// CellVisibilityFromRootTests.cs — UCG W2 Task 2 + Stage 3: tests for
// CellVisibility.ComputeVisibilityFromRoot.
//
// Acceptance criteria (Stage 3 — W2 null-fallback deleted):
//   (a) ComputeVisibilityFromRoot(null, pos) returns NULL (outdoor root), regardless
//       of whether any cells are registered. The AABB FindCameraCell fallback is gone.
//   (b) ComputeVisibilityFromRoot(root, pos) with a registered root returns
//       a result whose CameraCell is that root, regardless of whether 'pos'
//       is geometrically inside it.
//
// CellVisibility is intentionally free of GL types — it can be unit-tested
// without a GPU context (confirmed: only System.Numerics dependency).

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

namespace AcDream.App.Tests.Rendering;

public class CellVisibilityFromRootTests
{
    // ------------------------------------------------------------------
    // Helpers
    // ------------------------------------------------------------------

    /// <summary>
    /// Build a minimal LoadedCell with an axis-aligned bounding box and identity
    /// transform so PointInCell works for a position inside the box.
    /// </summary>
    private static LoadedCell MakeCell(uint cellId, Vector3 boundsMin, Vector3 boundsMax)
    {
        return new LoadedCell
        {
            CellId = cellId,
            WorldTransform = Matrix4x4.Identity,
            InverseWorldTransform = Matrix4x4.Identity,
            LocalBoundsMin = boundsMin,
            LocalBoundsMax = boundsMax,
            Portals = new(),
            ClipPlanes = new(),
            PortalPolygons = new(),
        };
    }

    // ------------------------------------------------------------------
    // (a) Stage 3: null root → null (outdoor root), not a position fallback
    // ------------------------------------------------------------------

    [Fact]
    public void ComputeVisibilityFromRoot_NullRoot_ReturnsNull_WhenCellExists()
    {
        // Stage 3: null root → outdoor root → null result, even when a cell covers the
        // fallback position. Pre-Stage 3 this called FindCameraCell(pos); now the caller
        // must supply the root (physics CellGraph.CurrCell). Retail: CellManager::ChangePosition
        // reads the transition-owned curr_cell — it does not re-derive from a static position.
        var cv = new CellVisibility();
        var cell = MakeCell(0xA9B40101u, Vector3.Zero, new Vector3(10, 10, 10));
        cv.AddCell(cell);

        var pos = new Vector3(5, 5, 5); // inside the cell — null root overrides

        var fromNull = cv.ComputeVisibilityFromRoot(null, pos);

        // Stage 3: null root → null (outdoor root path).
        Assert.Null(fromNull);
    }

    [Fact]
    public void ComputeVisibilityFromRoot_NullRoot_NoCells_ReturnsNull()
    {
        // With no cells registered and null root: always null (outdoor root).
        var cv = new CellVisibility();
        var posOutdoors = new Vector3(100, 100, 100);

        var fromNull = cv.ComputeVisibilityFromRoot(null, posOutdoors);

        Assert.Null(fromNull);
    }

    [Fact]
    public void ComputeVisibilityFromRoot_NullRoot_PositionOutsideAllCells_ReturnsNull()
    {
        // Cell exists but null root: always null regardless of position.
        var cv = new CellVisibility();
        var cell = MakeCell(0xA9B40102u, Vector3.Zero, new Vector3(5, 5, 5));
        cv.AddCell(cell);

        var posOutside = new Vector3(100, 100, 100);

        var fromNull = cv.ComputeVisibilityFromRoot(null, posOutside);

        Assert.Null(fromNull);
    }

    // ------------------------------------------------------------------
    // (b) Supplied root is used as BFS root → CameraCell == root
    // ------------------------------------------------------------------

    [Fact]
    public void ComputeVisibilityFromRoot_RegisteredRoot_CameraCellIsSuppliedRoot()
    {
        // Arrange: cell registered in CellVisibility.
        var cv = new CellVisibility();
        var cell = MakeCell(0xA9B40103u, Vector3.Zero, new Vector3(10, 10, 10));
        cv.AddCell(cell);

        // The position can be OUTSIDE the cell — physics already determined membership
        // via BSP, we just trust that answer.
        var posAnywhere = new Vector3(999, 999, 999);

        // Act
        var result = cv.ComputeVisibilityFromRoot(cell, posAnywhere);

        // Assert: CameraCell is the supplied root.
        Assert.NotNull(result);
        Assert.Same(cell, result!.CameraCell);
    }

    [Fact]
    public void ComputeVisibilityFromRoot_RegisteredRoot_IncludesRootInVisibleCells()
    {
        var cv = new CellVisibility();
        var cell = MakeCell(0xA9B40104u, Vector3.Zero, new Vector3(10, 10, 10));
        cv.AddCell(cell);

        var result = cv.ComputeVisibilityFromRoot(cell, Vector3.Zero);

        Assert.NotNull(result);
        Assert.Contains(cell.CellId, result!.VisibleCellIds);
    }

    [Fact]
    public void ComputeVisibilityFromRoot_RegisteredRoot_LastVisibilityResultUpdated()
    {
        var cv = new CellVisibility();
        var cell = MakeCell(0xA9B40105u, Vector3.Zero, new Vector3(10, 10, 10));
        cv.AddCell(cell);

        var result = cv.ComputeVisibilityFromRoot(cell, Vector3.Zero);

        Assert.Same(result, cv.LastVisibilityResult);
    }
}