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

#pragma once

#include "CoreTypes.h"
#include "Hash/xxhash.h"
#include "Misc/Guid.h"
#include "Serialization/Archive.h"
#include "UObject/NameTypes.h"
#include <type_traits>

namespace UE::DerivedData
{

/**
 * A type that builds a build version from arbitrary values serialized to it.
 *
 * FGuid GetVersion() const final
 * {
 *     FBuildVersionBuilder Builder;
 *     Builder << FGuid(TEXT("a3ae79ff-6a89-4124-afd6-dc095e000488"));
 *     Builder << ThirdPartyLibraryVersion;
 *     return Builder.Build();
 * }
 */
class FBuildVersionBuilder final : public FArchive
{
public:
	inline FBuildVersionBuilder();

	inline FGuid Build() const;

	inline FString GetArchiveName() const final { return TEXT("FBuildVersionBuilder"); }

	inline void Serialize(void* Data, int64 Num) final;

	using FArchive::operator<<;
	FArchive& operator<<(FName& Name) final;

	template <typename ArgType>
	inline FBuildVersionBuilder& operator<<(ArgType&& Arg)
	{
		FArchive& Ar = *this;
		Ar << const_cast<std::decay_t<ArgType>&>(Arg);
		return *this;
	}

private:
	FXxHash128Builder HashBuilder;
};

inline FBuildVersionBuilder::FBuildVersionBuilder()
{
	SetIsSaving(true);
	SetIsPersistent(false);

	// Hash this as the namespace of the Version 3 UUID created in Build().
	static FGuid BaseVersion(TEXT("b9080e6a-9eb2-4c25-8810-e957009fa0a1"));
	HashBuilder.Update(&BaseVersion, sizeof(FGuid));
}

inline FGuid FBuildVersionBuilder::Build() const
{
	FXxHash128 Hash = HashBuilder.Finalize();
	uint32 A = uint32(Hash.HashHigh >> 32);
	uint32 B = uint32(Hash.HashHigh);
	uint32 C = uint32(Hash.HashLow >> 32);
	uint32 D = uint32(Hash.HashLow);
	// Convert to a Variant 1 Version 3 UUID, which is meant to be created
	// by hashing the namespace and name with MD5, but this is using XXH3.
	B = (B & ~0x0000f000) | 0x00003000; // Version 3 (MD5)
	C = (C & ~0xc0000000) | 0x80000000; // Variant 1 (RFC 4122 UUID)
	return FGuid(A, B, C, D);
}

inline void FBuildVersionBuilder::Serialize(void* Data, int64 Num)
{
	HashBuilder.Update(Data, uint64(Num));
}

inline FArchive& FBuildVersionBuilder::operator<<(FName& Name)
{
	FString NameString = Name.ToString();
	return *this << NameString;
}

} // UE::DerivedData