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

namespace AcDream.App.Tests.Rendering.Walk;

/// <summary>Campaign FW3.1 — hermetic (no DAT) coverage of the production
/// landscape assembler: publish/retire lifecycle, the LOD ring pyramid, and
/// the viewer-recentre grid reflow. The DAT-backed equivalence to the FW1
/// test builder is proven by <c>WalkProductionWorldConformanceTests</c>
/// (Lane=InstalledDat); this class covers the incremental publish/retire
/// machinery that harness doesn't exercise (it publishes and calls
/// SetViewer exactly once per fixture).</summary>
public sealed class WalkLandscapeAssemblerTests
{
    private const uint LandblockId = 0xA9B4FFFFu;      // block (0xA9, 0xB4)
    private const uint CameraCellId = 0xA9B40001u;     // same block, outdoor landcell 1

    private static int GridIndex(int gx, int gy) => gx * WalkLandscapeAssembler.GridWidth + gy;

    private static int CenterIndex() =>
        GridIndex(WalkLandscapeAssembler.MidRadius, WalkLandscapeAssembler.MidRadius);

    [Fact]
    public void PublishBeforeSetViewer_IsVisibleOnceSetViewerRuns()
    {
        var assembler = new WalkLandscapeAssembler();

        assembler.PublishLandblock(LandblockId, maxZ: 100f, minZ: -5f, Array.Empty<WalkBuildingFactory.Entry>());
        assembler.SetViewer(CameraCellId, Vector3.Zero);

        WalkLandBlock? block = assembler.Landscape.Blocks[CenterIndex()];
        Assert.NotNull(block);
        Assert.Equal(8, block!.SideCellCount);
        Assert.Equal(100f, block.MaxZ);
        Assert.Equal(-5f, block.MinZ);
    }

    [Fact]
    public void PublishAfterSetViewer_RefreshesTheAlreadyWindowedSlotImmediately()
    {
        var assembler = new WalkLandscapeAssembler();
        assembler.SetViewer(CameraCellId, Vector3.Zero);

        assembler.PublishLandblock(LandblockId, maxZ: 42f, minZ: 3f, Array.Empty<WalkBuildingFactory.Entry>());

        Assert.Equal(42f, assembler.Landscape.Blocks[CenterIndex()]!.MaxZ);
    }

    [Fact]
    public void RingPyramid_FarBlockDegradesSideCellCountAndNeverAttachesBuildings()
    {
        var assembler = new WalkLandscapeAssembler();
        var building = new WalkBuildingFactory.Entry(
            new WalkBuilding { PositionCellId = (LandblockId & 0xFFFF0000u) | 1u },
            Matrix4x4.Identity, Matrix4x4.Identity);
        assembler.PublishLandblock(LandblockId, 1f, 0f, new[] { building });

        // Three blocks north of the camera's own block -> ring 3 -> SideCellCount 2.
        const uint FarLandblockId = 0xA9B7FFFFu;
        assembler.PublishLandblock(FarLandblockId, 1f, 0f, new[] { building });
        assembler.SetViewer(CameraCellId, Vector3.Zero);

        WalkLandBlock center = assembler.Landscape.Blocks[CenterIndex()]!;
        WalkLandBlock far = assembler.Landscape.Blocks[
            GridIndex(WalkLandscapeAssembler.MidRadius, WalkLandscapeAssembler.MidRadius + 3)]!;
        Assert.Equal(8, center.SideCellCount);
        Assert.Contains(center.CellBuildings, b => b is not null);
        Assert.Equal(2, far.SideCellCount);
        Assert.All(far.CellBuildings, Assert.Null);
    }

    [Fact]
    public void RetireLandblock_NullsTheWindowedSlot()
    {
        var assembler = new WalkLandscapeAssembler();
        assembler.PublishLandblock(LandblockId, 1f, 0f, Array.Empty<WalkBuildingFactory.Entry>());
        assembler.SetViewer(CameraCellId, Vector3.Zero);
        Assert.NotNull(assembler.Landscape.Blocks[CenterIndex()]);

        assembler.RetireLandblock(LandblockId);

        Assert.Null(assembler.Landscape.Blocks[CenterIndex()]);
    }

    [Fact]
    public void RetireLandblock_UnpublishedLandblockIsANoOp()
    {
        var assembler = new WalkLandscapeAssembler();

        assembler.RetireLandblock(LandblockId);

        Assert.Null(assembler.Landscape.Blocks[CenterIndex()]);
    }

    [Fact]
    public void SetViewer_RecentresTheWindowWhenTheCameraCrossesIntoAnotherBlock()
    {
        var assembler = new WalkLandscapeAssembler();
        assembler.PublishLandblock(LandblockId, 7f, -1f, Array.Empty<WalkBuildingFactory.Entry>());
        assembler.SetViewer(CameraCellId, Vector3.Zero);
        Assert.NotNull(assembler.Landscape.Blocks[CenterIndex()]);

        // Move the camera one block east; the published landblock should now
        // sit one grid slot WEST of center instead of at center.
        assembler.SetViewer(0xAAB40001u, Vector3.Zero);

        Assert.Null(assembler.Landscape.Blocks[CenterIndex()]);
        WalkLandBlock? shifted = assembler.Landscape.Blocks[
            GridIndex(WalkLandscapeAssembler.MidRadius - 1, WalkLandscapeAssembler.MidRadius)];
        Assert.NotNull(shifted);
        Assert.Equal(7f, shifted!.MaxZ);
    }

    [Fact]
    public void SetViewer_LandcellIndexDerivesViewerCellFromLowWord()
    {
        var assembler = new WalkLandscapeAssembler();

        // Low word 10 -> landcell index 9 -> (9/8, 9%8) = (1, 1).
        assembler.SetViewer(0xA9B4000Au, Vector3.Zero);

        Assert.Equal(1, assembler.Landscape.ViewerCellX);
        Assert.Equal(1, assembler.Landscape.ViewerCellY);
    }

    [Fact]
    public void SetViewer_InteriorCameraDerivesViewerCellFromOrigin()
    {
        var assembler = new WalkLandscapeAssembler();

        assembler.SetViewer(0xA9B40105u, new Vector3(50f, 74f, 0f));

        Assert.Equal(2, assembler.Landscape.ViewerCellX);   // floor(50 / 24) = 2
        Assert.Equal(3, assembler.Landscape.ViewerCellY);   // floor(74 / 24) = 3
    }

    [Fact]
    public void SetViewer_SameBlockRepeatCallDoesNotClearAlreadyPublishedSlots()
    {
        var assembler = new WalkLandscapeAssembler();
        assembler.PublishLandblock(LandblockId, 1f, 0f, Array.Empty<WalkBuildingFactory.Entry>());
        assembler.SetViewer(CameraCellId, Vector3.Zero);

        assembler.SetViewer(CameraCellId, new Vector3(5f, 5f, 0f));

        Assert.NotNull(assembler.Landscape.Blocks[CenterIndex()]);
    }
}