// Copyright 1998-2019 Epic Games, Inc. All Rights Reserved.

#include "DerivedDataBackendAsyncPutWrapper.h"
#include "MemoryDerivedDataBackend.h"

/** 
 * Async task to handle the fire and forget async put
 */
class FCachePutAsyncWorker
{
public:
	/** Cache Key for the put to InnerBackend **/
	FString								CacheKey;
	/** Data for the put to InnerBackend **/
	TArray<uint8>						Data;
	/** Backend to use for storage, my responsibilities are about async puts **/
	FDerivedDataBackendInterface*		InnerBackend;
	/** Memory based cache to clear once the put is finished **/
	FDerivedDataBackendInterface*		InflightCache;
	/** We remember outstanding puts so that we don't do them redundantly **/
	FThreadSet*							FilesInFlight;
	/**If true, then do not attempt skip the put even if CachedDataProbablyExists returns true **/
	bool								bPutEvenIfExists;
	/** Usage stats to track thread times. */
	FDerivedDataCacheUsageStats&        UsageStats;

	/** Constructor
	*/
	FCachePutAsyncWorker(const TCHAR* InCacheKey, const TArray<uint8>* InData, FDerivedDataBackendInterface* InInnerBackend, bool InbPutEvenIfExists, FDerivedDataBackendInterface* InInflightCache, FThreadSet* InInFilesInFlight, FDerivedDataCacheUsageStats& InUsageStats)
		: CacheKey(InCacheKey)
		, Data(*InData)
		, InnerBackend(InInnerBackend)
		, InflightCache(InInflightCache)
		, FilesInFlight(InInFilesInFlight)
		, bPutEvenIfExists(InbPutEvenIfExists)
		, UsageStats(InUsageStats)
	{
		check(InnerBackend);
	}
		
	/** Call the inner backend and when that completes, remove the memory cache */
	void DoWork()
	{
		COOK_STAT(auto Timer = UsageStats.TimePut());
		bool bOk = true;
		const bool bAlreadyExists = InnerBackend->CachedDataProbablyExists(*CacheKey);
		if (!bAlreadyExists || bPutEvenIfExists)
		{
			InnerBackend->PutCachedData(*CacheKey, Data, bPutEvenIfExists);
			COOK_STAT(Timer.AddHit(Data.Num()));
		}
		// if it already existed, don't bother checking if we need to retry. We don't.
		if (InflightCache && !bAlreadyExists && !InnerBackend->CachedDataProbablyExists(*CacheKey))
		{
			// retry
			InnerBackend->PutCachedData(*CacheKey, Data, false);
			if (!InnerBackend->CachedDataProbablyExists(*CacheKey))
			{
				UE_LOG(LogDerivedDataCache, Log, TEXT("FDerivedDataBackendAsyncPutWrapper: Put failed, keeping in memory copy %s."),*CacheKey);
				bOk = false;
			}
		}
		if (bOk && InflightCache)
		{
			InflightCache->RemoveCachedData(*CacheKey, /*bTransient=*/ false); // we can remove this from the temp cache, since the real cache will hit now
		}
		FilesInFlight->Remove(CacheKey);
		FDerivedDataBackend::Get().AddToAsyncCompletionCounter(-1);
	}

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

	/** Indicates to the thread pool that this task is abandonable */
	bool CanAbandon()
	{
		return true;
	}

	/** Abandon routine, we need to remove the item from the in flight cache because something might be waiting for that */
	void Abandon()
	{
		if (InflightCache)
		{
			InflightCache->RemoveCachedData(*CacheKey, /*bTransient=*/ false); // we can remove this from the temp cache, since the real cache will hit now
		}
		FilesInFlight->Remove(CacheKey);
		FDerivedDataBackend::Get().AddToAsyncCompletionCounter(-1);
	}
};

FDerivedDataBackendAsyncPutWrapper::FDerivedDataBackendAsyncPutWrapper(FDerivedDataBackendInterface* InInnerBackend, bool bCacheInFlightPuts)
	: InnerBackend(InInnerBackend)
	, InflightCache(bCacheInFlightPuts ? (new FMemoryDerivedDataBackend) : NULL)
{
	check(InnerBackend);
}

/** return true if this cache is writable **/
bool FDerivedDataBackendAsyncPutWrapper::IsWritable()
{
	return InnerBackend->IsWritable();
}

/**
 * Synchronous test for the existence of a cache item
 *
 * @param	CacheKey	Alphanumeric+underscore key of this cache item
 * @return				true if the data probably will be found, this can't be guaranteed because of concurrency in the backends, corruption, etc
 */
bool FDerivedDataBackendAsyncPutWrapper::CachedDataProbablyExists(const TCHAR* CacheKey)
{
	COOK_STAT(auto Timer = UsageStats.TimeProbablyExists());
	bool Result = (InflightCache && InflightCache->CachedDataProbablyExists(CacheKey)) || InnerBackend->CachedDataProbablyExists(CacheKey);
	COOK_STAT(if (Result) {	Timer.AddHit(0); });
	return Result;
}

bool FDerivedDataBackendAsyncPutWrapper::GetCachedData(const TCHAR* CacheKey, TArray<uint8>& OutData)
{
	COOK_STAT(auto Timer = UsageStats.TimeGet());
	if (InflightCache && InflightCache->GetCachedData(CacheKey, OutData))
	{
		COOK_STAT(Timer.AddHit(OutData.Num()));
		return true;
	}
	bool bSuccess = InnerBackend->GetCachedData(CacheKey, OutData);
	if (bSuccess)
	{
		COOK_STAT(Timer.AddHit(OutData.Num()));
	}
	return bSuccess;
}

void FDerivedDataBackendAsyncPutWrapper::PutCachedData(const TCHAR* CacheKey, TArray<uint8>& InData, bool bPutEvenIfExists)
{
	COOK_STAT(auto Timer = PutSyncUsageStats.TimePut());
	if (!InnerBackend->IsWritable())
	{
		return; // no point in continuing down the chain
	}
	const bool bAdded = FilesInFlight.AddIfNotExists(CacheKey);
	if (!bAdded)
	{
		return; // if it is already on its way, we don't need to send it again
	}
	if (InflightCache)
	{
		if (InflightCache->CachedDataProbablyExists(CacheKey))
		{
			return; // if it is already on its way, we don't need to send it again
		}
		InflightCache->PutCachedData(CacheKey, InData, true); // temp copy stored in memory while the async task waits to complete
		COOK_STAT(Timer.AddHit(InData.Num()));
	}
	FDerivedDataBackend::Get().AddToAsyncCompletionCounter(1);
	(new FAutoDeleteAsyncTask<FCachePutAsyncWorker>(CacheKey, &InData, InnerBackend, bPutEvenIfExists, InflightCache.Get(), &FilesInFlight, UsageStats))->StartBackgroundTask();
}

void FDerivedDataBackendAsyncPutWrapper::RemoveCachedData(const TCHAR* CacheKey, bool bTransient)
{
	if (!InnerBackend->IsWritable())
	{
		return; // no point in continuing down the chain
	}
	while (FilesInFlight.Exists(CacheKey))
	{
		FPlatformProcess::Sleep(0.0f); // this is an exception condition (corruption), spin and wait for it to clear
	}
	if (InflightCache)
	{
		InflightCache->RemoveCachedData(CacheKey, bTransient);
	}
	InnerBackend->RemoveCachedData(CacheKey, bTransient);
}

void FDerivedDataBackendAsyncPutWrapper::GatherUsageStats(TMap<FString, FDerivedDataCacheUsageStats>& UsageStatsMap, FString&& GraphPath)
{
	COOK_STAT(
		{
		UsageStatsMap.Add(GraphPath + TEXT(": AsyncPut"), UsageStats);
		UsageStatsMap.Add(GraphPath + TEXT(": AsyncPutSync"), PutSyncUsageStats);
		if (InnerBackend)
		{
			InnerBackend->GatherUsageStats(UsageStatsMap, GraphPath + TEXT(". 0"));
		}
		if (InflightCache)
		{
			InflightCache->GatherUsageStats(UsageStatsMap, GraphPath + TEXT(". 1"));
		}
	});
}