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

#include "Virtualization/IVirtualizationBackend.h"

#include "ISourceControlModule.h"
#include "ISourceControlProvider.h"
#include "Misc/Parse.h"
#include "SourceControlOperations.h"
#include "Virtualization/PayloadId.h"
#include "VirtualizationSourceControlUtilities.h"
#include "VirtualizationUtilities.h"

// When the SourceControl module (or at least the perforce source control module) is thread safe we
// can enable this and stop using the hacky work around 'TryToDownloadFileFromBackgroundThread'
#define IS_SOURCE_CONTROL_THREAD_SAFE 0

namespace UE::Virtualization
{

/**
 * This backend can be used to access payloads stored in source control.
 * The backend doesn't 'check out' a payload file but instead will just download the payload as
 * a binary blob.
 * It is assumed that the files are stored with the same path convention as the file system 
 * backend, found in Utils::PayloadIdToPath.
 * 
 * Ini file setup:
 * 'Name'=(Type=SourceControl, DepotRoot="//XXX/")
 * Where 'Name' is the backend name in the hierarchy and 'XXX' is the path in the source control
 * depot where the payload files are being stored.
 */
class FSourceControlBackend : public IVirtualizationBackend
{
public:
	FSourceControlBackend(FStringView ConfigName)
		: IVirtualizationBackend(EOperations::Pull)
	{
	}

	virtual bool Initialize(const FString& ConfigEntry) override
	{
		TRACE_CPUPROFILER_EVENT_SCOPE(FSourceControlBackend::Initialize);

		// We require that a valid depot root has been provided
		if (!FParse::Value(*ConfigEntry, TEXT("DepotRoot="), DepotRoot))
		{
			UE_LOG(LogVirtualization, Error, TEXT("'DepotRoot=' not found in the config file"));
			return false;
		}

		ISourceControlModule& SSCModule = ISourceControlModule::Get();

		// We require perforce as the source control provider as it is currently the only one that has the virtualization functionality implemented
		const FName SourceControlName = SSCModule.GetProvider().GetName();
		if (SourceControlName.IsNone())
		{
			// No source control provider is set so we can try to set it to "Perforce"
			// Note this call will fatal error if "Perforce" is not a valid option
			SSCModule.SetProvider(FName("Perforce"));
		}
		else if (SourceControlName != TEXT("Perforce"))
		{
			UE_LOG(LogVirtualization, Error, TEXT("Attempting to initialize FSourceControlBackend but source control is '%s' and only Perforce is currently supported!"), *SourceControlName.ToString());
			return false;
		}

		ISourceControlProvider& SCCProvider = SSCModule.GetProvider();

		if (!SCCProvider.IsAvailable())
		{
			SCCProvider.Init();
		}

		// When a source control depot is set up a file named 'payload_metainfo.txt' should be submitted to it's root.
		// This allows us to check for the existence of the file to confirm that the depot root is indeed valid.
		const FString PayloadMetaInfoPath = FString::Printf(TEXT("%spayload_metainfo.txt"), *DepotRoot);

#if IS_SOURCE_CONTROL_THREAD_SAFE
		TSharedRef<FDownloadFile, ESPMode::ThreadSafe> DownloadCommand = ISourceControlOperation::Create<FDownloadFile>();
		if (SCCProvider.Execute(DownloadCommand, PayloadMetaInfoPath, EConcurrency::Synchronous) != ECommandResult::Succeeded)
		{
			UE_LOG(LogVirtualization, Error, TEXT("Failed to find 'payload_metainfo.txt' in the depot '%s', is your config set up correctly?"), *DepotRoot);
			return false;
		}	
#else
		TSharedRef<FDownloadFile, ESPMode::ThreadSafe> DownloadCommand = ISourceControlOperation::Create<FDownloadFile>();
		if (!SCCProvider.TryToDownloadFileFromBackgroundThread(DownloadCommand, PayloadMetaInfoPath))
		{
			UE_LOG(LogVirtualization, Error, TEXT("Failed to find 'payload_metainfo.txt' in the depot '%s', is your config set up correctly?"), *DepotRoot);
			return false;
		}		
#endif //IS_SOURCE_CONTROL_THREAD_SAFE

		FSharedBuffer MetaInfoBuffer = DownloadCommand->GetFileData(PayloadMetaInfoPath);
		if (MetaInfoBuffer.IsNull())
		{
			UE_LOG(LogVirtualization, Error, TEXT("Failed to find 'payload_metainfo.txt' in the depot '%s', is your config set up correctly?"), *DepotRoot);
			return false;
		}

		// Currently we do not do anything with the payload meta info, in the future we could structure
		// it's format to include more information that might be worth logging or something. 
		// But for now being able to pull the payload meta info path at least shows that we can use the
		// depot.

		return true;
	}

	virtual EPushResult PushData(const FPayloadId& Id, const FCompressedBuffer& Payload) override
	{
		// This backend will not actually push data to source control, that will be done by
		// a separate submission tool. Since files submitted to source control are there forever 
		// we don't want the user to be uploaded new entries each time that they save the asset
		// but instead upload once when the package is committed to source control.
		// TODO: As we put the pieces together it is likely that we will change the backend API
		// so that we don't need dummy implementations of PushData for backends that don't need it.
		// Especially considering that it is most likely that no backend will push.

		checkNoEntry(); 
		return EPushResult::Failed;
	}

	virtual FCompressedBuffer PullData(const FPayloadId& Id) override
	{
		TRACE_CPUPROFILER_EVENT_SCOPE(FSourceControlBackend::PullData);

		TStringBuilder<512> DepotPath;
		CreateDepotPath(Id, DepotPath);

		ISourceControlProvider& SCCProvider = ISourceControlModule::Get().GetProvider();

#if IS_SOURCE_CONTROL_THREAD_SAFE
		TSharedRef<FDownloadFile, ESPMode::ThreadSafe> DownloadCommand = ISourceControlOperation::Create<FDownloadFile>(FDownloadFile::EVerbosity::None);
		if (SCCProvider.Execute(DownloadCommand, DepotPath.ToString(), EConcurrency::Synchronous) != ECommandResult::Succeeded)
		{
			return FCompressedBuffer();
		}
#else
		TSharedRef<FDownloadFile> DownloadCommand = ISourceControlOperation::Create<FDownloadFile>(FDownloadFile::EVerbosity::None);
		if (!SCCProvider.TryToDownloadFileFromBackgroundThread(DownloadCommand, DepotPath.ToString()))
		{
			return FCompressedBuffer();
		}
#endif

		// The payload was created by FCompressedBuffer::Compress so we can return it 
		// as a FCompressedBuffer.
		FSharedBuffer Buffer = DownloadCommand->GetFileData(DepotPath);
		return FCompressedBuffer::FromCompressed(Buffer);
	}

	virtual FString GetDebugString() const override
	{
		return FString(TEXT("SourceControl"));
	}

	void CreateDepotPath(const FPayloadId& PayloadId, FStringBuilderBase& OutPath)
	{
		TStringBuilder<52> PayloadPath;
		Utils::PayloadIdToPath(PayloadId, PayloadPath);

		OutPath << DepotRoot << PayloadPath;
	}

private:

	/** The root where the virtualized payloads are stored in source control */
	FString DepotRoot;
};

UE_REGISTER_VIRTUALIZATION_BACKEND_FACTORY(FSourceControlBackend, SourceControl);

} // namespace UE::Virtualization