using Server.Engines.Pathing.Cache;
using Server.Mobiles;
using Server.PathAlgorithms;
using Server.Systems.FeatureFlags;
using Xunit;
using Xunit.Abstractions;

namespace Server.Tests.Pathfinding;

/// <summary>
/// Smoke tests for <see cref="BitmapAStarAlgorithm"/>'s two branches: cache-direct fast
/// path (default walkers) and per-cell slow path (capability creatures and non-GM players).
/// Exercised end-to-end against the real Trammel TileMatrix to ensure neither regresses
/// to "no path found" on reachable goals.
/// </summary>
[Collection("Sequential Pathfinding Tests")]
public class BitmapAStarAlgorithmTests
{
    private readonly ITestOutputHelper _output;

    public BitmapAStarAlgorithmTests(ITestOutputHelper output)
    {
        _output = output;
    }

    [Theory]
    // Pinned cell (1500, 1600, z=10): mask=0xC1 → N, W, NW walkable.
    // Use start.Z for goal.Z so destNode lands in the same Z plane the algorithm reaches
    // during expansion (GetAverageZ at the goal cell may differ from the engine's
    // runtime-computed standing Z, which would break the destNode equality check).
    [InlineData(1500, 1600, 1498, 1598)] // NW, 2 cells diagonal
    [InlineData(1500, 1600, 1497, 1599)] // NW-ish, 3 W + 1 N
    public void DefaultWalker_FindsPath_ViaCacheFastPath(int sx, int sy, int gx, int gy)
    {
        StepCache.Instance.Clear();
        var map = Map.Maps[1];
        Assert.NotNull(map);

        var stub = new DefaultWalkerStub();
        map.GetAverageZ(sx, sy, out _, out var startZ, out _);
        var start = new Point3D(sx, sy, (sbyte)startZ);
        var goal = new Point3D(gx, gy, (sbyte)startZ);

        stub.MoveToWorld(start, map);

        var result = BitmapAStarAlgorithm.Instance.Find(stub, map, start, goal);

        stub.Delete();

        Assert.NotNull(result);
        Assert.NotEmpty(result);
        _output.WriteLine($"default-walker ({sx},{sy})->({gx},{gy}): {result.Length} steps");
    }

    [Theory]
    [InlineData(1500, 1600, 1498, 1598)] // NW, 2 cells diagonal
    [InlineData(1500, 1600, 1497, 1599)] // NW-ish, 3 W + 1 N
    public void SwimCreature_FindsPath_ViaCacheCapabilityOverlay(int sx, int sy, int gx, int gy)
    {
        StepCache.Instance.Clear();
        StepCache.Instance.MissPromotionThreshold = 1;
        var map = Map.Maps[1];
        Assert.NotNull(map);

        var stub = new SwimmingStub(World.NewMobile);
        stub.DefaultMobileInit();
        stub.CanSwim = true; // overlay route — cache + (walkMask | wetMask&canSwim)
        map.GetAverageZ(sx, sy, out _, out var startZ, out _);
        var start = new Point3D(sx, sy, (sbyte)startZ);
        var goal = new Point3D(gx, gy, (sbyte)startZ);

        stub.MoveToWorld(start, map);

        var statsBefore = StepCache.Instance.GetStats();
        var result = BitmapAStarAlgorithm.Instance.Find(stub, map, start, goal);
        var statsAfter = StepCache.Instance.GetStats();

        stub.Delete();

        Assert.NotNull(result);
        Assert.NotEmpty(result);
        Assert.True(statsAfter.BuildsTotal > statsBefore.BuildsTotal,
            "CanSwim creature should use the cache via capability overlay, not the slow path");
        _output.WriteLine($"swimmer ({sx},{sy})->({gx},{gy}): {result.Length} steps");
    }

    [Fact]
    public void DynamicObstaclePass_RejectsCellOccupiedByLivingMobile()
    {
        StepCache.Instance.Clear();
        var map = Map.Maps[1];
        Assert.NotNull(map);

        // (1500, 1600) walks N/W/NW only (mask=0xC1). Path NW two cells; plant a blocker
        // on the direct NW step so the algorithm must route via N→W or W→N around it.
        var sx = 1500;
        var sy = 1600;
        var gx = 1498;
        var gy = 1598;
        var blockX = 1499;
        var blockY = 1599;

        map.GetAverageZ(sx, sy, out _, out var startZ, out _);
        var start = new Point3D(sx, sy, (sbyte)startZ);
        var goal = new Point3D(gx, gy, (sbyte)startZ);

        var walker = new DefaultWalkerStub();
        walker.MoveToWorld(start, map);

        // Living blocker on the only direct-line cell. CanMoveOver returns false for an
        // alive non-staff mobile, so the dynamic-obstacle pass must reject this cell.
        map.GetAverageZ(blockX, blockY, out _, out var blockZ, out _);
        var blocker = new DefaultWalkerStub();
        blocker.MoveToWorld(new Point3D(blockX, blockY, (sbyte)blockZ), map);

        var result = BitmapAStarAlgorithm.Instance.Find(walker, map, start, goal);

        // Path may exist via an alternate route, but must NOT pass through the blocker.
        Assert.NotNull(result);
        var x = sx;
        var y = sy;
        foreach (var dir in result)
        {
            Movement.Movement.Offset(dir, ref x, ref y);
            Assert.False(x == blockX && y == blockY,
                $"path traversed blocker cell ({blockX},{blockY})");
        }

        walker.Delete();
        blocker.Delete();
    }

    [Fact]
    public void DynamicObstaclePass_RejectsCellOccupiedByImpassableItem()
    {
        StepCache.Instance.Clear();
        var map = Map.Maps[1];
        Assert.NotNull(map);

        // Same NW-around-blocker scenario as the mobile-blocker test, but with an item.
        var sx = 1500;
        var sy = 1600;
        var gx = 1498;
        var gy = 1598;
        var blockX = 1499;
        var blockY = 1599;

        // Find any ItemID whose TileData has ImpassableSurface so the dynamic pass
        // rejects the cell. Pinning to a specific ID would couple the test to UO art data.
        ushort blockerItemId = 0;
        for (ushort id = 1; id < TileData.MaxItemValue; id++)
        {
            if (TileData.ItemTable[id].ImpassableSurface)
            {
                blockerItemId = id;
                break;
            }
        }
        Assert.NotEqual<ushort>(0, blockerItemId);

        map.GetAverageZ(sx, sy, out _, out var startZ, out _);
        var start = new Point3D(sx, sy, (sbyte)startZ);
        var goal = new Point3D(gx, gy, (sbyte)startZ);

        var walker = new DefaultWalkerStub();
        walker.MoveToWorld(start, map);

        map.GetAverageZ(blockX, blockY, out _, out var blockZ, out _);
        var blocker = new Item(World.NewItem)
        {
            ItemID = blockerItemId,
            Map = map,
            Location = new Point3D(blockX, blockY, (sbyte)blockZ)
        };

        var result = BitmapAStarAlgorithm.Instance.Find(walker, map, start, goal);

        Assert.NotNull(result);
        var x = sx;
        var y = sy;
        foreach (var dir in result)
        {
            Movement.Movement.Offset(dir, ref x, ref y);
            Assert.False(x == blockX && y == blockY,
                $"path traversed item-blocker cell ({blockX},{blockY})");
        }

        walker.Delete();
        blocker.Delete();
    }

    [Fact]
    public void FeatureFlagDisabled_RoutesToSlowPath_NoCacheUse()
    {
        StepCache.Instance.Clear();
        var map = Map.Maps[1];
        Assert.NotNull(map);

        var stub = new DefaultWalkerStub();
        map.GetAverageZ(1500, 1600, out _, out var startZ, out _);
        var start = new Point3D(1500, 1600, (sbyte)startZ);
        var goal = new Point3D(1498, 1598, (sbyte)startZ);
        stub.MoveToWorld(start, map);

        var statsBefore = StepCache.Instance.GetStats();
        var prevFlag = ContentFeatureFlags.BitmapPathfindingCache;
        try
        {
            ContentFeatureFlags.BitmapPathfindingCache = false;
            var result = BitmapAStarAlgorithm.Instance.Find(stub, map, start, goal);
            Assert.NotNull(result);
            Assert.NotEmpty(result);
        }
        finally
        {
            ContentFeatureFlags.BitmapPathfindingCache = prevFlag;
        }
        var statsAfter = StepCache.Instance.GetStats();

        stub.Delete();
        Assert.Equal(statsBefore.BuildsTotal, statsAfter.BuildsTotal);
    }

    [Fact]
    public void FlyCreature_RoutesToSlowPath_NoCacheUse()
    {
        StepCache.Instance.Clear();
        var map = Map.Maps[1];

        var stub = new FlyingStub(World.NewMobile);
        stub.DefaultMobileInit();
        map.GetAverageZ(1500, 1600, out _, out var startZ, out _);
        var start = new Point3D(1500, 1600, (sbyte)startZ);
        var goal = new Point3D(1498, 1598, (sbyte)startZ);

        stub.MoveToWorld(start, map);

        var statsBefore = StepCache.Instance.GetStats();
        var result = BitmapAStarAlgorithm.Instance.Find(stub, map, start, goal);
        var statsAfter = StepCache.Instance.GetStats();

        stub.Delete();

        Assert.NotNull(result);
        Assert.NotEmpty(result);
        Assert.Equal(statsBefore.BuildsTotal, statsAfter.BuildsTotal);
    }

    [Fact]
    public void NonGmPlayer_UsesCache_WithStrictDiagonalRule()
    {
        StepCache.Instance.Clear();
        StepCache.Instance.MissPromotionThreshold = 1;
        var map = Map.Maps[1];
        Assert.NotNull(map);

        var stub = new PlayerStub();
        map.GetAverageZ(1500, 1600, out _, out var startZ, out _);
        var start = new Point3D(1500, 1600, (sbyte)startZ);
        var goal = new Point3D(1498, 1598, (sbyte)startZ);

        stub.MoveToWorld(start, map);

        var statsBefore = StepCache.Instance.GetStats();
        var result = BitmapAStarAlgorithm.Instance.Find(stub, map, start, goal);
        var statsAfter = StepCache.Instance.GetStats();

        stub.Delete();

        Assert.NotNull(result);
        Assert.NotEmpty(result);
        // BuildsTotal increments on every chunk build, which happens only when the cache
        // is queried. Slow path never touches the cache.
        Assert.True(statsAfter.BuildsTotal > statsBefore.BuildsTotal,
            "Non-GM player should use the cache, not the slow path");
    }

    [Fact]
    public void DoorCreature_UsesCache_NotSlowPath()
    {
        StepCache.Instance.Clear();
        StepCache.Instance.MissPromotionThreshold = 1;
        var map = Map.Maps[1];

        var stub = new DoorOpenerStub(World.NewMobile);
        stub.DefaultMobileInit();
        map.GetAverageZ(1500, 1600, out _, out var startZ, out _);
        var start = new Point3D(1500, 1600, (sbyte)startZ);
        var goal = new Point3D(1498, 1598, (sbyte)startZ);

        stub.MoveToWorld(start, map);

        var statsBefore = StepCache.Instance.GetStats();
        var result = BitmapAStarAlgorithm.Instance.Find(stub, map, start, goal);
        var statsAfter = StepCache.Instance.GetStats();

        stub.Delete();

        Assert.NotNull(result);
        Assert.NotEmpty(result);
        Assert.True(statsAfter.BuildsTotal > statsBefore.BuildsTotal,
            "CanOpenDoors creature should use the cache (doors are dynamic items)");
    }

    [Fact]
    public void ObstacleCreature_UsesCache_NotSlowPath()
    {
        StepCache.Instance.Clear();
        StepCache.Instance.MissPromotionThreshold = 1;
        var map = Map.Maps[1];

        var stub = new ObstacleClimberStub(World.NewMobile);
        stub.DefaultMobileInit();
        map.GetAverageZ(1500, 1600, out _, out var startZ, out _);
        var start = new Point3D(1500, 1600, (sbyte)startZ);
        var goal = new Point3D(1498, 1598, (sbyte)startZ);

        stub.MoveToWorld(start, map);

        var statsBefore = StepCache.Instance.GetStats();
        var result = BitmapAStarAlgorithm.Instance.Find(stub, map, start, goal);
        var statsAfter = StepCache.Instance.GetStats();

        stub.Delete();

        Assert.NotNull(result);
        Assert.NotEmpty(result);
        Assert.True(statsAfter.BuildsTotal > statsBefore.BuildsTotal,
            "CanMoveOverObstacles creature should use the cache (movables are dynamic items)");
    }

    // ---------------------------------------------------------------------------------
    // Promotion-gate integration tests. These exercise BitmapAStarAlgorithm.Find()
    // end-to-end against the live StepCache to prove the per-Find generation gate
    // actually defers BuildChunk on a single pathfind. They duplicate behavior that
    // unit tests cover at the cache layer; the value is end-to-end verification that
    // the bench-relevant scenario (single Find on cleared cache) skips builds entirely.
    // TODO: REMOVE these two tests once PR-6's gate is proven stable in production BDN.
    // ---------------------------------------------------------------------------------

    [Fact]
    public void Find_SinglePathfindOnClearedCache_DoesNotBuildAnyChunk()
    {
        StepCache.Instance.Clear();
        StepCache.Instance.MissPromotionThreshold = 2;

        var map = Map.Maps[1];
        var stub = new DefaultWalkerStub();
        map.GetAverageZ(1500, 1600, out _, out var startZ, out _);
        var start = new Point3D(1500, 1600, (sbyte)startZ);
        var goal = new Point3D(1498, 1598, (sbyte)startZ);
        stub.MoveToWorld(start, map);

        var result = BitmapAStarAlgorithm.Instance.Find(stub, map, start, goal);

        var stats = StepCache.Instance.GetStats();
        stub.Delete();

        Assert.NotNull(result);
        Assert.Equal(0L, stats.BuildsTotal);
        Assert.True(stats.FallthroughNotBuilt > 0L,
            $"expected fallthrough on every chunk touched once; got 0 (residents={stats.ResidentChunks})");
        _output.WriteLine(
            $"single-Find gate: builds={stats.BuildsTotal} fallthrough_not_built={stats.FallthroughNotBuilt}"
        );
    }

    [Fact]
    public void Find_TwoPathfindsOverlappingChunks_PromoteToBuildOnSecondFind()
    {
        StepCache.Instance.Clear();
        StepCache.Instance.MissPromotionThreshold = 2;

        var map = Map.Maps[1];
        var stub = new DefaultWalkerStub();
        map.GetAverageZ(1500, 1600, out _, out var startZ, out _);
        var start = new Point3D(1500, 1600, (sbyte)startZ);
        var goal = new Point3D(1498, 1598, (sbyte)startZ);
        stub.MoveToWorld(start, map);

        // Find #1: first time anyone touches these chunks. Gate defers; no builds.
        BitmapAStarAlgorithm.Instance.Find(stub, map, start, goal);
        var afterFirst = StepCache.Instance.GetStats();
        Assert.Equal(0L, afterFirst.BuildsTotal);

        // Find #2: same path; chunks now hit their second distinct Find inside the window.
        // Gate promotes — at least one BuildChunk fires.
        BitmapAStarAlgorithm.Instance.Find(stub, map, start, goal);
        var afterSecond = StepCache.Instance.GetStats();

        stub.Delete();

        Assert.True(afterSecond.BuildsTotal > 0L,
            $"second Find through overlapping chunks must promote (got {afterSecond.BuildsTotal} builds)");
        _output.WriteLine(
            $"two-Find gate: first builds={afterFirst.BuildsTotal} second builds={afterSecond.BuildsTotal}"
        );
    }

    /// <summary>
    /// Plain Mobile — RequiresSlowPath returns false, the bitmap algorithm uses the cache
    /// fast path on every expansion.
    /// </summary>
    private sealed class DefaultWalkerStub : Mobile
    {
        public DefaultWalkerStub()
        {
            Body = 0xC9;
        }
    }

    /// <summary>
    /// Mobile with Player=true and default AccessLevel (Player). Triggers the strict
    /// AND-rule for diagonal corner-cut while still using the cache.
    /// </summary>
    private sealed class PlayerStub : Mobile
    {
        public PlayerStub()
        {
            Body = 0xC9;
            Player = true;
        }
    }

    /// <summary>
    /// BaseCreature with CanSwim=true — uses the cache via capability overlay (walk OR
    /// (wet AND canSwim)). Use the Serial constructor (deserialization path) to bypass
    /// NPCSpeeds init, which requires the npc-speeds.json table loaded — not available
    /// in tests.
    /// </summary>
    private sealed class SwimmingStub : BaseCreature
    {
        public SwimmingStub(Serial serial) : base(serial)
        {
            Body = 0xC9;
        }
    }

    /// <summary>
    /// BaseCreature with CanFly=true — RequiresSlowPath returns true (Z-jumping is beyond
    /// the cache's static-only scope), so GetSuccessors short-circuits to the slow path.
    /// </summary>
    private sealed class FlyingStub : BaseCreature
    {
        public FlyingStub(Serial serial) : base(serial)
        {
            Body = 0xC9;
        }

        public override bool CanFly => true;
    }

    private sealed class DoorOpenerStub : BaseCreature
    {
        public DoorOpenerStub(Serial serial) : base(serial)
        {
            Body = 0xC9;
        }

        public override bool CanOpenDoors => true;
    }

    private sealed class ObstacleClimberStub : BaseCreature
    {
        public ObstacleClimberStub(Serial serial) : base(serial)
        {
            Body = 0xC9;
        }

        public override bool CanMoveOverObstacles => true;
    }
}