using System;
using System.Runtime.InteropServices;
using FidelityFX;
using FidelityFX.FSR2;
using UnityEngine.Experimental.Rendering;

namespace UnityEngine.Rendering.PostProcessing
{
	internal abstract class Upscaler
	{
		public abstract void CreateContext(PostProcessRenderContext context, Upscaling config);

		public virtual void DestroyContext()
		{
			DestroyRenderTexture(ref _reactiveMask);
			DestroyConstantsBuffer(ref _reactiveMaskConstants);
			DestroyConstantsBuffer(ref _sharpeningConstants);
		}
		
		public abstract void Render(PostProcessRenderContext context, Upscaling config);

		private ConstantsBuffer<GenerateReactiveConstants> _reactiveMaskConstants;
		private RenderTexture _reactiveMask;
		
		/// <summary>
		/// Generalized standalone version of the FSR2 reactive mask auto-generating pass that can be used without needing an active FSR2 context.
		/// This allows auto-generated reactive masks to be reused for other non-FSR upscaling techniques.
		/// </summary>
		protected Texture GenerateReactiveMask(CommandBuffer cmd, PostProcessRenderContext context, Upscaling config, GraphicsFormat format = GraphicsFormat.R8_UNorm)
		{
			ComputeShader shader = context.resources.computeShaders.fsr2Upscaler?.autoGenReactivePass;
			if (shader == null)
				return Texture2D.blackTexture;

			_reactiveMaskConstants ??= ConstantsBuffer<GenerateReactiveConstants>.Create();

			if (_reactiveMask == null)
			{
				// Use a persistent RT so it can easily be passed to native render plugins
				CreateRenderTexture(ref _reactiveMask, "Reactive Mask", config.MaxRenderSize, format, true);
			}

			Vector2Int scaledRenderSize = config.GetScaledRenderSize(context.camera); 
			
			const int threadGroupWorkRegionDim = 8;
			int dispatchX = (scaledRenderSize.x + (threadGroupWorkRegionDim - 1)) / threadGroupWorkRegionDim;
			int dispatchY = (scaledRenderSize.y + (threadGroupWorkRegionDim - 1)) / threadGroupWorkRegionDim;

			cmd.BeginSample("Generate Reactive Mask");
			
			_reactiveMaskConstants.Value.scale = config.generateReactiveParameters.scale;
			_reactiveMaskConstants.Value.threshold = config.generateReactiveParameters.cutoffThreshold;
			_reactiveMaskConstants.Value.binaryValue = config.generateReactiveParameters.binaryValue;
			_reactiveMaskConstants.Value.flags = (uint)config.generateReactiveParameters.flags;
			_reactiveMaskConstants.UpdateBufferData(cmd);

			int kernelIndex = shader.FindKernel("CS");
			cmd.SetComputeTextureParam(shader, kernelIndex, Fsr2ShaderIDs.SrvOpaqueOnly, config.ColorOpaqueOnly);
			cmd.SetComputeTextureParam(shader, kernelIndex, Fsr2ShaderIDs.SrvInputColor, context.source);
			cmd.SetComputeTextureParam(shader, kernelIndex, Fsr2ShaderIDs.UavAutoReactive, _reactiveMask);
            
			cmd.SetComputeConstantBufferParam(shader, Fsr2ShaderIDs.CbGenReactive, _reactiveMaskConstants, 0, Marshal.SizeOf<GenerateReactiveConstants>());
            
			cmd.DispatchCompute(shader, kernelIndex, dispatchX, dispatchY, 1);
            
			cmd.EndSample("Generate Reactive Mask");
			return _reactiveMask;
		}
		
		[Serializable, StructLayout(LayoutKind.Sequential)]
		internal struct GenerateReactiveConstants
		{
			public float scale;
			public float threshold;
			public float binaryValue;
			public uint flags;
		}

		private ConstantsBuffer<CasConstants> _sharpeningConstants;
		private static readonly int CasInputColor = Shader.PropertyToID("r_input_color");
		private static readonly int CasOutputColor = Shader.PropertyToID("rw_output_color");
		private static readonly int CasConstantBuffer = Shader.PropertyToID("cbCAS");

		/// <summary>
		/// Generalized standalone version of the CAS sharpening filter that can be applied after any non-FSR upscaling technique.
		/// </summary>
		protected void ApplySharpening(CommandBuffer cmd, PostProcessRenderContext context, in Vector2Int imageSize, float sharpness, RenderTargetIdentifier input, RenderTargetIdentifier output)
		{
			ComputeShader shader = context.resources.computeShaders.casSharpening;
			if (shader == null)
			{
				cmd.CopyTexture(input, output);
				return;
			}

			const int threadGroupWorkRegionDimRcas = 16;
			int threadGroupsX = (imageSize.x + threadGroupWorkRegionDimRcas - 1) / threadGroupWorkRegionDimRcas;
			int threadGroupsY = (imageSize.y + threadGroupWorkRegionDimRcas - 1) / threadGroupWorkRegionDimRcas;
			
			cmd.BeginSample("CAS Sharpening");
			
			// Compute the constants
			_sharpeningConstants ??= ConstantsBuffer<CasConstants>.Create();
			int sharpnessIndex = Mathf.RoundToInt(Mathf.Clamp01(sharpness) * (CasConfigs.Length - 1));
			_sharpeningConstants.Value = CasConfigs[sharpnessIndex];
			_sharpeningConstants.UpdateBufferData(cmd);
            
			// Dispatch CAS
			int kernelIndex = shader.FindKernel("CS");
			cmd.SetComputeTextureParam(shader, kernelIndex, CasInputColor, input);
			cmd.SetComputeTextureParam(shader, kernelIndex, CasOutputColor, output);
			
			cmd.SetComputeConstantBufferParam(shader, CasConstantBuffer, _sharpeningConstants, 0, Marshal.SizeOf<CasConstants>());
			
			cmd.DispatchCompute(shader, kernelIndex, threadGroupsX, threadGroupsY, 1);
			
			cmd.EndSample("CAS Sharpening");
		}

		[Serializable, StructLayout(LayoutKind.Sequential)]
		private struct CasConstants
		{
			public CasConstants(uint sharpness, uint halfSharp)
			{
				// Since we don't use CAS for scaling, most of these values end up being constants
				scaling0 = scaling1 = 1065353216;
				scaling2 = scaling3 = 0;
				sharpness0 = sharpness;
				sharpness1 = halfSharp;
				sharpness2 = 1090519040;
				sharpness3 = 0;
			}
			
			public readonly uint scaling0;
			public readonly uint scaling1;
			public readonly uint scaling2;
			public readonly uint scaling3;
			public readonly uint sharpness0;
			public readonly uint sharpness1;
			public readonly uint sharpness2;
			public readonly uint sharpness3;
		}
		
		/// <summary>
		/// The FidelityFX C++ codebase uses floats bitwise converted to ints to pass sharpness parameters to the CAS shader.
		/// This is not possible in C# without enabling unsafe code compilation, so to avoid that we instead use a table of precomputed values.
		/// </summary>
		private static readonly CasConstants[] CasConfigs = 
		{
			new(3187671040u, 45056u),
			new(3187831332u, 45075u),
			new(3187997869u, 45095u),
			new(3188171023u, 45117u),
			new(3188351197u, 45139u),
			new(3188538827u, 45161u),
			new(3188734385u, 45185u),
			new(3188938384u, 45210u),
			new(3189151382u, 45236u),
			new(3189373991u, 45263u),
			new(3189606873u, 45292u),
			new(3189850757u, 45322u),
			new(3190106443u, 45353u),
			new(3190374807u, 45386u),
			new(3190656816u, 45420u),
			new(3190953540u, 45456u),
			new(3191266159u, 45494u),
			new(3191595985u, 45535u),
			new(3191944482u, 45577u),
			new(3192313280u, 45622u),
			new(3192704205u, 45670u),
		};
		
		protected bool CreateRenderTexture(ref RenderTexture rt, string name, in Vector2Int size, GraphicsFormat format, bool enableRandomWrite = false)
		{
			rt = new RenderTexture(size.x, size.y, 0, format) { name = name, enableRandomWrite = enableRandomWrite };
			return rt.Create();
		}
		
		protected bool CreateRenderTexture(ref RenderTexture rt, string name, in Vector2Int size, RenderTextureFormat format, bool enableRandomWrite = false)
		{
			rt = new RenderTexture(size.x, size.y, 0, format) { name = name, enableRandomWrite = enableRandomWrite };
			return rt.Create();
		}

		protected void DestroyRenderTexture(ref RenderTexture rt)
		{
			if (rt == null)
				return;
			
			rt.Release();
			rt = null;
		}

		protected void DestroyConstantsBuffer<TConst>(ref ConstantsBuffer<TConst> cb)
			where TConst: struct
		{
			if (cb == null)
				return;
			
			cb.Destroy();
			cb = null;
		}
	}
}