// Phase A8 — portal mesh triangle-fan generation tests.
//
// Pure-math coverage of PortalMeshBuilder.BuildTriangles — the part of
// IndoorCellStencilPipeline that converts a list of LoadedCell with
// PortalPolygons + WorldTransform into a flat Vector3[] of triangles
// in world space. The GL/upload portion is exercised at runtime only.

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

namespace AcDream.App.Tests.Rendering;

public class IndoorCellStencilPipelineTests
{
    [Fact]
    public void BuildTriangles_NoCells_ReturnsEmpty()
    {
        var verts = PortalMeshBuilder.BuildTriangles(new List<LoadedCell>());
        Assert.Empty(verts);
    }

    [Fact]
    public void BuildTriangles_SkipsInnerPortals()
    {
        // Two portals on one cell: one exit (OtherCellId=0xFFFF, should be
        // included), one inner (OtherCellId=0x0102, should be skipped).
        var cell = new LoadedCell
        {
            WorldTransform = Matrix4x4.Identity,
            Portals = new()
            {
                new CellPortalInfo(0xFFFF, 100, 0),  // exit — included
                new CellPortalInfo(0x0102, 101, 0),  // inner — skipped
            },
            ClipPlanes = new() { default, default },
            PortalPolygons = new()
            {
                new[]
                {
                    new Vector3(0, 0, 0),
                    new Vector3(1, 0, 0),
                    new Vector3(1, 1, 0),
                },
                new[]
                {
                    new Vector3(10, 0, 0),
                    new Vector3(11, 0, 0),
                    new Vector3(11, 1, 0),
                },
            },
        };

        var verts = PortalMeshBuilder.BuildTriangles(new List<LoadedCell> { cell });

        // Only the exit polygon (3 verts → 1 triangle → 3 vertices).
        Assert.Equal(3, verts.Length);
        Assert.Equal(new Vector3(0, 0, 0), verts[0]);
        Assert.Equal(new Vector3(1, 0, 0), verts[1]);
        Assert.Equal(new Vector3(1, 1, 0), verts[2]);
    }

    [Fact]
    public void BuildTriangles_OnlyIncludesProvidedVisibleCells()
    {
        // The render path now feeds BuildTriangles from the portal traversal's
        // visible cells, not every cell in the building. A hidden room's exit
        // portal must not punch outdoor terrain into the current view.
        var visibleInnerCell = new LoadedCell
        {
            WorldTransform = Matrix4x4.Identity,
            Portals = new() { new CellPortalInfo(0x0102, 100, 0) },
            ClipPlanes = new() { default },
            PortalPolygons = new()
            {
                new[]
                {
                    new Vector3(0, 0, 0),
                    new Vector3(1, 0, 0),
                    new Vector3(1, 1, 0),
                },
            },
        };

        var hiddenExitCell = new LoadedCell
        {
            WorldTransform = Matrix4x4.Identity,
            Portals = new() { new CellPortalInfo(0xFFFF, 101, 0) },
            ClipPlanes = new() { default },
            PortalPolygons = new()
            {
                new[]
                {
                    new Vector3(10, 0, 0),
                    new Vector3(11, 0, 0),
                    new Vector3(11, 1, 0),
                },
            },
        };

        var visibleOnly = PortalMeshBuilder.BuildTriangles(new List<LoadedCell> { visibleInnerCell });
        var allBuildingCells = PortalMeshBuilder.BuildTriangles(new List<LoadedCell> { visibleInnerCell, hiddenExitCell });

        Assert.Empty(visibleOnly);
        Assert.Equal(3, allBuildingCells.Length);
        Assert.Equal(new Vector3(10, 0, 0), allBuildingCells[0]);
    }

    [Fact]
    public void BuildTriangles_CameraSideFilterSkipsExitPortalsBehindCamera()
    {
        var cell = new LoadedCell
        {
            WorldTransform = Matrix4x4.Identity,
            InverseWorldTransform = Matrix4x4.Identity,
            Portals = new() { new CellPortalInfo(0xFFFF, 100, 0) },
            ClipPlanes = new()
            {
                new PortalClipPlane
                {
                    Normal = Vector3.UnitX,
                    D = 0f,
                    InsideSide = 0,
                },
            },
            PortalPolygons = new()
            {
                new[]
                {
                    new Vector3(0, 0, 0),
                    new Vector3(0, 1, 0),
                    new Vector3(0, 0, 1),
                },
            },
        };

        var visible = PortalMeshBuilder.BuildTriangles(new List<LoadedCell> { cell }, new Vector3(1, 0, 0));
        var rejected = PortalMeshBuilder.BuildTriangles(new List<LoadedCell> { cell }, new Vector3(-1, 0, 0));

        Assert.Equal(3, visible.Length);
        Assert.Empty(rejected);
    }

    [Fact]
    public void BuildTriangles_TriangulatesAsFan()
    {
        // 4-vertex quad → fan = 2 triangles → 6 vertices.
        // Quad: (0,0,0), (1,0,0), (1,1,0), (0,1,0).
        // Fan from vertex 0: (0,1,2), (0,2,3).
        var cell = new LoadedCell
        {
            WorldTransform = Matrix4x4.Identity,
            Portals = new() { new CellPortalInfo(0xFFFF, 100, 0) },
            ClipPlanes = new() { default },
            PortalPolygons = new()
            {
                new[]
                {
                    new Vector3(0, 0, 0),
                    new Vector3(1, 0, 0),
                    new Vector3(1, 1, 0),
                    new Vector3(0, 1, 0),
                },
            },
        };

        var verts = PortalMeshBuilder.BuildTriangles(new List<LoadedCell> { cell });

        Assert.Equal(6, verts.Length);
        // Triangle 1: (0,1,2)
        Assert.Equal(new Vector3(0, 0, 0), verts[0]);
        Assert.Equal(new Vector3(1, 0, 0), verts[1]);
        Assert.Equal(new Vector3(1, 1, 0), verts[2]);
        // Triangle 2: (0,2,3)
        Assert.Equal(new Vector3(0, 0, 0), verts[3]);
        Assert.Equal(new Vector3(1, 1, 0), verts[4]);
        Assert.Equal(new Vector3(0, 1, 0), verts[5]);
    }

    [Fact]
    public void BuildTriangles_AppliesWorldTransform()
    {
        // Identity cell-local triangle, translated by WorldTransform.
        var translate = Matrix4x4.CreateTranslation(new Vector3(100, 200, 300));
        var cell = new LoadedCell
        {
            WorldTransform = translate,
            Portals = new() { new CellPortalInfo(0xFFFF, 100, 0) },
            ClipPlanes = new() { default },
            PortalPolygons = new()
            {
                new[]
                {
                    new Vector3(0, 0, 0),
                    new Vector3(1, 0, 0),
                    new Vector3(0, 1, 0),
                },
            },
        };

        var verts = PortalMeshBuilder.BuildTriangles(new List<LoadedCell> { cell });

        Assert.Equal(3, verts.Length);
        Assert.Equal(new Vector3(100, 200, 300), verts[0]);
        Assert.Equal(new Vector3(101, 200, 300), verts[1]);
        Assert.Equal(new Vector3(100, 201, 300), verts[2]);
    }

    [Fact]
    public void BuildTriangles_SkipsEmptyOrDegeneratePolygons()
    {
        var cell = new LoadedCell
        {
            WorldTransform = Matrix4x4.Identity,
            Portals = new()
            {
                new CellPortalInfo(0xFFFF, 100, 0),
                new CellPortalInfo(0xFFFF, 101, 0),
            },
            ClipPlanes = new() { default, default },
            PortalPolygons = new()
            {
                System.Array.Empty<Vector3>(),                 // empty
                new[] { new Vector3(0, 0, 0), new Vector3(1, 0, 0) },  // degenerate (2 verts)
            },
        };

        var verts = PortalMeshBuilder.BuildTriangles(new List<LoadedCell> { cell });
        Assert.Empty(verts);
    }
}