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

namespace AcDream.App.Tests.Rendering;

// Regression tests for the indoor-render HANG (2026-06-06): the portal-visibility flood
// re-queues a cell whenever its CellView grows, so it only terminates when CellView.Add's
// dedup catches a duplicate. Across BFS rounds the same region comes back float-drifted,
// vertex-rotated, or with a ±1 vertex count; the old exact index-by-index SamePolygon
// (eps 1e-4) missed all three, so the region grew forever -> CPU-spin hang in CellView.Add.
// A drift-tolerant, rotation-invariant dedup makes the key space finite, so the flood
// converges (and these duplicates collapse).
public class CellViewDedupTests
{
    private static ViewPolygon Quad(float ox, float oy) => new(new[]
    {
        new Vector2(ox - 0.5f, oy - 0.5f), new Vector2(ox + 0.5f, oy - 0.5f),
        new Vector2(ox + 0.5f, oy + 0.5f), new Vector2(ox - 0.5f, oy + 0.5f),
    });

    [Fact]
    public void Add_DropsSubGridDriftDuplicate()
    {
        var v = new CellView();
        Assert.True(v.Add(Quad(0f, 0f)));
        // Same quad, every vertex nudged 3e-4 — beyond the old 1e-4 SamePolygon eps,
        // within the 1e-3 dedup grid. This is the per-round float drift that caused the hang.
        var drifted = new ViewPolygon(new[]
        {
            new Vector2(-0.5f + 3e-4f, -0.5f - 3e-4f), new Vector2(0.5f + 3e-4f, -0.5f - 3e-4f),
            new Vector2(0.5f + 3e-4f, 0.5f - 3e-4f), new Vector2(-0.5f + 3e-4f, 0.5f - 3e-4f),
        });
        Assert.False(v.Add(drifted));
        Assert.Single(v.Polygons);
    }

    [Fact]
    public void Add_DropsRotatedStartDuplicate()
    {
        var v = new CellView();
        Assert.True(v.Add(Quad(0f, 0f)));
        // Same 4 corners (same CCW cycle), but emitted starting at the 2nd vertex — what
        // Sutherland-Hodgman can do when the subject order differs across rounds.
        var rotated = new ViewPolygon(new[]
        {
            new Vector2(0.5f, -0.5f), new Vector2(0.5f, 0.5f),
            new Vector2(-0.5f, 0.5f), new Vector2(-0.5f, -0.5f),
        });
        Assert.False(v.Add(rotated));
        Assert.Single(v.Polygons);
    }

    [Fact]
    public void Add_KeepsGenuinelyDistinctPolygons()
    {
        // The fix must NOT over-merge: two regions 0.4 NDC apart (far beyond the 1e-3 grid)
        // remain distinct, so a real second portal opening is not silently dropped.
        var v = new CellView();
        Assert.True(v.Add(Quad(0f, 0f)));
        Assert.True(v.Add(Quad(0.4f, 0f)));
        Assert.Equal(2, v.Polygons.Count);
    }

    [Fact]
    public void Add_RepeatedDuplicate_DoesNotAllocatePerProbe()
    {
        var view = new CellView();
        ViewPolygon polygon = Quad(0f, 0f);
        Assert.True(view.Add(polygon));

        // Warm the method/JIT before measuring. Duplicate portal emissions are the hot path.
        Assert.False(view.Add(polygon));
        long before = GC.GetAllocatedBytesForCurrentThread();
        for (int i = 0; i < 1_000; i++)
            Assert.False(view.Add(polygon));
        long allocated = GC.GetAllocatedBytesForCurrentThread() - before;

        Assert.True(allocated <= 256, $"duplicate probes allocated {allocated:N0} bytes");
    }

    [Fact]
    public void ResetAndRebuild_ReusesCanonicalKeyStorage()
    {
        var view = new CellView();
        ViewPolygon polygon = Quad(0f, 0f);

        // Warm the retained polygon list, hash table, collision link, and
        // coordinate payload before measuring frame-to-frame rebuilds.
        Assert.True(view.Add(polygon));
        view.Reset();
        Assert.True(view.Add(polygon));

        long before = GC.GetAllocatedBytesForCurrentThread();
        for (int i = 0; i < 1_000; i++)
        {
            view.Reset();
            Assert.True(view.Add(polygon));
        }
        long allocated = GC.GetAllocatedBytesForCurrentThread() - before;

        Assert.True(allocated <= 256, $"steady rebuilds allocated {allocated:N0} bytes");
    }
}