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

#include "DerivedDataCache.h"
#include "DerivedDataCacheInterface.h"

#include "CoreMinimal.h"
#include "Misc/CommandLine.h"
#include "HAL/ThreadSafeCounter.h"
#include "Misc/ScopeLock.h"
#include "Stats/StatsMisc.h"
#include "Stats/Stats.h"
#include "Async/AsyncWork.h"
#include "Async/TaskGraphInterfaces.h"
#include "Serialization/MemoryReader.h"
#include "Serialization/MemoryWriter.h"
#include "Modules/ModuleManager.h"

#include "DerivedDataBackendInterface.h"
#include "DerivedDataPluginInterface.h"
#include "DDCCleanup.h"
#include "ProfilingDebugging/CookStats.h"

#include "Algo/AllOf.h"
#include "Algo/Transform.h"
#include "DerivedDataBackendInterface.h"
#include "Misc/CoreMisc.h"
#include "Misc/ScopeExit.h"
#include "Misc/StringBuilder.h"
#include "Serialization/CompactBinary.h"
#include "Serialization/CompactBinaryValidation.h"
#include "Serialization/CompactBinaryWriter.h"

#include <atomic>

DEFINE_STAT(STAT_DDC_NumGets);
DEFINE_STAT(STAT_DDC_NumPuts);
DEFINE_STAT(STAT_DDC_NumBuilds);
DEFINE_STAT(STAT_DDC_NumExist);
DEFINE_STAT(STAT_DDC_SyncGetTime);
DEFINE_STAT(STAT_DDC_ASyncWaitTime);
DEFINE_STAT(STAT_DDC_PutTime);
DEFINE_STAT(STAT_DDC_SyncBuildTime);
DEFINE_STAT(STAT_DDC_ExistTime);

//#define DDC_SCOPE_CYCLE_COUNTER(x) QUICK_SCOPE_CYCLE_COUNTER(STAT_ ## x)
#define DDC_SCOPE_CYCLE_COUNTER(x) TRACE_CPUPROFILER_EVENT_SCOPE(x);


#if ENABLE_COOK_STATS
#include "DerivedDataCacheUsageStats.h"
namespace DerivedDataCacheCookStats
{
	// Use to prevent potential divide by zero issues
	inline double SafeDivide(const int64 Numerator, const int64 Denominator)
	{
		return Denominator != 0 ? (double)Numerator / (double)Denominator : 0.0;
	}

	// AddCookStats cannot be a lambda because of false positives in static analysis.
	// See https://developercommunity.visualstudio.com/content/problem/576913/c6244-regression-in-new-lambda-processorpermissive.html
	static void AddCookStats(FCookStatsManager::AddStatFuncRef AddStat)
	{
		TMap<FString, FDerivedDataCacheUsageStats> DDCStats;
		GetDerivedDataCacheRef().GatherUsageStats(DDCStats);
		{
			const FString StatName(TEXT("DDC.Usage"));
			for (const auto& UsageStatPair : DDCStats)
			{
				UsageStatPair.Value.LogStats(AddStat, StatName, UsageStatPair.Key);
			}
		}

		// Now lets add some summary data to that applies some crazy knowledge of how we set up our DDC. The goal 
		// is to print out the global hit rate, and the hit rate of the local and shared DDC.
		// This is done by adding up the total get/miss calls the root node receives.
		// Then we find the FileSystem nodes that correspond to the local and shared cache using some hacky logic to detect a "network drive".
		// If the DDC graph ever contains more than one local or remote filesystem, this will only find one of them.
		{
			TArray<FString, TInlineAllocator<20>> Keys;
			DDCStats.GenerateKeyArray(Keys);
			FString* RootKey = Keys.FindByPredicate([](const FString& Key) {return Key.StartsWith(TEXT(" 0:")); });
			// look for a Filesystem DDC that doesn't have a UNC path. Ugly, yeah, but we only cook on PC at the moment.
			FString* LocalDDCKey = Keys.FindByPredicate([](const FString& Key) {return Key.Contains(TEXT(": FileSystem.")) && !Key.Contains(TEXT("//")); });
			// look for a UNC path
			FString* SharedDDCKey = Keys.FindByPredicate([](const FString& Key) {return Key.Contains(TEXT(": FileSystem.//")); });
			if (RootKey)
			{
				const FDerivedDataCacheUsageStats& RootStats = DDCStats[*RootKey];
				int64 TotalGetHits =
					RootStats.GetStats.GetAccumulatedValue(FCookStats::CallStats::EHitOrMiss::Hit, FCookStats::CallStats::EStatType::Counter, true) +
					RootStats.GetStats.GetAccumulatedValue(FCookStats::CallStats::EHitOrMiss::Hit, FCookStats::CallStats::EStatType::Counter, false);
				int64 TotalGetMisses =
					RootStats.GetStats.GetAccumulatedValue(FCookStats::CallStats::EHitOrMiss::Miss, FCookStats::CallStats::EStatType::Counter, true) +
					RootStats.GetStats.GetAccumulatedValue(FCookStats::CallStats::EHitOrMiss::Miss, FCookStats::CallStats::EStatType::Counter, false);
				int64 TotalGets = TotalGetHits + TotalGetMisses;

				int64 LocalHits = 0;
				if (LocalDDCKey)
				{
					const FDerivedDataCacheUsageStats& LocalDDCStats = DDCStats[*LocalDDCKey];
					LocalHits =
						LocalDDCStats.GetStats.GetAccumulatedValue(FCookStats::CallStats::EHitOrMiss::Hit, FCookStats::CallStats::EStatType::Counter, true) +
						LocalDDCStats.GetStats.GetAccumulatedValue(FCookStats::CallStats::EHitOrMiss::Hit, FCookStats::CallStats::EStatType::Counter, false);
				}
				int64 SharedHits = 0;
				if (SharedDDCKey)
				{
					// The shared DDC is only queried if the local one misses (or there isn't one). So it's hit rate is technically 
					const FDerivedDataCacheUsageStats& SharedDDCStats = DDCStats[*SharedDDCKey];
					SharedHits =
						SharedDDCStats.GetStats.GetAccumulatedValue(FCookStats::CallStats::EHitOrMiss::Hit, FCookStats::CallStats::EStatType::Counter, true) +
						SharedDDCStats.GetStats.GetAccumulatedValue(FCookStats::CallStats::EHitOrMiss::Hit, FCookStats::CallStats::EStatType::Counter, false);
				}

				int64 TotalPutHits =
					RootStats.PutStats.GetAccumulatedValue(FCookStats::CallStats::EHitOrMiss::Hit, FCookStats::CallStats::EStatType::Counter, true) +
					RootStats.PutStats.GetAccumulatedValue(FCookStats::CallStats::EHitOrMiss::Hit, FCookStats::CallStats::EStatType::Counter, false);
				int64 TotalPutMisses =
					RootStats.PutStats.GetAccumulatedValue(FCookStats::CallStats::EHitOrMiss::Miss, FCookStats::CallStats::EStatType::Counter, true) +
					RootStats.PutStats.GetAccumulatedValue(FCookStats::CallStats::EHitOrMiss::Miss, FCookStats::CallStats::EStatType::Counter, false);
				int64 TotalPuts = TotalPutHits + TotalPutMisses;

				AddStat(TEXT("DDC.Summary"), FCookStatsManager::CreateKeyValueArray(
					TEXT("TotalGetHits"), TotalGetHits,
					TEXT("TotalGets"), TotalGets,
					TEXT("TotalGetHitPct"), SafeDivide(TotalGetHits, TotalGets),
					TEXT("LocalGetHitPct"), SafeDivide(LocalHits, TotalGets),
					TEXT("SharedGetHitPct"), SafeDivide(SharedHits, TotalGets),
					TEXT("OtherGetHitPct"), SafeDivide((TotalGetHits - LocalHits - SharedHits), TotalGets),
					TEXT("GetMissPct"), SafeDivide(TotalGetMisses, TotalGets),
					TEXT("TotalPutHits"), TotalPutHits,
					TEXT("TotalPuts"), TotalPuts,
					TEXT("TotalPutHitPct"), SafeDivide(TotalPutHits, TotalPuts),
					TEXT("PutMissPct"), SafeDivide(TotalPutMisses, TotalPuts)
					));
			}
		}
	}

	FCookStatsManager::FAutoRegisterCallback RegisterCookStats(AddCookStats);
}
#endif

namespace UE
{
namespace DerivedData
{

ICache* CreateCache();

} // DerivedData
} // UE

/** Whether we want to verify the DDC (pass in -VerifyDDC on the command line)*/
bool GVerifyDDC = false;

/**
 * Implementation of the derived data cache
 * This API is fully threadsafe
**/
class FDerivedDataCache : public FDerivedDataCacheInterface
{

	/** 
	 * Async worker that checks the cache backend and if that fails, calls the deriver to build the data and then puts the results to the cache
	**/
	friend class FBuildAsyncWorker;
	class FBuildAsyncWorker : public FNonAbandonableTask
	{
	public:
		enum EWorkerState : uint32
		{
			WorkerStateNone			= 0,
			WorkerStateRunning		= 1 << 0,
			WorkerStateFinished		= 1 << 1,
			WorkerStateDestroyed	= 1 << 2,
		};

		/** 
		 * Constructor for async task 
		 * @param	InDataDeriver	plugin to produce cache key and in the event of a miss, return the data.
		 * @param	InCacheKey		Complete cache key for this data.
		**/
		FBuildAsyncWorker(FDerivedDataPluginInterface* InDataDeriver, const TCHAR* InCacheKey, bool bInSynchronousForStats)
		: bSuccess(false)
		, bSynchronousForStats(bInSynchronousForStats)
		, bDataWasBuilt(false)
		, DataDeriver(InDataDeriver)
		, CacheKey(InCacheKey)
		{
		}

		virtual ~FBuildAsyncWorker()
		{
			// Record that the task is destroyed and check that it was not running or destroyed previously.
			{
				const uint32 PreviousState = WorkerState.fetch_or(WorkerStateDestroyed, std::memory_order_relaxed);
				checkf(!(PreviousState & WorkerStateRunning), TEXT("Destroying DDC worker that is still running! Key: %s"), *CacheKey);
				checkf(!(PreviousState & WorkerStateDestroyed), TEXT("Destroying DDC worker that has been destroyed previously! Key: %s"), *CacheKey);
			}
		}

		/** Async worker that checks the cache backend and if that fails, calls the deriver to build the data and then puts the results to the cache **/
		void DoWork()
		{
			// Record that the task is running and check that it was not running, finished, or destroyed previously.
			{
				const uint32 PreviousState = WorkerState.fetch_or(WorkerStateRunning, std::memory_order_relaxed);
				checkf(!(PreviousState & WorkerStateRunning), TEXT("Starting DDC worker that is already running! Key: %s"), *CacheKey);
				checkf(!(PreviousState & WorkerStateFinished), TEXT("Starting DDC worker that is already finished! Key: %s"), *CacheKey);
				checkf(!(PreviousState & WorkerStateDestroyed), TEXT("Starting DDC worker that has been destroyed! Key: %s"), *CacheKey);
			}

			TRACE_CPUPROFILER_EVENT_SCOPE(DDC_DoWork);

			const int32 NumBeforeDDC = Data.Num();
			bool bGetResult;
			{
				TRACE_CPUPROFILER_EVENT_SCOPE(DDC_Get);

				INC_DWORD_STAT(STAT_DDC_NumGets);
				STAT(double ThisTime = 0);
				{
					SCOPE_SECONDS_COUNTER(ThisTime);
					bGetResult = FDerivedDataBackend::Get().GetRoot().GetCachedData(*CacheKey, Data);
				}
				INC_FLOAT_STAT_BY(STAT_DDC_SyncGetTime, bSynchronousForStats ? (float)ThisTime : 0.0f);
			}
			if (bGetResult)
			{
				
				if(GVerifyDDC && DataDeriver && DataDeriver->IsDeterministic())
				{
					TArray<uint8> CmpData;
					DataDeriver->Build(CmpData);
					const int32 NumInDDC = Data.Num() - NumBeforeDDC;
					const int32 NumGenerated = CmpData.Num();
					
					bool bMatchesInSize = NumGenerated == NumInDDC;
					bool bDifferentMemory = true;
					int32 DifferentOffset = 0;
					if (bMatchesInSize)
					{
						bDifferentMemory = false;
						for (int32 i = 0; i < NumGenerated; i++)
						{
							if (CmpData[i] != Data[i])
							{
								bDifferentMemory = true;
								DifferentOffset = i;
								break;
							}
						}
					}

					if(!bMatchesInSize || bDifferentMemory)
					{
						FString ErrMsg = FString::Printf(TEXT("There is a mismatch between the DDC data and the generated data for plugin (%s) for asset (%s). BytesInDDC:%d, BytesGenerated:%d, bDifferentMemory:%d, offset:%d"), DataDeriver->GetPluginName(), *DataDeriver->GetDebugContextString(), NumInDDC, NumGenerated, bDifferentMemory, DifferentOffset);
						ensureMsgf(false, TEXT("%s"), *ErrMsg);
						UE_LOG(LogDerivedDataCache, Error, TEXT("%s"), *ErrMsg );
					}
					
				}

				check(Data.Num());
				bSuccess = true;
				delete DataDeriver;
				DataDeriver = NULL;
			}
			else if (DataDeriver)
			{
				{
					TRACE_CPUPROFILER_EVENT_SCOPE(DDC_Build);

					INC_DWORD_STAT(STAT_DDC_NumBuilds);
					STAT(double ThisTime = 0);
					{
						SCOPE_SECONDS_COUNTER(ThisTime);
						bSuccess = DataDeriver->Build(Data);
						bDataWasBuilt = true;
					}
					INC_FLOAT_STAT_BY(STAT_DDC_SyncBuildTime, bSynchronousForStats ? (float)ThisTime : 0.0f);
				}
				delete DataDeriver;
				DataDeriver = NULL;
				if (bSuccess)
				{
					check(Data.Num());

					TRACE_CPUPROFILER_EVENT_SCOPE(DDC_Put);

					INC_DWORD_STAT(STAT_DDC_NumPuts);
					STAT(double ThisTime = 0);
					{
						SCOPE_SECONDS_COUNTER(ThisTime);
						FDerivedDataBackend::Get().GetRoot().PutCachedData(*CacheKey, Data, true);
					}
					INC_FLOAT_STAT_BY(STAT_DDC_PutTime, bSynchronousForStats ? (float)ThisTime : 0.0f);
				}
			}
			if (!bSuccess)
			{
				Data.Empty();
			}
			FDerivedDataBackend::Get().AddToAsyncCompletionCounter(-1);

			// Record that the task is finished and check that it was running and not finished or destroyed previously.
			{
				const uint32 PreviousState = WorkerState.fetch_xor(WorkerStateRunning | WorkerStateFinished, std::memory_order_relaxed);
				checkf((PreviousState & WorkerStateRunning), TEXT("Finishing DDC worker that was not running! Key: %s"), *CacheKey);
				checkf(!(PreviousState & WorkerStateFinished), TEXT("Finishing DDC worker that is already finished! Key: %s"), *CacheKey);
				checkf(!(PreviousState & WorkerStateDestroyed), TEXT("Finishing DDC worker that has been destroyed! Key: %s"), *CacheKey);
			}
		}

		FORCEINLINE TStatId GetStatId() const
		{
			RETURN_QUICK_DECLARE_CYCLE_STAT(FBuildAsyncWorker, STATGROUP_ThreadPoolAsyncTasks);
		}

		std::atomic<uint32>				WorkerState{WorkerStateNone};
		/** true in the case of a cache hit, otherwise the result of the deriver build call **/
		bool							bSuccess;
		/** true if we should record the timing **/
		bool							bSynchronousForStats;
		/** true if we had to build the data */
		bool							bDataWasBuilt;
		/** Data dervier we are operating on **/
		FDerivedDataPluginInterface*	DataDeriver;
		/** Cache key associated with this build **/
		FString							CacheKey;
		/** Data to return to caller, later **/
		TArray<uint8>					Data;
	};

public:

	/** Constructor, called once to cereate a singleton **/
	FDerivedDataCache()
		: CurrentHandle(19248) // we will skip some potential handles to catch errors
		, Cache(UE::DerivedData::CreateCache())
	{
		FDerivedDataBackend::Get(); // we need to make sure this starts before we all us to start

		GVerifyDDC = FParse::Param(FCommandLine::Get(), TEXT("VerifyDDC"));

		UE_CLOG(GVerifyDDC, LogDerivedDataCache, Display, TEXT("Items retrieved from the DDC will be verified (-VerifyDDC)"));
	}

	/** Destructor, flushes all sync tasks **/
	~FDerivedDataCache()
	{
		FScopeLock ScopeLock(&SynchronizationObject);
		for (TMap<uint32,FAsyncTask<FBuildAsyncWorker>*>::TIterator It(PendingTasks); It; ++It)
		{
			It.Value()->EnsureCompletion();
			delete It.Value();
		}
		PendingTasks.Empty();
	}

	virtual UE::DerivedData::ICache& GetCache()
	{
		return *Cache;
	}

	virtual bool GetSynchronous(FDerivedDataPluginInterface* DataDeriver, TArray<uint8>& OutData, bool* bDataWasBuilt = nullptr) override
	{
		DDC_SCOPE_CYCLE_COUNTER(DDC_GetSynchronous);
		check(DataDeriver);
		FString CacheKey = FDerivedDataCache::BuildCacheKey(DataDeriver);
		UE_LOG(LogDerivedDataCache, VeryVerbose, TEXT("GetSynchronous %s from '%s'"), *CacheKey, *DataDeriver->GetDebugContextString());
		FAsyncTask<FBuildAsyncWorker> PendingTask(DataDeriver, *CacheKey, true);
		AddToAsyncCompletionCounter(1);
		PendingTask.StartSynchronousTask();
		OutData = PendingTask.GetTask().Data;
		if (bDataWasBuilt)
		{
			*bDataWasBuilt = PendingTask.GetTask().bDataWasBuilt;
		}
		return PendingTask.GetTask().bSuccess;
	}

	virtual uint32 GetAsynchronous(FDerivedDataPluginInterface* DataDeriver) override
	{
		DDC_SCOPE_CYCLE_COUNTER(DDC_GetAsynchronous);
		FScopeLock ScopeLock(&SynchronizationObject);
		const uint32 Handle = NextHandle();
		FString CacheKey = FDerivedDataCache::BuildCacheKey(DataDeriver);
		UE_LOG(LogDerivedDataCache, VeryVerbose, TEXT("GetAsynchronous %s from '%s', Handle %d"), *CacheKey, *DataDeriver->GetDebugContextString(), Handle);
		const bool bSync = !DataDeriver->IsBuildThreadsafe();
		FAsyncTask<FBuildAsyncWorker>* AsyncTask = new FAsyncTask<FBuildAsyncWorker>(DataDeriver, *CacheKey, bSync);
		check(!PendingTasks.Contains(Handle));
		PendingTasks.Add(Handle,AsyncTask);
		AddToAsyncCompletionCounter(1);
		if (!bSync)
		{
			AsyncTask->StartBackgroundTask();
		}
		else
		{
			AsyncTask->StartSynchronousTask();
		}
		// Must return a valid handle
		check(Handle != 0);
		return Handle;
	}

	virtual bool PollAsynchronousCompletion(uint32 Handle) override
	{
		DDC_SCOPE_CYCLE_COUNTER(DDC_PollAsynchronousCompletion);
		FAsyncTask<FBuildAsyncWorker>* AsyncTask = NULL;
		{
			FScopeLock ScopeLock(&SynchronizationObject);
			AsyncTask = PendingTasks.FindRef(Handle);
		}
		check(AsyncTask);
		return AsyncTask->IsDone();
	}

	virtual void WaitAsynchronousCompletion(uint32 Handle) override
	{
		DDC_SCOPE_CYCLE_COUNTER(DDC_WaitAsynchronousCompletion);
		STAT(double ThisTime = 0);
		{
			SCOPE_SECONDS_COUNTER(ThisTime);
			FAsyncTask<FBuildAsyncWorker>* AsyncTask = NULL;
			{
				FScopeLock ScopeLock(&SynchronizationObject);
				AsyncTask = PendingTasks.FindRef(Handle);
			}
			check(AsyncTask);
			AsyncTask->EnsureCompletion();
			UE_LOG(LogDerivedDataCache, Verbose, TEXT("WaitAsynchronousCompletion, Handle %d"), Handle);
		}
		INC_FLOAT_STAT_BY(STAT_DDC_ASyncWaitTime,(float)ThisTime);
	}

	virtual bool GetAsynchronousResults(uint32 Handle, TArray<uint8>& OutData, bool* bOutDataWasBuilt = nullptr) override
	{
		DDC_SCOPE_CYCLE_COUNTER(DDC_GetAsynchronousResults);
		FAsyncTask<FBuildAsyncWorker>* AsyncTask = NULL;
		{
			FScopeLock ScopeLock(&SynchronizationObject);
			PendingTasks.RemoveAndCopyValue(Handle,AsyncTask);
		}
		check(AsyncTask);
		const bool bDataWasBuilt = AsyncTask->GetTask().bDataWasBuilt;
		if (bOutDataWasBuilt)
		{
			*bOutDataWasBuilt = bDataWasBuilt;
		}
		if (!AsyncTask->GetTask().bSuccess)
		{
			UE_LOG(LogDerivedDataCache, Verbose, TEXT("GetAsynchronousResults, bDataWasBuilt: %d, Handle %d, FAILED"), (int32)bDataWasBuilt, Handle);
			delete AsyncTask;
			return false;
		}

		UE_LOG(LogDerivedDataCache, Verbose, TEXT("GetAsynchronousResults, bDataWasBuilt: %d, Handle %d, SUCCESS"), (int32)bDataWasBuilt, Handle);
		OutData = MoveTemp(AsyncTask->GetTask().Data);
		delete AsyncTask;
		check(OutData.Num());
		return true;
	}

	virtual bool GetSynchronous(const TCHAR* CacheKey, TArray<uint8>& OutData, FStringView DataContext) override
	{
		DDC_SCOPE_CYCLE_COUNTER(DDC_GetSynchronous_Data);
		UE_LOG(LogDerivedDataCache, VeryVerbose, TEXT("GetSynchronous %s from '%.*s'"), CacheKey, DataContext.Len(), DataContext.GetData());
		FAsyncTask<FBuildAsyncWorker> PendingTask((FDerivedDataPluginInterface*)NULL, CacheKey, true);
		AddToAsyncCompletionCounter(1);
		PendingTask.StartSynchronousTask();
		OutData = PendingTask.GetTask().Data;
		return PendingTask.GetTask().bSuccess;
	}

	virtual uint32 GetAsynchronous(const TCHAR* CacheKey, FStringView DataContext) override
	{
		DDC_SCOPE_CYCLE_COUNTER(DDC_GetAsynchronous_Handle);
		FScopeLock ScopeLock(&SynchronizationObject);
		const uint32 Handle = NextHandle();
		UE_LOG(LogDerivedDataCache, VeryVerbose, TEXT("GetAsynchronous %s from '%.*s', Handle %d"), CacheKey, DataContext.Len(), DataContext.GetData(), Handle);
		FAsyncTask<FBuildAsyncWorker>* AsyncTask = new FAsyncTask<FBuildAsyncWorker>((FDerivedDataPluginInterface*)NULL, CacheKey, false);
		check(!PendingTasks.Contains(Handle));
		PendingTasks.Add(Handle, AsyncTask);
		AddToAsyncCompletionCounter(1);
		AsyncTask->StartBackgroundTask();
		return Handle;
	}

	virtual void Put(const TCHAR* CacheKey, TArrayView<const uint8> Data, FStringView DataContext, bool bPutEvenIfExists = false) override
	{
		DDC_SCOPE_CYCLE_COUNTER(DDC_Put);
		UE_LOG(LogDerivedDataCache, VeryVerbose, TEXT("Put %s from '%.*s'"), CacheKey, DataContext.Len(), DataContext.GetData());
		STAT(double ThisTime = 0);
		{
			SCOPE_SECONDS_COUNTER(ThisTime);
			FDerivedDataBackend::Get().GetRoot().PutCachedData(CacheKey, Data, bPutEvenIfExists);
		}
		INC_FLOAT_STAT_BY(STAT_DDC_PutTime,(float)ThisTime);
		INC_DWORD_STAT(STAT_DDC_NumPuts);
	}

	virtual void MarkTransient(const TCHAR* CacheKey) override
	{
		FDerivedDataBackend::Get().GetRoot().RemoveCachedData(CacheKey, /*bTransient=*/ true);
	}

	virtual bool CachedDataProbablyExists(const TCHAR* CacheKey) override
	{
		DDC_SCOPE_CYCLE_COUNTER(DDC_CachedDataProbablyExists);
		bool bResult;
		INC_DWORD_STAT(STAT_DDC_NumExist);
		STAT(double ThisTime = 0);
		{
			SCOPE_SECONDS_COUNTER(ThisTime);
			bResult = FDerivedDataBackend::Get().GetRoot().CachedDataProbablyExists(CacheKey);
		}
		INC_FLOAT_STAT_BY(STAT_DDC_ExistTime, (float)ThisTime);
		return bResult;
	}

	virtual TBitArray<> CachedDataProbablyExistsBatch(TConstArrayView<FString> CacheKeys) override
	{
		TBitArray<> Result;
		if (CacheKeys.Num() > 1)
		{
			DDC_SCOPE_CYCLE_COUNTER(DDC_CachedDataProbablyExistsBatch);
			INC_DWORD_STAT(STAT_DDC_NumExist);
			STAT(double ThisTime = 0);
			{
				SCOPE_SECONDS_COUNTER(ThisTime);
				Result = FDerivedDataBackend::Get().GetRoot().CachedDataProbablyExistsBatch(CacheKeys);
				check(Result.Num() == CacheKeys.Num());
			}
			INC_FLOAT_STAT_BY(STAT_DDC_ExistTime, (float)ThisTime);
		}
		else if (CacheKeys.Num() == 1)
		{
			Result.Add(CachedDataProbablyExists(*CacheKeys[0]));
		}
		return Result;
	}

	virtual bool AllCachedDataProbablyExists(TConstArrayView<FString> CacheKeys) override
	{
		return CacheKeys.Num() == 0 || CachedDataProbablyExistsBatch(CacheKeys).CountSetBits() == CacheKeys.Num();
	}

	void NotifyBootComplete() override
	{
		DDC_SCOPE_CYCLE_COUNTER(DDC_NotifyBootComplete);
		FDerivedDataBackend::Get().NotifyBootComplete();
	}

	void AddToAsyncCompletionCounter(int32 Addend) override
	{
		FDerivedDataBackend::Get().AddToAsyncCompletionCounter(Addend);
	}

	void WaitForQuiescence(bool bShutdown) override
	{
		DDC_SCOPE_CYCLE_COUNTER(DDC_WaitForQuiescence);
		FDerivedDataBackend::Get().WaitForQuiescence(bShutdown);
	}

	/** Get whether a Shared Data Cache is in use */
	virtual bool GetUsingSharedDDC() const override
	{		
		return FDerivedDataBackend::Get().GetUsingSharedDDC();
	}

	virtual const TCHAR* GetGraphName() const override
	{
		return FDerivedDataBackend::Get().GetGraphName();
	}

	void GetDirectories(TArray<FString>& OutResults) override
	{
		FDerivedDataBackend::Get().GetDirectories(OutResults);
	}

	virtual void GatherUsageStats(TMap<FString, FDerivedDataCacheUsageStats>& UsageStatsMap) override
	{
		FDerivedDataBackend::Get().GatherUsageStats(UsageStatsMap);
	}

	/** Get event delegate for data cache notifications */
	virtual FOnDDCNotification& GetDDCNotificationEvent()
	{
		return DDCNotificationEvent;
	}

protected:
	uint32 NextHandle()
	{
		return (uint32)CurrentHandle.Increment();
	}


private:

	/** 
	 * Internal function to build a cache key out of the plugin name, versions and plugin specific info
	 * @param	DataDeriver	plugin to produce the elements of the cache key.
	 * @return				Assembled cache key
	**/
	static FString BuildCacheKey(FDerivedDataPluginInterface* DataDeriver)
	{
		FString Result = FDerivedDataCacheInterface::BuildCacheKey(DataDeriver->GetPluginName(), DataDeriver->GetVersionString(), *DataDeriver->GetPluginSpecificCacheKeySuffix());
		return Result;
	}


	/** Counter used to produce unique handles **/
	FThreadSafeCounter			CurrentHandle;
	/** Object used for synchronization via a scoped lock **/
	FCriticalSection			SynchronizationObject;
	/** Map of handle to pending task **/
	TMap<uint32,FAsyncTask<FBuildAsyncWorker>*>	PendingTasks;

	/** Cache notification delegate */
	FOnDDCNotification DDCNotificationEvent;

	TUniquePtr<UE::DerivedData::ICache> Cache;
};

/**
 * Module for the DDC
 */
class FDerivedDataCacheModule : public IDerivedDataCacheModule
{
public:
	virtual FDerivedDataCacheInterface& GetDDC() override
	{
		static FDerivedDataCache SingletonInstance;
		return SingletonInstance;
	}

	virtual void StartupModule() override
	{
		GetDDC();
	}

	virtual void ShutdownModule() override
	{
		FDDCCleanup::Shutdown();
	}
};

IMPLEMENT_MODULE( FDerivedDataCacheModule, DerivedDataCache);

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

namespace UE
{
namespace DerivedData
{

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

class FCache final : public ICache
{
public:
	virtual ~FCache() = default;

	virtual FCacheRequest Get(
		TConstArrayView<FCacheKey> Keys,
		FStringView Context,
		ECachePolicy Policy,
		ECachePriority Priority,
		FOnCacheGetComplete&& Callback) final;

	virtual FCacheRequest Put(
		TConstArrayView<FCacheRecord> Records,
		FStringView Context,
		ECachePolicy Policy,
		ECachePriority Priority,
		FOnCachePutComplete&& Callback) final;

	virtual FCacheRequest GetAttachments(
		TConstArrayView<FCacheAttachmentKey> Keys,
		FStringView Context,
		ECachePolicy Policy,
		ECachePriority Priority,
		FOnCacheGetAttachmentComplete&& Callback) final;

	virtual void CancelAll() final;

private:
	void Get(
		const FCacheKey& Key,
		FStringView Context,
		ECachePolicy Policy,
		ECachePriority Priority,
		FOnCacheGetComplete& Callback);

	void Put(
		const FCacheRecord& Record,
		FStringView Context,
		ECachePolicy Policy,
		ECachePriority Priority,
		FOnCachePutComplete& Callback);

	void GetAttachment(
		const FCacheAttachmentKey& Key,
		FStringView Context,
		ECachePolicy Policy,
		ECachePriority Priority,
		FOnCacheGetAttachmentComplete& Callback);

	template <int32 BufferSize>
	class TToString
	{
	public:
		template <typename T>
		explicit TToString(const T& Input)
		{
			Buffer << Input;
		}

		inline const TCHAR* operator*() const { return Buffer.ToString(); }
		inline const TCHAR* ToString() const { return Buffer.ToString(); }
		inline operator const TCHAR*() const { return Buffer.ToString(); }

	private:
		TStringBuilder<BufferSize> Buffer;
	};

	static FString MakeRecordKey(const FCacheKey& Key)
	{
		check(Key);
		TStringBuilder<96> Out;
		Out << Key.GetBucket() << TEXT("_") << Key.GetHash();
		return FDerivedDataCacheInterface::SanitizeCacheKey(Out.ToString());
	}

	static FString MakeContentKey(const FCacheAttachmentKey& AttachmentKey)
	{
		check(AttachmentKey);
		TStringBuilder<128> Out;
		Out << AttachmentKey.GetKey().GetBucket() << TEXT("_BLAKE3_") << AttachmentKey.GetHash();
		return FDerivedDataCacheInterface::SanitizeCacheKey(Out.ToString());
	}
};

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

void FCache::Get(
	const FCacheKey& Key,
	FStringView Context,
	ECachePolicy Policy,
	ECachePriority Priority,
	FOnCacheGetComplete& Callback)
{
	FCacheGetCompleteParams Params;
	Params.Record.SetKey(Key);

	ON_SCOPE_EXIT
	{
		if (Callback)
		{
			Callback(MoveTemp(Params));
		}
	};

	// Skip the request if querying the cache is disabled.
	if (!EnumHasAnyFlags(Policy, ECachePolicy::Query))
	{
		UE_LOG(LogDerivedDataCache, VeryVerbose, TEXT("Cache: Get skipped for %s from '%.*s'"),
			*TToString<96>(Key), Context.Len(), Context.GetData());
		return;
	}

	// Request the metadata and references from storage.
	TArray<uint8> Data;
	if (!GetDerivedDataCacheRef().GetSynchronous(*MakeRecordKey(Key), Data, Context))
	{
		UE_LOG(LogDerivedDataCache, Verbose, TEXT("Cache: Get cache miss for %s from '%.*s'"),
			*TToString<96>(Key), Context.Len(), Context.GetData());
		return;
	}

	// Validate that Data can be read as compact binary without crashing.
	if (ValidateCompactBinaryRange(MakeMemoryView(Data), ECbValidateMode::Default) != ECbValidateError::None)
	{
		UE_LOG(LogDerivedDataCache, Verbose, TEXT("Cache: Get cache miss with corrupted record for %s from '%.*s'"),
			*TToString<96>(Key), Context.Len(), Context.GetData());
		return;
	}

	// Read the record from its compact binary fields.
	FCbObject RecordObject(Data.GetData());
	FCbField MetaField = RecordObject["Meta"_ASV];
	FCbField ValueField = RecordObject["Value"_ASV];
	FCbField AttachmentsField = RecordObject["Attachments"_ASV];
	FCbArray AttachmentsArray = AttachmentsField.AsArray();

	// Validate that the record was serialized in the expected format.
	if ((MetaField && !MetaField.IsObject()) ||
		(ValueField && !ValueField.IsAnyReference()) ||
		(AttachmentsField && !AttachmentsField.IsArray()) ||
		!Algo::AllOf(AttachmentsArray, &FCbField::IsAnyReference))
	{
		UE_LOG(LogDerivedDataCache, Verbose, TEXT("Cache: Get cache miss with invalid format for %s from '%.*s'"),
			*TToString<96>(Key), Context.Len(), Context.GetData());
		return;
	}

	// Check for existence of the value and attachments if they are being skipped.
	{
		TArray<FBlake3Hash, TInlineAllocator<1>> KeysToCheck;
		if (EnumHasAnyFlags(Policy, ECachePolicy::SkipValue) && ValueField.IsAnyReference())
		{
			KeysToCheck.Add(ValueField.AsAnyReference());
			if (KeysToCheck.Last().IsZero())
			{
				KeysToCheck.Pop();
			}
		}
		if (EnumHasAnyFlags(Policy, ECachePolicy::SkipAttachments))
		{
			KeysToCheck.Reserve(KeysToCheck.Num() + AttachmentsArray.Num());
			for (FCbField AttachmentField : AttachmentsArray)
			{
				KeysToCheck.Add(AttachmentField.AsAnyReference());
			}
		}
		if (KeysToCheck.Num())
		{
			TArray<FString, TInlineAllocator<1>> ContentKeysToCheck;
			ContentKeysToCheck.Reserve(KeysToCheck.Num());
			Algo::Transform(KeysToCheck, ContentKeysToCheck,
				[&Key](const FBlake3Hash& Hash) -> FString { return MakeContentKey(FCacheAttachmentKey(Key, Hash)); });
			if (!GetDerivedDataCacheRef().AllCachedDataProbablyExists(ContentKeysToCheck))
			{
				UE_LOG(LogDerivedDataCache, Verbose, TEXT("Cache: Get cache miss with missing content for %s from '%.*s'"),
					*TToString<96>(Key), Context.Len(), Context.GetData());
				return;
			}
		}
	}

	// Read the value and attachments if they have been requested.
	const auto GetContent = [&Key, Context](FCbField ReferenceField) -> FCbAttachment
	{
		TArray<uint8> ContentData;
		const FBlake3Hash Hash = ReferenceField.AsAnyReference();
		check(!ReferenceField.HasError());
		const FCacheAttachmentKey ContentKey(Key, Hash);
		if (GetDerivedDataCacheRef().GetSynchronous(*MakeContentKey(ContentKey), ContentData, Context))
		{
			if (FBlake3::HashBuffer(MakeMemoryView(ContentData)) == Hash)
			{
				FSharedBuffer ContentBuffer = FSharedBuffer::Clone(MakeMemoryView(ContentData));
				if (ReferenceField.IsReference())
				{
					return FCbAttachment(FCbFieldRefIterator::MakeRange(MoveTemp(ContentBuffer)), Hash);
				}
				else
				{
					return FCbAttachment(MoveTemp(ContentBuffer), Hash);
				}
			}
			else
			{
				UE_LOG(LogDerivedDataCache, Verbose, TEXT("Cache: Get cache miss with corrupted content for %s from '%.*s'"),
					*TToString<160>(ContentKey), Context.Len(), Context.GetData());
			}
		}
		else
		{
			UE_LOG(LogDerivedDataCache, Verbose, TEXT("Cache: Get cache miss with missing content for %s from '%.*s'"),
				*TToString<160>(ContentKey), Context.Len(), Context.GetData());
		}
		return FCbAttachment();
	};

	FCbAttachment Value;
	if (!EnumHasAnyFlags(Policy, ECachePolicy::SkipValue) && ValueField.IsAnyReference() && !(Value = GetContent(ValueField)))
	{
		return;
	}

	TArray<FCbAttachment> Attachments;
	if (!EnumHasAnyFlags(Policy, ECachePolicy::SkipAttachments) && AttachmentsField.IsArray())
	{
		Attachments.Reserve(AttachmentsArray.Num());
		for (FCbField AttachmentField : AttachmentsArray)
		{
			Attachments.Add(GetContent(AttachmentField));
			if (!Attachments.Last())
			{
				return;
			}
		}
	}

	// Package
	if (AttachmentsField.IsArray() && !EnumHasAllFlags(Policy, ECachePolicy::SkipValue | ECachePolicy::SkipAttachments))
	{
		FCbPackage Package;
		if (Value && Value.IsCompactBinary())
		{
			Package.SetObject(Value.AsCompactBinary().AsObjectRef(), Value.GetHash());
		}
		for (FCbAttachment Attachment : Attachments)
		{
			Package.AddAttachment(MoveTemp(Attachment));
		}
		Params.Record.SetPackage(MoveTemp(Package));
	}
	else if (Value)
	{
		// Object
		if (Value.IsCompactBinary())
		{
			Params.Record.SetObject(Value.AsCompactBinary().AsObjectRef());
		}
		// Binary
		else
		{
			Params.Record.SetBinary(Value.AsBinary());
		}
	}

	// Meta
	if (!EnumHasAnyFlags(Policy, ECachePolicy::SkipMeta) && MetaField.IsObject())
	{
		Params.Record.SetMeta(FCbObjectRef::Clone(MetaField.AsObject()));
	}

	UE_LOG(LogDerivedDataCache, Verbose, TEXT("Cache: Get cache hit for %s from '%.*s'"),
		*TToString<96>(Key), Context.Len(), Context.GetData());
	Params.Status = ECacheStatus::Cached;
}

FCacheRequest FCache::Get(
	TConstArrayView<FCacheKey> Keys,
	FStringView Context,
	ECachePolicy Policy,
	ECachePriority Priority,
	FOnCacheGetComplete&& Callback)
{
	for (const FCacheKey& Key : Keys)
	{
		Get(Key, Context, Policy, Priority, Callback);
	}
	return FCacheRequest();
}

void FCache::Put(
	const FCacheRecord& Record,
	FStringView Context,
	ECachePolicy Policy,
	ECachePriority Priority,
	FOnCachePutComplete& Callback)
{
	FCachePutCompleteParams Params;
	Params.Key = Record.GetKey();

	ON_SCOPE_EXIT
	{
		if (Callback)
		{
			Callback(MoveTemp(Params));
		}
	};

	if (!EnumHasAnyFlags(Policy, ECachePolicy::Store))
	{
		UE_LOG(LogDerivedDataCache, VeryVerbose, TEXT("Cache: Put skipped for %s from '%.*s'"),
			*TToString<96>(Params.Key), Context.Len(), Context.GetData());
		Params.Status = ECacheStatus::NotCached;
		return;
	}

	FCbAttachment Value;
	TConstArrayView<FCbAttachment> Attachments;

	switch (Record.GetType())
	{
	case ECacheRecordType::None:
		break;
	case ECacheRecordType::Binary:
		Value = FCbAttachment(Record.AsBinary());
		break;
	case ECacheRecordType::Object:
		Value = FCbAttachment(FCbFieldRefIterator::MakeSingle(Record.AsObject().AsFieldRef()));
		break;
	case ECacheRecordType::Package:
		{
			const FCbPackage& Package = Record.AsPackage();
			Value = FCbAttachment(FCbFieldRefIterator::MakeSingle(Package.GetObject().AsFieldRef()));
			Attachments = Package.GetAttachments();
		}
		break;
	default:
		checkNoEntry();
		break;
	}

	const auto PutContent = [&Key = Params.Key, Context](const FSharedBuffer& Buffer, const FBlake3Hash& Hash)
	{
		check(Buffer.GetSize() <= MAX_int32);
		TConstArrayView<uint8> BufferView = MakeArrayView(
			static_cast<const uint8*>(Buffer.GetData()),
			static_cast<int32>(Buffer.GetSize()));
		GetDerivedDataCacheRef().Put(*MakeContentKey(FCacheAttachmentKey(Key, Hash)), BufferView, Context);
	};

	if (Value)
	{
		PutContent(Value.AsBinary(), Value.GetHash());
	}
	for (const FCbAttachment& Attachment : Attachments)
	{
		PutContent(Attachment.AsBinary(), Attachment.GetHash());
	}

	FCbWriter Writer;
	Writer.BeginObject();
	{
		if (Value.IsCompactBinary())
		{
			Writer.Name("Value"_ASV).Reference(Value.GetHash());
		}
		else if (Value.IsBinary())
		{
			Writer.Name("Value"_ASV).BinaryReference(Value.GetHash());
		}

		if (Record.GetType() == ECacheRecordType::Package)
		{
			Writer.Name("Attachments"_ASV);
			Writer.BeginArray();
			for (const FCbAttachment& Attachment : Attachments)
			{
				if (Attachment.IsCompactBinary())
				{
					Writer.Reference(Attachment.GetHash());
				}
				else
				{
					Writer.BinaryReference(Attachment.GetHash());
				}
			}
			Writer.EndArray();
		}

		const FCbObjectRef& Meta = Record.GetMeta();
		if (Meta.CreateIterator())
		{
			Writer.Name("Meta"_ASV).Object(Meta);
		}
	}
	Writer.EndObject();

	TArray<uint8> Data;
	const uint64 SaveSize = Writer.GetSaveSize();
	check(SaveSize <= MAX_int32);
	Data.SetNumUninitialized(static_cast<int32>(SaveSize));
	Writer.Save(MakeMemoryView(Data));

	GetDerivedDataCacheRef().Put(*MakeRecordKey(Params.Key), Data, Context);

	UE_LOG(LogDerivedDataCache, VeryVerbose, TEXT("Cache: Put for %s from '%.*s'"),
		*TToString<96>(Params.Key), Context.Len(), Context.GetData());
	Params.Status = ECacheStatus::Cached;
}

FCacheRequest FCache::Put(
	TConstArrayView<FCacheRecord> Records,
	FStringView Context,
	ECachePolicy Policy,
	ECachePriority Priority,
	FOnCachePutComplete&& Callback)
{
	for (const FCacheRecord& Record : Records)
	{
		Put(Record, Context, Policy, Priority, Callback);
	}
	return FCacheRequest();
}

void FCache::GetAttachment(
	const FCacheAttachmentKey& Key,
	FStringView Context,
	ECachePolicy Policy,
	ECachePriority Priority,
	FOnCacheGetAttachmentComplete& Callback)
{
	FCacheGetAttachmentCompleteParams Params;
	Params.Key = Key;

	ON_SCOPE_EXIT
	{
		if (Callback)
		{
			Callback(MoveTemp(Params));
		}
	};

	// Skip the request if querying the cache is disabled.
	if (!EnumHasAnyFlags(Policy, ECachePolicy::Query))
	{
		UE_LOG(LogDerivedDataCache, VeryVerbose, TEXT("Cache: GetAttachment skipped on content for %s from '%.*s'"),
			*TToString<160>(Key), Context.Len(), Context.GetData());
		return;
	}

	// Check for existence of the attachment if it is being skipped.
	if (EnumHasAnyFlags(Policy, ECachePolicy::SkipAttachments))
	{
		if (GetDerivedDataCacheRef().CachedDataProbablyExists(*MakeContentKey(Key)))
		{
			UE_LOG(LogDerivedDataCache, Verbose, TEXT("Cache: GetAttachment (exists) cache hit on content for %s from '%.*s'"),
				*TToString<160>(Key), Context.Len(), Context.GetData());
			Params.Status = ECacheStatus::Cached;
		}
		else
		{
			UE_LOG(LogDerivedDataCache, Verbose, TEXT("Cache: GetAttachment (exists) cache miss on content for %s from '%.*s'"),
				*TToString<160>(Key), Context.Len(), Context.GetData());
		}
		return;
	}

	// Request the attachment from storage.
	TArray<uint8> Data;
	if (!GetDerivedDataCacheRef().GetSynchronous(*MakeContentKey(Key), Data, Context))
	{
		UE_LOG(LogDerivedDataCache, Verbose, TEXT("Cache: GetAttachment cache miss on content for %s from '%.*s'"),
			*TToString<160>(Key), Context.Len(), Context.GetData());
		return;
	}

	if (FBlake3::HashBuffer(MakeMemoryView(Data)) != Key.GetHash())
	{
		UE_LOG(LogDerivedDataCache, Verbose, TEXT("Cache: GetAttachment cache miss with corrupted content for %s from '%.*s'"),
			*TToString<160>(Key), Context.Len(), Context.GetData());
		return;
	}

	Params.Value = FSharedBuffer::Clone(MakeMemoryView(Data));

	UE_LOG(LogDerivedDataCache, Verbose, TEXT("Cache: GetAttachment cache hit on content for %s from '%.*s'"),
		*TToString<160>(Key), Context.Len(), Context.GetData());
	Params.Status = ECacheStatus::Cached;
}

FCacheRequest FCache::GetAttachments(
	TConstArrayView<FCacheAttachmentKey> Keys,
	FStringView Context,
	ECachePolicy Policy,
	ECachePriority Priority,
	FOnCacheGetAttachmentComplete&& Callback)
{
	for (const FCacheAttachmentKey& Key : Keys)
	{
		GetAttachment(Key, Context, Policy, Priority, Callback);
	}
	return FCacheRequest();
}

void FCache::CancelAll()
{
}

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

ICache* CreateCache()
{
	return new FCache();
}

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

} // DerivedData
} // UE