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

namespace AcDream.App.Tests.Rendering;

/// <summary>
/// Phase U.4: GL-free proof that <see cref="ClipFrameAssembler"/> implements the
/// slot/gate policy — slot 0 no-clip, one CellClip slot per visible cell with a
/// convex region, OutsideView routed to the terrain decision + the outdoor mesh
/// slot, and the three Count==0 dispositions (nothing-visible cull, scissor
/// fallback → no-clip, planes). Hand-built <see cref="PortalVisibilityFrame"/>s
/// drive the assembler directly (no portal BFS needed) so each disposition is
/// exercised in isolation.
/// </summary>
public class ClipFrameAssemblerTests
{
    // A convex NDC square → ClipPlaneSet.From yields 4 planes (Count > 0).
    private static ViewPolygon Square(float cx, float cy, float half) => new(new[]
    {
        new Vector2(cx - half, cy - half), new Vector2(cx + half, cy - half),
        new Vector2(cx + half, cy + half), new Vector2(cx - half, cy + half),
    });

    private static CellView ViewOf(params ViewPolygon[] polys)
    {
        var v = new CellView();
        foreach (var p in polys) v.Add(p);
        return v;
    }

    [Fact]
    public void TwoVisibleCells_PlusOutsideView_ProducesCorrectSlotMapAndCounts()
    {
        // Two cells with single convex regions (→ planes, mapped to slots 1 and 2)
        // and a single-convex OutsideView (→ planes, the outdoor slot 3).
        const uint cellA = 0xA9B40100;
        const uint cellB = 0xA9B40101;

        var pv = new PortalVisibilityFrame();
        pv.CellViews[cellA] = ViewOf(Square(-0.3f, 0f, 0.3f));
        pv.CellViews[cellB] = ViewOf(Square(0.3f, 0f, 0.2f));
        pv.OrderedVisibleCells.Add(cellA);
        pv.OrderedVisibleCells.Add(cellB);
        pv.OutsideView.Add(Square(0f, 0.5f, 0.25f));

        var frame = ClipFrame.NoClip();
        var asm = ClipFrameAssembler.Assemble(frame, pv);

        // slot 0 reserved (no-clip) + 2 cells + 1 outdoor = 4 slots.
        Assert.Equal(4, asm.Frame.SlotCount);

        // Both cells mapped to NON-zero slots (real plane regions), distinct.
        Assert.True(asm.CellIdToSlot.ContainsKey(cellA));
        Assert.True(asm.CellIdToSlot.ContainsKey(cellB));
        Assert.NotEqual(0, asm.CellIdToSlot[cellA]);
        Assert.NotEqual(0, asm.CellIdToSlot[cellB]);
        Assert.NotEqual(asm.CellIdToSlot[cellA], asm.CellIdToSlot[cellB]);

        // Per-cell plane counts recorded (a convex square reduces to 4 planes).
        Assert.Equal(4, asm.PerCellPlaneCounts[cellA]);
        Assert.Equal(4, asm.PerCellPlaneCounts[cellB]);

        // OutsideView: visible, convex → planes, a non-zero outdoor slot, terrain
        // gated via planes.
        Assert.True(asm.OutdoorVisible);
        Assert.NotEqual(0, asm.OutdoorSlot);
        Assert.Equal(TerrainClipMode.Planes, asm.TerrainMode);
        Assert.Equal(4, asm.OutsidePlaneCount);
        Assert.Equal(0, asm.ScissorFallbacks);

        // The outdoor slot differs from both cell slots and from slot 0.
        Assert.NotEqual(asm.CellIdToSlot[cellA], asm.OutdoorSlot);
        Assert.NotEqual(asm.CellIdToSlot[cellB], asm.OutdoorSlot);
    }

    [Fact]
    public void NothingVisibleCell_IsExcludedFromSlotMap_AndNotAppended()
    {
        // cellA is a real convex region; cellB's CellView is EMPTY → ClipPlaneSet
        // .IsNothingVisible → it must NOT be mapped and NOT consume a slot.
        const uint cellA = 0xA9B40100;
        const uint cellB = 0xA9B40101;

        var pv = new PortalVisibilityFrame();
        pv.CellViews[cellA] = ViewOf(Square(0f, 0f, 0.3f));
        pv.CellViews[cellB] = new CellView(); // empty ⇒ nothing visible
        pv.OrderedVisibleCells.Add(cellA);
        pv.OrderedVisibleCells.Add(cellB);
        // OutsideView empty ⇒ terrain Skip (the bleed fix), outdoor not visible.

        var frame = ClipFrame.NoClip();
        var asm = ClipFrameAssembler.Assemble(frame, pv);

        // slot 0 + cellA only = 2 slots. cellB consumed none.
        Assert.Equal(2, asm.Frame.SlotCount);
        Assert.True(asm.CellIdToSlot.ContainsKey(cellA));
        Assert.False(asm.CellIdToSlot.ContainsKey(cellB)); // culled — not drawable

        // Empty OutsideView ⇒ outdoor culled + terrain skipped (the bleed fix).
        Assert.False(asm.OutdoorVisible);
        Assert.Equal(TerrainClipMode.Skip, asm.TerrainMode);
        Assert.Equal(0, asm.OutsidePlaneCount);
    }

    [Fact]
    public void OutsideViewScissorFallback_MapsTerrainToScissor_AndCountsFallback()
    {
        // A MULTI-polygon OutsideView is a union (non-convex) ⇒ ClipPlaneSet falls
        // back to the union AABB scissor: mesh outdoor slot 0 (no-clip over-include),
        // terrain → Scissor, one fallback counted.
        const uint cellA = 0xA9B40100;

        var pv = new PortalVisibilityFrame();
        pv.CellViews[cellA] = ViewOf(Square(0f, 0f, 0.3f));
        pv.OrderedVisibleCells.Add(cellA);
        pv.OutsideView.Add(Square(-0.5f, 0f, 0.1f));
        pv.OutsideView.Add(Square(0.5f, 0f, 0.1f)); // 2 polys ⇒ scissor fallback

        var frame = ClipFrame.NoClip();
        var asm = ClipFrameAssembler.Assemble(frame, pv);

        Assert.True(asm.OutdoorVisible);
        Assert.Equal(0, asm.OutdoorSlot);                    // no-clip over-include
        Assert.Equal(TerrainClipMode.Scissor, asm.TerrainMode);
        Assert.Equal(0, asm.OutsidePlaneCount);              // scissor ⇒ 0 planes
        Assert.Equal(1, asm.ScissorFallbacks);

        // The terrain scissor AABB is a valid (min <= max) NDC box spanning both
        // OutsideView squares: minX <= -0.6, maxX >= 0.6.
        Assert.True(asm.TerrainScissorNdcAabb.X <= asm.TerrainScissorNdcAabb.Z);
        Assert.True(asm.TerrainScissorNdcAabb.Y <= asm.TerrainScissorNdcAabb.W);
        Assert.True(asm.TerrainScissorNdcAabb.X <= -0.59f);
        Assert.True(asm.TerrainScissorNdcAabb.Z >= 0.59f);
    }

    [Fact]
    public void CellScissorFallback_MapsCellToSlotZero_AndCountsFallback()
    {
        // A cell with a MULTI-polygon region → scissor fallback → mapped to slot 0
        // (no-clip over-include), recorded with 0 planes, one fallback counted. The
        // OutsideView is a single convex region (planes) so only the CELL counts.
        const uint cellA = 0xA9B40100;

        var pv = new PortalVisibilityFrame();
        pv.CellViews[cellA] = ViewOf(Square(-0.4f, 0f, 0.1f), Square(0.4f, 0f, 0.1f));
        pv.OrderedVisibleCells.Add(cellA);
        pv.OutsideView.Add(Square(0f, 0f, 0.3f));

        var frame = ClipFrame.NoClip();
        var asm = ClipFrameAssembler.Assemble(frame, pv);

        // cellA → slot 0 (no-clip). slot 0 + the OutsideView's planes slot = 2.
        Assert.Equal(0, asm.CellIdToSlot[cellA]);
        Assert.Equal(0, asm.PerCellPlaneCounts[cellA]);
        Assert.Equal(2, asm.Frame.SlotCount);               // slot0 + OutsideView
        Assert.Equal(1, asm.ScissorFallbacks);              // the cell fallback
        Assert.Equal(TerrainClipMode.Planes, asm.TerrainMode);
    }

    // -----------------------------------------------------------------------
    // Phase W Stage 4: HasOutsideView + OutsideViewNdcAabb
    // -----------------------------------------------------------------------

    [Fact]
    public void Assemble_OutsideViewWithExitPortal_HasOutsideViewTrue_AabbMatchesBounds()
    {
        // A single convex quad in OutsideView reduces to Planes. HasOutsideView must
        // be true and OutsideViewNdcAabb must match the polygon's own Min/Max values.
        var pv = new PortalVisibilityFrame();
        var poly = Square(-0.3f, 0.2f, 0.25f);
        pv.OutsideView.Add(poly);
        // No interior cells needed for this assertion.

        var frame = ClipFrame.NoClip();
        var asm = ClipFrameAssembler.Assemble(frame, pv);

        Assert.True(asm.HasOutsideView);
        Assert.Equal(TerrainClipMode.Planes, asm.TerrainMode);

        // The OutsideViewNdcAabb must equal the CellView's accumulated Min/Max.
        var expected = new System.Numerics.Vector4(
            pv.OutsideView.MinX, pv.OutsideView.MinY,
            pv.OutsideView.MaxX, pv.OutsideView.MaxY);
        Assert.Equal(expected, asm.OutsideViewNdcAabb);
    }

    [Fact]
    public void Assemble_OutsideViewMultiPolygon_ScissorMode_HasOutsideViewTrue_AabbValid()
    {
        // Two polygons in OutsideView → union (non-convex) → ClipPlaneSet forces
        // scissor fallback. HasOutsideView must still be true, TerrainMode must be
        // Scissor, and OutsideViewNdcAabb must equal the union bounds (same values
        // as TerrainScissorNdcAabb in this mode).
        var pv = new PortalVisibilityFrame();
        pv.OutsideView.Add(Square(-0.6f, 0f, 0.15f));
        pv.OutsideView.Add(Square(0.6f, 0f, 0.15f));

        var frame = ClipFrame.NoClip();
        var asm = ClipFrameAssembler.Assemble(frame, pv);

        Assert.True(asm.HasOutsideView);
        Assert.Equal(TerrainClipMode.Scissor, asm.TerrainMode);

        // Union bounds from the CellView (spans both squares).
        var expectedAabb = new System.Numerics.Vector4(
            pv.OutsideView.MinX, pv.OutsideView.MinY,
            pv.OutsideView.MaxX, pv.OutsideView.MaxY);
        Assert.Equal(expectedAabb, asm.OutsideViewNdcAabb);

        // In Scissor mode OutsideViewNdcAabb and TerrainScissorNdcAabb are the same
        // value (both are the union CellView bounds).
        Assert.Equal(asm.TerrainScissorNdcAabb, asm.OutsideViewNdcAabb);
    }

    [Fact]
    public void Assemble_EmptyOutsideView_HasOutsideViewFalse_AabbZero()
    {
        // An empty OutsideView means no exit portal was in view → TerrainMode.Skip,
        // HasOutsideView false, OutsideViewNdcAabb degenerate zero.
        const uint cellA = 0xA9B40100;
        var pv = new PortalVisibilityFrame();
        pv.CellViews[cellA] = ViewOf(Square(0f, 0f, 0.3f));
        pv.OrderedVisibleCells.Add(cellA);
        // OutsideView left empty (no exit portal).

        var frame = ClipFrame.NoClip();
        var asm = ClipFrameAssembler.Assemble(frame, pv);

        Assert.False(asm.HasOutsideView);
        Assert.Equal(TerrainClipMode.Skip, asm.TerrainMode);
        Assert.Equal(System.Numerics.Vector4.Zero, asm.OutsideViewNdcAabb);
    }

    [Fact]
    public void Reset_ReusesFrame_NoSlotLeakAcrossAssemblies()
    {
        // First assembly packs 2 cells + outdoor (4 slots). Re-assembling the SAME
        // frame from a smaller pvFrame must Reset back to slot 0 — no leak.
        var frame = ClipFrame.NoClip();

        var pv1 = new PortalVisibilityFrame();
        pv1.CellViews[0xA9B40100] = ViewOf(Square(-0.3f, 0f, 0.2f));
        pv1.CellViews[0xA9B40101] = ViewOf(Square(0.3f, 0f, 0.2f));
        pv1.OrderedVisibleCells.Add(0xA9B40100);
        pv1.OrderedVisibleCells.Add(0xA9B40101);
        pv1.OutsideView.Add(Square(0f, 0.4f, 0.2f));
        var asm1 = ClipFrameAssembler.Assemble(frame, pv1);
        Assert.Equal(4, asm1.Frame.SlotCount);

        // Second assembly: a single cell, no OutsideView.
        var pv2 = new PortalVisibilityFrame();
        pv2.CellViews[0xA9B40200] = ViewOf(Square(0f, 0f, 0.25f));
        pv2.OrderedVisibleCells.Add(0xA9B40200);
        var asm2 = ClipFrameAssembler.Assemble(frame, pv2);

        // slot 0 + 1 cell = 2 — the prior 4-slot state did not leak.
        Assert.Equal(2, asm2.Frame.SlotCount);
        Assert.True(asm2.CellIdToSlot.ContainsKey(0xA9B40200));
        Assert.False(asm2.CellIdToSlot.ContainsKey(0xA9B40100)); // gone after Reset
        Assert.False(asm2.OutdoorVisible);                       // no OutsideView this time
        Assert.Equal(TerrainClipMode.Skip, asm2.TerrainMode);
    }
}