using System.Numerics;
using AcDream.App.Rendering;

namespace AcDream.App.Tests.Rendering;

public sealed class TerrainParticleCellVisibilityTests
{
    [Fact]
    public void CollectVisibleCells_PublishesLandscapeCellsWithoutEntitySurvivors()
    {
        var cells = new HashSet<uint>();

        TerrainModernRenderer.CollectVisibleCells(
            cells,
            0xA9B4FFFFu,
            Vector3.Zero,
            zMin: 0f,
            zMax: 20f,
            frustum: null,
            Matrix4x4.Identity,
            ReadOnlySpan<Vector4>.Empty);

        Assert.Equal(64, cells.Count);
        Assert.Contains(0xA9B40001u, cells);
        Assert.Contains(0xA9B40040u, cells);
    }

    [Fact]
    public void CollectVisibleCells_ForceDrawnParentStillUsesCellFrustum()
    {
        var cells = new HashSet<uint>();
        FrustumPlanes frustum = FrustumPlanes.FromViewProjection(Matrix4x4.Identity);

        // The parent landblock may have entered TerrainModernRenderer's draw
        // list through neverCullLandblockId. The cell collector deliberately
        // receives no such bypass and still rejects its off-frustum cells.
        TerrainModernRenderer.CollectVisibleCells(
            cells,
            0xA9B4FFFFu,
            new Vector3(100f, 100f, 100f),
            zMin: 100f,
            zMax: 120f,
            frustum,
            Matrix4x4.Identity,
            ReadOnlySpan<Vector4>.Empty);

        Assert.Empty(cells);
    }

    [Fact]
    public void CollectVisibleCells_RejectsCellsOutsideDoorwayClipPlanes()
    {
        var cells = new HashSet<uint>();
        var planes = new[] { new Vector4(-1f, 0f, 0f, -2f) };

        TerrainModernRenderer.CollectVisibleCells(
            cells,
            0xA9B4FFFFu,
            Vector3.Zero,
            zMin: 0f,
            zMax: 20f,
            frustum: null,
            Matrix4x4.Identity,
            planes);

        Assert.Empty(cells);
    }

    [Fact]
    public void CollectVisibleCells_RejectsCellsOutsideDoorwayScissorAabb()
    {
        var cells = new HashSet<uint>();

        TerrainModernRenderer.CollectVisibleCells(
            cells,
            0xA9B4FFFFu,
            Vector3.Zero,
            zMin: 0f,
            zMax: 20f,
            frustum: null,
            Matrix4x4.Identity,
            ReadOnlySpan<Vector4>.Empty,
            ndcClipAabb: new Vector4(-4f, -4f, -2f, -2f));

        Assert.Empty(cells);
    }

    [Fact]
    public void CollectVisibleCells_UnionsCellsFromEveryLandscapeSlice()
    {
        var cells = new HashSet<uint>();

        TerrainModernRenderer.CollectVisibleCells(
            cells,
            0xA9B4FFFFu,
            Vector3.Zero,
            zMin: 0f,
            zMax: 20f,
            frustum: null,
            Matrix4x4.Identity,
            ReadOnlySpan<Vector4>.Empty,
            ndcClipAabb: new Vector4(1f, -1_000f, 23f, 1_000f));
        TerrainModernRenderer.CollectVisibleCells(
            cells,
            0xA9B4FFFFu,
            Vector3.Zero,
            zMin: 0f,
            zMax: 20f,
            frustum: null,
            Matrix4x4.Identity,
            ReadOnlySpan<Vector4>.Empty,
            ndcClipAabb: new Vector4(49f, -1_000f, 71f, 1_000f));

        Assert.Equal(16, cells.Count);
        Assert.Contains(0xA9B40001u, cells);
        Assert.Contains(0xA9B40011u, cells);
        Assert.DoesNotContain(0xA9B40009u, cells);
    }
}