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

namespace AcDream.App.Tests.Rendering;

/// <summary>
/// R-A2 conformance: the per-building flood (<see cref="PortalVisibilityBuilder.ConstructViewBuilding"/>)
/// is the robustness mechanism for the doorway flap. These are SOUNDNESS gates against the measured
/// retail values (handoff 2026-06-08 OPTION-A §3.4): a per-building flood touches ≈2 cells and its
/// membership is stable under the eye's ~36 µm rest jitter. They prove the per-building path is built
/// correctly and does not regress; the live doorway is the visual acceptance test for "the flap is
/// gone" (a synthetic fixture cannot reproduce the cottage's exact knife-edge geometry).
/// </summary>
public class PortalVisibilityRobustnessTests
{
    private static Matrix4x4 ViewProj()
    {
        var view = Matrix4x4.CreateLookAt(Vector3.Zero, new Vector3(0, 0, -1), Vector3.UnitY);
        var proj = Matrix4x4.CreatePerspectiveFieldOfView(1.2f, 1.0f, 0.1f, 1000f);
        return view * proj;
    }

    private static Vector3[] Quad(float cx, float cy, float halfW, float halfH, float z) => new[]
    {
        new Vector3(cx - halfW, cy - halfH, z), new Vector3(cx + halfW, cy - halfH, z),
        new Vector3(cx + halfW, cy + halfH, z), new Vector3(cx - halfW, cy + halfH, z),
    };

    private static LoadedCell Cell(uint id, params CellPortalInfo[] portals) => new LoadedCell
    {
        CellId = id, WorldTransform = Matrix4x4.Identity, InverseWorldTransform = Matrix4x4.Identity,
        Portals = new List<CellPortalInfo>(portals),
    };

    // A realistic 2-cell building viewed from OUTSIDE: a vestibule (0x0170) with an entrance portal to
    // the outdoors plus an interior portal to a back room (0x0171). The entrance clip plane puts the
    // origin eye on the EXTERIOR side (D=3, InsideSide=1 → dot=3 > ε), so the exterior seed fires —
    // exactly the BuildFromExterior seeding contract (mirrors the existing BuildFromExterior_* fixtures).
    private static (LoadedCell[] cells, Dictionary<uint, LoadedCell> lookup) TwoCellBuilding()
    {
        const uint VEST = 0x0170, ROOM = 0x0171;
        var vest = Cell(VEST,
            new CellPortalInfo(0xFFFF, PolygonId: 0, Flags: 0, OtherPortalId: 0),   // entrance to outdoors
            new CellPortalInfo((ushort)ROOM, PolygonId: 1, Flags: 0, OtherPortalId: 0)); // interior to room
        vest.PortalPolygons.Add(Quad(0f, 0f, 0.5f, 0.5f, -2f));  // entrance opening, in front of eye
        vest.PortalPolygons.Add(Quad(0f, 0f, 0.6f, 0.6f, -4f));  // vestibule -> room, deeper
        vest.ClipPlanes.Add(new PortalClipPlane { Normal = new Vector3(0, 0, 1), D = 3f, InsideSide = 1 });

        var room = Cell(ROOM, new CellPortalInfo((ushort)VEST, PolygonId: 0, Flags: 0, OtherPortalId: 1));
        room.PortalPolygons.Add(Quad(0f, 0f, 0.6f, 0.6f, -4f)); // reciprocal back to vestibule

        var all = new Dictionary<uint, LoadedCell> { [VEST] = vest, [ROOM] = room };
        return (new[] { vest, room }, all);
    }

    [Fact]
    public void ConstructViewBuilding_FloodsTheBuildingFromItsEntrance()
    {
        var (cells, lookup) = TwoCellBuilding();
        var frame = PortalVisibilityBuilder.ConstructViewBuilding(
            cells, Vector3.Zero, id => lookup.TryGetValue(id, out var c) ? c : null, ViewProj());

        Assert.Contains(0x0170u, frame.OrderedVisibleCells); // entrance cell seeded
        Assert.Contains(0x0171u, frame.OrderedVisibleCells); // back room reached through the interior portal
    }

    [Fact]
    public void ConstructViewBuilding_TouchesAboutTwoCells()
    {
        // Conformance to §3.4: each retail per-building flood has cell_draw_num ≈ 2.
        var (cells, lookup) = TwoCellBuilding();
        var frame = PortalVisibilityBuilder.ConstructViewBuilding(
            cells, Vector3.Zero, id => lookup.TryGetValue(id, out var c) ? c : null, ViewProj());

        Assert.InRange(frame.OrderedVisibleCells.Count, 1, 3);
    }

    [Fact]
    public void ConstructViewBuilding_MembershipStableUnderMicrometreEyeJitter()
    {
        // Conformance to §3.4: retail's per-building membership is stable while the eye jitters ~36 µm
        // at rest (measured X≈15 µm, Y≈36 µm, Z≈8 µm). The entrance-bounded seed must return the SAME
        // OrderedVisibleCells for the eye and the eye + that per-axis jitter — no flap.
        var (cells, lookup) = TwoCellBuilding();
        var vp = ViewProj();
        System.Func<uint, LoadedCell?> lk = id => lookup.TryGetValue(id, out var c) ? c : null;

        var a = PortalVisibilityBuilder.ConstructViewBuilding(cells, Vector3.Zero, lk, vp);
        var b = PortalVisibilityBuilder.ConstructViewBuilding(
            cells, new Vector3(15e-6f, 36e-6f, 8e-6f), lk, vp);

        Assert.Equal(a.OrderedVisibleCells, b.OrderedVisibleCells);
    }
}