////////////////////////////////////////////////////
// Shared helpers for subprocess-based backends

namespace {

	// CreateProc parses the command line as space-separated tokens, so argv[0]
	// must be quoted if the resolved executable path contains spaces (e.g. an
	// Xcode toolchain location on macOS).
	std::string QuoteIfNeeded(std::string_view Path)
	{
		if (Path.find(' ') == std::string_view::npos)
		{
			return std::string(Path);
		}
		return fmt::format("\"{}\"", Path);
	}

}  // namespace

//////////////////////////////////////////////////////////////////////////////
// llvm-symbolizer backend — cross-platform, shells out to `llvm-symbolizer`
// and speaks its interactive protocol over pipes.
//
// Protocol (one request / response):
//   We write:   "<path-to-binary> 0x<relative-address>\n"
//   It replies: "FunctionName\n"
//               "file:line:col\n"
//               "\n"                  <-- blank line terminates the record
//
// Launch flags:
//   --demangle              demangle C++ names (default, but explicit)
//   --output-style=LLVM     stable two-line format described above
//   --functions=linkage     keep template arguments visible
//   --relative-address      treat the address as an offset from module base
//   --inlining=false        emit one frame per address (no inline expansion)

class LlvmSymbolizerResolver final : public SymbolResolver
{
public:
	LlvmSymbolizerResolver() = default;
	~LlvmSymbolizerResolver() override;

	void		LoadModule(const ModuleInfo& Module) override;
	std::string Resolve(uint64_t Address) const override;

private:
	struct Module
	{
		std::string FullPath;
		uint64_t	Base = 0;
		uint64_t	End	 = 0;
	};

	const Module* FindModule(uint64_t Address) const;
	bool		  EnsureProcess() const;
	bool		  ReadLine(std::string& Out) const;
	std::string	  DoQuery(const Module& M, uint64_t RelAddress) const;

	std::vector<Module> m_Modules;

	// Subprocess + IO state. All accesses serialized under m_Mutex.
	mutable std::mutex			   m_Mutex;
	mutable bool				   m_Attempted = false;
	mutable bool				   m_Alive	   = false;
	mutable zen::ProcessHandle	   m_Process;
	mutable zen::StdinPipeHandles  m_StdinPipe;
	mutable zen::StdoutPipeHandles m_StdoutPipe;
	mutable std::string			   m_ReadBuffer;

	// Cache resolved addresses (same mutex).
	mutable std::unordered_map<uint64_t, std::string> m_Cache;
};

LlvmSymbolizerResolver::~LlvmSymbolizerResolver()
{
	std::lock_guard Lock(m_Mutex);
	if (m_Alive)
	{
		// Closing stdin lets llvm-symbolizer exit cleanly on EOF.
		m_StdinPipe.CloseWriteEnd();
		m_Process.Wait(2000);
		if (m_Process.IsRunning())
		{
			m_Process.Terminate(0);
		}
	}
}

void
LlvmSymbolizerResolver::LoadModule(const ModuleInfo& Mod)
{
	if (Mod.FullPath.empty() || Mod.Base == 0)
	{
		return;
	}

	// llvm-symbolizer auto-discovers adjacent debug info (Foo.dSYM on Mac,
	// .gnu_debuglink / build-id sources on Linux, Foo.pdb on Windows). If the
	// binary itself isn't present locally, there's nothing we can do.
	std::error_code Ec;
	if (!std::filesystem::exists(Mod.FullPath, Ec))
	{
		ZEN_DEBUG("llvm-symbolizer: binary not found for {} at {}", Mod.Name, Mod.FullPath);
		return;
	}

	uint64_t End = Mod.Base + (Mod.Size > 0 ? Mod.Size : 0x1000000);

	std::lock_guard Lock(m_Mutex);
	m_Modules.push_back({Mod.FullPath, Mod.Base, End});
	ZEN_INFO("llvm-symbolizer: registered {} [0x{:X}..0x{:X})", Mod.Name, Mod.Base, End);
}

std::string
LlvmSymbolizerResolver::Resolve(uint64_t Address) const
{
	std::lock_guard Lock(m_Mutex);

	auto CacheIt = m_Cache.find(Address);
	if (CacheIt != m_Cache.end())
	{
		return CacheIt->second;
	}

	const Module* M = FindModule(Address);
	if (M == nullptr)
	{
		m_Cache.emplace(Address, std::string{});
		return {};
	}

	std::string Result = DoQuery(*M, Address - M->Base);
	m_Cache.emplace(Address, Result);
	return Result;
}

const LlvmSymbolizerResolver::Module*
LlvmSymbolizerResolver::FindModule(uint64_t Address) const
{
	for (const Module& M : m_Modules)
	{
		if (Address >= M.Base && Address < M.End)
		{
			return &M;
		}
	}
	return nullptr;
}

bool
LlvmSymbolizerResolver::EnsureProcess() const
{
	if (m_Attempted)
	{
		return m_Alive;
	}
	m_Attempted = true;

	std::filesystem::path Executable = SearchPathForExecutable("llvm-symbolizer");

	if (!CreateStdinPipe(m_StdinPipe) || !CreateStdoutPipe(m_StdoutPipe))
	{
		ZEN_WARN("llvm-symbolizer: failed to create pipes");
		return false;
	}

	// Build the command line. CommandLine begins with the executable name (arg[0]).
	std::string CommandLine = fmt::format("{} --demangle --output-style=LLVM --functions=linkage --relative-address --inlining=false",
										  QuoteIfNeeded(Executable.string()));

	CreateProcOptions Options;
	Options.StdinPipe  = &m_StdinPipe;
	Options.StdoutPipe = &m_StdoutPipe;

	CreateProcResult Handle = CreateProc(Executable, CommandLine, Options);

#if ZEN_PLATFORM_WINDOWS
	if (Handle == nullptr)
#else
	if (Handle <= 0)
#endif
	{
		ZEN_WARN("llvm-symbolizer: failed to launch '{}' - install LLVM or add to PATH", Executable.string());
		m_StdinPipe.Close();
		m_StdoutPipe.Close();
		return false;
	}

#if ZEN_PLATFORM_WINDOWS
	m_Process.Initialize(Handle);
#else
	std::error_code Ec;
	m_Process.Initialize(int(Handle), Ec);
	if (Ec)
	{
		ZEN_WARN("llvm-symbolizer: ProcessHandle init failed: {}", Ec.message());
		m_StdinPipe.Close();
		m_StdoutPipe.Close();
		return false;
	}
#endif

	// Close the child-side handles in the parent.
	m_StdinPipe.CloseReadEnd();
	m_StdoutPipe.CloseWriteEnd();

	m_Alive = true;
	return true;
}

bool
LlvmSymbolizerResolver::ReadLine(std::string& Out) const
{
	// Search for a newline already in the buffer; if not, read more.
	for (;;)
	{
		size_t NewlinePos = m_ReadBuffer.find('\n');
		if (NewlinePos != std::string::npos)
		{
			Out.assign(m_ReadBuffer, 0, NewlinePos);
			m_ReadBuffer.erase(0, NewlinePos + 1);
			// Trim a trailing \r (in case of CRLF line endings).
			if (!Out.empty() && Out.back() == '\r')
			{
				Out.pop_back();
			}
			return true;
		}

		char Buffer[1024];
#if ZEN_PLATFORM_WINDOWS
		DWORD BytesRead = 0;
		if (!::ReadFile(m_StdoutPipe.ReadHandle, Buffer, sizeof(Buffer), &BytesRead, nullptr) || BytesRead == 0)
		{
			return false;
		}
		m_ReadBuffer.append(Buffer, BytesRead);
#else
		ssize_t BytesRead = ::read(m_StdoutPipe.ReadFd, Buffer, sizeof(Buffer));
		if (BytesRead <= 0)
		{
			if (BytesRead < 0 && errno == EINTR)
			{
				continue;
			}
			return false;
		}
		m_ReadBuffer.append(Buffer, static_cast<size_t>(BytesRead));
#endif
	}
}

std::string
LlvmSymbolizerResolver::DoQuery(const Module& M, uint64_t RelAddress) const
{
	if (!EnsureProcess())
	{
		return {};
	}

	// Write "<path> 0x<addr>\n". Paths with spaces must be quoted for llvm-symbolizer
	// interactive input; it accepts double quotes.
	std::string Line;
	if (M.FullPath.find(' ') != std::string::npos)
	{
		Line = fmt::format("\"{}\" 0x{:X}\n", M.FullPath, RelAddress);
	}
	else
	{
		Line = fmt::format("{} 0x{:X}\n", M.FullPath, RelAddress);
	}

#if ZEN_PLATFORM_WINDOWS
	DWORD BytesWritten = 0;
	if (!::WriteFile(m_StdinPipe.WriteHandle, Line.data(), static_cast<DWORD>(Line.size()), &BytesWritten, nullptr) ||
		BytesWritten != Line.size())
	{
		ZEN_WARN("llvm-symbolizer: write failed, disabling backend");
		m_Alive = false;
		return {};
	}
#else
	const char* Ptr		  = Line.data();
	size_t		Remaining = Line.size();
	while (Remaining > 0)
	{
		ssize_t N = ::write(m_StdinPipe.WriteFd, Ptr, Remaining);
		if (N <= 0)
		{
			if (N < 0 && errno == EINTR)
			{
				continue;
			}
			ZEN_WARN("llvm-symbolizer: write failed, disabling backend");
			m_Alive = false;
			return {};
		}
		Ptr += N;
		Remaining -= static_cast<size_t>(N);
	}
#endif

	// Read lines until a blank line terminates the record.
	std::string Function;
	std::string Location;
	std::string Buf;
	int			LineIdx = 0;
	while (ReadLine(Buf))
	{
		if (Buf.empty())
		{
			break;
		}
		if (LineIdx == 0)
		{
			Function = Buf;
		}
		else if (LineIdx == 1)
		{
			Location = Buf;
		}
		// Additional lines would be inline frames (--inlining=false suppresses them); ignore.
		++LineIdx;
	}

	if (Function.empty() || Function == "??")
	{
		return {};
	}

	std::string Result = std::move(Function);
	if (!Location.empty() && Location != "??:0:0")
	{
		// Location is "path:line:col" — trim to "basename:line" to match Windows output.
		std::string_view LocView(Location);
		size_t			 LastColon = LocView.find_last_of(':');
		if (LastColon != std::string_view::npos)
		{
			LocView = LocView.substr(0, LastColon);
		}
		size_t			 Slash	  = LocView.find_last_of("/\\");
		std::string_view FileLine = (Slash == std::string_view::npos) ? LocView : LocView.substr(Slash + 1);
		Result += fmt::format(" [{}]", FileLine);
	}
	return Result;
}

//////////////////////////////////////////////////////////////////////////////
// atos backend — macOS only. Apple's symbolizer; ships with Xcode + the CLT.
//
// Unlike llvm-symbolizer, atos accepts only one binary per process. We keep
// one subprocess per loaded module and demultiplex queries by module path.
//
// Protocol (one request / response):
//   We write:   "0x<absolute-address>\n"
//   It replies: "Function (in Binary) (file.cpp:NN)\n"
//               or "Function (in Binary) + 0x<disp>\n"  (no debug info)
//               or "0x<address>\n"                       (nothing known)
//
// Launched with: atos -o <binary> -l 0x<module-base>
// atos subtracts -l from each input address to get the file offset.

#if ZEN_PLATFORM_MAC

class AtosSymbolizerResolver final : public SymbolResolver
{
public:
	AtosSymbolizerResolver() = default;
	~AtosSymbolizerResolver() override;

	void		LoadModule(const ModuleInfo& Module) override;
	std::string Resolve(uint64_t Address) const override;

private:
	struct Module
	{
		std::string FullPath;
		uint64_t	Base = 0;
		uint64_t	End	 = 0;
	};

	// One atos subprocess per loaded module (atos is single-binary).
	struct AtosProcess
	{
		zen::ProcessHandle	   Process;
		zen::StdinPipeHandles  StdinPipe;
		zen::StdoutPipeHandles StdoutPipe;
		std::string			   ReadBuffer;
		bool				   Alive = false;
	};

	const Module* FindModule(uint64_t Address) const;
	AtosProcess*  EnsureProcessFor(const Module& M) const;
	bool		  ReadLine(AtosProcess& P, std::string& Out) const;
	std::string	  DoQuery(const Module& M, uint64_t Address) const;

	std::vector<Module> m_Modules;

	mutable std::mutex													  m_Mutex;
	mutable std::unordered_map<std::string, std::unique_ptr<AtosProcess>> m_Processes;
	mutable std::unordered_map<uint64_t, std::string>					  m_Cache;
};

AtosSymbolizerResolver::~AtosSymbolizerResolver()
{
	std::lock_guard Lock(m_Mutex);
	for (auto& [Path, P] : m_Processes)
	{
		if (P && P->Alive)
		{
			P->StdinPipe.CloseWriteEnd();
			P->Process.Wait(2000);
			if (P->Process.IsRunning())
			{
				P->Process.Terminate(0);
			}
		}
	}
}

void
AtosSymbolizerResolver::LoadModule(const ModuleInfo& Mod)
{
	if (Mod.FullPath.empty() || Mod.Base == 0)
	{
		return;
	}

	std::error_code Ec;
	if (!std::filesystem::exists(Mod.FullPath, Ec))
	{
		ZEN_DEBUG("atos: binary not found for {} at {}", Mod.Name, Mod.FullPath);
		return;
	}

	uint64_t End = Mod.Base + (Mod.Size > 0 ? Mod.Size : 0x1000000);

	std::lock_guard Lock(m_Mutex);
	m_Modules.push_back({Mod.FullPath, Mod.Base, End});
	ZEN_INFO("atos: registered {} [0x{:X}..0x{:X})", Mod.Name, Mod.Base, End);
}

std::string
AtosSymbolizerResolver::Resolve(uint64_t Address) const
{
	std::lock_guard Lock(m_Mutex);

	auto CacheIt = m_Cache.find(Address);
	if (CacheIt != m_Cache.end())
	{
		return CacheIt->second;
	}

	const Module* M = FindModule(Address);
	if (M == nullptr)
	{
		m_Cache.emplace(Address, std::string{});
		return {};
	}

	std::string Result = DoQuery(*M, Address);
	m_Cache.emplace(Address, Result);
	return Result;
}

const AtosSymbolizerResolver::Module*
AtosSymbolizerResolver::FindModule(uint64_t Address) const
{
	for (const Module& M : m_Modules)
	{
		if (Address >= M.Base && Address < M.End)
		{
			return &M;
		}
	}
	return nullptr;
}

AtosSymbolizerResolver::AtosProcess*
AtosSymbolizerResolver::EnsureProcessFor(const Module& M) const
{
	auto It = m_Processes.find(M.FullPath);
	if (It != m_Processes.end())
	{
		return It->second.get();
	}

	auto P = std::make_unique<AtosProcess>();

	if (!CreateStdinPipe(P->StdinPipe) || !CreateStdoutPipe(P->StdoutPipe))
	{
		ZEN_WARN("atos: failed to create pipes for {}", M.FullPath);
		auto [Ins, _] = m_Processes.emplace(M.FullPath, std::move(P));
		return Ins->second.get();  // Alive = false
	}

	std::filesystem::path Executable  = SearchPathForExecutable("atos");
	std::string			  CommandLine = fmt::format("{} -o \"{}\" -l 0x{:X}", QuoteIfNeeded(Executable.string()), M.FullPath, M.Base);

	CreateProcOptions Options;
	Options.StdinPipe  = &P->StdinPipe;
	Options.StdoutPipe = &P->StdoutPipe;

	CreateProcResult Handle = CreateProc(Executable, CommandLine, Options);
	if (Handle <= 0)
	{
		ZEN_WARN("atos: failed to launch for {} - `atos` should be on PATH on macOS", M.FullPath);
		P->StdinPipe.Close();
		P->StdoutPipe.Close();
		auto [Ins, _] = m_Processes.emplace(M.FullPath, std::move(P));
		return Ins->second.get();  // Alive = false
	}

	std::error_code Ec;
	P->Process.Initialize(int(Handle), Ec);
	if (Ec)
	{
		ZEN_WARN("atos: ProcessHandle init failed for {}: {}", M.FullPath, Ec.message());
		P->StdinPipe.Close();
		P->StdoutPipe.Close();
		auto [Ins, _] = m_Processes.emplace(M.FullPath, std::move(P));
		return Ins->second.get();  // Alive = false
	}

	P->StdinPipe.CloseReadEnd();
	P->StdoutPipe.CloseWriteEnd();
	P->Alive = true;

	auto [Ins, _] = m_Processes.emplace(M.FullPath, std::move(P));
	return Ins->second.get();
}

bool
AtosSymbolizerResolver::ReadLine(AtosProcess& P, std::string& Out) const
{
	for (;;)
	{
		size_t NewlinePos = P.ReadBuffer.find('\n');
		if (NewlinePos != std::string::npos)
		{
			Out.assign(P.ReadBuffer, 0, NewlinePos);
			P.ReadBuffer.erase(0, NewlinePos + 1);
			return true;
		}

		char	Buffer[1024];
		ssize_t BytesRead = ::read(P.StdoutPipe.ReadFd, Buffer, sizeof(Buffer));
		if (BytesRead <= 0)
		{
			if (BytesRead < 0 && errno == EINTR)
			{
				continue;
			}
			return false;
		}
		P.ReadBuffer.append(Buffer, static_cast<size_t>(BytesRead));
	}
}

std::string
AtosSymbolizerResolver::DoQuery(const Module& M, uint64_t Address) const
{
	AtosProcess* P = EnsureProcessFor(M);
	if (P == nullptr || !P->Alive)
	{
		return {};
	}

	std::string Line = fmt::format("0x{:X}\n", Address);

	const char* Ptr		  = Line.data();
	size_t		Remaining = Line.size();
	while (Remaining > 0)
	{
		ssize_t N = ::write(P->StdinPipe.WriteFd, Ptr, Remaining);
		if (N <= 0)
		{
			if (N < 0 && errno == EINTR)
			{
				continue;
			}
			ZEN_WARN("atos: write failed for {}, disabling", M.FullPath);
			P->Alive = false;
			return {};
		}
		Ptr += N;
		Remaining -= static_cast<size_t>(N);
	}

	std::string Reply;
	if (!ReadLine(*P, Reply) || Reply.empty())
	{
		return {};
	}

	// Parse "Function (in Binary) (file.cpp:NN)" or "... + 0xNN" or just "0xADDR".
	// Extract everything before " (in " as the function name.
	size_t InPos = Reply.find(" (in ");
	if (InPos == std::string::npos)
	{
		// No match — either raw "0xADDR" (no info) or an error message. Skip.
		return {};
	}

	std::string_view Function(Reply.data(), InPos);

	// Look for a trailing "(file:line)" after the "(in ...)" block.
	std::string_view LocationView;
	size_t			 AfterIn = Reply.find(')', InPos);
	if (AfterIn != std::string::npos)
	{
		size_t OpenParen = Reply.find('(', AfterIn);
		if (OpenParen != std::string::npos)
		{
			size_t CloseParen = Reply.find(')', OpenParen);
			if (CloseParen != std::string::npos && CloseParen > OpenParen + 1)
			{
				LocationView = std::string_view(Reply).substr(OpenParen + 1, CloseParen - OpenParen - 1);
			}
		}
	}

	std::string Result(Function);
	if (!LocationView.empty())
	{
		// atos gives us "file.cpp:NN" directly — no need to strip a directory.
		Result += fmt::format(" [{}]", LocationView);
	}
	return Result;
}

#endif	// ZEN_PLATFORM_MAC

//////////////////////////////////////////////////////////////////////////////
// Factory

namespace {

#if ZEN_PLATFORM_MAC
	// Probe PATH for a tool and return true if something usable was found.
	// SearchPathForExecutable returns the input unchanged if the tool can't be
	// found, so we compare against the filesystem to detect a hit.
	bool ToolIsOnPath(std::string_view Name)
	{
		std::filesystem::path Resolved = SearchPathForExecutable(Name);
		std::error_code		  Ec;
		return std::filesystem::exists(Resolved, Ec) && std::filesystem::is_regular_file(Resolved, Ec);
	}
#endif

	SymbolBackend ResolveAutoBackend()
	{
#if ZEN_PLATFORM_WINDOWS
		return SymbolBackend::Pdb;
#elif ZEN_PLATFORM_MAC
		if (ToolIsOnPath("llvm-symbolizer"))
		{
			return SymbolBackend::LlvmSymbolizer;
		}
		return SymbolBackend::Atos;
#else
		// Linux: llvm-symbolizer is the only backend we ship.
		return SymbolBackend::LlvmSymbolizer;
#endif
	}

}  // namespace

std::unique_ptr<SymbolResolver>
CreateSymbolResolver(SymbolBackend Backend)
{
	if (Backend == SymbolBackend::Auto)
	{
		Backend = ResolveAutoBackend();
	}

	if (Backend == SymbolBackend::Off)
	{
		return std::make_unique<NullSymbolResolver>();
	}

	if (Backend == SymbolBackend::LlvmSymbolizer)
	{
		return std::make_unique<LlvmSymbolizerResolver>();
	}

#if ZEN_PLATFORM_MAC
	if (Backend == SymbolBackend::Atos)
	{
		return std::make_unique<AtosSymbolizerResolver>();
	}
#else
	if (Backend == SymbolBackend::Atos)
	{
		ZEN_WARN("atos backend is macOS-only; falling back to llvm-symbolizer");
		return std::make_unique<LlvmSymbolizerResolver>();
	}
#endif

#if ZEN_PLATFORM_WINDOWS
	if (Backend == SymbolBackend::DbgHelp)
	{
		return std::make_unique<DbgHelpSymbolResolver>();
	}
	return std::make_unique<PdbSymbolResolver>();
#else
	// Pdb / DbgHelp aren't available on non-Windows; any other request falls back to llvm-symbolizer.
	return std::make_unique<LlvmSymbolizerResolver>();
#endif
}

SymbolBackend
ParseSymbolBackend(std::string_view Name)
{
	if (Name == "auto")
	{
		return SymbolBackend::Auto;
	}
	if (Name == "pdb")
	{
		return SymbolBackend::Pdb;
	}
	if (Name == "dbghelp")
	{
		return SymbolBackend::DbgHelp;
	}
	if (Name == "llvm" || Name == "llvm-symbolizer")
	{
		return SymbolBackend::LlvmSymbolizer;
	}
	if (Name == "atos")
	{
		return SymbolBackend::Atos;
	}
	if (Name == "off")
	{
		return SymbolBackend::Off;
	}
	return SymbolBackend::Off;
}

}  // namespace zen::trace_detail