using System;
using System.Collections.Generic;
using System.Numerics;
using DatReaderWriter.Enums;
using DatReaderWriter.Types;
using AcDream.Core.Physics;
using Xunit;

namespace AcDream.Core.Tests.Physics;

/// <summary>
/// Unit tests for the result-combine helper used by
/// <see cref="Transition.CheckOtherCells"/>. The iteration / per-cell
/// BSP-query parts are covered end-to-end by
/// <see cref="FindEnvCollisionsMultiCellTests"/>; this file pins the
/// retail-faithful halt semantics that
/// <c>acclient_2013_pseudo_c.txt:272739-272752</c> spells out.
/// </summary>
public class TransitionCheckOtherCellsTests
{
    private static Transition MakeTransition(bool contactFlag = false)
    {
        var t = new Transition();
        t.SpherePath.InitPath(Vector3.Zero, Vector3.Zero, cellId: 0xA9B40100u, sphereRadius: 0.48f);
        t.ObjectInfo.State = contactFlag ? ObjectInfoState.Contact : ObjectInfoState.None;
        // Pre-set CP fields to non-default so the Slid-clears-CP assertion
        // can detect the clear.
        t.CollisionInfo.ContactPlaneValid   = true;
        t.CollisionInfo.ContactPlaneIsWater = true;
        return t;
    }

    [Fact]
    public void OK_ContinuesIteration_DoesNotMutate()
    {
        var t = MakeTransition();

        bool halt = t.ApplyOtherCellResult(TransitionState.OK, out var finalState);

        Assert.False(halt);
        Assert.Equal(TransitionState.OK, finalState);
        Assert.True(t.CollisionInfo.ContactPlaneValid);
        Assert.True(t.CollisionInfo.ContactPlaneIsWater);
        Assert.False(t.CollisionInfo.CollidedWithEnvironment);
    }

    [Fact]
    public void Collided_HaltsAndSetsCollidedWithEnvironment_WhenNotInContact()
    {
        var t = MakeTransition(contactFlag: false);

        bool halt = t.ApplyOtherCellResult(TransitionState.Collided, out var finalState);

        Assert.True(halt);
        Assert.Equal(TransitionState.Collided, finalState);
        Assert.True(t.CollisionInfo.CollidedWithEnvironment);
    }

    [Fact]
    public void Collided_DoesNotSetCollidedWithEnvironment_WhenInContact()
    {
        // Retail oracle gating: the CollidedWithEnvironment flip mirrors
        // the existing primary-cell behavior in FindEnvCollisions —
        // skipped when ObjectInfo.State has Contact bit set.
        var t = MakeTransition(contactFlag: true);

        bool halt = t.ApplyOtherCellResult(TransitionState.Collided, out var finalState);

        Assert.True(halt);
        Assert.Equal(TransitionState.Collided, finalState);
        Assert.False(t.CollisionInfo.CollidedWithEnvironment);
    }

    [Fact]
    public void Adjusted_HaltsAndSetsCollidedWithEnvironment_WhenNotInContact()
    {
        var t = MakeTransition(contactFlag: false);

        bool halt = t.ApplyOtherCellResult(TransitionState.Adjusted, out var finalState);

        Assert.True(halt);
        Assert.Equal(TransitionState.Adjusted, finalState);
        Assert.True(t.CollisionInfo.CollidedWithEnvironment);
    }

    [Fact]
    public void Slid_HaltsAndClearsContactPlaneFields()
    {
        // Retail oracle: acclient_2013_pseudo_c.txt:272746-272750
        //   case 4:
        //     this->collision_info.contact_plane_valid = 0;
        //     this->collision_info.contact_plane_is_water = 0;
        //     return result;
        var t = MakeTransition();
        Assert.True(t.CollisionInfo.ContactPlaneValid);    // pre-condition
        Assert.True(t.CollisionInfo.ContactPlaneIsWater);  // pre-condition

        bool halt = t.ApplyOtherCellResult(TransitionState.Slid, out var finalState);

        Assert.True(halt);
        Assert.Equal(TransitionState.Slid, finalState);
        Assert.False(t.CollisionInfo.ContactPlaneValid);
        Assert.False(t.CollisionInfo.ContactPlaneIsWater);
    }

    [Fact]
    public void CheckOtherCells_CellWithNullBspRoot_IsSkippedNoCrash()
    {
        // Iteration safety: a CellPhysics in the candidate set with
        // `BSP = null` (loaded for render but not physics) must be skipped,
        // not crash. Matches the spec's R2 guard at design §Edge cases E2.
        var cell = new CellPhysics
        {
            BSP                   = null,  // <-- the guard target
            WorldTransform        = Matrix4x4.Identity,
            InverseWorldTransform = Matrix4x4.Identity,
            Resolved              = new Dictionary<ushort, ResolvedPolygon>(),
        };

        var engine = new PhysicsEngine();
        engine.DataCache = new PhysicsDataCache();   // PhysicsEngine has nullable DataCache
        // FindEnvCollisions has terrain probes downstream; populate a
        // minimal landblock so the cache + engine are coherent. The cell
        // we test against doesn't need a real landblock entry.
        var heights = new byte[81];
        Array.Fill(heights, (byte)0);
        var ht = new float[256];
        for (int i = 0; i < 256; i++) ht[i] = i * 1.0f;
        engine.AddLandblock(0xA9B4FFFFu, new TerrainSurface(heights, ht),
            Array.Empty<CellSurface>(), Array.Empty<PortalPlane>(),
            worldOffsetX: 0f, worldOffsetY: 0f);
        engine.DataCache.RegisterCellStructForTest(0xA9B40157u, cell);

        var t = MakeTransition();
        var cellSet = new HashSet<uint> { 0xA9B40157u };

        // Call CheckOtherCells directly via the internal seam.
        var result = t.CheckOtherCells(engine, Vector3.Zero, 0.48f, cellSet);

        Assert.Equal(TransitionState.OK, result);
    }

    [Fact]
    public void CheckOtherCells_OutdoorLandcellCandidate_UsesTerrainWalkable()
    {
        var engine = new PhysicsEngine();
        engine.DataCache = new PhysicsDataCache();

        var heights = new byte[81];
        Array.Fill(heights, (byte)0);
        var ht = new float[256];
        for (int i = 0; i < 256; i++) ht[i] = i * 1.0f;
        engine.AddLandblock(0xA9B4FFFFu, new TerrainSurface(heights, ht),
            Array.Empty<CellSurface>(), Array.Empty<PortalPlane>(),
            worldOffsetX: 0f, worldOffsetY: 0f);

        var t = MakeTransition(contactFlag: true);
        t.SpherePath.InitPath(new Vector3(10f, 10f, -0.28f), new Vector3(10f, 10f, -0.28f),
            cellId: 0xA9B40147u, sphereRadius: 0.48f);

        var footCenter = new Vector3(10f, 10f, 0.20f);
        var cellSet = new HashSet<uint> { 0xA9B40001u };

        var result = t.CheckOtherCells(engine, footCenter, 0.48f, cellSet);

        Assert.Equal(TransitionState.Adjusted, result);
        Assert.True(t.CollisionInfo.ContactPlaneValid);
        Assert.Equal(0xA9B40001u, t.CollisionInfo.ContactPlaneCellId);
        Assert.True(t.SpherePath.CheckPos.Z > -0.28f);
    }
}