using AcDream.Core.Terrain;
using Xunit;

namespace AcDream.Core.Tests.Terrain;

public class TerrainBlendingTests
{
    // Asheron's Call terrain texture type values (from TerrainTextureType enum)
    private const int Grass = 1;
    private const int Dirt = 4;

    [Fact]
    public void GetPalCode_AllGrassNoRoads_ProducesHandComputedValue()
    {
        // sizeBits   = 1 << 28       = 0x10000000
        // terrainBits= (1<<15)|(1<<10)|(1<<5)|1 = 0x8421  (t1..t4 = Grass=1)
        // roadBits   = 0
        // total      = 0x10008421
        uint actual = TerrainBlending.GetPalCode(0, 0, 0, 0, Grass, Grass, Grass, Grass);
        Assert.Equal(0x10008421u, actual);
    }

    [Fact]
    public void GetPalCode_AllZeros_ProducesOnlySizeBit()
    {
        uint actual = TerrainBlending.GetPalCode(0, 0, 0, 0, 0, 0, 0, 0);
        Assert.Equal(0x10000000u, actual);
    }

    [Fact]
    public void GetPalCode_IsDeterministic()
    {
        uint a = TerrainBlending.GetPalCode(1, 0, 0, 1, Grass, Dirt, Grass, Dirt);
        uint b = TerrainBlending.GetPalCode(1, 0, 0, 1, Grass, Dirt, Grass, Dirt);
        Assert.Equal(a, b);
    }

    [Fact]
    public void GetPalCode_DifferentTerrainCornersProduceDifferentCodes()
    {
        uint allGrass = TerrainBlending.GetPalCode(0, 0, 0, 0, Grass, Grass, Grass, Grass);
        uint grassDirtMix = TerrainBlending.GetPalCode(0, 0, 0, 0, Grass, Dirt, Grass, Dirt);
        Assert.NotEqual(allGrass, grassDirtMix);
    }

    [Fact]
    public void GetPalCode_RoadFlagAffectsOutput()
    {
        uint noRoad = TerrainBlending.GetPalCode(0, 0, 0, 0, Grass, Grass, Grass, Grass);
        uint withRoad = TerrainBlending.GetPalCode(1, 0, 0, 0, Grass, Grass, Grass, Grass);
        Assert.NotEqual(noRoad, withRoad);
        // r1 occupies bits 26-27, so a road-only delta changes only those bits
        Assert.Equal(1u << 26, noRoad ^ withRoad);
    }

    [Fact]
    public void GetPalCode_SizeBitAlwaysSet()
    {
        uint code = TerrainBlending.GetPalCode(3, 3, 3, 3, Dirt, Dirt, Dirt, Dirt);
        Assert.Equal(1u << 28, code & (1u << 28));
    }

    [Fact]
    public void GetPalCode_TerrainBitsOccupyLowFifteen()
    {
        // With all roads zero, the top 15 bits (above bit 15) should only contain
        // the sizeBits marker. Terrain fields occupy bits 0-19: t1=15..19, t2=10..14,
        // t3=5..9, t4=0..4. With t values up to 31 (5 bits), the terrain region
        // stays within bits 0-19.
        uint code = TerrainBlending.GetPalCode(0, 0, 0, 0, 31, 31, 31, 31);
        // Nothing between bits 20-27 should be set.
        uint forbiddenRegion = code & 0x0FF00000u;
        Assert.Equal(0u, forbiddenRegion);
    }

    [Fact]
    public void CalculateSplitDirection_OriginCell_IsSWtoNE()
    {
        // Hand-computed:
        //   seedA   = 0, seedB = 0
        //   magicA  = 1813693831, magicB = 0
        //   uintRes = 1813693831 - 0 - 1369149221 = 444544610
        //   norm    = 444544610 * (1/2^32) ≈ 0.1035  < 0.5  → SWtoNE
        var actual = TerrainBlending.CalculateSplitDirection(0, 0, 0, 0);
        Assert.Equal(CellSplitDirection.SWtoNE, actual);
    }

    [Fact]
    public void CalculateSplitDirection_IsDeterministic()
    {
        var a = TerrainBlending.CalculateSplitDirection(0xA9, 3, 0xB4, 5);
        var b = TerrainBlending.CalculateSplitDirection(0xA9, 3, 0xB4, 5);
        Assert.Equal(a, b);
    }

    [Fact]
    public void CalculateSplitDirection_DifferentCellsCanDiffer()
    {
        // We can't assert the exact value for every cell without instrumenting
        // WorldBuilder, but across a full landblock's 64 cells the hash is
        // designed to produce a mix of both directions — if we see only one,
        // the hash has collapsed.
        int swCount = 0, seCount = 0;
        for (uint cx = 0; cx < 8; cx++)
        for (uint cy = 0; cy < 8; cy++)
        {
            var dir = TerrainBlending.CalculateSplitDirection(0xA9, cx, 0xB4, cy);
            if (dir == CellSplitDirection.SWtoNE) swCount++; else seCount++;
        }
        Assert.True(swCount > 0, "Expected at least one SWtoNE cell in a landblock");
        Assert.True(seCount > 0, "Expected at least one SEtoNW cell in a landblock");
    }
}