using System.Runtime.InteropServices;
using FidelityFX;
using UnityEngine.Experimental.Rendering;

namespace UnityEngine.Rendering.PostProcessing
{
    internal abstract class SGSR2Upscaler: Upscaler
    {
        public static bool IsSupported => SystemInfo.supportsComputeShaders;
        
        protected abstract string VariantName { get; }
        
        protected RenderTexture _colorLuma;
        protected RenderTexture _motionDepthAlpha;
        protected RenderTexture _motionDepthClipAlpha;
        protected readonly RenderTexture[] _lumaHistory = new RenderTexture[2];
        protected readonly RenderTexture[] _upscaleHistory = new RenderTexture[2];

        protected readonly ConstantsBuffer<SGSR2.Params> _paramsBuffer = new();

        protected uint _frameCount = 0;

        public override void CreateContext(PostProcessRenderContext context, Upscaling config)
        {
            CreateRenderTexture(ref _colorLuma, "ColorLuma", config.MaxRenderSize, GraphicsFormat.R32_UInt, true);
            CreateRenderTexture(ref _motionDepthAlpha, "MotionDepthAlpha", config.MaxRenderSize, GraphicsFormat.R16G16B16A16_SFloat, true);
            CreateRenderTexture(ref _motionDepthClipAlpha, "MotionDepthClipAlpha", config.MaxRenderSize, GraphicsFormat.R16G16B16A16_SFloat, true);
            CreateRenderTextureArray(_lumaHistory, "LumaHistory", config.MaxRenderSize, GraphicsFormat.R32_UInt, true);
            CreateRenderTextureArray(_upscaleHistory, "History", config.UpscaleSize, context.sourceFormat, true);
            
            _paramsBuffer.Init();
        }

        public override void DestroyContext()
        {
            base.DestroyContext();
            
            _paramsBuffer.Destroy();
            
            DestroyRenderTextureArray(_upscaleHistory);
            DestroyRenderTextureArray(_lumaHistory);
            DestroyRenderTexture(ref _motionDepthClipAlpha);
            DestroyRenderTexture(ref _motionDepthAlpha);
            DestroyRenderTexture(ref _colorLuma);
        }
        
        public override void Render(PostProcessRenderContext context, Upscaling config)
        {
            var cmd = context.command;
            cmd.BeginSample(VariantName);
            
            Matrix4x4 clipToPrevClip = Matrix4x4.identity;
            bool isCameraStill = false;
            if (_frameCount > 0 && !config.Reset)
            {
                // We need to use the projection matrix as it is used on the GPU to match what Unity keeps in Camera.previousViewProjectionMatrix
                Matrix4x4 viewProj = GL.GetGPUProjectionMatrix(context.camera.nonJitteredProjectionMatrix, true) * context.camera.worldToCameraMatrix;
                clipToPrevClip = context.camera.previousViewProjectionMatrix * viewProj.inverse;
                isCameraStill = IsCameraStill(viewProj, context.camera.previousViewProjectionMatrix);
            }
            
            ref var parms = ref _paramsBuffer.Value;
            parms.renderSize = config.GetScaledRenderSize(context.camera);
            parms.displaySize = config.UpscaleSize;
            parms.renderSizeRcp = new Vector2(1.0f / parms.renderSize.x, 1.0f / parms.renderSize.y);
            parms.displaySizeRcp = new Vector2(1.0f / parms.displaySize.x, 1.0f / parms.displaySize.y);
            parms.jitterOffset = config.JitterOffset;
            parms.clipToPrevClip = clipToPrevClip;
            parms.preExposure = config.preExposure;
            parms.cameraFovAngleHor = Mathf.Tan(context.camera.fieldOfView * Mathf.Deg2Rad * 0.5f) * (float)parms.renderSize.x / parms.renderSize.y;
            parms.cameraNear = context.camera.nearClipPlane;
            parms.minLerpContribution = 0f;
            parms.bSameCamera = isCameraStill ? 1u : 0u;
            parms.reset = config.Reset ? 1u : 0u;
            _paramsBuffer.UpdateBufferData(cmd);

            if (_frameCount == 0 || config.Reset)
            {
                cmd.SetRenderTarget(_lumaHistory[0]);
                cmd.ClearRenderTarget(false, true, Color.clear);
                cmd.SetRenderTarget(_lumaHistory[1]);
                cmd.ClearRenderTarget(false, true, Color.clear);
                cmd.SetRenderTarget(_upscaleHistory[0]);
                cmd.ClearRenderTarget(false, true, Color.clear);
                cmd.SetRenderTarget(_upscaleHistory[1]);
                cmd.ClearRenderTarget(false, true, Color.clear);
            }
            
            DoRender(cmd, context, config);

            cmd.EndSample(VariantName);
            _frameCount++;
        }

        protected abstract void DoRender(CommandBuffer cmd, PostProcessRenderContext context, Upscaling config);

        private static bool IsCameraStill(in Matrix4x4 currViewProj, in Matrix4x4 prevViewProj, float threshold = 1e-5f)
        {
            float vpDiff = 0f;
            for (int i = 0; i < 16; i++)
            {
                vpDiff += Mathf.Abs(currViewProj[i] - prevViewProj[i]);
            }

            return vpDiff < threshold;
        }
    }
}