#if UNITY_POST_PROCESSING_STACK_V2
using System;
using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.Rendering.PostProcessing;

namespace FidelityFX
{
    [Serializable]
    [PostProcess(typeof(Fsr2PostProcessRenderer), PostProcessEvent.BeforeStack, "FidelityFX/FSR 2", false)]
    public class Fsr2PostProcessEffect : PostProcessEffectSettings
    {
        public Fsr2QualityModeParameter qualityMode = new Fsr2QualityModeParameter() { value = Fsr2.QualityMode.Quality };

        public BoolParameter performSharpenPass = new BoolParameter() { value = true };
        [Range(0, 1)] public FloatParameter sharpness = new FloatParameter() { value = 0.8f };
        
        [Tooltip("Allow the use of half precision compute operations, potentially improving performance")]
        public BoolParameter enableFP16 = new BoolParameter() { value = false };

        [Header("Exposure")]
        public BoolParameter enableAutoExposure = new BoolParameter() { value = true };
        public FloatParameter preExposure = new FloatParameter() { value = 1.0f };
        
        [Header("Reactivity, Transparency & Composition")]
        public BoolParameter autoGenerateReactiveMask = new BoolParameter() { value = true };

        public override bool IsEnabledAndSupported(PostProcessRenderContext context)
        {
            return base.IsEnabledAndSupported(context) && SystemInfo.supportsComputeShaders;
        }
    }

    [Serializable]
    public class Fsr2QualityModeParameter : ParameterOverride<Fsr2.QualityMode>
    {
    }

    public class Fsr2PostProcessRenderer : PostProcessEffectRenderer<Fsr2PostProcessEffect>
    {
        private Fsr2Context _fsrContext;
        private Fsr2PostProcessHelper _helper;

        private Vector2Int _displaySize;
        private Vector2Int _renderSize;
        
        private Fsr2.QualityMode _prevQualityMode;
        
        public override void Init()
        {
            base.Init();
            
            Debug.Log($"Initializing FSR2 post-process effect, quality = {settings.qualityMode.value}");
        }

        public override void Release()
        {
            Debug.Log("Releasing FSR2 post-process effect");
            
            base.Release();
        }

        public override DepthTextureMode GetCameraFlags()
        {
            return DepthTextureMode.Depth | DepthTextureMode.MotionVectors;
        }

        public override void Render(PostProcessRenderContext context)
        {
            var cmd = context.command;

            if (!Application.isPlaying)
            {
                // We don't want this effect to start injecting scripts in edit mode, so just blit and skip the rest entirely
                cmd.BlitFullscreenTriangle(context.source, context.destination);
                return;
            }

            // Monitor for any resolution changes and recreate the FSR2 context if necessary
            // We can't create an FSR2 context without info from the post-processing context, so delay the initial setup until here
            if (_fsrContext == null || context.screenWidth != _displaySize.x || context.screenHeight != _displaySize.y || settings.qualityMode != _prevQualityMode)
            {
                DestroyFsrContext();
                CreateFsrContext(context);
                
                _prevQualityMode = settings.qualityMode;
            }
            
            // Ensure that the helper script exists and is enabled
            if (_helper == null || !_helper.enabled)
            {
                if (_helper == null)
                    Inject(context);
                
                _helper.enabled = settings.IsEnabledAndSupported(context);
                
                // The injected script won't come into effect until the next frame, so just do a simple blit this frame
                cmd.BlitFullscreenTriangle(context.source, context.destination);
                return;
            }

            //Debug.Log("[FSR2] Render, where am I being called from?");  // In OnPreCull... OH
            // TODO: executing in OnPreCull means we can do jittering in here, at least. Rect manipulation should still happen before PPV2 entirely.
            ApplyJitter(context.camera);
            
            cmd.BlitFullscreenTriangle(context.source, context.destination);
        }

        /// <summary>
        /// Inject ourselves into the camera's render loop at points where PPV2 normally wouldn't allow us.
        /// This also sets up PPV2's own stack to use FSR2's upscaled output as its source. 
        /// </summary>
        private void Inject(PostProcessRenderContext context)
        {
            var go = context.camera.gameObject;
            _helper = go.AddComponent<Fsr2PostProcessHelper>();
            
            _helper.Settings = settings;
            // TODO: create output RT, set it as PPV2's post-transparency stack source
        }
        
        private void CreateFsrContext(PostProcessRenderContext context)
        {
            _displaySize = new Vector2Int(context.screenWidth, context.screenHeight);
            Fsr2.GetRenderResolutionFromQualityMode(out var renderWidth, out var renderHeight, _displaySize.x, _displaySize.y, settings.qualityMode);
            _renderSize = new Vector2Int(renderWidth, renderHeight);
            
            Fsr2.InitializationFlags flags = 0;
            if (context.camera.allowHDR) flags |= Fsr2.InitializationFlags.EnableHighDynamicRange;
            if (settings.enableFP16) flags |= Fsr2.InitializationFlags.EnableFP16Usage;
            if (settings.enableAutoExposure) flags |= Fsr2.InitializationFlags.EnableAutoExposure;

#if UNITY_EDITOR || DEVELOPMENT_BUILD
            flags |= Fsr2.InitializationFlags.EnableDebugChecking;
#endif
            
            _fsrContext = Fsr2.CreateContext(_displaySize, _renderSize, flags);
        }
        
        private void DestroyFsrContext()
        {
            if (_fsrContext != null)
            {
                _fsrContext.Destroy();
                _fsrContext = null;
            }
        }

        private void ApplyJitter(Camera camera)
        {
            // Perform custom jittering of the camera's projection matrix according to FSR2's recipe
            int jitterPhaseCount = Fsr2.GetJitterPhaseCount(_renderSize.x, _displaySize.x);
            Fsr2.GetJitterOffset(out float jitterX, out float jitterY, Time.frameCount, jitterPhaseCount);

            jitterX = 2.0f * jitterX / _renderSize.x;
            jitterY = 2.0f * jitterY / _renderSize.y;

            var jitterTranslationMatrix = Matrix4x4.Translate(new Vector3(jitterX, jitterY, 0));
            camera.nonJitteredProjectionMatrix = camera.projectionMatrix;
            camera.projectionMatrix = jitterTranslationMatrix * camera.nonJitteredProjectionMatrix;
            camera.useJitteredProjectionMatrixForTransparentRendering = true;
        }
    }

    internal class Fsr2PostProcessHelper : MonoBehaviour
    {
        internal Fsr2PostProcessEffect Settings;

        private Camera _camera;

        private void Awake()
        {
            _camera = GetComponent<Camera>();
            // TODO: inject opaque-only command buffer & anything else?
        }

        private void OnPreCull()    // TODO: may need to do this in LateUpdate instead? So we execute before PPV2's OnPreCull
        {
            // TODO: check if FSR2 is still enabled; if not: reset PPV2 source texture & disable self
            // TODO: fiddle with the camera parameters, rect, jitter, etc
            // Debug.Log("[FSR2] OnPreCull");
        }

        private void OnPostRender()
        {
            _camera.ResetProjectionMatrix();
        }
    }
}
#endif  // UNITY_POST_PROCESSING_STACK_V2