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

namespace AcDream.App.Tests.Rendering.Walk;

public sealed class RetailFrameWalkTests
{
    private sealed class Recorder : IWalkEventSink
    {
        public readonly List<WalkEvent> Events = new();
        public void Emit(in WalkEvent walkEvent) => Events.Add(walkEvent);

        public string Signature()
            => string.Join("|", Events.Select(e => e.Kind switch
            {
                WalkEventKind.Landscape => "LS",
                WalkEventKind.Building => $"BLD:{e.CellId:x8}",
                WalkEventKind.DrawInside => $"DI:{e.CellId:x8}",
                WalkEventKind.DrawCells =>
                    $"DC:ov={e.OutsideViewCount}:{string.Join(',', e.Cells.Select(c => c.ToString("x8")))}",
                _ => "?",
            }));
    }

    private sealed class Caster : IWalkRayCaster
    {
        public Vector3 RayThrough(float screenX, float screenY)
            => new(screenX, screenY, 100f);
    }

    private sealed class TestContext : IWalkFrameContext, IRetailFrameWalkContext
    {
        public readonly Dictionary<uint, WalkCell> Cells = new();
        private readonly Matrix4x4 _viewProj;

        public TestContext()
        {
            Matrix4x4 view = Matrix4x4.CreateLookAt(
                Vector3.Zero, new Vector3(0, 0, -1), Vector3.UnitY);
            Matrix4x4 proj = Matrix4x4.CreatePerspectiveFieldOfView(1.2f, 1f, 0.1f, 1000f);
            _viewProj = view * proj;
        }

        public Vector3 ViewpointIn(WalkCell cell) => Vector3.Zero;
        public Matrix4x4 ObjectToClip(WalkCell cell) => _viewProj;
        public WalkCell? GetVisible(uint cellId) => Cells.GetValueOrDefault(cellId);
        public IWalkRayCaster Rays { get; } = new Caster();
        public Vector3 WorldViewpoint => Vector3.Zero;
        public float ViewportWidth => 640f;
        public float ViewportHeight => 480f;

        public Vector3 ViewpointInBuilding(WalkBuilding building) => Vector3.Zero;
        public float ViewerDistanceTo(WalkBuilding building) => 0f;
        public IWalkFrameContext CellContext => this;
        // Permissive near plane: every column wholly inside.
        public WalkPlane CyPlane => new(new Vector3(0, 0, 1), 0f);
        public void SetActiveView(WalkPortalView views, int index) { }

        public int ClipBuildingPolygon(
            WalkBuilding building, WalkPolygon polygon, int side, Span<WalkScreenPoint> output)
            => 0;   // no BSP-driven look-ins in these composition fixtures
    }

    private static WalkPolygon Quad(float z, bool facingViewer = true) => new()
    {
        Vertices =
        [
            new Vector3(-0.5f, -0.5f, z), new Vector3(0.5f, -0.5f, z),
            new Vector3(0.5f, 0.5f, z), new Vector3(-0.5f, 0.5f, z),
        ],
        Plane = new WalkPlane(new Vector3(0, 0, facingViewer ? 1f : -1f), facingViewer ? -z : z),
    };

    private static WalkLandscape Landscape3x3()
    {
        var landscape = new WalkLandscape
        {
            MidWidth = 3,
            Blocks = new WalkLandBlock?[9],
            ViewerBlockX = 1,
            ViewerBlockY = 1,
            ViewerCellX = 0,
            ViewerCellY = 0,
        };
        for (int i = 0; i < 9; i++)
        {
            landscape.Blocks[i] = new WalkLandBlock { MaxZ = 10f, MinZ = 0f };
            landscape.Blocks[i]!.EnsureCellArrays();
        }
        return landscape;
    }

    [Fact]
    public void Outdoor_frame_emits_landscape_then_buildings_far_to_near()
    {
        var ctx = new TestContext();
        WalkLandscape landscape = Landscape3x3();
        // A building in ring-1 block (0,0), and two in the viewer block:
        // one at the block's far corner, one at the viewer's closest cell.
        var ringBuilding = new WalkBuilding { PositionCellId = 0xAAAA0001 };
        var farBuilding = new WalkBuilding { PositionCellId = 0xBBBB0002 };
        var nearBuilding = new WalkBuilding { PositionCellId = 0xCCCC0003 };
        landscape.Blocks[0]!.CellBuildings[0] = ringBuilding;              // block (0,0)
        WalkLandBlock viewerBlock = landscape.Blocks[1 * 3 + 1]!;
        viewerBlock.CellBuildings[7 * 8 + 7] = farBuilding;                // far corner cell
        viewerBlock.CellBuildings[0] = nearBuilding;                       // the closest cell (viewer at 0,0)
        var walk = new RetailFrameWalk();
        var recorder = new Recorder();

        // ViewCount == 0 exercises the CY-only visibility arm deterministically.
        walk.DrawLandscape(landscape, new WalkPortalView(), ctx, recorder);

        Assert.Equal(
            "LS|BLD:aaaa0001|BLD:bbbb0002|BLD:cccc0003",
            recorder.Signature());
    }

    [Fact]
    public void Degraded_building_still_emits_its_entry_event()
    {
        var ctx = new TestContext();
        var walk = new RetailFrameWalk();
        var recorder = new Recorder();
        var building = new WalkBuilding { PositionCellId = 0xF518002E, HasGeometry = false };

        walk.DrawBuilding(building, new WalkPortalView(), ctx, recorder);

        Assert.Equal("BLD:f518002e", recorder.Signature());
    }

    [Fact]
    public void Interior_frame_without_exit_views_skips_the_landscape()
    {
        var ctx = new TestContext();
        // One facing portal only: the flood stays in the cell, no exit view.
        var cell = new WalkCell
        {
            CellId = 0xA9B40178,
            Portals = [new WalkCellPortal
            {
                OtherCellId = 0xA9B40179, PolygonIndex = 0, PortalSide = 1, OtherPortalId = 0,
            }],
            PortalPolygons = [Quad(-2f)],
        };
        ctx.Cells[cell.CellId] = cell;
        var walk = new RetailFrameWalk();
        var recorder = new Recorder();

        walk.WalkFrame(cell.CellId, cell, Landscape3x3(), ctx, recorder);

        Assert.Equal("DI:a9b40178|DC:ov=0:a9b40178", recorder.Signature());
    }

    [Fact]
    public void Interior_frame_with_an_exit_view_draws_the_landscape_through_it()
    {
        var ctx = new TestContext();
        var cell = new WalkCell
        {
            CellId = 0xA9B40150,
            Portals = [new WalkCellPortal
            {
                OtherCellId = 0xFFFFFFFF, PolygonIndex = 0, PortalSide = 0, OtherPortalId = -1,
            }],
            PortalPolygons = [Quad(-2f)],
        };
        ctx.Cells[cell.CellId] = cell;
        var walk = new RetailFrameWalk();
        var recorder = new Recorder();
        var landscape = new WalkLandscape
        {
            MidWidth = 1,
            Blocks = new WalkLandBlock?[1],
            ViewerBlockX = 0,
            ViewerBlockY = 0,
        };

        walk.WalkFrame(cell.CellId, cell, landscape, ctx, recorder);

        Assert.Equal("DI:a9b40150|DC:ov=1:a9b40150|LS", recorder.Signature());
    }

    [Fact]
    public void Outdoor_camera_cell_roots_the_landscape_walk()
    {
        var ctx = new TestContext();
        var walk = new RetailFrameWalk();
        var recorder = new Recorder();

        // Low word < 0x100 = an outdoor landcell id.
        walk.WalkFrame(0xA9B40015, null, Landscape3x3(), ctx, recorder);

        Assert.StartsWith("LS", recorder.Signature());
    }

    [Fact]
    public void View_state_unwinds_completely_after_an_interior_frame()
    {
        var ctx = new TestContext();
        var stabCell = new WalkCell { CellId = 0xA9B40151 };
        var cell = new WalkCell
        {
            CellId = 0xA9B40150,
            StabList = [0xA9B40151u],
            Portals = [new WalkCellPortal
            {
                OtherCellId = 0xA9B40151, PolygonIndex = 0, PortalSide = 0, OtherPortalId = 0,
            }],
            PortalPolygons = [Quad(-2f)],
        };
        stabCell.Portals = [new WalkCellPortal
        {
            OtherCellId = 0xA9B40150, PolygonIndex = 0, PortalSide = 1, OtherPortalId = 0,
        }];
        stabCell.PortalPolygons = [Quad(-2f)];
        ctx.Cells[cell.CellId] = cell;
        ctx.Cells[stabCell.CellId] = stabCell;
        var walk = new RetailFrameWalk();

        walk.WalkFrame(cell.CellId, cell, Landscape3x3(), ctx, new Recorder());

        Assert.Equal(0, cell.NumView);
        Assert.Equal(0, stabCell.NumView);
    }
}