/* Copyright (c) 2013-2016 Jeffrey Pfau
 *
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
#include <mgba/core/rewind.h>

#include <mgba/core/core.h>
#include <mgba/core/serialize.h>
#include <mgba-util/patch/fast.h>
#include <mgba-util/vfs.h>

DEFINE_VECTOR(mCoreRewindPatches, struct PatchFast);

void _rewindDiff(struct mCoreRewindContext* context);

#ifndef DISABLE_THREADING
THREAD_ENTRY _rewindThread(void* context);
#endif

void mCoreRewindContextInit(struct mCoreRewindContext* context, size_t entries, bool onThread) {
	if (context->currentState) {
		return;
	}
	mCoreRewindPatchesInit(&context->patchMemory, entries);
	size_t e;
	for (e = 0; e < entries; ++e) {
		initPatchFast(mCoreRewindPatchesAppend(&context->patchMemory));
	}
	context->previousState = VFileMemChunk(0, 0);
	context->currentState = VFileMemChunk(0, 0);
	context->size = 0;
#ifndef DISABLE_THREADING
	context->onThread = onThread;
	context->ready = false;
	if (onThread) {
		MutexInit(&context->mutex);
		ConditionInit(&context->cond);
		ThreadCreate(&context->thread, _rewindThread, context);
	}
#else
	UNUSED(onThread);
#endif
}

void mCoreRewindContextDeinit(struct mCoreRewindContext* context) {
	if (!context->currentState) {
		return;
	}
#ifndef DISABLE_THREADING
	if (context->onThread) {
		MutexLock(&context->mutex);
		context->onThread = false;
		MutexUnlock(&context->mutex);
		ConditionWake(&context->cond);
		ThreadJoin(context->thread);
		MutexDeinit(&context->mutex);
		ConditionDeinit(&context->cond);
	}
#endif
	context->previousState->close(context->previousState);
	context->currentState->close(context->currentState);
	context->previousState = NULL;
	context->currentState = NULL;
	size_t s;
	for (s = 0; s < mCoreRewindPatchesSize(&context->patchMemory); ++s) {
		deinitPatchFast(mCoreRewindPatchesGetPointer(&context->patchMemory, s));
	}
	mCoreRewindPatchesDeinit(&context->patchMemory);
}

void mCoreRewindAppend(struct mCoreRewindContext* context, struct mCore* core) {
#ifndef DISABLE_THREADING
	if (context->onThread) {
		MutexLock(&context->mutex);
	}
#endif
	struct VFile* nextState = context->previousState;
	mCoreSaveStateNamed(core, nextState, SAVESTATE_SAVEDATA | SAVESTATE_RTC);
	context->previousState = context->currentState;
	context->currentState = nextState;
#ifndef DISABLE_THREADING
	if (context->onThread) {
		context->ready = true;
		ConditionWake(&context->cond);
		MutexUnlock(&context->mutex);
		return;
	}
#endif
	_rewindDiff(context);
}

void _rewindDiff(struct mCoreRewindContext* context) {
	++context->current;
	if (context->size < mCoreRewindPatchesSize(&context->patchMemory)) {
		++context->size;
	}
	if (context->current >= mCoreRewindPatchesSize(&context->patchMemory)) {
		context->current = 0;
	}
	struct PatchFast* patch = mCoreRewindPatchesGetPointer(&context->patchMemory, context->current);
	size_t size2 = context->currentState->size(context->currentState);
	size_t size = context->previousState->size(context->previousState);
	if (size2 > size) {
		context->previousState->truncate(context->previousState, size2);
		size = size2;
	} else if (size > size2) {
		context->currentState->truncate(context->currentState, size);
	}
	void* current = context->previousState->map(context->previousState, size, MAP_READ);
	void* next = context->currentState->map(context->currentState, size, MAP_READ);
	diffPatchFast(patch, current, next, size);
	context->previousState->unmap(context->previousState, current, size);
	context->currentState->unmap(context->currentState, next, size);
}

bool mCoreRewindRestore(struct mCoreRewindContext* context, struct mCore* core) {
#ifndef DISABLE_THREADING
	if (context->onThread) {
		MutexLock(&context->mutex);
	}
#endif
	if (!context->size) {
#ifndef DISABLE_THREADING
		if (context->onThread) {
			MutexUnlock(&context->mutex);
		}
#endif
		return false;
	}
	--context->size;

	mCoreLoadStateNamed(core, context->previousState, SAVESTATE_SAVEDATA | SAVESTATE_RTC);
	if (context->current == 0) {
		context->current = mCoreRewindPatchesSize(&context->patchMemory);
	}
	--context->current;

	struct PatchFast* patch = mCoreRewindPatchesGetPointer(&context->patchMemory, context->current);
	size_t size2 = context->previousState->size(context->previousState);
	size_t size = context->currentState->size(context->currentState);
	if (size2 < size) {
		size = size2;
	}
	void* current = context->currentState->map(context->currentState, size, MAP_READ);
	void* previous = context->previousState->map(context->previousState, size, MAP_WRITE);
	patch->d.applyPatch(&patch->d, previous, size, current, size);
	context->currentState->unmap(context->currentState, current, size);
	context->previousState->unmap(context->previousState, previous, size);
	struct VFile* nextState = context->previousState;
	context->previousState = context->currentState;
	context->currentState = nextState;
#ifndef DISABLE_THREADING
	if (context->onThread) {
		MutexUnlock(&context->mutex);
	}
#endif
	return true;
}

#ifndef DISABLE_THREADING
THREAD_ENTRY _rewindThread(void* context) {
	struct mCoreRewindContext* rewindContext = context;
	ThreadSetName("Rewind Diff Thread");
	MutexLock(&rewindContext->mutex);
	while (rewindContext->onThread) {
		while (!rewindContext->ready && rewindContext->onThread) {
			ConditionWait(&rewindContext->cond, &rewindContext->mutex);
		}
		if (rewindContext->ready) {
			_rewindDiff(rewindContext);
		}
		rewindContext->ready = false;
	}
	MutexUnlock(&rewindContext->mutex);
	return 0;
}
#endif

