using System;
using System.Collections.Generic;
using UnityEditor.Build;
using UnityEditor.Rendering;
using UnityEngine;
using UnityEngine.Rendering;
using UnityEngine.Experimental.Rendering.HDPipeline;

namespace UnityEditor.Experimental.Rendering.HDPipeline
{
    public class LitShaderPreprocessor : BaseShaderPreprocessor
    {
        protected ShaderKeyword m_WriteNormalBuffer;

        public LitShaderPreprocessor()
        {
            m_WriteNormalBuffer = new ShaderKeyword("WRITE_NORMAL_BUFFER");
        }

        bool LitShaderStripper(HDRenderPipelineAsset hdrpAsset, Shader shader, ShaderSnippetData snippet, ShaderCompilerData inputData)
        {
            if (CommonShaderStripper(hdrpAsset, shader, snippet, inputData))
                return true;

            bool isGBufferPass = snippet.passName == "GBuffer";
            bool isForwardPass = snippet.passName == "Forward";
            bool isDepthOnlyPass = snippet.passName == "DepthOnly";
            bool isTransparentForwardPass = snippet.passName == "TransparentDepthPostpass" || snippet.passName == "TransparentBackface" || snippet.passName == "TransparentDepthPrepass";

            // When using forward only, we never need GBuffer pass (only Forward)
            if (hdrpAsset.renderPipelineSettings.supportOnlyForward && isGBufferPass)
                return true;

            if (inputData.shaderKeywordSet.IsEnabled(m_Transparent))
            {
                // If transparent, we never need GBuffer pass.
                if (isGBufferPass)
                    return true;
            }
            else // Opaque
            {
                // If opaque, we never need transparent specific passes (even in forward only mode)
                if (isTransparentForwardPass)
                    return true;

                // When we are in deferred (i.e !hdrpAsset.renderPipelineSettings.supportOnlyForward), we only support tile lighting
                if (!hdrpAsset.renderPipelineSettings.supportOnlyForward && inputData.shaderKeywordSet.IsEnabled(m_ClusterLighting))
                    return true;

                if (isDepthOnlyPass)
                {
                    // When we are full forward, we don't have depth prepass without writeNormalBuffer
                    if (hdrpAsset.renderPipelineSettings.supportOnlyForward && !inputData.shaderKeywordSet.IsEnabled(m_WriteNormalBuffer))
                        return true;
                }

                if (!hdrpAsset.renderPipelineSettings.supportOnlyForward)
                {
                    // If opaque and not forward only, then we only need the forward debug pass.
                    if (isForwardPass && !inputData.shaderKeywordSet.IsEnabled(m_DebugDisplay))
                        return true;
                }
            }

            // TODO: Tests for later
            // We need to find a way to strip useless shader features for passes/shader stages that don't need them (example, vertex shaders won't ever need SSS Feature flag)
            // This causes several problems:
            // - Runtime code that "finds" shader variants based on feature flags might not find them anymore... thus fall backing to the "let's give a score to variant" code path that may find the wrong variant.
            // - Another issue is that if a feature is declared without a "_" fall-back, if we strip the other variants, none may be left to use! This needs to be changed on our side.
            //if (snippet.shaderType == ShaderType.Vertex && inputData.shaderKeywordSet.IsEnabled(m_FeatureSSS))
            //    return true;

            return false;
        }

        public override void AddStripperFuncs(Dictionary<string, VariantStrippingFunc> stripperFuncs)
        {
            // Add name of the shader and corresponding delegate to call to strip variant
            stripperFuncs.Add("HDRenderPipeline/Lit", LitShaderStripper);
            stripperFuncs.Add("HDRenderPipeline/LitTessellation", LitShaderStripper);
            stripperFuncs.Add("HDRenderPipeline/LayeredLit", LitShaderStripper);
            stripperFuncs.Add("HDRenderPipeline/LayeredLitTessellation", LitShaderStripper);
        }
    }
}