using System.Numerics;
using AcDream.Core.Terrain;
using DatReaderWriter.DBObjs;
using DatReaderWriter.Types;

namespace AcDream.Core.Tests.Terrain;

public class LandblockMeshTests
{
    /// <summary>
    /// Synthetic height table with a * 2.0f scale (mirrors Phase 1's ramp so
    /// existing test intuition carries through the Phase 3c rewrite).
    /// </summary>
    private static readonly float[] IdentityHeightTable =
        Enumerable.Range(0, 256).Select(i => i * 2f).ToArray();

    private static TerrainBlendingContext MakeContext() => new(
        TerrainTypeToLayer: new Dictionary<uint, byte> { [0u] = 0 },
        RoadLayer: SurfaceInfo.None,
        CornerAlphaLayers: Array.Empty<byte>(),
        SideAlphaLayers:   Array.Empty<byte>(),
        RoadAlphaLayers:   Array.Empty<byte>(),
        CornerAlphaTCodes: Array.Empty<uint>(),
        SideAlphaTCodes:   Array.Empty<uint>(),
        RoadAlphaRCodes:   Array.Empty<uint>());

    private static LandBlock BuildFlatLandBlock(byte heightIndex = 0)
    {
        var block = new LandBlock
        {
            HasObjects = false,
            Terrain = new TerrainInfo[81],
            Height = new byte[81],
        };
        for (int i = 0; i < 81; i++)
        {
            block.Terrain[i] = (ushort)0;
            block.Height[i] = heightIndex;
        }
        return block;
    }

    [Fact]
    public void Build_FlatBlock_Produces384VerticesAnd128Triangles()
    {
        var block = BuildFlatLandBlock();
        var cache = new Dictionary<uint, SurfaceInfo>();

        var mesh = LandblockMesh.Build(block, 0, 0, IdentityHeightTable, MakeContext(), cache);

        // 64 cells × 6 vertices per cell = 384
        Assert.Equal(384, mesh.Vertices.Length);
        // Each cell emits 2 triangles = 6 indices, 64 cells → 384 indices (= 128 triangles)
        Assert.Equal(128 * 3, mesh.Indices.Length);
    }

    [Fact]
    public void Build_Vertices_CoverExactly192x192WorldUnits()
    {
        var block = BuildFlatLandBlock();
        var cache = new Dictionary<uint, SurfaceInfo>();

        var mesh = LandblockMesh.Build(block, 0, 0, IdentityHeightTable, MakeContext(), cache);

        var minX = mesh.Vertices.Min(v => v.Position.X);
        var maxX = mesh.Vertices.Max(v => v.Position.X);
        var minY = mesh.Vertices.Min(v => v.Position.Y);
        var maxY = mesh.Vertices.Max(v => v.Position.Y);
        Assert.Equal(0.0f, minX);
        Assert.Equal(192.0f, maxX);
        Assert.Equal(0.0f, minY);
        Assert.Equal(192.0f, maxY);
    }

    [Fact]
    public void Build_FlatBlock_AllVerticesSameZ()
    {
        var block = BuildFlatLandBlock(heightIndex: 10);
        var cache = new Dictionary<uint, SurfaceInfo>();

        var mesh = LandblockMesh.Build(block, 0, 0, IdentityHeightTable, MakeContext(), cache);

        var zs = mesh.Vertices.Select(v => v.Position.Z).Distinct().ToArray();
        Assert.Single(zs);
        Assert.Equal(20.0f, zs[0]);  // heightIndex 10 × IdentityHeightTable[10] = 20
    }

    [Fact]
    public void Build_FlatBlock_NormalsPointStraightUp()
    {
        var block = BuildFlatLandBlock();
        var cache = new Dictionary<uint, SurfaceInfo>();

        var mesh = LandblockMesh.Build(block, 0, 0, IdentityHeightTable, MakeContext(), cache);

        foreach (var v in mesh.Vertices)
        {
            Assert.Equal(new Vector3(0, 0, 1), v.Normal);
        }
    }

    [Fact]
    public void Build_AllVerticesOfACellShareIdenticalData()
    {
        var block = BuildFlatLandBlock();
        var cache = new Dictionary<uint, SurfaceInfo>();

        var mesh = LandblockMesh.Build(block, 0, 0, IdentityHeightTable, MakeContext(), cache);

        // Vertices are emitted in strides of 6 per cell. Within each stride,
        // Data0..3 must be identical — the vertex shader relies on that when
        // it propagates the cell's blend recipe to all 3 fragment-shader outputs.
        for (int cellIdx = 0; cellIdx < 64; cellIdx++)
        {
            int baseIdx = cellIdx * 6;
            var d0 = mesh.Vertices[baseIdx].Data0;
            var d1 = mesh.Vertices[baseIdx].Data1;
            var d2 = mesh.Vertices[baseIdx].Data2;
            var d3 = mesh.Vertices[baseIdx].Data3;
            for (int i = 1; i < 6; i++)
            {
                Assert.Equal(d0, mesh.Vertices[baseIdx + i].Data0);
                Assert.Equal(d1, mesh.Vertices[baseIdx + i].Data1);
                Assert.Equal(d2, mesh.Vertices[baseIdx + i].Data2);
                Assert.Equal(d3, mesh.Vertices[baseIdx + i].Data3);
            }
        }
    }

    [Fact]
    public void Build_SurfaceCacheIsReusedAcrossIdenticalCells()
    {
        var block = BuildFlatLandBlock();  // every cell has identical all-zero corners
        var cache = new Dictionary<uint, SurfaceInfo>();

        LandblockMesh.Build(block, 0, 0, IdentityHeightTable, MakeContext(), cache);

        // A uniform flat landblock produces exactly ONE palette code (all
        // corners are type 0, no roads) → BuildSurface called once, cache
        // contains a single entry even though 64 cells were processed.
        Assert.Single(cache);
    }

    [Fact]
    public void Build_CellsWithDistinctTerrainTypes_ProducesDistinctPaletteCodes()
    {
        // Put a dirt cell (type 4) at the center of an otherwise grass landblock.
        // Grass cells all share one palCode; the "dirt + grass border" cells
        // around the center introduce additional palette codes.
        var block = BuildFlatLandBlock();
        // Type is at bits 2-6, so type=4 → ushort = (4 << 2) = 0x10.
        block.Terrain[4 * 9 + 4] = (ushort)(4 << 2);

        var ctx = new TerrainBlendingContext(
            TerrainTypeToLayer: new Dictionary<uint, byte> { [0u] = 0, [4u] = 1 },
            RoadLayer: SurfaceInfo.None,
            CornerAlphaLayers: new byte[] { 0, 1, 2, 3 },
            SideAlphaLayers:   Array.Empty<byte>(),
            RoadAlphaLayers:   Array.Empty<byte>(),
            CornerAlphaTCodes: new uint[] { 1, 2, 4, 8 },
            SideAlphaTCodes:   Array.Empty<uint>(),
            RoadAlphaRCodes:   Array.Empty<uint>());
        var cache = new Dictionary<uint, SurfaceInfo>();

        LandblockMesh.Build(block, 0, 0, IdentityHeightTable, ctx, cache);

        // Should have more than one palette code now — uniform-grass cells
        // plus at least one boundary cell with a non-zero corner type.
        Assert.True(cache.Count >= 2, $"Expected mix of palette codes, got {cache.Count}");
    }

    [Fact]
    public void Build_HeightmapPackedAsXMajor_NotYMajor()
    {
        // Regression from the Phase 1 → 2a transpose bug. The underlying
        // heightmap is indexed x*9+y; testing this lives on even after the
        // per-cell refactor because the corner lookup in the cell loop still
        // reads block.Height[cx*9+cy] for the BL corner.
        var block = BuildFlatLandBlock();
        block.Height[2 * 9 + 0] = 5;  // x=2, y=0 → world (48, 0), Z should be 10

        var cache = new Dictionary<uint, SurfaceInfo>();
        var mesh = LandblockMesh.Build(block, 0, 0, IdentityHeightTable, MakeContext(), cache);

        // Search the vertex buffer for a vertex at world position (48, 0).
        var atX48Y0 = mesh.Vertices.FirstOrDefault(v =>
            Math.Abs(v.Position.X - 48f) < 0.01f && Math.Abs(v.Position.Y) < 0.01f);
        var atX0Y48 = mesh.Vertices.FirstOrDefault(v =>
            Math.Abs(v.Position.X) < 0.01f && Math.Abs(v.Position.Y - 48f) < 0.01f);

        Assert.Equal(10.0f, atX48Y0.Position.Z);
        Assert.Equal(0.0f, atX0Y48.Position.Z);
    }
}