using System.Collections.Generic;
using System.Linq;
using System.Text.RegularExpressions;
using NUnit.Framework;
using UnityEditor.Rendering.Universal.ShaderGraph;
using UnityEditor.ShaderGraph;

namespace UnityEditor.Rendering.Universal.Tests
{
    [TestFixture]
    class UniversalTerrainLitCodeGenTests
    {
        internal enum VertexContext
        {
            WithPositionBlock,
            Empty,
        }

        // TerrainLit emits the primary shader plus the hidden _AddPass and _BaseMapGen shaders, so
        // assertions have to cover all of them, not just Generator.generatedShader.
        static List<(string name, string code)> GenerateShaders(VertexContext vertexContext, GenerationMode mode)
        {
            var target = new UniversalTarget();
            Assert.IsTrue(target.TrySetActiveSubTarget(typeof(UniversalTerrainLitSubTarget)),
                "TerrainLit subtarget is not registered on UniversalTarget");

            var blocks = vertexContext == VertexContext.WithPositionBlock
                ? new[] { BlockFields.VertexDescription.Position, BlockFields.SurfaceDescription.BaseColor }
                : new[] { BlockFields.SurfaceDescription.BaseColor };

            var graph = new GraphData();
            graph.AddContexts();
            graph.InitializeOutputs(new Target[] { target }, blocks);

            // outputNode stays null for a non-subgraph. A non-null one would make Generator swap in
            // PreviewTarget and drop the terrain subtarget entirely.
            var shaders = new Generator(graph, graph.outputNode, mode, "TerrainLitCodeGen").allGeneratedShaders
                .Select(shader => (shader.shaderName, shader.codeString))
                .ToList();

            Assert.IsNotEmpty(shaders, "TerrainLit generated no shaders");

            // The template preprocessor treats '$' as a command marker even inside a comment, and on a
            // malformed directive it splices a marker into the shader instead of failing. Without this
            // check a broken template would leave the assertions below passing on text that is wrong.
            // Every marker is a comment line carrying a caret under the offending column. Matching the
            // caret rather than the word ERROR also catches Expect(), which reports "^ Expected ')'".
            foreach (var (name, code) in shaders)
                StringAssert.DoesNotMatch(@"(?m)^\s*//\s*\^ ", code, $"template preprocessor error in {name}");

            return shaders;
        }

        // Asserting mere presence would be satisfied by a single pass out of fifteen, so a new terrain
        // pass whose template forgot the include would slip through. Every terrain pass emits exactly one
        // UNIVERSAL_TERRAIN_ENABLED define and should carry exactly one copy of the function.
        static void AssertDefinedInEveryTerrainPass(string function, VertexContext vertexContext, GenerationMode mode)
        {
            foreach (var (name, code) in GenerateTerrainShaders(vertexContext, mode))
            {
                var passes = Regex.Matches(code, @"#define UNIVERSAL_TERRAIN_ENABLED 1").Count;
                var definitions = Regex.Matches(code, Regex.Escape(function) + @"\(").Count;
                Assert.AreEqual(passes, definitions, $"{function} in {name}");
            }
        }

        // Preview generation emits the _AddPass shader with no passes at all, and a shader with no
        // terrain pass has nothing to define. Key off the define the terrain passes themselves add.
        static List<(string name, string code)> GenerateTerrainShaders(VertexContext vertexContext, GenerationMode mode)
        {
            var shaders = GenerateShaders(vertexContext, mode)
                .Where(shader => shader.code.Contains("UNIVERSAL_TERRAIN_ENABLED"))
                .ToList();

            Assert.IsNotEmpty(shaders, "no generated shader turns on the terrain path");
            return shaders;
        }

        // Varyings.hlsl calls TerrainVaryingGeneration outside of any FEATURES_GRAPH_VERTEX guard, so the
        // terrain passes have to emit it even when the graph's Vertex context is empty. That state is one
        // Delete away: TerrainLit's only active vertex block is Position, it is unconnected by default, and
        // removing it does not trigger the auto re-add. Gating the definition on graphVertex breaks every pass.
        [TestCase(VertexContext.WithPositionBlock, GenerationMode.ForReals)]
        [TestCase(VertexContext.Empty, GenerationMode.ForReals)]
        [TestCase(VertexContext.WithPositionBlock, GenerationMode.Preview)]
        [TestCase(VertexContext.Empty, GenerationMode.Preview)]
        public void TerrainShadersDefineTerrainVaryingGeneration(VertexContext vertexContext, GenerationMode mode)
        {
            AssertDefinedInEveryTerrainPass("TerrainVaryingGeneration", vertexContext, mode);
        }

        // Same for ConstructTerrainTangent, which the forward and gbuffer passes call under
        // ENABLE_TERRAIN_PERPIXEL_NORMAL.
        [TestCase(VertexContext.WithPositionBlock, GenerationMode.ForReals)]
        [TestCase(VertexContext.Empty, GenerationMode.ForReals)]
        [TestCase(VertexContext.WithPositionBlock, GenerationMode.Preview)]
        [TestCase(VertexContext.Empty, GenerationMode.Preview)]
        public void TerrainShadersDefineConstructTerrainTangent(VertexContext vertexContext, GenerationMode mode)
        {
            AssertDefinedInEveryTerrainPass("ConstructTerrainTangent", vertexContext, mode);
        }
    }
}