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 that mirrors Phase 1's simplified "* 2.0f" scale so
    /// the existing tests continue to describe the same behavior. Real AC uses a
    /// non-linear table from Region.LandDefs.LandHeightTable loaded at runtime.
    /// </summary>
    private static readonly float[] IdentityHeightTable =
        Enumerable.Range(0, 256).Select(i => i * 2f).ToArray();

    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_Produces81VerticesAnd128Triangles()
    {
        var block = BuildFlatLandBlock();

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

        Assert.Equal(81, mesh.Vertices.Length);
        Assert.Equal(128 * 3, mesh.Indices.Length);
    }

    [Fact]
    public void Build_Vertices_Cover192x192WorldUnits()
    {
        var block = BuildFlatLandBlock();

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

        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 mesh = LandblockMesh.Build(block, IdentityHeightTable);

        var zs = mesh.Vertices.Select(v => v.Position.Z).Distinct().ToArray();
        Assert.Single(zs);
    }

    [Fact]
    public void Build_HeightValues_ScaleByTwo()
    {
        var block = BuildFlatLandBlock(heightIndex: 5);

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

        // AC's Land::LandHeightTable scales height byte index by 2.0f for the simple ramp case.
        Assert.Equal(10.0f, mesh.Vertices[0].Position.Z);
    }
}