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

namespace FidelityFX
{
    internal abstract class Fsr2Pipeline: IDisposable
    {
        private readonly Fsr2Callbacks _callbacks;
        protected readonly ComputeBuffer Constants;
        
        protected ComputeShader ComputeShader;
        protected int KernelIndex;

        protected Fsr2Pipeline(Fsr2Callbacks callbacks, ComputeBuffer constants)
        {
            _callbacks = callbacks;
            Constants = constants;
        }

        public virtual void Dispose()
        {
            UnloadComputeShader();
        }
        
        public abstract void ScheduleDispatch(CommandBuffer commandBuffer, Fsr2.DispatchDescription dispatchParams, int dispatchX, int dispatchY);
        
        protected void LoadComputeShader(string name, Fsr2.InitializationFlags flags)
        {
            LoadComputeShader(name, flags, ref ComputeShader, out KernelIndex);
        }
        
        private void LoadComputeShader(string name, Fsr2.InitializationFlags flags, ref ComputeShader shaderRef, out int kernelIndex)
        {
            if (shaderRef == null)
                shaderRef = _callbacks.LoadComputeShader(name);

            kernelIndex = shaderRef.FindKernel("CS");
            
            if ((flags & Fsr2.InitializationFlags.EnableHighDynamicRange) != 0) shaderRef.EnableKeyword("FFX_FSR2_OPTION_HDR_COLOR_INPUT");
            if ((flags & Fsr2.InitializationFlags.EnableDisplayResolutionMotionVectors) == 0) shaderRef.EnableKeyword("FFX_FSR2_OPTION_LOW_RESOLUTION_MOTION_VECTORS");
            if ((flags & Fsr2.InitializationFlags.EnableMotionVectorsJitterCancellation) != 0) shaderRef.EnableKeyword("FFX_FSR2_OPTION_JITTERED_MOTION_VECTORS");
            if ((flags & Fsr2.InitializationFlags.EnableDepthInverted) != 0) shaderRef.EnableKeyword("FFX_FSR2_OPTION_INVERTED_DEPTH");
            // TODO: enable FFX_FSR2_OPTION_REPROJECT_USE_LANCZOS_TYPE if the device capabilities allow (default subgroup size == 32 or 64)
            // TODO: enable FFX_HALF if FP16 is supported (except RCAS)
        }

        private void UnloadComputeShader()
        {
            UnloadComputeShader(ref ComputeShader);
        }
        
        private void UnloadComputeShader(ref ComputeShader shaderRef)
        {
            if (shaderRef == null)
                return;

            _callbacks.UnloadComputeShader(shaderRef);
            shaderRef = null;
        }
    }

    internal class Fsr2ComputeLuminancePyramidPipeline : Fsr2Pipeline
    {
        public Fsr2ComputeLuminancePyramidPipeline(Fsr2Callbacks callbacks, Fsr2.InitializationFlags flags, ComputeBuffer constants)
            : base(callbacks, constants)
        {
            LoadComputeShader("FSR2/ffx_fsr2_compute_luminance_pyramid_pass", flags);
        }

        public override void ScheduleDispatch(CommandBuffer commandBuffer, Fsr2.DispatchDescription dispatchParams, int dispatchX, int dispatchY)
        {
            //throw new NotImplementedException();
        }
    }

    internal class Fsr2AccumulatePipeline : Fsr2Pipeline
    {
        public Fsr2AccumulatePipeline(Fsr2Callbacks callbacks, Fsr2.InitializationFlags flags, ComputeBuffer constants)
            : base(callbacks, constants)
        {
            LoadComputeShader("FSR2/ffx_fsr2_accumulate_pass", flags);
        }

        public override void ScheduleDispatch(CommandBuffer commandBuffer, Fsr2.DispatchDescription dispatchParams, int dispatchX, int dispatchY)
        {
            //throw new NotImplementedException();
        }
    }

    internal class Fsr2AccumulateSharpenPipeline : Fsr2AccumulatePipeline
    {
        private readonly ComputeShader _shaderCopy;
        
        public Fsr2AccumulateSharpenPipeline(Fsr2Callbacks callbacks, Fsr2.InitializationFlags flags, ComputeBuffer constants)
            : base(callbacks, flags, constants)
        {
            // Simply loading the accumulate_pass compute shader will give us the same instance as the non-sharpen pipeline
            // So we have to clone the shader instance and set the extra keyword on the new copy
            _shaderCopy = UnityEngine.Object.Instantiate(ComputeShader);
            foreach (var keyword in ComputeShader.enabledKeywords)
            {
                _shaderCopy.EnableKeyword(keyword.name);
            }
            _shaderCopy.EnableKeyword("FFX_FSR2_OPTION_APPLY_SHARPENING");
        }

        public override void ScheduleDispatch(CommandBuffer commandBuffer, Fsr2.DispatchDescription dispatchParams, int dispatchX, int dispatchY)
        {
            // Temporarily swap around the shaders so that the dispatch will bind and execute the correct one
            ComputeShader tmp = ComputeShader;
            ComputeShader = _shaderCopy;
            base.ScheduleDispatch(commandBuffer, dispatchParams, dispatchX, dispatchY);
            ComputeShader = tmp;
        }

        public override void Dispose()
        {
            // Since we instantiated this copy, we have to destroy it instead of unloading the shader resource
            UnityEngine.Object.Destroy(_shaderCopy);
            base.Dispose();
        }
    }
    
    internal class Fsr2RcasPipeline : Fsr2Pipeline
    {
        private readonly ComputeBuffer _rcasConstants;
        
        public Fsr2RcasPipeline(Fsr2Callbacks callbacks, Fsr2.InitializationFlags flags, ComputeBuffer constants, ComputeBuffer rcasConstants)
            : base(callbacks, constants)
        {
            _rcasConstants = rcasConstants;
            
            LoadComputeShader("FSR2/ffx_fsr2_rcas_pass", flags);
        }

        public override void ScheduleDispatch(CommandBuffer commandBuffer, Fsr2.DispatchDescription dispatchParams, int dispatchX, int dispatchY)
        {
            // Run the RCAS sharpening filter on the upscaled image
            ComputeShader.SetTexture(KernelIndex, "r_input_exposure", dispatchParams.Exposure);
            ComputeShader.SetTexture(KernelIndex, "r_rcas_input", dispatchParams.Input);
            ComputeShader.SetTexture(KernelIndex, "rw_upscaled_output", dispatchParams.Output);
            ComputeShader.SetConstantBuffer("cbFSR2", Constants, 0, Marshal.SizeOf<Fsr2.Fsr2Constants>());
            ComputeShader.SetConstantBuffer("cbRCAS", _rcasConstants, 0, Marshal.SizeOf<Fsr2.RcasConstants>());

            commandBuffer.DispatchCompute(ComputeShader, KernelIndex, dispatchX, dispatchY, 1);
        }
    }
}