using System;
using UnityEngine.Experimental.Rendering;
using UnityEngine.Experimental.Rendering.RenderGraphModule;

#if UNITY_EDITOR
using UnityEditor;
#endif // UNITY_EDITOR

namespace UnityEngine.Rendering.HighDefinition
{
    /// <summary>
    /// A volume component that holds settings for the Path Tracing effect.
    /// </summary>
    [Serializable, VolumeComponentMenu("Ray Tracing/Path Tracing (Preview)")]
    [HelpURL(Documentation.baseURL + Documentation.version + Documentation.subURL + "Ray-Tracing-Path-Tracing" + Documentation.endURL)]
    public sealed class PathTracing : VolumeComponent
    {
        /// <summary>
        /// Enables path tracing (thus disabling most other passes).
        /// </summary>
        [Tooltip("Enables path tracing (thus disabling most other passes).")]
        public BoolParameter enable = new BoolParameter(false);

        /// <summary>
        /// Defines the layers that path tracing should include.
        /// </summary>
        [Tooltip("Defines the layers that path tracing should include.")]
        public LayerMaskParameter layerMask = new LayerMaskParameter(-1);

        /// <summary>
        /// Defines the maximum number of paths cast within each pixel, over time (one per frame).
        /// </summary>
        [Tooltip("Defines the maximum number of paths cast within each pixel, over time (one per frame).")]
        public ClampedIntParameter maximumSamples = new ClampedIntParameter(256, 1, 16384);

        /// <summary>
        /// Defines the minimum number of bounces for each path, in [1, 10].
        /// </summary>
        [Tooltip("Defines the minimum number of bounces for each path, in [1, 10].")]
        public ClampedIntParameter minimumDepth = new ClampedIntParameter(1, 1, 10);

        /// <summary>
        /// Defines the maximum number of bounces for each path, in [minimumDepth, 10].
        /// </summary>
        [Tooltip("Defines the maximum number of bounces for each path, in [minimumDepth, 10].")]
        public ClampedIntParameter maximumDepth = new ClampedIntParameter(4, 1, 10);

        /// <summary>
        /// Defines the maximum, post-exposed luminance computed for indirect path segments.
        /// </summary>
        [Tooltip("Defines the maximum, post-exposed luminance computed for indirect path segments. Lower values help against noise and fireflies (very bright pixels), but introduce bias by darkening the overall result. Increase this value if your image looks too dark.")]
        public MinFloatParameter maximumIntensity = new MinFloatParameter(10f, 0f);

        /// <summary>
        /// Default constructor for the path tracing volume component.
        /// </summary>
        public PathTracing()
        {
            displayName = "Path Tracing (Preview)";
        }
    }

    public partial class HDRenderPipeline
    {
        PathTracing m_PathTracingSettings = null;

#if UNITY_EDITOR
        uint  m_CacheMaxIteration = 0;
#endif // UNITY_EDITOR
        ulong m_CacheAccelSize = 0;
        uint m_CacheLightCount = 0;

        RTHandle m_RadianceTexture; // stores the per-pixel results of path tracing for this frame

        void InitPathTracing()
        {
#if UNITY_EDITOR
            Undo.postprocessModifications += OnUndoRecorded;
            Undo.undoRedoPerformed += OnSceneEdit;
            SceneView.duringSceneGui += OnSceneGui;
#endif // UNITY_EDITOR

            m_RadianceTexture = RTHandles.Alloc(Vector2.one, TextureXR.slices, colorFormat: GraphicsFormat.R32G32B32A32_SFloat, dimension: TextureXR.dimension,
                enableRandomWrite: true, useMipMap: false, autoGenerateMips: false,
                name: "PathTracingFrameBuffer");
        }

        void ReleasePathTracing()
        {
#if UNITY_EDITOR
            Undo.postprocessModifications -= OnUndoRecorded;
            Undo.undoRedoPerformed -= OnSceneEdit;
            SceneView.duringSceneGui -= OnSceneGui;
#endif // UNITY_EDITOR

            RTHandles.Release(m_RadianceTexture);
        }

        internal void ResetPathTracing()
        {
            m_SubFrameManager.Reset();
        }

        private Vector4 ComputeDoFConstants(HDCamera hdCamera, PathTracing settings)
        {
            var dofSettings = hdCamera.volumeStack.GetComponent<DepthOfField>();
            bool enableDof = (dofSettings.focusMode.value == DepthOfFieldMode.UsePhysicalCamera) && !(hdCamera.camera.cameraType == CameraType.SceneView);

            // focalLength is in mm, so we need to convert to meters. We also want the aperture radius, not diameter, so we divide by two.
            float apertureRadius = (enableDof && hdCamera.physicalParameters != null && hdCamera.physicalParameters.aperture > 0) ? 0.5f * 0.001f * hdCamera.camera.focalLength / hdCamera.physicalParameters.aperture : 0.0f;

            return new Vector4(apertureRadius, dofSettings.focusDistance.value, 0.0f, 0.0f);
        }

#if UNITY_EDITOR

        private void OnSceneEdit()
        {
            // If we just change the sample count, we don't necessarily want to reset iteration
            if (m_PathTracingSettings && m_CacheMaxIteration != m_PathTracingSettings.maximumSamples.value)
            {
                m_CacheMaxIteration = (uint)m_PathTracingSettings.maximumSamples.value;
                m_SubFrameManager.SelectiveReset(m_CacheMaxIteration);
            }
            else
                ResetPathTracing();
        }

        private UndoPropertyModification[] OnUndoRecorded(UndoPropertyModification[] modifications)
        {
            OnSceneEdit();

            return modifications;
        }

        private void OnSceneGui(SceneView sv)
        {
            if (Event.current.type == EventType.MouseDrag)
                m_SubFrameManager.Reset(sv.camera.GetInstanceID());
        }

#endif // UNITY_EDITOR

        private void CheckDirtiness(HDCamera hdCamera)
        {
            // Grab the cached data for the current camera
            int camID = hdCamera.camera.GetInstanceID();
            CameraData camData = m_SubFrameManager.GetCameraData(camID);

            if (m_SubFrameManager.isRecording)
            {
                // If we are recording, we still want to know whether sky rendering is enabled or not
                camData.skyEnabled = (hdCamera.clearColorMode == HDAdditionalCameraData.ClearColorMode.Sky);
                m_SubFrameManager.SetCameraData(camID, camData);
                return;
            }

            // Check camera resolution dirtiness
            if (hdCamera.actualWidth != camData.width || hdCamera.actualHeight != camData.height)
            {
                camData.width = (uint)hdCamera.actualWidth;
                camData.height = (uint)hdCamera.actualHeight;
                camData.ResetIteration();
                m_SubFrameManager.SetCameraData(camID, camData);
                return;
            }

            // Check camera sky dirtiness
            bool enabled = (hdCamera.clearColorMode == HDAdditionalCameraData.ClearColorMode.Sky);
            if (enabled != camData.skyEnabled)
            {
                camData.skyEnabled = enabled;
                camData.ResetIteration();
                m_SubFrameManager.SetCameraData(camID, camData);
                return;
            }

            // Check camera fog dirtiness
            enabled = Fog.IsFogEnabled(hdCamera);
            if (enabled != camData.fogEnabled)
            {
                camData.fogEnabled = enabled;
                camData.ResetIteration();
                m_SubFrameManager.SetCameraData(camID, camData);
                return;
            }

            // Check camera matrix dirtiness
            if (hdCamera.mainViewConstants.nonJitteredViewProjMatrix != (hdCamera.mainViewConstants.prevViewProjMatrix))
            {
                camData.ResetIteration();
                m_SubFrameManager.SetCameraData(camID, camData);
                return;
            }

            // Check materials dirtiness
            if (m_MaterialsDirty)
            {
                m_MaterialsDirty = false;
                ResetPathTracing();
                return;
            }

            // Check light or geometry transforms dirtiness
            if (m_TransformDirty)
            {
                m_TransformDirty = false;
                ResetPathTracing();
            }

            // Check lights dirtiness
            if (m_CacheLightCount != m_RayTracingLights.lightCount)
            {
                m_CacheLightCount = (uint)m_RayTracingLights.lightCount;
                ResetPathTracing();
                return;
            }

            // Check geometry dirtiness
            ulong accelSize = m_CurrentRAS.GetSize();
            if (accelSize != m_CacheAccelSize)
            {
                m_CacheAccelSize = accelSize;
                ResetPathTracing();
            }
        }

        static RTHandle PathTracingHistoryBufferAllocatorFunction(string viewName, int frameIndex, RTHandleSystem rtHandleSystem)
        {
            return rtHandleSystem.Alloc(Vector2.one, TextureXR.slices, colorFormat: GraphicsFormat.R32G32B32A32_SFloat, dimension: TextureXR.dimension,
                enableRandomWrite: true, useMipMap: false, autoGenerateMips: false,
                name: string.Format("{0}_PathTracingHistoryBuffer{1}", viewName, frameIndex));
        }

        struct PathTracingParameters
        {
            public RayTracingShader pathTracingShader;
            public CameraData cameraData;
            public BlueNoise.DitheredTextureSet ditheredTextureSet;
            public ShaderVariablesRaytracing shaderVariablesRaytracingCB;
            public Color backgroundColor;
            public Texture skyReflection;
            public Matrix4x4 pixelCoordToViewDirWS;
            public Vector4 dofParameters;
            public int width, height;
            public RayTracingAccelerationStructure accelerationStructure;
            public HDRaytracingLightCluster lightCluster;
        }

        PathTracingParameters PreparePathTracingParameters(HDCamera hdCamera)
        {
            PathTracingParameters parameters = new PathTracingParameters();

            parameters.pathTracingShader = m_Asset.renderPipelineRayTracingResources.pathTracing;
            parameters.cameraData = m_SubFrameManager.GetCameraData(hdCamera.camera.GetInstanceID());
            parameters.ditheredTextureSet = GetBlueNoiseManager().DitheredTextureSet256SPP();
            parameters.backgroundColor = hdCamera.backgroundColorHDR;
            parameters.skyReflection = m_SkyManager.GetSkyReflection(hdCamera);
            parameters.pixelCoordToViewDirWS = hdCamera.mainViewConstants.pixelCoordToViewDirWS;
            parameters.dofParameters = ComputeDoFConstants(hdCamera, m_PathTracingSettings);
            parameters.width = hdCamera.actualWidth;
            parameters.height = hdCamera.actualHeight;
            parameters.accelerationStructure = RequestAccelerationStructure();
            parameters.lightCluster = RequestLightCluster();

            parameters.shaderVariablesRaytracingCB = m_ShaderVariablesRayTracingCB;
            parameters.shaderVariablesRaytracingCB._RaytracingNumSamples = (int)m_SubFrameManager.subFrameCount;
            parameters.shaderVariablesRaytracingCB._RaytracingMinRecursion = m_PathTracingSettings.minimumDepth.value;
#if NO_RAY_RECURSION
            parameters.shaderVariablesRaytracingCB._RaytracingMaxRecursion = 1;
#else
            parameters.shaderVariablesRaytracingCB._RaytracingMaxRecursion = m_PathTracingSettings.maximumDepth.value;
#endif
            parameters.shaderVariablesRaytracingCB._RaytracingIntensityClamp = m_PathTracingSettings.maximumIntensity.value;
            parameters.shaderVariablesRaytracingCB._RaytracingSampleIndex = (int)parameters.cameraData.currentIteration;

            return parameters;
        }

        static void RenderPathTracing(in PathTracingParameters parameters, RTHandle radianceTexture, CommandBuffer cmd)
        {
            // Define the shader pass to use for the path tracing pass
            cmd.SetRayTracingShaderPass(parameters.pathTracingShader, "PathTracingDXR");

            // Set the acceleration structure for the pass
            cmd.SetRayTracingAccelerationStructure(parameters.pathTracingShader, HDShaderIDs._RaytracingAccelerationStructureName, parameters.accelerationStructure);

            // Inject the ray-tracing sampling data
            BlueNoise.BindDitheredTextureSet(cmd, parameters.ditheredTextureSet);

            // Update the global constant buffer
            ConstantBuffer.PushGlobal(cmd, parameters.shaderVariablesRaytracingCB, HDShaderIDs._ShaderVariablesRaytracing);

            // LightLoop data
            cmd.SetGlobalBuffer(HDShaderIDs._RaytracingLightCluster, parameters.lightCluster.GetCluster());
            cmd.SetGlobalBuffer(HDShaderIDs._LightDatasRT, parameters.lightCluster.GetLightDatas());

            // Set the data for the ray miss
            cmd.SetRayTracingIntParam(parameters.pathTracingShader, HDShaderIDs._RaytracingCameraSkyEnabled, parameters.cameraData.skyEnabled ? 1 : 0);
            cmd.SetRayTracingVectorParam(parameters.pathTracingShader, HDShaderIDs._RaytracingCameraClearColor, parameters.backgroundColor);
            cmd.SetRayTracingTextureParam(parameters.pathTracingShader, HDShaderIDs._SkyTexture, parameters.skyReflection);

            // Additional data for path tracing
            cmd.SetRayTracingTextureParam(parameters.pathTracingShader, HDShaderIDs._RadianceTexture, radianceTexture);
            cmd.SetRayTracingMatrixParam(parameters.pathTracingShader, HDShaderIDs._PixelCoordToViewDirWS, parameters.pixelCoordToViewDirWS);
            cmd.SetRayTracingVectorParam(parameters.pathTracingShader, HDShaderIDs._PathTracedDoFConstants, parameters.dofParameters);

            // Run the computation
            cmd.DispatchRays(parameters.pathTracingShader, "RayGen", (uint)parameters.width, (uint)parameters.height, 1);
        }

        class RenderPathTracingData
        {
            public PathTracingParameters parameters;
            public TextureHandle output;
        }

        TextureHandle RenderPathTracing(RenderGraph renderGraph, in PathTracingParameters parameters, TextureHandle pathTracingBuffer)
        {
            using (var builder = renderGraph.AddRenderPass<RenderPathTracingData>("Render PathTracing", out var passData))
            {
                passData.parameters = parameters;
                passData.output = builder.WriteTexture(pathTracingBuffer);

                builder.SetRenderFunc(
                    (RenderPathTracingData data, RenderGraphContext ctx) =>
                    {
                        RenderPathTracing(data.parameters, data.output, ctx.cmd);
                    });

                return passData.output;
            }
        }

        TextureHandle RenderPathTracing(RenderGraph renderGraph, HDCamera hdCamera)
        {
            RayTracingShader pathTracingShader = m_Asset.renderPipelineRayTracingResources.pathTracing;
            m_PathTracingSettings = hdCamera.volumeStack.GetComponent<PathTracing>();

            // Check the validity of the state before moving on with the computation
            if (!pathTracingShader || !m_PathTracingSettings.enable.value)
                return TextureHandle.nullHandle;

            CheckDirtiness(hdCamera);

            var parameters = PreparePathTracingParameters(hdCamera);
            TextureHandle outputTexture = CreateColorBuffer(renderGraph, hdCamera, false);
            // TODO RENDERGRAPH: This texture needs to be persistent
            // (apparently it only matters for some tests, loading a regular scene with pathtracing works even if this one is not persistent)
            // So we need to import a regular RTHandle. This is not good because it means the texture will always be allocate even if not used...
            // Refactor that when we formalize how to handle persistent textures better (with automatic lifetime and such).
            var radianceTexture = renderGraph.ImportTexture(m_RadianceTexture);

            if (!m_SubFrameManager.isRecording)
            {
                // If we are recording, the max iteration is set/overridden by the subframe manager, otherwise we read it from the path tracing volume
                m_SubFrameManager.subFrameCount = (uint)m_PathTracingSettings.maximumSamples.value;
            }


#if UNITY_HDRP_DXR_TESTS_DEFINE
            if (Application.isPlaying)
                m_SubFrameManager.subFrameCount = 1;
#endif

            if (parameters.cameraData.currentIteration < m_SubFrameManager.subFrameCount)
            {
                RenderPathTracing(m_RenderGraph, parameters, radianceTexture);
            }

            RenderAccumulation(m_RenderGraph, hdCamera, radianceTexture, outputTexture, true);

            return outputTexture;
        }
    }
}