using System;
using System.Collections.Generic;
using System.Numerics;
using AcDream.Core.Physics;
using Xunit;

namespace AcDream.Core.Tests.Physics;

public class CellSurfaceTests
{
    /// <summary>
    /// Build a minimal CellSurface representing a flat square floor
    /// centered at (originX, originY) with the given half-size and Z.
    /// The floor polygon is a quad: 4 vertices at the corners.
    /// </summary>
    private static CellSurface MakeFlatFloor(
        uint cellId, float originX, float originY, float z,
        float halfSize = 10f)
    {
        // 4 vertices forming a square floor at the given Z, in WORLD space.
        var vertices = new Dictionary<ushort, Vector3>
        {
            [0] = new(originX - halfSize, originY - halfSize, z),
            [1] = new(originX + halfSize, originY - halfSize, z),
            [2] = new(originX + halfSize, originY + halfSize, z),
            [3] = new(originX - halfSize, originY + halfSize, z),
        };

        // One quad polygon with 4 vertex IDs.
        var polygonVertexIds = new List<List<short>>
        {
            new() { 0, 1, 2, 3 },
        };

        return new CellSurface(cellId, vertices, polygonVertexIds);
    }

    [Fact]
    public void SampleFloorZ_InsideFlat_ReturnsZ()
    {
        var surface = MakeFlatFloor(0x0100, originX: 50f, originY: 50f, z: 10f);

        float? z = surface.SampleFloorZ(50f, 50f);

        Assert.NotNull(z);
        Assert.Equal(10f, z!.Value, precision: 2);
    }

    [Fact]
    public void SampleFloorZ_OutsideFloor_ReturnsNull()
    {
        var surface = MakeFlatFloor(0x0100, originX: 50f, originY: 50f, z: 10f, halfSize: 5f);

        float? z = surface.SampleFloorZ(100f, 100f);

        Assert.Null(z);
    }

    [Fact]
    public void SampleFloorZ_AtEdge_ReturnsZ()
    {
        var surface = MakeFlatFloor(0x0100, originX: 50f, originY: 50f, z: 10f, halfSize: 10f);

        // Right at the edge of the polygon.
        float? z = surface.SampleFloorZ(60f, 50f);

        Assert.NotNull(z);
        Assert.Equal(10f, z!.Value, precision: 2);
    }

    [Fact]
    public void SampleFloorZ_SlopedFloor_InterpolatesZ()
    {
        // A triangular floor that slopes from Z=0 to Z=20.
        var vertices = new Dictionary<ushort, Vector3>
        {
            [0] = new(0f, 0f, 0f),
            [1] = new(20f, 0f, 0f),
            [2] = new(10f, 20f, 20f),
        };
        var polygons = new List<List<short>> { new() { 0, 1, 2 } };
        var surface = new CellSurface(0x0100, vertices, polygons);

        // At the centroid (10, 6.67): Z should be roughly 6.67
        float? z = surface.SampleFloorZ(10f, 6.67f);

        Assert.NotNull(z);
        Assert.InRange(z!.Value, 5f, 8f);  // approximate
    }
}