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

#include <zencore/compress.h>

#include <zencore/blake3.h>
#include <zencore/compositebuffer.h>
#include <zencore/crc32.h>
#include <zencore/endian.h>

#include <doctest/doctest.h>
#include <lz4.h>
#include <functional>

namespace zen::detail {

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

static constexpr uint64_t DefaultBlockSize = 256 * 1024;

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

/** Header used on every compressed buffer. Always stored in big-endian format. */
struct BufferHeader
{
	static constexpr uint32_t ExpectedMagic = 0xb7756362;  // <dot>ucb

	uint32_t		  Magic = ExpectedMagic;  // A magic number to identify a compressed buffer. Always 0xb7756362.
	uint32_t		  Crc32 = 0;			  // A CRC-32 used to check integrity of the buffer. Uses the polynomial 0x04c11db7
	CompressionMethod Method =
		CompressionMethod::None;	   // The method used to compress the buffer. Affects layout of data following the header
	uint8_t	 Reserved[2]{};			   // The reserved bytes must be initialized to zero
	uint8_t	 BlockSizeExponent	 = 0;  // The power of two size of every uncompressed block except the last. Size is 1 << BlockSizeExponent
	uint32_t BlockCount			 = 0;  // The number of blocks that follow the header
	uint64_t TotalRawSize		 = 0;  // The total size of the uncompressed data
	uint64_t TotalCompressedSize = 0;  // The total size of the compressed data including the header
	BLAKE3	 RawHash;				   // The hash of the uncompressed data

	/** Checks validity of the buffer based on the magic number, method, and CRC-32. */
	static bool IsValid(const CompositeBuffer& CompressedData);
	static bool IsValid(const SharedBuffer& CompressedData) { return IsValid(CompositeBuffer(CompressedData)); }

	/** Read a header from a buffer that is at least sizeof(BufferHeader) without any validation. */
	static BufferHeader Read(const CompositeBuffer& CompressedData)
	{
		BufferHeader Header;
		if (sizeof(BufferHeader) <= CompressedData.GetSize())
		{
			CompressedData.CopyTo(MakeMutableMemoryView(&Header, &Header + 1));
			Header.ByteSwap();
		}
		return Header;
	}

	/**
	 * Write a header to a memory view that is at least sizeof(BufferHeader).
	 *
	 * @param HeaderView   View of the header to write, including any method-specific header data.
	 */
	void Write(MutableMemoryView HeaderView) const
	{
		BufferHeader Header = *this;
		Header.ByteSwap();
		HeaderView.CopyFrom(MakeMemoryView(&Header, &Header + 1));
		Header.ByteSwap();
		Header.Crc32 = CalculateCrc32(HeaderView);
		Header.ByteSwap();
		HeaderView.CopyFrom(MakeMemoryView(&Header, &Header + 1));
	}

	void ByteSwap()
	{
		Magic				= zen::ByteSwap(Magic);
		Crc32				= zen::ByteSwap(Crc32);
		BlockCount			= zen::ByteSwap(BlockCount);
		TotalRawSize		= zen::ByteSwap(TotalRawSize);
		TotalCompressedSize = zen::ByteSwap(TotalCompressedSize);
	}

	/** Calculate the CRC-32 from a view of a header including any method-specific header data. */
	static uint32_t CalculateCrc32(MemoryView HeaderView)
	{
		uint32_t		   Crc32		= 0;
		constexpr uint64_t MethodOffset = offsetof(BufferHeader, Method);
		for (MemoryView View = HeaderView + MethodOffset; const uint64_t ViewSize = View.GetSize();)
		{
			const int32_t Size = static_cast<int32_t>(zen::Min<uint64_t>(ViewSize, INT_MAX));
			Crc32			   = zen::MemCrc32(View.GetData(), Size, Crc32);
			View += Size;
		}
		return Crc32;
	}
};

static_assert(sizeof(BufferHeader) == 64, "BufferHeader is the wrong size.");

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

class CompressionMethodBase
{
public:
	virtual CompositeBuffer Compress(const CompositeBuffer& RawData, uint64_t BlockSize = DefaultBlockSize) const					 = 0;
	virtual CompositeBuffer Decompress(const BufferHeader& Header, const CompositeBuffer& CompressedData) const						 = 0;
	virtual bool TryDecompressTo(const BufferHeader& Header, const CompositeBuffer& CompressedData, MutableMemoryView RawView) const = 0;
	virtual uint64_t GetHeaderSize(const BufferHeader& Header) const																 = 0;
};

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

class MethodNone final : public CompressionMethodBase
{
public:
	[[nodiscard]] CompositeBuffer Compress(const CompositeBuffer& RawData, uint64_t /* BlockSize */) const final
	{
		BufferHeader Header;
		Header.Method			   = CompressionMethod::None;
		Header.BlockCount		   = 1;
		Header.TotalRawSize		   = RawData.GetSize();
		Header.TotalCompressedSize = Header.TotalRawSize + sizeof(BufferHeader);
		Header.RawHash			   = BLAKE3::HashBuffer(RawData);

		UniqueBuffer HeaderData = UniqueBuffer::Alloc(sizeof(BufferHeader));
		Header.Write(HeaderData);
		return CompositeBuffer(HeaderData.MoveToShared(), RawData.MakeOwned());
	}

	[[nodiscard]] CompositeBuffer Decompress(const BufferHeader& Header, const CompositeBuffer& CompressedData) const final
	{
		if (Header.Method == CompressionMethod::None && Header.TotalCompressedSize == CompressedData.GetSize() &&
			Header.TotalCompressedSize == Header.TotalRawSize + sizeof(BufferHeader))
		{
			return CompressedData.Mid(sizeof(BufferHeader), Header.TotalRawSize).MakeOwned();
		}
		return CompositeBuffer();
	}

	[[nodiscard]] bool TryDecompressTo(const BufferHeader&	  Header,
									   const CompositeBuffer& CompressedData,
									   MutableMemoryView	  RawView) const final
	{
		if (Header.Method == CompressionMethod::None && Header.TotalRawSize == RawView.GetSize() &&
			Header.TotalCompressedSize == CompressedData.GetSize() &&
			Header.TotalCompressedSize == Header.TotalRawSize + sizeof(BufferHeader))
		{
			CompressedData.CopyTo(RawView, sizeof(BufferHeader));
			return true;
		}
		return false;
	}

	[[nodiscard]] uint64_t GetHeaderSize(const BufferHeader&) const final { return sizeof(BufferHeader); }
};

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

class MethodBlockBase : public CompressionMethodBase
{
public:
	CompositeBuffer		   Compress(const CompositeBuffer& RawData, uint64_t BlockSize = DefaultBlockSize) const final;
	CompositeBuffer		   Decompress(const BufferHeader& Header, const CompositeBuffer& CompressedData) const final;
	[[nodiscard]] bool	   TryDecompressTo(const BufferHeader&	  Header,
										   const CompositeBuffer& CompressedData,
										   MutableMemoryView	  RawView) const final;
	[[nodiscard]] uint64_t GetHeaderSize(const BufferHeader& Header) const final
	{
		return sizeof(BufferHeader) + sizeof(uint32_t) * uint64_t(Header.BlockCount);
	}

protected:
	virtual CompressionMethod GetMethod() const															  = 0;
	virtual uint64_t		  CompressBlockBound(uint64_t RawSize) const								  = 0;
	virtual bool			  CompressBlock(MutableMemoryView& CompressedData, MemoryView RawData) const  = 0;
	virtual bool			  DecompressBlock(MutableMemoryView RawData, MemoryView CompressedData) const = 0;

private:
	uint64_t GetCompressedBlocksBound(uint64_t BlockCount, uint64_t BlockSize, uint64_t RawSize) const
	{
		switch (BlockCount)
		{
			case 0:
				return 0;
			case 1:
				return CompressBlockBound(RawSize);
			default:
				return CompressBlockBound(BlockSize) - BlockSize + RawSize;
		}
	}
};

CompositeBuffer
MethodBlockBase::Compress(const CompositeBuffer& RawData, const uint64_t BlockSize) const
{
	ZEN_ASSERT(IsPow2(BlockSize) && BlockSize <= (1 << 31));

	const uint64_t RawSize = RawData.GetSize();
	BLAKE3Stream   RawHash;

	const uint64_t BlockCount = RoundUp(RawSize, BlockSize) / BlockSize;
	ZEN_ASSERT(BlockCount <= ~uint32_t(0));

	// Allocate the buffer for the header, metadata, and compressed blocks.
	const uint64_t MetaSize			  = BlockCount * sizeof(uint32_t);
	const uint64_t CompressedDataSize = sizeof(BufferHeader) + MetaSize + GetCompressedBlocksBound(BlockCount, BlockSize, RawSize);
	UniqueBuffer   CompressedData	  = UniqueBuffer::Alloc(CompressedDataSize);

	// Compress the raw data in blocks and store the raw data for incompressible blocks.
	std::vector<uint32_t> CompressedBlockSizes;
	CompressedBlockSizes.reserve(BlockCount);
	uint64_t CompressedSize = 0;
	{
		UniqueBuffer	  RawBlockCopy;
		MutableMemoryView CompressedBlocksView = CompressedData.GetMutableView() + sizeof(BufferHeader) + MetaSize;
		for (uint64_t RawOffset = 0; RawOffset < RawSize;)
		{
			const uint64_t	 RawBlockSize = zen::Min(RawSize - RawOffset, BlockSize);
			const MemoryView RawBlock	  = RawData.ViewOrCopyRange(RawOffset, RawBlockSize, RawBlockCopy);
			RawHash.Append(RawBlock);

			MutableMemoryView CompressedBlock = CompressedBlocksView;
			if (!CompressBlock(CompressedBlock, RawBlock))
			{
				return CompositeBuffer();
			}

			uint64_t CompressedBlockSize = CompressedBlock.GetSize();
			if (RawBlockSize <= CompressedBlockSize)
			{
				CompressedBlockSize	 = RawBlockSize;
				CompressedBlocksView = CompressedBlocksView.CopyFrom(RawBlock);
			}
			else
			{
				CompressedBlocksView += CompressedBlockSize;
			}

			CompressedBlockSizes.push_back(static_cast<uint32_t>(CompressedBlockSize));
			CompressedSize += CompressedBlockSize;
			RawOffset += RawBlockSize;
		}
	}

	// Return an uncompressed buffer if the compressed data is larger than the raw data.
	if (RawSize <= MetaSize + CompressedSize)
	{
		CompressedData.Reset();
		return MethodNone().Compress(RawData, BlockSize);
	}

	// Write the header and calculate the CRC-32.
	for (uint32_t& Size : CompressedBlockSizes)
	{
		Size = ByteSwap(Size);
	}
	CompressedData.GetMutableView().Mid(sizeof(BufferHeader), MetaSize).CopyFrom(MakeMemoryView(CompressedBlockSizes));

	BufferHeader Header;
	Header.Method			   = GetMethod();
	Header.BlockSizeExponent   = static_cast<uint8_t>(zen::FloorLog2_64(BlockSize));
	Header.BlockCount		   = static_cast<uint32_t>(BlockCount);
	Header.TotalRawSize		   = RawSize;
	Header.TotalCompressedSize = sizeof(BufferHeader) + MetaSize + CompressedSize;
	Header.RawHash			   = RawHash.GetHash();
	Header.Write(CompressedData.GetMutableView().Left(sizeof(BufferHeader) + MetaSize));

	const MemoryView CompositeView = CompressedData.GetView().Left(Header.TotalCompressedSize);
	return CompositeBuffer(SharedBuffer::MakeView(CompositeView, CompressedData.MoveToShared()));
}

CompositeBuffer
MethodBlockBase::Decompress(const BufferHeader& Header, const CompositeBuffer& CompressedData) const
{
	if (Header.BlockCount == 0 || Header.TotalCompressedSize != CompressedData.GetSize())
	{
		return CompositeBuffer();
	}

	// The raw data cannot reference the compressed data unless it is owned.
	// An empty raw buffer requires an empty segment, which this path creates.
	if (!CompressedData.IsOwned() || Header.TotalRawSize == 0)
	{
		UniqueBuffer Buffer = UniqueBuffer::Alloc(Header.TotalRawSize);
		return TryDecompressTo(Header, CompressedData, Buffer) ? CompositeBuffer(Buffer.MoveToShared()) : CompositeBuffer();
	}

	std::vector<uint32_t> CompressedBlockSizes;
	CompressedBlockSizes.resize(Header.BlockCount);
	CompressedData.CopyTo(MakeMutableMemoryView(CompressedBlockSizes), sizeof(BufferHeader));

	for (uint32_t& Size : CompressedBlockSizes)
	{
		Size = ByteSwap(Size);
	}

	// Allocate the buffer for the raw blocks that were compressed.
	SharedBuffer	  RawData;
	MutableMemoryView RawDataView;
	const uint64_t	  BlockSize = uint64_t(1) << Header.BlockSizeExponent;
	{
		uint64_t RawDataSize	  = 0;
		uint64_t RemainingRawSize = Header.TotalRawSize;
		for (const uint32_t CompressedBlockSize : CompressedBlockSizes)
		{
			const uint64_t RawBlockSize = zen::Min(RemainingRawSize, BlockSize);
			if (CompressedBlockSize < BlockSize)
			{
				RawDataSize += RawBlockSize;
			}
			RemainingRawSize -= RawBlockSize;
		}
		UniqueBuffer RawDataBuffer = UniqueBuffer::Alloc(RawDataSize);
		RawDataView				   = RawDataBuffer;
		RawData					   = RawDataBuffer.MoveToShared();
	}

	// Decompress the compressed data in blocks and reference the uncompressed blocks.
	uint64_t				  PendingCompressedSegmentOffset = sizeof(BufferHeader) + uint64_t(Header.BlockCount) * sizeof(uint32_t);
	uint64_t				  PendingCompressedSegmentSize	 = 0;
	uint64_t				  PendingRawSegmentOffset		 = 0;
	uint64_t				  PendingRawSegmentSize			 = 0;
	std::vector<SharedBuffer> Segments;

	const auto CommitPendingCompressedSegment =
		[&PendingCompressedSegmentOffset, &PendingCompressedSegmentSize, &CompressedData, &Segments] {
			if (PendingCompressedSegmentSize)
			{
				CompressedData.IterateRange(PendingCompressedSegmentOffset,
											PendingCompressedSegmentSize,
											[&Segments](MemoryView View, const SharedBuffer& ViewOuter) {
												Segments.push_back(SharedBuffer::MakeView(View, ViewOuter));
											});
				PendingCompressedSegmentOffset += PendingCompressedSegmentSize;
				PendingCompressedSegmentSize = 0;
			}
		};

	const auto CommitPendingRawSegment = [&PendingRawSegmentOffset, &PendingRawSegmentSize, &RawData, &Segments] {
		if (PendingRawSegmentSize)
		{
			const MemoryView PendingSegment = RawData.GetView().Mid(PendingRawSegmentOffset, PendingRawSegmentSize);
			Segments.push_back(SharedBuffer::MakeView(PendingSegment, RawData));
			PendingRawSegmentOffset += PendingRawSegmentSize;
			PendingRawSegmentSize = 0;
		}
	};

	UniqueBuffer CompressedBlockCopy;
	uint64_t	 RemainingRawSize		 = Header.TotalRawSize;
	uint64_t	 RemainingCompressedSize = CompressedData.GetSize();
	for (const uint32_t CompressedBlockSize : CompressedBlockSizes)
	{
		if (RemainingCompressedSize < CompressedBlockSize)
		{
			return CompositeBuffer();
		}

		const uint64_t RawBlockSize = zen::Min(RemainingRawSize, BlockSize);
		if (RawBlockSize == CompressedBlockSize)
		{
			CommitPendingRawSegment();
			PendingCompressedSegmentSize += RawBlockSize;
		}
		else
		{
			CommitPendingCompressedSegment();
			const MemoryView CompressedBlock =
				CompressedData.ViewOrCopyRange(PendingCompressedSegmentOffset, CompressedBlockSize, CompressedBlockCopy);
			if (!DecompressBlock(RawDataView.Left(RawBlockSize), CompressedBlock))
			{
				return CompositeBuffer();
			}
			PendingCompressedSegmentOffset += CompressedBlockSize;
			PendingRawSegmentSize += RawBlockSize;
			RawDataView += RawBlockSize;
		}

		RemainingCompressedSize -= CompressedBlockSize;
		RemainingRawSize -= RawBlockSize;
	}

	CommitPendingCompressedSegment();
	CommitPendingRawSegment();

	return CompositeBuffer(std::move(Segments));
}

bool
MethodBlockBase::TryDecompressTo(const BufferHeader& Header, const CompositeBuffer& CompressedData, MutableMemoryView RawView) const
{
	if (Header.TotalRawSize != RawView.GetSize() || Header.TotalCompressedSize != CompressedData.GetSize())
	{
		return false;
	}

	std::vector<uint32_t> CompressedBlockSizes;
	CompressedBlockSizes.resize(Header.BlockCount);
	CompressedData.CopyTo(MakeMutableMemoryView(CompressedBlockSizes), sizeof(BufferHeader));

	for (uint32_t& Size : CompressedBlockSizes)
	{
		Size = ByteSwap(Size);
	}

	UniqueBuffer   CompressedBlockCopy;
	const uint64_t BlockSize			   = uint64_t(1) << Header.BlockSizeExponent;
	uint64_t	   CompressedOffset		   = sizeof(BufferHeader) + uint64_t(Header.BlockCount) * sizeof(uint32_t);
	uint64_t	   RemainingRawSize		   = Header.TotalRawSize;
	uint64_t	   RemainingCompressedSize = CompressedData.GetSize();
	for (uint32_t CompressedBlockSize : CompressedBlockSizes)
	{
		if (RemainingCompressedSize < CompressedBlockSize)
		{
			return false;
		}

		const uint64_t RawBlockSize = zen::Min(RemainingRawSize, BlockSize);
		if (RawBlockSize == CompressedBlockSize)
		{
			CompressedData.CopyTo(RawView.Left(RawBlockSize), CompressedOffset);
		}
		else
		{
			const MemoryView CompressedBlock = CompressedData.ViewOrCopyRange(CompressedOffset, CompressedBlockSize, CompressedBlockCopy);
			if (!DecompressBlock(RawView.Left(RawBlockSize), CompressedBlock))
			{
				return false;
			}
		}

		RemainingCompressedSize -= CompressedBlockSize;
		RemainingRawSize -= RawBlockSize;
		CompressedOffset += CompressedBlockSize;
		RawView += RawBlockSize;
	}

	return RemainingRawSize == 0;
}

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

class MethodLZ4 final : public MethodBlockBase
{
protected:
	CompressionMethod GetMethod() const final { return CompressionMethod::LZ4; }

	uint64_t CompressBlockBound(uint64_t RawSize) const final
	{
		if (RawSize <= LZ4_MAX_INPUT_SIZE)
		{
			return static_cast<uint64_t>(LZ4_compressBound(static_cast<int>(RawSize)));
		}
		return 0;
	}

	bool CompressBlock(MutableMemoryView& CompressedData, MemoryView RawData) const final
	{
		if (RawData.GetSize() <= LZ4_MAX_INPUT_SIZE)
		{
			const int Size =
				LZ4_compress_default(static_cast<const char*>(RawData.GetData()),
									 static_cast<char*>(CompressedData.GetData()),
									 static_cast<int>(RawData.GetSize()),
									 static_cast<int>(zen::Min<uint64_t>(CompressedData.GetSize(), std::numeric_limits<int>::max())));
			CompressedData.LeftInline(static_cast<uint64_t>(Size));
			return Size > 0;
		}
		return false;
	}

	bool DecompressBlock(MutableMemoryView RawData, MemoryView CompressedData) const final
	{
		if (CompressedData.GetSize() <= std::numeric_limits<int>::max())
		{
			const int Size = LZ4_decompress_safe(static_cast<const char*>(CompressedData.GetData()),
												 static_cast<char*>(RawData.GetData()),
												 static_cast<int>(CompressedData.GetSize()),
												 static_cast<int>(zen::Min<uint64_t>(RawData.GetSize(), LZ4_MAX_INPUT_SIZE)));
			return static_cast<uint64_t>(Size) == RawData.GetSize();
		}
		return false;
	}
};

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

static const CompressionMethodBase*
GetMethod(CompressionMethod Method)
{
	static MethodNone None;
	static MethodLZ4  LZ4;
	switch (Method)
	{
		default:
			return nullptr;
		case CompressionMethod::None:
			return &None;
		case CompressionMethod::LZ4:
			return &LZ4;
	}
}

static const char*
GetMethodName(CompressionMethod Method)
{
	switch (Method)
	{
		default:
			return "error";
		case CompressionMethod::None:
			return "None";
		case CompressionMethod::LZ4:
			return "LZ4";
	}
}

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

bool
BufferHeader::IsValid(const CompositeBuffer& CompressedData)
{
	if (sizeof(BufferHeader) <= CompressedData.GetSize())
	{
		const BufferHeader Header = Read(CompressedData);
		if (Header.Magic == BufferHeader::ExpectedMagic)
		{
			if (const CompressionMethodBase* const Method = GetMethod(Header.Method))
			{
				UniqueBuffer	 HeaderCopy;
				const MemoryView HeaderView = CompressedData.ViewOrCopyRange(0, Method->GetHeaderSize(Header), HeaderCopy);
				if (Header.Crc32 == BufferHeader::CalculateCrc32(HeaderView))
				{
					return true;
				}
			}
		}
	}
	return false;
}

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

template<typename BufferType>
inline CompositeBuffer
ValidBufferOrEmpty(BufferType&& CompressedData)
{
	return BufferHeader::IsValid(CompressedData) ? CompositeBuffer(std::forward<BufferType>(CompressedData)) : CompositeBuffer();
}

}  // namespace zen::detail

namespace zen {

CompressedBuffer
CompressedBuffer::Compress(CompressionMethod Method, const CompositeBuffer& RawData)
{
	using namespace detail;

	CompressedBuffer Local;
	if (const CompressionMethodBase* const Impl = GetMethod(Method))
	{
		Local.CompressedData = Impl->Compress(RawData);
	}
	return Local;
}

CompressedBuffer
CompressedBuffer::Compress(CompressionMethod Method, const SharedBuffer& RawData)
{
	return Compress(Method, CompositeBuffer(RawData));
}

CompressedBuffer
CompressedBuffer::FromCompressed(const CompositeBuffer& InCompressedData)
{
	CompressedBuffer Local;
	Local.CompressedData = detail::ValidBufferOrEmpty(InCompressedData);
	return Local;
}

CompressedBuffer
CompressedBuffer::FromCompressed(CompositeBuffer&& InCompressedData)
{
	CompressedBuffer Local;
	Local.CompressedData = detail::ValidBufferOrEmpty(std::move(InCompressedData));
	return Local;
}

CompressedBuffer
CompressedBuffer::FromCompressed(const SharedBuffer& InCompressedData)
{
	CompressedBuffer Local;
	Local.CompressedData = detail::ValidBufferOrEmpty(InCompressedData);
	return Local;
}

CompressedBuffer
CompressedBuffer::FromCompressed(SharedBuffer&& InCompressedData)
{
	CompressedBuffer Local;
	Local.CompressedData = detail::ValidBufferOrEmpty(std::move(InCompressedData));
	return Local;
}

uint64_t
CompressedBuffer::GetRawSize() const
{
	return CompressedData ? detail::BufferHeader::Read(CompressedData).TotalRawSize : 0;
}

BLAKE3
CompressedBuffer::GetRawHash() const
{
	return CompressedData ? detail::BufferHeader::Read(CompressedData).RawHash : BLAKE3();
}

bool
CompressedBuffer::TryDecompressTo(MutableMemoryView RawView) const
{
	using namespace detail;
	if (CompressedData)
	{
		const BufferHeader Header = BufferHeader::Read(CompressedData);
		if (const CompressionMethodBase* const Method = GetMethod(Header.Method))
		{
			return Method->TryDecompressTo(Header, CompressedData, RawView);
		}
	}
	return false;
}

SharedBuffer
CompressedBuffer::Decompress() const
{
	using namespace detail;
	if (CompressedData)
	{
		const BufferHeader Header = BufferHeader::Read(CompressedData);
		if (const CompressionMethodBase* const Method = GetMethod(Header.Method))
		{
			if (Header.Method == CompressionMethod::None)
			{
				return Method->Decompress(Header, CompressedData).Flatten();
			}
			UniqueBuffer RawData = UniqueBuffer::Alloc(Header.TotalRawSize);
			if (Method->TryDecompressTo(Header, CompressedData, RawData))
			{
				return RawData.MoveToShared();
			}
		}
	}
	return SharedBuffer();
}

CompositeBuffer
CompressedBuffer::DecompressToComposite() const
{
	using namespace detail;
	if (CompressedData)
	{
		const BufferHeader Header = BufferHeader::Read(CompressedData);
		if (const CompressionMethodBase* const Method = GetMethod(Header.Method))
		{
			return Method->Decompress(Header, CompressedData);
		}
	}
	return CompositeBuffer();
}

const char*
CompressedBuffer::GetFormatName() const
{
	return detail::GetMethodName(CompressedData ? detail::BufferHeader::Read(CompressedData).Method : CompressionMethod::None);
}

/**
	______________________ _____________________________
	\__    ___/\_   _____//   _____/\__    ___/   _____/
	  |    |    |    __)_ \_____  \   |    |  \_____  \
	  |    |    |        \/        \  |    |  /        \
	  |____|   /_______  /_______  /  |____| /_______  /
					   \/        \/                  \/
 */

TEST_CASE("CompressedBuffer")
{
	uint8_t Zeroes[256]{};
	uint8_t Ones[256];
	memset(Ones, 1, sizeof Ones);

	CompressedBuffer Buffer1 =
		CompressedBuffer::Compress(CompressionMethod::None, CompositeBuffer(SharedBuffer::MakeView(MakeMemoryView(Zeroes))));

	CHECK(Buffer1.GetRawSize() == sizeof(Zeroes));
	CHECK(Buffer1.GetCompressedSize() == (sizeof(Zeroes) + sizeof(detail::BufferHeader)));

	CompressedBuffer Buffer2 = CompressedBuffer::Compress(
		CompressionMethod::None,
		CompositeBuffer(SharedBuffer::MakeView(MakeMemoryView(Zeroes)), SharedBuffer::MakeView(MakeMemoryView(Ones))));

	CHECK(Buffer2.GetRawSize() == (sizeof(Zeroes) + sizeof(Ones)));
	CHECK(Buffer2.GetCompressedSize() == (sizeof(Zeroes) + sizeof(Ones) + sizeof(detail::BufferHeader)));

	CompressedBuffer Buffer3 =
		CompressedBuffer::Compress(CompressionMethod::LZ4, CompositeBuffer(SharedBuffer::MakeView(MakeMemoryView(Zeroes))));

	CHECK(Buffer3.GetRawSize() == sizeof(Zeroes));
	CHECK(Buffer3.GetCompressedSize() == (15 + sizeof(detail::BufferHeader)));

	CompressedBuffer Buffer4 = CompressedBuffer::Compress(
		CompressionMethod::LZ4,
		CompositeBuffer(SharedBuffer::MakeView(MakeMemoryView(Zeroes)), SharedBuffer::MakeView(MakeMemoryView(Ones))));

	CHECK(Buffer4.GetRawSize() == (sizeof(Zeroes) + sizeof(Ones)));
	CHECK(Buffer4.GetCompressedSize() == (20 + sizeof(detail::BufferHeader)));
}

void
compress_forcelink()
{
}

}  // namespace zen