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

namespace FidelityFX.FrameGen
{
    public static class FrameInterpolation
    {
        public static FrameInterpolationContext CreateContext(Vector2Int displaySize, Vector2Int maxRenderSize, FrameInterpolationShaders shaders, GraphicsFormat backBufferFormat, InitializationFlags flags = 0)
        {
            if (SystemInfo.usesReversedZBuffer)
                flags |= InitializationFlags.EnableDepthInverted;
            else
                flags &= ~InitializationFlags.EnableDepthInverted;
            
            var contextDescription = new ContextDescription
            {
                flags = flags,
                maxRenderSize = maxRenderSize,
                displaySize = displaySize,
                backBufferFormat = backBufferFormat,
                shaders = shaders,
            };
            
            Debug.Log($"Setting up Frame Interpolation with render size: {maxRenderSize.x}x{maxRenderSize.y}, display size: {displaySize.x}x{displaySize.y}, backbuffer format: {backBufferFormat}, flags: {flags}");
            
            var context = new FrameInterpolationContext();
            context.Create(contextDescription);
            return context;
        }
        
        public struct ContextDescription
        {
            public InitializationFlags flags;
            public Vector2Int maxRenderSize;
            public Vector2Int displaySize;
            public GraphicsFormat backBufferFormat;
            public FrameInterpolationShaders shaders;
        }

        public struct PrepareDescription
        {
            public DispatchFlags flags;
            public Vector2Int renderSize;
            public Vector2 jitterOffset;
            public Vector2 motionVectorScale;

            public float frameTimeDelta;
            public float cameraNear;
            public float cameraFar;
            public float viewSpaceToMetersFactor;
            public float cameraFovAngleVertical;

            public ResourceView depth;
            public ResourceView motionVectors;
            public ulong frameID;
        }

        public struct DispatchDescription
        {
            public DispatchFlags flags;
            public Vector2Int displaySize;
            public Vector2Int renderSize;
            public ResourceView currentBackBuffer;
            public ResourceView currentBackBuffer_HUDLess;  // Optional
            public ResourceView output;

            public RectInt interpolationRect;

            public ResourceView opticalFlowVector;
            public ResourceView opticalFlowSceneChangeDetection;
            public Vector2Int opticalFlowBufferSize;
            public Vector2 opticalFlowScale;
            public int opticalFlowBlockSize;

            public float cameraNear;
            public float cameraFar;
            public float cameraFovAngleVertical;
            public float viewSpaceToMetersFactor;

            public float frameTimeDelta;
            public bool reset;

            public BackbufferTransferFunction backbufferTransferFunction;
            public Vector2 minMaxLuminance;
            public ulong frameID;

            public ResourceView InterpolationSource
            {
                get
                {
                    if (currentBackBuffer_HUDLess.IsValid)
                        return currentBackBuffer_HUDLess;
                    
                    return currentBackBuffer;
                }
            }
        }

        [Flags]
        public enum InitializationFlags
        {
            EnableDepthInverted = 1 << 0,
            EnableDepthInfinite = 1 << 1,
            EnableHDRColorInput = 1 << 3,
            EnableDisplayResolutionMotionVectors = 1 << 4,
            EnableJitterMotionVectors = 1 << 5,
            EnableAsyncSupport = 1 << 6,
        }

        [Flags]
        public enum DispatchFlags
        {
            DrawDebugTearLines = 1 << 0,
            DrawDebugResetIndicators = 1 << 1,
            DrawDebugView = 1 << 2,
        }

        [Serializable, StructLayout(LayoutKind.Sequential)]
        internal struct Constants
        {
            public Vector2Int renderSize;
            public Vector2Int displaySize;

            public Vector2 displaySizeRcp;
            public float cameraNear;
            public float cameraFar;

            public Vector2Int upscalerTargetSize;
            public int mode;
            public int reset;

            public Vector4 deviceToViewDepth;

            public float deltaTime;
            public int HUDLessAttachedFactor;
            public Vector2 unused;

            public Vector2 opticalFlowScale;
            public int opticalFlowBlockSize;
            public uint dispatchFlags;

            public Vector2Int maxRenderSize;
            public int opticalFlowHalfResMode;
            public int numInstances;

            public Vector2Int interpolationRectBase;
            public Vector2Int interpolationRectSize;

            public Vector3 debugBarColor;
            public uint backBufferTransferFunction;

            public Vector2 minMaxLuminance;
            public float tanHalfFOV;
            public float pad;

            public Vector2 jitter;
            public Vector2 motionVectorScale;
        }
    }
}