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

namespace FidelityFX
{
    public static class Fsr2
    {
        // Allow overriding of certain Unity resource management behaviors by the programmer 
        public static Fsr2Callbacks GlobalCallbacks { get; set; } = new Fsr2Callbacks();

        /// <summary>
        /// Creates a new FSR2 context with standard parameters that are appropriate for the current platform. 
        /// </summary>
        public static Fsr2Context CreateContext(Vector2Int displaySize, Vector2Int maxRenderSize, InitializationFlags flags = 0)
        {
            if (SystemInfo.usesReversedZBuffer)
                flags |= InitializationFlags.EnableDepthInverted;
            else
                flags &= ~InitializationFlags.EnableDepthInverted;
            
            var contextDescription = new ContextDescription
            {
                Flags = flags,
                DisplaySize = displaySize,
                MaxRenderSize = maxRenderSize,
                Callbacks = GlobalCallbacks,
            };
            
            var context = new Fsr2Context();
            context.Create(contextDescription);
            return context;
        }

        public static float GetUpscaleRatioFromQualityMode(QualityMode qualityMode)
        {
            switch (qualityMode)
            {
                case QualityMode.Quality:
                    return 1.5f;
                case QualityMode.Balanced:
                    return 1.7f;
                case QualityMode.Performance:
                    return 2.0f;
                case QualityMode.UltraPerformance:
                    return 3.0f;
                default:
                    return 1.0f;
            }
        }

        public static void GetRenderResolutionFromQualityMode(
            out uint renderWidth, out uint renderHeight,
            int displayWidth, int displayHeight, QualityMode qualityMode)
        {
            float ratio = GetUpscaleRatioFromQualityMode(qualityMode);
            renderWidth = (uint)(displayWidth / ratio);
            renderHeight = (uint)(displayHeight / ratio);
        }

        public static int GetJitterPhaseCount(int renderWidth, int displayWidth)
        {
            const float basePhaseCount = 8.0f;
            int jitterPhaseCount = (int)(basePhaseCount * Mathf.Pow((float)displayWidth / renderWidth, 2.0f));
            return jitterPhaseCount;
        }

        public static void GetJitterOffset(out float outX, out float outY, int index, int phaseCount)
        {
            outX = Halton((index % phaseCount) + 1, 2) - 0.5f;
            outY = Halton((index % phaseCount) + 1, 3) - 0.5f;
        }
        
        // Calculate halton number for index and base.
        private static float Halton(int index, int @base)
        {
            float f = 1.0f, result = 0.0f;

            for (int currentIndex = index; currentIndex > 0;) {

                f /= @base;
                result += f * (currentIndex % @base);
                currentIndex = (int)Mathf.Floor((float)currentIndex / @base);
            }

            return result;
        }
        
        public static float Lanczos2(float value)
        {
            return Mathf.Abs(value) < Mathf.Epsilon ? 1.0f : 
                Mathf.Sin(Mathf.PI * value) / (Mathf.PI * value) * (Mathf.Sin(0.5f * Mathf.PI * value) / (0.5f * Mathf.PI * value));
        }
        
        public enum QualityMode
        {
            Quality = 1,
            Balanced = 2,
            Performance = 3,
            UltraPerformance = 4,
        }

        [Flags]
        public enum InitializationFlags
        {
            EnableHighDynamicRange = 1 << 0,
            EnableDisplayResolutionMotionVectors = 1 << 1,
            EnableMotionVectorsJitterCancellation = 1 << 2,
            EnableDepthInverted = 1 << 3,
            EnableDepthInfinite = 1 << 4,
            EnableAutoExposure = 1 << 5,
            EnableDynamicResolution = 1 << 6,
            EnableTexture1DUsage = 1 << 7,
            EnableDebugChecking = 1 << 8,
        }

        public enum MessageType
        {
            Error = 0,
            Warning = 1,
        }

        public struct ContextDescription
        {
            public InitializationFlags Flags;
            public Vector2Int MaxRenderSize;
            public Vector2Int DisplaySize;
            public Fsr2Callbacks Callbacks;
        }

        public class DispatchDescription
        {
            // Texture2D Color, Depth, MotionVectors;  // Will be passed using ComputeShader.SetTextureFromGlobal
            public Texture2D Exposure;
            public Texture2D Reactive;
            public Texture2D TransparencyAndComposition;
            public RenderTexture Input;
            public RenderTexture Output;
            public Vector2 JitterOffset;
            public Vector2 MotionVectorScale;
            public Vector2Int RenderSize;
            public bool EnableSharpening;
            public float Sharpness;
            public float FrameTimeDelta;
            public float PreExposure;
            public bool Reset;
            public float CameraNear;
            public float CameraFar;
            public float CameraFovAngleVertical;
            public float ViewSpaceToMetersFactor;
        }
        
        [Serializable, StructLayout(LayoutKind.Sequential)]
        internal struct Fsr2Constants
        {
            public Vector2Int renderSize;
            public Vector2Int maxRenderSize;
            public Vector2Int displaySize;
            public Vector2Int inputColorResourceDimensions;
            public Vector2Int lumaMipDimensions;
            public int lumaMipLevelToUse;
            public int frameIndex;
            
            public Vector4 deviceToViewDepth;
            public Vector2 jitterOffset;
            public Vector2 motionVectorScale;
            public Vector2 downscaleFactor;
            public Vector2 motionVectorJitterCancellation;
            public float preExposure;
            public float previousFramePreExposure;
            public float tanHalfFOV;
            public float jitterPhaseCount;
            public float deltaTime;
            public float dynamicResChangeFactor;
            public float viewSpaceToMetersFactor;
        }
        
        [Serializable, StructLayout(LayoutKind.Sequential)]
        internal struct SpdConstants
        {
            public uint mips;
            public uint numWorkGroups;
            public uint workGroupOffsetX, workGroupOffsetY;
            public uint renderSizeX, renderSizeY;
        }

        [Serializable, StructLayout(LayoutKind.Sequential)]
        internal struct GenerateReactiveConstants
        {
            public float scale;
            public float threshold;
            public float binaryValue;
            public uint flags;
        }
        
        [Serializable, StructLayout(LayoutKind.Sequential)]
        internal struct RcasConstants
        {
            public RcasConstants(uint sharpness, uint halfSharp)
            {
                this.sharpness = sharpness;
                this.halfSharp = halfSharp;
                dummy0 = dummy1 = 0;
            }
        
            public readonly uint sharpness;
            public readonly uint halfSharp;
            public readonly uint dummy0;
            public readonly uint dummy1;
        }
    }
}