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

namespace AcDream.Core.Tests.Physics;

// #145 — far-town teleport resolver runaway. A teleport to a far town places the
// player at a landblock EDGE; the first physics tick crosses into a neighbour that
// has NOT streamed in yet. Pre-fix, the membership pick derived the block origin from
// the terrain registry, which returns (0,0) for an unstreamed neighbour, so
// AdjustToOutside marched the cell id one landblock per tick (the cascade) until lbY
// hit 0 and the outbound wire synthesized the bogus localY (17410) that ACE rejects.
//
// The fix (Slice 3): the resolve threads the CARRIED cell-relative frame anchor
// (body.Position − body.CellPosition.Frame.Origin) into the pick. That anchor is the
// TRUE landblock world origin — correct even for an unstreamed neighbour — so the pick
// re-derives the SAME (consistent) cell and never marches.
//
// These tests exercise CellTransit.FindCellSet directly with an EMPTY cache (so the
// neighbour landblock is unstreamed → TryGetTerrainOrigin returns false). With
// #145 Slice 3 (CarriedBlockOrigin), the explicit anchor prevents the march. With
// #145 D (2026-06-22, the TryGetTerrainOrigin-bool fix), the no-anchor path ALSO
// preserves the seed — "no frame → preserve verbatim". Both are verified here.
public class TeleportFarTownRunawayTests
{
    private static int LbX(uint cellId) => (int)((cellId >> 24) & 0xFFu);
    private static int LbY(uint cellId) => (int)((cellId >> 16) & 0xFFu);

    [Fact]
    public void SouthEdge_UnstreamedNeighbour_CarriedAnchor_DoesNotMarch()
    {
        // Streaming center is the far town 0xC95B; the player just crossed its south
        // edge (world Y ≈ −0.088) into 0xC95A (origin (0,−192), UNSTREAMED).
        var cache = new PhysicsDataCache();
        var spheres = new[] { new DatReaderWriter.Types.Sphere { Origin = new Vector3(14.8f, -0.088f, 12f), Radius = 0.48f } };
        const uint currentCell = 0xC95A0001u;
        var anchor = new Vector3(0f, -192f, 0f);   // body.Position − CellPosition.Origin

        uint withAnchor = CellTransit.FindCellSet(cache, spheres, 1, currentCell, out _, anchor);
        Assert.Equal(0x5A, LbY(withAnchor));       // stays in 0xC95A — no march

        // #145 D (2026-06-22): no-anchor path also preserves when terrain is unregistered.
        // Pre-D this marched south to 0x59; post-D returns currentCell unchanged.
        uint noAnchor = CellTransit.FindCellSet(cache, spheres, 1, currentCell, out _, null);
        Assert.Equal(currentCell, noAnchor);
    }

    [Fact]
    public void EastEdge_UnstreamedNeighbour_CarriedAnchor_DoesNotMarch()
    {
        // Player crossed the center's east edge (world X ≈ 192.088) into 0xCA5B
        // (origin (+192,0), UNSTREAMED). lbX 0xCA > 0xC9.
        var cache = new PhysicsDataCache();
        var spheres = new[] { new DatReaderWriter.Types.Sphere { Origin = new Vector3(192.088f, 14.8f, 12f), Radius = 0.48f } };
        const uint currentCell = 0xCA5B0001u;
        var anchor = new Vector3(192f, 0f, 0f);

        uint withAnchor = CellTransit.FindCellSet(cache, spheres, 1, currentCell, out _, anchor);
        Assert.Equal(0xCA, LbX(withAnchor));       // stays in 0xCA5B — no march

        // #145 D: no-anchor path also preserves when terrain is unregistered.
        uint noAnchor = CellTransit.FindCellSet(cache, spheres, 1, currentCell, out _, null);
        Assert.Equal(currentCell, noAnchor);
    }
}