ModernUO/Projects/UOContent.Tests/Tests/Mobiles/AI/ApproachTargetTests.cs

using Server.Tests.Terrain;
using System;
using System.Collections.Generic;
using Server.Engines.Pathing.Cache;
using Server.Mobiles;
using Xunit;

namespace Server.Tests.Mobiles.AI;

// AI movement tests drive the real BaseAI primitives against live map statics. The
// pathfinder uses non-reentrant static buffers, so we share the pathfinding sequential
// collection to avoid parallel interference.
[Collection("Sequential Pathfinding Tests")]
public class ApproachTargetTests : IDisposable
{
    private readonly List<IEntity> _created = [];

    public void Dispose()
    {
        for (var i = _created.Count - 1; i >= 0; i--)
        {
            _created[i].Delete();
        }

        _created.Clear();
    }

    private (BareCreatureStub bc, BaseAI ai) NewFollower(Map map, Point3D loc)
    {
        var bc = new BareCreatureStub(World.NewMobile);
        bc.DefaultMobileInit();
        bc.MoveToWorld(loc, map);
        _created.Add(bc);
        BaseAI ai = new AnimalAI(bc);
        ai.AITimer?.Stop(); // we drive movement manually; no background timer
        return (bc, ai);
    }

    private WalkerStub NewTarget(Map map, Point3D loc)
    {
        var target = new WalkerStub();
        target.MoveToWorld(loc, map);
        _created.Add(target);
        return target;
    }

    private void PlaceBlocker(Map map, ushort itemId, int x, int y)
    {
        map.GetAverageZ(x, y, out _, out var z, out _);
        _created.Add(new Item(World.NewItem) { ItemID = itemId, Map = map, Location = new Point3D(x, y, (sbyte)z) });
    }

    // Drives the pet follow primitive once per tick; returns true once it reaches within
    // arriveDist tiles. Uses InRange (Chebyshev) to match the game's own range semantics —
    // a diagonal neighbor at Euclidean ~2.24 is "within 2" to the engine.
    private static bool DriveFollow(BaseAI ai, Mobile bc, Mobile target, int arriveDist, int maxTicks)
    {
        for (var i = 0; i < maxTicks; i++)
        {
            ai.NextMove = 0;
            ai.WalkMobileRange(target, 1, 1, 2);
            if (bc.InRange(target, arriveDist))
            {
                return true;
            }
        }
        return false;
    }

    [Fact]
    public void OpenTerrain_ReachesTarget_WithoutPathfinding()
    {
        var map = Map.Maps[1];
        Assert.NotNull(map);
        map.GetAverageZ(1500, 1600, out _, out var z, out _);

        var (bc, ai) = NewFollower(map, new Point3D(1500, 1600, (sbyte)z));
        var target = NewTarget(map, new Point3D(1495, 1600, (sbyte)z)); // 5 tiles west, open

        StepCache.Instance.Clear();
        var buildsBefore = StepCache.Instance.GetStats().BuildsTotal;

        var arrived = DriveFollow(ai, bc, target, 2, 40);

        var buildsAfter = StepCache.Instance.GetStats().BuildsTotal;

        Assert.True(arrived, "creature should reach an open-terrain target by stepping");
        Assert.Equal(buildsBefore, buildsAfter); // greedy fast path: no chunk builds
    }

    // An upstairs room with an L-shaped counter: the pet is south of it, the master north.
    [Fact]
    public void InnCounter_PetReachesMaster()
    {
        var inn = Prefabs.InnUpstairs;
        inn.AssertPresent();
        var map = Map.Maps[1];
        Assert.NotNull(map);

        var (bc, ai) = NewFollower(map, inn.Anchor);
        var target = NewTarget(map, inn.Target);

        // The straight line north runs into the counter, so arriving means the pet went round it.
        var belowCounter = new Point3D(inn.Anchor.X, inn.Target.Y + 6, inn.Anchor.Z);
        Assert.False(Server.Movement.Movement.CheckMovement(bc, map, belowCounter, Direction.North, out _));

        StepCache.Instance.Clear();

        // 200 ticks is generous for the ~20-step detour at one step per tick.
        var arrived = DriveFollow(ai, bc, target, 2, 200);

        Assert.True(arrived, "pet must navigate around the L-shaped counter to reach the master");
    }

    [Fact]
    public void MoveTo_ReachesTargetAroundCounter()
    {
        var inn = Prefabs.InnUpstairs;
        inn.AssertPresent();
        var map = Map.Maps[1];
        Assert.NotNull(map);

        var (bc, ai) = NewFollower(map, inn.Anchor);
        var target = NewTarget(map, inn.Target);

        StepCache.Instance.Clear();

        var arrived = false;
        for (var i = 0; i < 200; i++)
        {
            ai.NextMove = 0;
            ai.MoveTo(target, 1);
            if (bc.InRange(target, 1))
            {
                arrived = true;
                break;
            }
        }

        Assert.True(arrived, "MoveTo chaser must reach the target around the counter");
    }

    [Fact]
    public void MoveTo_CatchesTargetWalkingAway_OpenTerrain()
    {
        var map = Map.Maps[1];
        Assert.NotNull(map);
        map.GetAverageZ(1500, 1600, out _, out var z, out _);

        var (bc, ai) = NewFollower(map, new Point3D(1500, 1600, (sbyte)z));
        var target = NewTarget(map, new Point3D(1498, 1600, (sbyte)z));

        StepCache.Instance.Clear();

        var caught = false;
        for (var i = 0; i < 60; i++)
        {
            ai.NextMove = 0;
            ai.MoveTo(target, 1);

            // Target walks west every other tick for its first several steps, then stops,
            // so a same-speed chaser eventually closes the gap.
            if (i % 2 == 0 && i < 16 && target.X > 1490)
            {
                target.MoveToWorld(new Point3D(target.X - 1, target.Y, target.Z), map);
            }

            if (bc.InRange(target, 1))
            {
                caught = true;
                break;
            }
        }

        Assert.True(caught, "chaser must catch a target that walks away then stops");
    }

    [Fact]
    public void UnreachableTarget_GivesUp_AndIdles()
    {
        var map = Map.Maps[1];
        Assert.NotNull(map);
        map.GetAverageZ(1500, 1601, out _, out var z, out _);

        var (bc, ai) = NewFollower(map, new Point3D(1500, 1601, (sbyte)z));
        var target = NewTarget(map, new Point3D(1500, 1596, (sbyte)z));

        // Full impassable ring around the target cell -> no path to within range 1.
        const ushort id = TestTiles.Counter;
        for (var x = 1499; x <= 1501; x++)
        {
            for (var y = 1595; y <= 1597; y++)
            {
                if (x == 1500 && y == 1596)
                {
                    continue; // leave the target's own cell
                }

                PlaceBlocker(map, id, x, y);
            }
        }

        StepCache.Instance.Clear();

        // Run well past the stuck window so give-up engages.
        for (var i = 0; i < 120; i++)
        {
            ai.NextMove = 0;
            ai.MoveTo(target, 1);
        }

        // After giving up, the creature must idle (not oscillate) while the goal is still.
        var idleStart = bc.Location;
        var stayedIdle = true;
        for (var i = 0; i < 20; i++)
        {
            ai.NextMove = 0;
            ai.MoveTo(target, 1);
            if (bc.Location != idleStart)
            {
                stayedIdle = false;
                break;
            }
        }

        Assert.False(bc.InRange(target, 1), "walled-off target must not be reached");
        Assert.True(stayedIdle, "after giving up, the creature must idle, not shuffle");
    }

    [Fact]
    public void WallBetween_RoutesAround_ReachesTarget()
    {
        var map = Map.Maps[1];
        Assert.NotNull(map);
        map.GetAverageZ(1500, 1600, out _, out var z, out _);

        var (bc, ai) = NewFollower(map, new Point3D(1500, 1600, (sbyte)z));
        var target = NewTarget(map, new Point3D(1500, 1595, (sbyte)z)); // 5 tiles north

        // Impassable wall on Y=1598 from X=1497..1503: blocks the straight line; ends open.
        const ushort id = TestTiles.Counter;
        for (var x = 1497; x <= 1503; x++)
        {
            PlaceBlocker(map, id, x, 1598);
        }

        StepCache.Instance.Clear();

        var arrived = DriveFollow(ai, bc, target, 2, 200);

        Assert.True(arrived, "creature must route around the wall to reach the target");
    }
}