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

namespace UnityEngine.Rendering.Universal.Internal
{
    /// <summary>
    /// Renders a shadow map for the main Light.
    /// </summary>
    public class MainLightShadowCasterPass : ScriptableRenderPass
    {
        private static class MainLightShadowConstantBuffer
        {
            public static int _WorldToShadow;
            public static int _ShadowParams;
            public static int _CascadeShadowSplitSpheres0;
            public static int _CascadeShadowSplitSpheres1;
            public static int _CascadeShadowSplitSpheres2;
            public static int _CascadeShadowSplitSpheres3;
            public static int _CascadeShadowSplitSphereRadii;
            public static int _ShadowOffset0;
            public static int _ShadowOffset1;
            public static int _ShadowmapSize;
        }

        const int k_MaxCascades = 4;
        const int k_ShadowmapBufferBits = 16;
        float m_CascadeBorder;
        float m_MaxShadowDistanceSq;
        int m_ShadowCasterCascadesCount;

        int m_MainLightShadowmapID;
        internal RTHandle m_MainLightShadowmapTexture;
        internal RTHandle m_EmptyLightShadowmapTexture;

        Matrix4x4[] m_MainLightShadowMatrices;
        ShadowSliceData[] m_CascadeSlices;
        Vector4[] m_CascadeSplitDistances;

        bool m_CreateEmptyShadowmap;
        bool m_EmptyShadowmapNeedsClear = false;

        int renderTargetWidth;
        int renderTargetHeight;

        ProfilingSampler m_ProfilingSetupSampler = new ProfilingSampler("Setup Main Shadowmap");
        private PassData m_PassData;
        /// <summary>
        /// Creates a new <c>MainLightShadowCasterPass</c> instance.
        /// </summary>
        /// <param name="evt">The <c>RenderPassEvent</c> to use.</param>
        /// <seealso cref="RenderPassEvent"/>
        public MainLightShadowCasterPass(RenderPassEvent evt)
        {
            base.profilingSampler = new ProfilingSampler(nameof(MainLightShadowCasterPass));
            renderPassEvent = evt;

            m_PassData = new PassData();
            m_MainLightShadowMatrices = new Matrix4x4[k_MaxCascades + 1];
            m_CascadeSlices = new ShadowSliceData[k_MaxCascades];
            m_CascadeSplitDistances = new Vector4[k_MaxCascades];

            MainLightShadowConstantBuffer._WorldToShadow = Shader.PropertyToID("_MainLightWorldToShadow");
            MainLightShadowConstantBuffer._ShadowParams = Shader.PropertyToID("_MainLightShadowParams");
            MainLightShadowConstantBuffer._CascadeShadowSplitSpheres0 = Shader.PropertyToID("_CascadeShadowSplitSpheres0");
            MainLightShadowConstantBuffer._CascadeShadowSplitSpheres1 = Shader.PropertyToID("_CascadeShadowSplitSpheres1");
            MainLightShadowConstantBuffer._CascadeShadowSplitSpheres2 = Shader.PropertyToID("_CascadeShadowSplitSpheres2");
            MainLightShadowConstantBuffer._CascadeShadowSplitSpheres3 = Shader.PropertyToID("_CascadeShadowSplitSpheres3");
            MainLightShadowConstantBuffer._CascadeShadowSplitSphereRadii = Shader.PropertyToID("_CascadeShadowSplitSphereRadii");
            MainLightShadowConstantBuffer._ShadowOffset0 = Shader.PropertyToID("_MainLightShadowOffset0");
            MainLightShadowConstantBuffer._ShadowOffset1 = Shader.PropertyToID("_MainLightShadowOffset1");
            MainLightShadowConstantBuffer._ShadowmapSize = Shader.PropertyToID("_MainLightShadowmapSize");

            m_MainLightShadowmapID = Shader.PropertyToID("_MainLightShadowmapTexture");

            m_EmptyLightShadowmapTexture = ShadowUtils.AllocShadowRT(1, 1, k_ShadowmapBufferBits, 1, 0, name: "_EmptyLightShadowmapTexture");
            m_EmptyShadowmapNeedsClear = true;
        }

        /// <summary>
        /// Cleans up resources used by the pass.
        /// </summary>
        public void Dispose()
        {
            m_MainLightShadowmapTexture?.Release();
            m_EmptyLightShadowmapTexture?.Release();
        }

        /// <summary>
        /// Sets up the pass.
        /// </summary>
        /// <param name="renderingData"></param>
        /// <returns>True if the pass should be enqueued, otherwise false.</returns>
        /// <seealso cref="RenderingData"/>
        public bool Setup(ref RenderingData renderingData)
        {
            if (!renderingData.shadowData.mainLightShadowsEnabled)
                return false;

            using var profScope = new ProfilingScope(m_ProfilingSetupSampler);

            ref ShadowData shadowData = ref renderingData.shadowData;
            if (!shadowData.supportsMainLightShadows)
                return SetupForEmptyRendering(ref renderingData);

            Clear();
            int shadowLightIndex = renderingData.lightData.mainLightIndex;
            if (shadowLightIndex == -1)
                return SetupForEmptyRendering(ref renderingData);

            VisibleLight shadowLight = renderingData.lightData.visibleLights[shadowLightIndex];
            Light light = shadowLight.light;
            if (light.shadows == LightShadows.None)
                return SetupForEmptyRendering(ref renderingData);

            if (shadowLight.lightType != LightType.Directional)
            {
                Debug.LogWarning("Only directional lights are supported as main light.");
            }

            Bounds bounds;
            if (!renderingData.cullResults.GetShadowCasterBounds(shadowLightIndex, out bounds))
                return SetupForEmptyRendering(ref renderingData);

            m_ShadowCasterCascadesCount = shadowData.mainLightShadowCascadesCount;
            renderTargetWidth = shadowData.mainLightRenderTargetWidth;
            renderTargetHeight = shadowData.mainLightRenderTargetHeight;

            ref readonly URPLightShadowCullingInfos shadowCullingInfos = ref renderingData.visibleLightsShadowCullingInfos.UnsafeElementAt(shadowLightIndex);

            for (int cascadeIndex = 0; cascadeIndex < m_ShadowCasterCascadesCount; ++cascadeIndex)
            {
                ref readonly ShadowSliceData sliceData = ref shadowCullingInfos.slices.UnsafeElementAt(cascadeIndex);
                m_CascadeSplitDistances[cascadeIndex] = sliceData.splitData.cullingSphere;
                m_CascadeSlices[cascadeIndex] = sliceData;

                if (!shadowCullingInfos.IsSliceValid(cascadeIndex))
                    return SetupForEmptyRendering(ref renderingData);
            }

            ShadowUtils.ShadowRTReAllocateIfNeeded(ref m_MainLightShadowmapTexture, renderTargetWidth, renderTargetHeight, k_ShadowmapBufferBits, name: "_MainLightShadowmapTexture");

            m_MaxShadowDistanceSq = renderingData.cameraData.maxShadowDistance * renderingData.cameraData.maxShadowDistance;
            m_CascadeBorder = renderingData.shadowData.mainLightShadowCascadeBorder;
            m_CreateEmptyShadowmap = false;
            useNativeRenderPass = true;

            return true;
        }

        bool SetupForEmptyRendering(ref RenderingData renderingData)
        {
            if (!renderingData.cameraData.renderer.stripShadowsOffVariants)
                return false;

            m_CreateEmptyShadowmap = true;
            useNativeRenderPass = false;

            // Required for scene view camera(URP renderer not initialized)
            if(ShadowUtils.ShadowRTReAllocateIfNeeded(ref m_EmptyLightShadowmapTexture, 1, 1, k_ShadowmapBufferBits, name: "_EmptyLightShadowmapTexture"))
                m_EmptyShadowmapNeedsClear = true;

            return true;
        }

        /// <inheritdoc />
        public override void Configure(CommandBuffer cmd, RenderTextureDescriptor cameraTextureDescriptor)
        {
            if (m_CreateEmptyShadowmap && !m_EmptyShadowmapNeedsClear)
            {
                // Reset pass RTs to null
                ResetTarget();
                return;
            }

            if (m_CreateEmptyShadowmap)
            {
                ConfigureTarget(m_EmptyLightShadowmapTexture);
                m_EmptyShadowmapNeedsClear = false;
            }
            else
                ConfigureTarget(m_MainLightShadowmapTexture);

            ConfigureClear(ClearFlag.All, Color.black);
        }

        /// <inheritdoc/>
        public override void Execute(ScriptableRenderContext context, ref RenderingData renderingData)
        {
            if (m_CreateEmptyShadowmap)
            {
                SetEmptyMainLightCascadeShadowmap(CommandBufferHelpers.GetRasterCommandBuffer(renderingData.commandBuffer));
                renderingData.commandBuffer.SetGlobalTexture(m_MainLightShadowmapID, m_EmptyLightShadowmapTexture.nameID);

                return;
            }

            InitPassData(ref m_PassData, ref renderingData);
            InitRendererLists(ref renderingData, ref m_PassData, context, default(RenderGraph), false);

            RenderMainLightCascadeShadowmap(CommandBufferHelpers.GetRasterCommandBuffer(renderingData.commandBuffer), ref m_PassData, ref renderingData, false);
            renderingData.commandBuffer.SetGlobalTexture(m_MainLightShadowmapID, m_MainLightShadowmapTexture.nameID);
        }

        void Clear()
        {
            for (int i = 0; i < m_MainLightShadowMatrices.Length; ++i)
                m_MainLightShadowMatrices[i] = Matrix4x4.identity;

            for (int i = 0; i < m_CascadeSplitDistances.Length; ++i)
                m_CascadeSplitDistances[i] = new Vector4(0.0f, 0.0f, 0.0f, 0.0f);

            for (int i = 0; i < m_CascadeSlices.Length; ++i)
                m_CascadeSlices[i].Clear();
        }

        void SetEmptyMainLightCascadeShadowmap(RasterCommandBuffer cmd)
        {
            CoreUtils.SetKeyword(cmd, ShaderKeywordStrings.MainLightShadows, true);
            cmd.SetGlobalVector(MainLightShadowConstantBuffer._ShadowParams,
                new Vector4(1, 0, 1, 0));
            cmd.SetGlobalVector(MainLightShadowConstantBuffer._ShadowmapSize,
                new Vector4(1f / m_EmptyLightShadowmapTexture.rt.width, 1f / m_EmptyLightShadowmapTexture.rt.height, m_EmptyLightShadowmapTexture.rt.width, m_EmptyLightShadowmapTexture.rt.height));
        }

        void RenderMainLightCascadeShadowmap(RasterCommandBuffer cmd, ref PassData data, ref RenderingData renderingData, bool isRenderGraph)
        {
            var lightData = renderingData.lightData;

            int shadowLightIndex = lightData.mainLightIndex;
            if (shadowLightIndex == -1)
                return;

            VisibleLight shadowLight = lightData.visibleLights[shadowLightIndex];

            using (new ProfilingScope(cmd, ProfilingSampler.Get(URPProfileId.MainLightShadow)))
            {
                // Need to start by setting the Camera position as that is not set for passes executed before normal rendering
                cmd.SetGlobalVector(ShaderPropertyId.worldSpaceCameraPos, renderingData.cameraData.worldSpaceCameraPos);

                for (int cascadeIndex = 0; cascadeIndex < m_ShadowCasterCascadesCount; ++cascadeIndex)
                {
                    Vector4 shadowBias = ShadowUtils.GetShadowBias(ref shadowLight, shadowLightIndex, ref renderingData.shadowData, m_CascadeSlices[cascadeIndex].projectionMatrix, m_CascadeSlices[cascadeIndex].resolution);
                    ShadowUtils.SetupShadowCasterConstantBuffer(cmd, ref shadowLight, shadowBias);
                    CoreUtils.SetKeyword(cmd, ShaderKeywordStrings.CastingPunctualLightShadow, false);
                    RendererList shadowRendererList = isRenderGraph? data.shadowRendererListsHandle[cascadeIndex] : data.shadowRendererLists[cascadeIndex];
                    ShadowUtils.RenderShadowSlice(cmd, ref m_CascadeSlices[cascadeIndex], ref shadowRendererList, m_CascadeSlices[cascadeIndex].projectionMatrix, m_CascadeSlices[cascadeIndex].viewMatrix);
                }

                renderingData.shadowData.isKeywordSoftShadowsEnabled = shadowLight.light.shadows == LightShadows.Soft && renderingData.shadowData.supportsSoftShadows;
                CoreUtils.SetKeyword(cmd, ShaderKeywordStrings.MainLightShadows, renderingData.shadowData.mainLightShadowCascadesCount == 1);
                CoreUtils.SetKeyword(cmd, ShaderKeywordStrings.MainLightShadowCascades, renderingData.shadowData.mainLightShadowCascadesCount > 1);
                CoreUtils.SetKeyword(cmd, ShaderKeywordStrings.SoftShadows, renderingData.shadowData.isKeywordSoftShadowsEnabled);

                SetupMainLightShadowReceiverConstants(cmd, ref shadowLight, ref renderingData.shadowData);
            }
        }

        void SetupMainLightShadowReceiverConstants(RasterCommandBuffer cmd, ref VisibleLight shadowLight, ref ShadowData shadowData)
        {
            Light light = shadowLight.light;
            bool softShadows = shadowLight.light.shadows == LightShadows.Soft && shadowData.supportsSoftShadows;

            int cascadeCount = m_ShadowCasterCascadesCount;
            for (int i = 0; i < cascadeCount; ++i)
                m_MainLightShadowMatrices[i] = m_CascadeSlices[i].shadowTransform;

            // We setup and additional a no-op WorldToShadow matrix in the last index
            // because the ComputeCascadeIndex function in Shadows.hlsl can return an index
            // out of bounds. (position not inside any cascade) and we want to avoid branching
            Matrix4x4 noOpShadowMatrix = Matrix4x4.zero;
            noOpShadowMatrix.m22 = (SystemInfo.usesReversedZBuffer) ? 1.0f : 0.0f;
            for (int i = cascadeCount; i <= k_MaxCascades; ++i)
                m_MainLightShadowMatrices[i] = noOpShadowMatrix;

            float invShadowAtlasWidth = 1.0f / renderTargetWidth;
            float invShadowAtlasHeight = 1.0f / renderTargetHeight;
            float invHalfShadowAtlasWidth = 0.5f * invShadowAtlasWidth;
            float invHalfShadowAtlasHeight = 0.5f * invShadowAtlasHeight;
            float softShadowsProp = ShadowUtils.SoftShadowQualityToShaderProperty(light, softShadows);

            ShadowUtils.GetScaleAndBiasForLinearDistanceFade(m_MaxShadowDistanceSq, m_CascadeBorder, out float shadowFadeScale, out float shadowFadeBias);

            cmd.SetGlobalMatrixArray(MainLightShadowConstantBuffer._WorldToShadow, m_MainLightShadowMatrices);
            cmd.SetGlobalVector(MainLightShadowConstantBuffer._ShadowParams,
                new Vector4(light.shadowStrength, softShadowsProp, shadowFadeScale, shadowFadeBias));

            if (m_ShadowCasterCascadesCount > 1)
            {
                cmd.SetGlobalVector(MainLightShadowConstantBuffer._CascadeShadowSplitSpheres0,
                    m_CascadeSplitDistances[0]);
                cmd.SetGlobalVector(MainLightShadowConstantBuffer._CascadeShadowSplitSpheres1,
                    m_CascadeSplitDistances[1]);
                cmd.SetGlobalVector(MainLightShadowConstantBuffer._CascadeShadowSplitSpheres2,
                    m_CascadeSplitDistances[2]);
                cmd.SetGlobalVector(MainLightShadowConstantBuffer._CascadeShadowSplitSpheres3,
                    m_CascadeSplitDistances[3]);
                cmd.SetGlobalVector(MainLightShadowConstantBuffer._CascadeShadowSplitSphereRadii, new Vector4(
                    m_CascadeSplitDistances[0].w * m_CascadeSplitDistances[0].w,
                    m_CascadeSplitDistances[1].w * m_CascadeSplitDistances[1].w,
                    m_CascadeSplitDistances[2].w * m_CascadeSplitDistances[2].w,
                    m_CascadeSplitDistances[3].w * m_CascadeSplitDistances[3].w));
            }

            // Inside shader soft shadows are controlled through global keyword.
            // If any additional light has soft shadows it will force soft shadows on main light too.
            // As it is not trivial finding out which additional light has soft shadows, we will pass main light properties if soft shadows are supported.
            // This workaround will be removed once we will support soft shadows per light.
            if (shadowData.supportsSoftShadows)
            {
                cmd.SetGlobalVector(MainLightShadowConstantBuffer._ShadowOffset0,
                    new Vector4(-invHalfShadowAtlasWidth, -invHalfShadowAtlasHeight,
                        invHalfShadowAtlasWidth, -invHalfShadowAtlasHeight));
                cmd.SetGlobalVector(MainLightShadowConstantBuffer._ShadowOffset1,
                    new Vector4(-invHalfShadowAtlasWidth, invHalfShadowAtlasHeight,
                        invHalfShadowAtlasWidth, invHalfShadowAtlasHeight));

                cmd.SetGlobalVector(MainLightShadowConstantBuffer._ShadowmapSize, new Vector4(invShadowAtlasWidth,
                    invShadowAtlasHeight,
                    renderTargetWidth, renderTargetHeight));
            }
        }

        private class PassData
        {
            internal MainLightShadowCasterPass pass;

            internal TextureHandle shadowmapTexture;
            internal RenderingData renderingData;
            internal int shadowmapID;
            internal bool emptyShadowmap;

            internal RendererListHandle[] shadowRendererListsHandle = new RendererListHandle[k_MaxCascades];
            internal RendererList[] shadowRendererLists = new RendererList[k_MaxCascades];
        }

        private void InitPassData(ref PassData passData, ref RenderingData renderingData)
        {
            passData.pass = this;

            passData.emptyShadowmap = m_CreateEmptyShadowmap;
            passData.shadowmapID = m_MainLightShadowmapID;
            passData.renderingData = renderingData;
        }

        void InitEmptyPassData(ref PassData passData, ref RenderingData renderingData)
        {
            passData.pass = this;

            passData.emptyShadowmap = m_CreateEmptyShadowmap;
            passData.shadowmapID = m_MainLightShadowmapID;
            passData.renderingData = renderingData;
        }

        private void InitRendererLists(ref RenderingData renderingData, ref PassData passData, ScriptableRenderContext context, RenderGraph renderGraph, bool useRenderGraph)
        {
            var cullResults = renderingData.cullResults;
            var lightData = renderingData.lightData;
            var shadowData = renderingData.shadowData;
            int shadowLightIndex = lightData.mainLightIndex;
            if (!m_CreateEmptyShadowmap && shadowLightIndex != -1)
            {
                var settings = new ShadowDrawingSettings(cullResults, shadowLightIndex);
                settings.useRenderingLayerMaskTest = UniversalRenderPipeline.asset.useRenderingLayers;
                for (int cascadeIndex = 0; cascadeIndex < m_ShadowCasterCascadesCount; ++cascadeIndex)
                {
                    if (useRenderGraph)
                        passData.shadowRendererListsHandle[cascadeIndex] = renderGraph.CreateShadowRendererList(ref settings);
                    else
                        passData.shadowRendererLists[cascadeIndex] = context.CreateShadowRendererList(ref settings);
                }
            }
        }

        internal TextureHandle Render(RenderGraph graph, ref RenderingData renderingData)
        {
            TextureHandle shadowTexture;

            using (var builder = graph.AddRasterRenderPass<PassData>("Main Light Shadowmap", out var passData, base.profilingSampler))
            {
                InitPassData(ref passData, ref renderingData);
                InitRendererLists(ref renderingData, ref passData, default(ScriptableRenderContext), graph, true);

                if (!m_CreateEmptyShadowmap)
                {
                    for (int cascadeIndex = 0; cascadeIndex < m_ShadowCasterCascadesCount; ++cascadeIndex)
                    {
                        builder.UseRendererList(passData.shadowRendererListsHandle[cascadeIndex]);
                    }

                    passData.shadowmapTexture = UniversalRenderer.CreateRenderGraphTexture(graph, m_MainLightShadowmapTexture.rt.descriptor, "Main Shadowmap", true, ShadowUtils.m_ForceShadowPointSampling ? FilterMode.Point : FilterMode.Bilinear);
                    builder.UseTextureFragmentDepth(passData.shadowmapTexture, IBaseRenderGraphBuilder.AccessFlags.Write);
                }

                // Need this as shadowmap is only used as Global Texture and not a buffer, so would get culled by RG
                builder.AllowPassCulling(false);
                builder.AllowGlobalStateModification(true);

                builder.SetRenderFunc((PassData data, RasterGraphContext context) =>
                {
                    if (!data.emptyShadowmap)
                        data.pass.RenderMainLightCascadeShadowmap(context.cmd, ref data, ref data.renderingData, true);
                });

                shadowTexture = passData.shadowmapTexture;
            }

            using (var builder = graph.AddRasterRenderPass<PassData>("Set Main Shadow Globals", out var passData, base.profilingSampler))
            {
                InitEmptyPassData(ref passData, ref renderingData);

                passData.shadowmapTexture = shadowTexture;

                if (shadowTexture.IsValid())
                    builder.UseTexture(shadowTexture, IBaseRenderGraphBuilder.AccessFlags.Read);

                builder.AllowPassCulling(false);
                builder.AllowGlobalStateModification(true);

                builder.SetRenderFunc((PassData data, RasterGraphContext context) =>
                {
                    if (data.emptyShadowmap)
                    {
                        data.pass.SetEmptyMainLightCascadeShadowmap(context.cmd);
                        data.shadowmapTexture = context.defaultResources.defaultShadowTexture;
                    }

                    context.cmd.SetGlobalTexture(data.shadowmapID, data.shadowmapTexture);
                });
                return passData.shadowmapTexture;
            }
        }
    };
}