using System;
using System.Runtime.InteropServices;
using UnityEngine;
using UnityEngine.Assertions;
using UnityEngine.Rendering;

namespace FidelityFX.OpticalFlow
{
    public class OpticalFlowContext
    {
        private const int MaxQueuedFrames = 16;
        
        private OpticalFlow.ContextDescription _contextDescription;
        
        private OpticalFlowPass _prepareLumaPass;
        private OpticalFlowPass _generateInputPyramidPass;
        private OpticalFlowPass _generateScdHistogramPass;
        private OpticalFlowPass _computeScdDivergencePass;
        private OpticalFlowPass _computeOpticalFlowPass;
        private OpticalFlowPass _filterOpticalFlowPass;
        private OpticalFlowPass _scaleOpticalFlowPass;

        private readonly OpticalFlowResources _resources = new OpticalFlowResources();
        
        private ComputeBuffer _opticalFlowConstantsBuffer;
        private readonly OpticalFlow.OpticalFlowConstants[] _opticalFlowConstantsArray = { new OpticalFlow.OpticalFlowConstants() };
        private ref OpticalFlow.OpticalFlowConstants Constants => ref _opticalFlowConstantsArray[0];
        
        private ComputeBuffer _spdConstantsBuffer;
        private readonly OpticalFlow.SpdConstants[] _spdConstantsArray = { new OpticalFlow.SpdConstants() };
        private ref OpticalFlow.SpdConstants SpdConsts => ref _spdConstantsArray[0];
        
        private bool _firstExecution;
        private int _resourceFrameIndex;
        private readonly Vector2Int[] _opticalFlowTextureSizes = new Vector2Int[OpticalFlowResources.OpticalFlowMaxPyramidLevels];

        public void Create(OpticalFlow.ContextDescription contextDescription)
        {
            _contextDescription = contextDescription;

            _opticalFlowConstantsBuffer = CreateConstantBuffer<OpticalFlow.OpticalFlowConstants>();
            _spdConstantsBuffer = CreateConstantBuffer<OpticalFlow.SpdConstants>();

            _firstExecution = true;
            _resourceFrameIndex = 0;

            Constants.inputLumaResolution = _contextDescription.resolution;
            
            _resources.Create(_contextDescription);
            CreatePasses();
        }

        private void CreatePasses()
        {
            _prepareLumaPass = new OpticalFlowPrepareLumaPass(_contextDescription, _resources, _opticalFlowConstantsBuffer);
            _generateInputPyramidPass = new OpticalFlowGenerateInputPyramidPass(_contextDescription, _resources, _opticalFlowConstantsBuffer, _spdConstantsBuffer);
            _generateScdHistogramPass = new OpticalFlowGenerateSCDHistogramPass(_contextDescription, _resources, _opticalFlowConstantsBuffer);
            _computeScdDivergencePass = new OpticalFlowComputeSCDDivergencePass(_contextDescription, _resources, _opticalFlowConstantsBuffer);
            _computeOpticalFlowPass = new OpticalFlowComputePass(_contextDescription, _resources, _opticalFlowConstantsBuffer);
            _filterOpticalFlowPass = new OpticalFlowFilterPass(_contextDescription, _resources, _opticalFlowConstantsBuffer);
            _scaleOpticalFlowPass = new OpticalFlowScalePass(_contextDescription, _resources, _opticalFlowConstantsBuffer);
        }

        public void Destroy()
        {
            DestroyPass(ref _scaleOpticalFlowPass);
            DestroyPass(ref _filterOpticalFlowPass);
            DestroyPass(ref _computeOpticalFlowPass);
            DestroyPass(ref _computeScdDivergencePass);
            DestroyPass(ref _generateScdHistogramPass);
            DestroyPass(ref _generateInputPyramidPass);
            DestroyPass(ref _prepareLumaPass);
            
            _resources.Destroy();
            
            DestroyConstantBuffer(ref _spdConstantsBuffer);
            DestroyConstantBuffer(ref _opticalFlowConstantsBuffer);
        }
        
        public void Dispatch(CommandBuffer commandBuffer, in OpticalFlow.DispatchDescription dispatchDescription)
        {
            const int advancedAlgorithmIterations = 7;
            const int opticalFlowBlockSize = 8;

            Constants.backbufferTransferFunction = (uint)dispatchDescription.backbufferTransferFunction;
            Constants.minMaxLuminance = dispatchDescription.minMaxLuminance;

            int frameIndex = _resourceFrameIndex % 2;
            bool resetAccumulation = dispatchDescription.reset || _firstExecution;
            _firstExecution = false;

            if (resetAccumulation)
                Constants.frameIndex = 0;
            else
                Constants.frameIndex++;

            if (resetAccumulation)
            {
                commandBuffer.SetRenderTarget(_resources.OpticalFlowSCDTemp);
                commandBuffer.ClearRenderTarget(false, true, Color.clear);
                commandBuffer.SetRenderTarget(dispatchDescription.opticalFlowSCD.RenderTarget);
                commandBuffer.ClearRenderTarget(false, true, Color.clear);
                commandBuffer.SetRenderTarget(_resources.OpticalFlowSCDHistogram);
                commandBuffer.ClearRenderTarget(false, true, Color.clear);
                commandBuffer.SetRenderTarget(_resources.OpticalFlowSCDPreviousHistogram);
                commandBuffer.ClearRenderTarget(false, true, Color.clear);
                for (int i = 0; i < 2; ++i)
                {
                    commandBuffer.SetRenderTarget(_resources.OpticalFlowInput[i]);
                    commandBuffer.ClearRenderTarget(false, true, Color.clear);
                    commandBuffer.SetRenderTarget(_resources.OpticalFlowInputLevel1[i]);
                    commandBuffer.ClearRenderTarget(false, true, Color.clear);
                    commandBuffer.SetRenderTarget(_resources.OpticalFlowInputLevel2[i]);
                    commandBuffer.ClearRenderTarget(false, true, Color.clear);
                    commandBuffer.SetRenderTarget(_resources.OpticalFlowInputLevel3[i]);
                    commandBuffer.ClearRenderTarget(false, true, Color.clear);
                    commandBuffer.SetRenderTarget(_resources.OpticalFlowInputLevel4[i]);
                    commandBuffer.ClearRenderTarget(false, true, Color.clear);
                    commandBuffer.SetRenderTarget(_resources.OpticalFlowInputLevel5[i]);
                    commandBuffer.ClearRenderTarget(false, true, Color.clear);
                    commandBuffer.SetRenderTarget(_resources.OpticalFlowInputLevel6[i]);
                    commandBuffer.ClearRenderTarget(false, true, Color.clear);
                }
            }

            SetupSpdConstants(out var threadGroupSizeOpticalFlowInputPyramid);
            
            commandBuffer.SetBufferData(_opticalFlowConstantsBuffer, _opticalFlowConstantsArray);
            commandBuffer.SetBufferData(_spdConstantsBuffer, _spdConstantsArray);

            {
                const int threadGroupSizeX = 16;
                const int threadGroupSizeY = 16;
                const int threadPixelsX = 2;
                const int threadPixelsY = 2;
                int dispatchX = ((_contextDescription.resolution.x + (threadPixelsX - 1)) / threadPixelsX + (threadGroupSizeX - 1)) / threadGroupSizeX;
                int dispatchY = ((_contextDescription.resolution.y + (threadPixelsY - 1)) / threadPixelsY + (threadGroupSizeY - 1)) / threadGroupSizeY;
                _prepareLumaPass.ScheduleDispatch(commandBuffer, dispatchDescription, frameIndex, dispatchX, dispatchY);
            }
            
            _generateInputPyramidPass.ScheduleDispatch(commandBuffer, dispatchDescription, frameIndex, threadGroupSizeOpticalFlowInputPyramid.x, threadGroupSizeOpticalFlowInputPyramid.y);

            {
                const int threadGroupSizeX = 32;
                const int threadGroupSizeY = 8;
                int strataWidth = (_contextDescription.resolution.x / 4) / OpticalFlowResources.HistogramsPerDim;
                int strataHeight = _contextDescription.resolution.y / OpticalFlowResources.HistogramsPerDim;
                int dispatchX = (strataWidth + threadGroupSizeX - 1) / threadGroupSizeX;
                const int dispatchY = 16;
                const int dispatchZ = OpticalFlowResources.HistogramsPerDim * OpticalFlowResources.HistogramsPerDim;
                _generateScdHistogramPass.ScheduleDispatch(commandBuffer, dispatchDescription, frameIndex, dispatchX, dispatchY, dispatchZ);
            }
            {
                const int dispatchX = OpticalFlowResources.HistogramsPerDim * OpticalFlowResources.HistogramsPerDim;
                const int dispatchY = OpticalFlowResources.HistogramShifts;
                _computeScdDivergencePass.ScheduleDispatch(commandBuffer, dispatchDescription, frameIndex, dispatchX, dispatchY);
            }

            const int pyramidMaxIterations = advancedAlgorithmIterations;
            Assert.IsTrue(pyramidMaxIterations <= OpticalFlowResources.OpticalFlowMaxPyramidLevels);

            _opticalFlowTextureSizes[0] = OpticalFlowResources.GetOpticalFlowTextureSize(_contextDescription.resolution, opticalFlowBlockSize);
            for (int i = 1; i < pyramidMaxIterations; ++i)
            {
                _opticalFlowTextureSizes[i] = new Vector2Int(
                    (_opticalFlowTextureSizes[i - 1].x + 1) / 2,
                    (_opticalFlowTextureSizes[i - 1].y + 1) / 2
                );
            }

            for (int level = pyramidMaxIterations - 1; level >= 0; --level)
            {
                // TODO: need to flip-flop Optical Flow output resources between levels as well (isOddFrame != isOddLevel)

                Constants.opticalFlowPyramidLevel = (uint)level;
                Constants.opticalFlowPyramidLevelCount = pyramidMaxIterations;
                commandBuffer.SetBufferData(_opticalFlowConstantsBuffer, _opticalFlowConstantsArray);
                
                // TODO: need to somehow address resources by level, not great when you've got a bazillion loose RT arrays... *sigh*
            }

            _resourceFrameIndex = (_resourceFrameIndex + 1) % MaxQueuedFrames;
        }
        
        private void SetupSpdConstants(out Vector2Int dispatchThreadGroupCount)
        {
            const int resolutionMultiplier = 1;
            
            RectInt rectInfo = new RectInt(0, 0, _contextDescription.resolution.x * resolutionMultiplier, _contextDescription.resolution.y * resolutionMultiplier);
            SpdSetup(rectInfo, out dispatchThreadGroupCount, out var workGroupOffset, out var numWorkGroupsAndMips, 4);
            
            ref OpticalFlow.SpdConstants spdConstants = ref SpdConsts;
            spdConstants.numWorkGroups = (uint)numWorkGroupsAndMips.x;
            spdConstants.mips = (uint)numWorkGroupsAndMips.y;
            spdConstants.workGroupOffsetX = (uint)workGroupOffset.x;
            spdConstants.workGroupOffsetY = (uint)workGroupOffset.y;
            spdConstants.numWorkGroupsOpticalFlowInputPyramid = (uint)numWorkGroupsAndMips.x;
        }

        private static void SpdSetup(RectInt rectInfo, out Vector2Int dispatchThreadGroupCount, out Vector2Int workGroupOffset, out Vector2Int numWorkGroupsAndMips, int mips = -1)
        {
            workGroupOffset = new Vector2Int(rectInfo.x / 64, rectInfo.y / 64);

            int endIndexX = (rectInfo.x + rectInfo.width - 1) / 64;
            int endIndexY = (rectInfo.y + rectInfo.height - 1) / 64;

            dispatchThreadGroupCount = new Vector2Int(endIndexX + 1 - workGroupOffset.x, endIndexY + 1 - workGroupOffset.y);

            numWorkGroupsAndMips = new Vector2Int(dispatchThreadGroupCount.x * dispatchThreadGroupCount.y, mips);
            if (mips < 0)
            {
                float resolution = Math.Max(rectInfo.width, rectInfo.height);
                numWorkGroupsAndMips.y = Math.Min(Mathf.FloorToInt(Mathf.Log(resolution, 2.0f)), 12);
            }
        }
        
        private static ComputeBuffer CreateConstantBuffer<TConstants>() where TConstants: struct
        {
            return new ComputeBuffer(1, Marshal.SizeOf<TConstants>(), ComputeBufferType.Constant);
        }
        
        private static void DestroyConstantBuffer(ref ComputeBuffer bufferRef)
        {
            if (bufferRef == null)
                return;
            
            bufferRef.Release();
            bufferRef = null;
        }

        private static void DestroyPass(ref OpticalFlowPass pass)
        {
            if (pass == null)
                return;
            
            pass.Dispose();
            pass = null;
        }
    }
}