using System;
using System.Collections.Generic;
using System.Numerics;
using AcDream.Core.Physics;
using AcDream.Core.World.Cells;
using DatReaderWriter.Enums;
using DatReaderWriter.Types;
using Xunit;
using DatEnvCell = DatReaderWriter.DBObjs.EnvCell;
using UcgCellPortal = AcDream.Core.World.Cells.CellPortal;

namespace AcDream.Core.Tests.Physics;

public class CellGraphMembershipTests
{
    [Fact]
    public void ResolveCellId_Resolved_WritesCurrCellTrackingTheResolvedId()
    {
        var engine = new PhysicsEngine();
        var cache = new PhysicsDataCache();
        engine.DataCache = cache;

        var cs = new CellStruct {
            VertexArray = new VertexArray { Vertices = new Dictionary<ushort, SWVertex>() },
            Polygons = new Dictionary<ushort, Polygon>(),
            PhysicsBSP = null,
        };
        var dat = new DatEnvCell {
            Flags = (DatReaderWriter.Enums.EnvCellFlags)0,
            CellPortals = new List<DatReaderWriter.Types.CellPortal>(),
            VisibleCells = new List<ushort>(),
        };
        cache.CacheCellStruct(0xA9B40174u, dat, cs, Matrix4x4.Identity);  // registers in the graph (W1)

        uint result = engine.ResolveCellId(new Vector3(0, 0, 0), 0.5f, 0xA9B40174u);

        // CurrCell tracks whatever id ResolveCellId returned (when that id is in the graph).
        Assert.NotNull(cache.CellGraph.CurrCell);
        Assert.Equal(result, cache.CellGraph.CurrCell!.Id);
        Assert.Equal(0xA9B40174u, cache.CellGraph.CurrCell!.Id);
    }

    // ── UCG W2 Task 3 — stab-list doorway hysteresis tests ───────────────────
    //
    // Geometry: indoor cell 0xA9B40175 with a CellBSP splitting plane at Y=3.5,
    // normal (0,-1,0). The interior is Y ≤ 3.5 (positive side of the plane).
    //
    // SphereIntersectsCellBsp with radius=0.3 fails (returns false) when:
    //   dist = dot((0,-1,0), center) + 3.5 = 3.5 - center.Y < -(0.3 + 0.01) = -0.31
    //   i.e. center.Y > 3.81
    //
    // SphereIntersectsCellBsp with expanded radius=0.3+0.2=0.5 fails when:
    //   center.Y > 3.5 + 0.51 = 4.01
    //
    // So the hysteresis band is Y ∈ (3.81, 4.01]:
    //   - Strict check failed (falls through to outdoor)
    //   - Expanded check passes (hold the indoor cell)
    //
    // Test positions:
    //   Y=3.9 → strict fails, expanded holds → hysteresis HOLD
    //   Y=4.5 → both fail → genuine step-out, RELEASE
    //
    // The landblock is registered at worldOffset=(0,0) so localX=worldPos.X,
    // localY=worldPos.Y. At X=0, Y=3.9: cx=0, cy=0 → lowCellId=1 →
    // outdoorCellId = 0xA9B40001.
    //
    // Retail anchor: CObjCell::find_cell_list do_not_load_cells prune
    // (acclient_2013_pseudo_c.txt:308829-308867).

    private const uint DoorwayIndoorId  = 0xA9B40175u;
    private const uint DoorwayLbId      = 0xA9B40000u;
    private const float SphereRadius    = 0.3f;
    // Y at which strict check fails but expanded (margin=0.2) still holds.
    private static readonly Vector3 HoldPos    = new(0f, 3.9f, 95f);
    // Y at which both strict and expanded fail (genuine step-out).
    private static readonly Vector3 ReleasedPos = new(0f, 4.5f, 95f);

    /// <summary>
    /// Builds the engine+cache+prevCell fixture shared by the three hysteresis tests.
    /// <paramref name="stabList"/> controls whether the outdoor candidate is in the stab list.
    /// <paramref name="setCurrCell"/> controls whether CellGraph.CurrCell is pre-set to prev.
    /// Returns the engine, cache, and the EnvCell registered as the previous indoor membership.
    /// </summary>
    private static (PhysicsEngine engine, PhysicsDataCache cache, EnvCell prev)
        BuildDoorwayFixture(IReadOnlyList<uint> stabList, bool setCurrCell = true)
    {
        var cache  = new PhysicsDataCache();
        var engine = new PhysicsEngine { DataCache = cache };

        // ── CellBSP: plane at Y=3.5 with normal (0,-1,0) ─────────────────
        // Interior is at Y ≤ 3.5 (positive-side leaf).
        // SphereIntersectsCellBsp(root, center, r) checks:
        //   dist = dot((0,-1,0), center) + 3.5 = 3.5 - center.Y
        //   if dist < -(r + 0.01) → sphere is fully outside → return false
        var cellBspLeaf = new CellBSPNode { Type = BSPNodeType.Leaf };
        var cellBspRoot = new CellBSPNode
        {
            SplittingPlane = new Plane(new Vector3(0f, -1f, 0f), 3.5f),
            PosNode        = cellBspLeaf,
        };
        var cellBsp = new CellBSPTree { Root = cellBspRoot };

        // ── CellPhysics registered for the indoor sphere-check branch ─────
        // This is what ResolveCellId's indoor branch looks up via GetCellStruct.
        // We set CellBSP to cellBsp so the overlap test uses it.
        var indoorCell = new CellPhysics
        {
            BSP                   = new PhysicsBSPTree { Root = new PhysicsBSPNode { Type = BSPNodeType.Leaf } },
            WorldTransform        = Matrix4x4.Identity,
            InverseWorldTransform = Matrix4x4.Identity,
            Resolved              = new Dictionary<ushort, ResolvedPolygon>(),
            CellBSP               = cellBsp,
            Portals               = Array.Empty<PortalInfo>(),
            PortalPolygons        = new Dictionary<ushort, ResolvedPolygon>(),
            VisibleCellIds        = new System.Collections.Generic.HashSet<uint>(),
        };
        cache.RegisterCellStructForTest(DoorwayIndoorId, indoorCell);

        // ── EnvCell in the CellGraph with the same ContainmentBsp ─────────
        // This is what the hysteresis prune reads from CellGraph.CurrCell.
        // We use the SAME cellBsp instance so the test geometry is consistent.
        var prev = new EnvCell(
            id:                   DoorwayIndoorId,
            worldTransform:       Matrix4x4.Identity,
            inverseWorldTransform: Matrix4x4.Identity,
            localBoundsMin:       new Vector3(-20f, -20f, -20f),
            localBoundsMax:       new Vector3(20f, 20f, 20f),
            portals:              Array.Empty<UcgCellPortal>(),
            stabList:             stabList,
            seenOutside:          true,
            containmentBsp:       cellBsp);

        cache.CellGraph.Add(prev);
        if (setCurrCell)
            cache.CellGraph.CurrCell = prev;

        // ── Stub landblock: terrain far below, worldOffset=(0,0) ──────────
        // worldPos.X, worldPos.Y map directly to localX, localY.
        // At X=0, Y=3.9: cx=0, cy=0 → lowCellId=1 → outdoorCellId=0xA9B40001.
        var heights     = new byte[81];
        var heightTable = new float[256];
        for (int i = 0; i < 256; i++) heightTable[i] = -1000f;
        var stubTerrain = new TerrainSurface(heights, heightTable);
        engine.AddLandblock(
            landblockId:  DoorwayLbId,
            terrain:      stubTerrain,
            cells:        Array.Empty<CellSurface>(),
            portals:      Array.Empty<PortalPlane>(),
            worldOffsetX: 0f,
            worldOffsetY: 0f);

        return (engine, cache, prev);
    }

    /// <summary>
    /// UCG W2 Task 3 — HOLD (the RED→GREEN test).
    ///
    /// Position Y=3.9 is inside the hysteresis band:
    ///   - The strict overlap check (radius=0.3) fails → indoor branch falls through to outdoor.
    ///   - The expanded check (radius=0.3+0.2=0.5) still passes → hold the indoor cell.
    ///   - The outdoor candidate (0xA9B40001) is NOT in the stab list → prune fires.
    ///
    /// Expected: ResolveCellId returns 0xA9B40175 (held indoor).
    /// Before the fix: returns 0xA9B40001 (outdoor — ping-pong side).
    /// After the fix: returns 0xA9B40175 (held indoor — anti-ping-pong).
    ///
    /// Retail anchor: CObjCell::find_cell_list do_not_load_cells prune
    /// (acclient_2013_pseudo_c.txt:308829-308867).
    /// </summary>
    [Fact]
    public void ResolveCellId_DoorwayHysteresis_HoldsIndoorWhenInsideMargin()
    {
        var (engine, _, _) = BuildDoorwayFixture(
            stabList:   Array.Empty<uint>(),
            setCurrCell: true);

        uint result = engine.ResolveCellId(HoldPos, SphereRadius, DoorwayIndoorId);

        Assert.Equal(DoorwayIndoorId, result);
    }

    /// <summary>
    /// UCG W2 Task 3 — RELEASE when fully outside (genuine step-out).
    ///
    /// Position Y=4.5 exceeds the expanded margin (4.01) — both the strict
    /// and expanded overlap checks fail. The prune must NOT hold — the player
    /// genuinely stepped out.
    ///
    /// Expected: ResolveCellId returns an outdoor cell id (low 16 bits &lt; 0x100)
    /// that is NOT 0xA9B40175.
    /// </summary>
    [Fact]
    public void ResolveCellId_DoorwayHysteresis_ReleasesWhenFullyOutside()
    {
        var (engine, _, _) = BuildDoorwayFixture(
            stabList:   Array.Empty<uint>(),
            setCurrCell: true);

        uint result = engine.ResolveCellId(ReleasedPos, SphereRadius, DoorwayIndoorId);

        // Must be an outdoor cell (low 16 bits < 0x100) and not the indoor cell.
        Assert.NotEqual(DoorwayIndoorId, result);
        Assert.True((result & 0xFFFFu) < 0x100u,
            $"Expected an outdoor cell (low 16 < 0x100), got 0x{result:X8}");
    }

    /// <summary>
    /// UCG W2 Task 3 — RELEASE when candidate is visible (stab-list gate).
    ///
    /// The prune only fires when the outdoor candidate is NOT in the previous
    /// indoor cell's stab list. If the candidate IS in the stab list (genuinely
    /// visible from the indoor cell), the transition should proceed normally —
    /// hysteresis must not block it.
    ///
    /// Expected: ResolveCellId returns the outdoor cell id even though Y=3.9
    /// is inside the hysteresis band.
    /// </summary>
    [Fact]
    public void ResolveCellId_DoorwayHysteresis_ReleasesWhenCandidateIsInStabList()
    {
        // Step 1: determine the outdoor id the engine picks at Y=3.9
        // by running with CurrCell=null (no hysteresis).
        var (engineNull, _, _) = BuildDoorwayFixture(
            stabList:   Array.Empty<uint>(),
            setCurrCell: false);
        uint outdoorId = engineNull.ResolveCellId(HoldPos, SphereRadius, DoorwayIndoorId);

        // Sanity: must be outdoor (low 16 < 0x100).
        Assert.True((outdoorId & 0xFFFFu) < 0x100u,
            $"Expected outdoor fallback id (low 16 < 0x100), got 0x{outdoorId:X8}");

        // Step 2: build a fresh fixture with the outdoor id IN the stab list.
        var (engine, _, _) = BuildDoorwayFixture(
            stabList:   new uint[] { outdoorId },
            setCurrCell: true);

        uint result = engine.ResolveCellId(HoldPos, SphereRadius, DoorwayIndoorId);

        // Stab-list gate: outdoor candidate is visible → prune must NOT hold.
        Assert.Equal(outdoorId, result);
    }
}