using Friflo.Engine.ECS;
using Microsoft.Xna.Framework;
using MrGameEng.Core;
using MrGameEng.Graphics;
using Xunit;

namespace MrGameEng.Collisions.Tests;

public class CollisionWorldTests
{
    private sealed class CollisionScene : Scene
    {
        public CollisionWorld World = null!;

        protected override void OnLoad() => World = this.UseCollisions(cellSize: 32f);
    }

    private static (EngineContext Context, CollisionScene Scene) CreateScene()
    {
        var context = new EngineContext();
        var scene = new CollisionScene();
        context.Scenes.Switch(scene);
        context.Scenes.Update(context.Clock); // применяет переключение и первый тик
        return (context, scene);
    }

    private static Entity Spawn(Scene scene, Vector2 position, in Collider collider) =>
        scene.Store.CreateEntity(Transform2D.At(position), collider);

    private static void Tick(EngineContext context)
    {
        context.Clock.Advance(0.016f);
        context.Scenes.Update(context.Clock);
    }

    [Fact]
    public void OverlappingCircles_ProduceOnePair()
    {
        var (context, scene) = CreateScene();
        var a = Spawn(scene, new Vector2(0f, 0f), Collider.Circle(10f));
        var b = Spawn(scene, new Vector2(15f, 0f), Collider.Circle(10f));
        Spawn(scene, new Vector2(100f, 100f), Collider.Circle(10f)); // далёкий — без пар

        Tick(context);

        var pair = Assert.Single(scene.World.Pairs.ToArray());
        Assert.True((pair.A == a && pair.B == b) || (pair.A == b && pair.B == a));
    }

    [Fact]
    public void SeparatedCircles_NoPairs()
    {
        var (context, scene) = CreateScene();
        Spawn(scene, new Vector2(0f, 0f), Collider.Circle(5f));
        Spawn(scene, new Vector2(11f, 0f), Collider.Circle(5f));

        Tick(context);

        Assert.Equal(0, scene.World.Pairs.Length);
    }

    [Fact]
    public void CircleAndBox_Overlap_DetectedBothWays()
    {
        var (context, scene) = CreateScene();
        Spawn(scene, new Vector2(0f, 0f), Collider.Box(20f, 20f));
        Spawn(scene, new Vector2(14f, 0f), Collider.Circle(5f)); // касается правой грани

        Tick(context);

        Assert.Equal(1, scene.World.Pairs.Length);
    }

    [Fact]
    public void CornerCircle_DoesNotTouchBox()
    {
        var (context, scene) = CreateScene();
        Spawn(scene, new Vector2(0f, 0f), Collider.Box(20f, 20f));
        // Угол бокса (10,10); круг r=5 в (16,16): расстояние до угла ~8.49 > 5.
        Spawn(scene, new Vector2(16f, 16f), Collider.Circle(5f));

        Tick(context);

        Assert.Equal(0, scene.World.Pairs.Length);
    }

    [Fact]
    public void LayerMasks_FilterPairs()
    {
        var (context, scene) = CreateScene();
        var ghost = Collider.Circle(10f);
        ghost.Layer = 0b10;
        ghost.CollidesWith = 0b10; // призраки сталкиваются только с призраками

        var wall = Collider.Circle(10f);
        wall.Layer = 0b01;
        wall.CollidesWith = 0b01;

        Spawn(scene, new Vector2(0f, 0f), ghost);
        Spawn(scene, new Vector2(5f, 0f), wall);

        Tick(context);

        Assert.Equal(0, scene.World.Pairs.Length);
    }

    [Fact]
    public void MovingApart_PairDisappearsNextTick()
    {
        var (context, scene) = CreateScene();
        Spawn(scene, new Vector2(0f, 0f), Collider.Circle(10f));
        var mover = Spawn(scene, new Vector2(5f, 0f), Collider.Circle(10f));

        Tick(context);
        Assert.Equal(1, scene.World.Pairs.Length);

        mover.GetComponent<Transform2D>().Position = new Vector2(100f, 0f);
        Tick(context);
        Assert.Equal(0, scene.World.Pairs.Length);
    }

    [Fact]
    public void LargeCluster_AllTouchingPairsFound_OnceEach()
    {
        var (context, scene) = CreateScene();
        // Цепочка из 10 кругов: касаются только соседи → ровно 9 пар.
        for (var i = 0; i < 10; i++)
        {
            Spawn(scene, new Vector2(i * 18f, 0f), Collider.Circle(10f));
        }

        Tick(context);

        Assert.Equal(9, scene.World.Pairs.Length);
    }

    [Fact]
    public void QueryAabb_ReturnsOnlyEntitiesInArea()
    {
        var (context, scene) = CreateScene();
        var inside = Spawn(scene, new Vector2(10f, 10f), Collider.Circle(5f));
        Spawn(scene, new Vector2(200f, 200f), Collider.Circle(5f));

        Tick(context);

        Span<Entity> results = new Entity[8];
        var found = scene.World.QueryAabb(new RectF(0f, 0f, 50f, 50f), results);

        Assert.Equal(1, found);
        Assert.Equal(inside, results[0]);
    }

    [Fact]
    public void Raycast_HitsClosestCollider_AndRespectsMask()
    {
        var (context, scene) = CreateScene();
        var near = Collider.Circle(5f);
        near.Layer = 0b01;
        var far = Collider.Circle(5f);
        far.Layer = 0b10;

        var nearEntity = Spawn(scene, new Vector2(30f, 0f), near);
        var farEntity = Spawn(scene, new Vector2(60f, 0f), far);

        Tick(context);

        Assert.True(scene.World.Raycast(new Vector2(0f, 0f), new Vector2(100f, 0f), out var hit));
        Assert.Equal(nearEntity, hit.Entity);
        Assert.Equal(25f, hit.Point.X, 1);

        Assert.True(
            scene.World.Raycast(new Vector2(0f, 0f), new Vector2(100f, 0f), out hit, mask: 0b10)
        );
        Assert.Equal(farEntity, hit.Entity);
    }

    [Fact]
    public void Raycast_Miss_ReturnsFalse()
    {
        var (context, scene) = CreateScene();
        Spawn(scene, new Vector2(0f, 50f), Collider.Box(10f, 10f));

        Tick(context);

        Assert.False(scene.World.Raycast(new Vector2(0f, 0f), new Vector2(100f, 0f), out _));
    }

    [Fact]
    public void QueryAabb_BeforeFirstRebuild_ReturnsZero()
    {
        // До первого EndRebuild хэш пуст; запрос не должен зависать и что-то находить.
        var world = new CollisionWorld();

        Span<Entity> results = new Entity[4];
        Assert.Equal(0, world.QueryAabb(new RectF(-10f, -10f, 20f, 20f), results));
    }

    [Fact]
    public void QueryAabb_TruncatedResults_DoNotPoisonNextQuery()
    {
        var (context, scene) = CreateScene();
        for (var i = 0; i < 3; i++)
        {
            Spawn(scene, new Vector2(i * 5f, 0f), Collider.Circle(4f));
        }

        Tick(context);

        var area = new RectF(-10f, -10f, 40f, 20f);
        Span<Entity> tiny = new Entity[1];
        Assert.Equal(1, scene.World.QueryAabb(area, tiny)); // обрезан по размеру буфера

        Span<Entity> all = new Entity[8];
        Assert.Equal(3, scene.World.QueryAabb(area, all)); // повторный запрос видит всех
    }

    [Fact]
    public void Raycast_FromInsideCircle_HitsAtOrigin()
    {
        var (context, scene) = CreateScene();
        var entity = Spawn(scene, new Vector2(0f, 0f), Collider.Circle(10f));

        Tick(context);

        Assert.True(scene.World.Raycast(new Vector2(0f, 0f), new Vector2(100f, 0f), out var hit));
        Assert.Equal(entity, hit.Entity);
        Assert.Equal(0f, hit.Fraction);
        Assert.Equal(Vector2.Zero, hit.Point);
    }

    [Fact]
    public void ExactlyTouchingBoxes_ProducePair()
    {
        var (context, scene) = CreateScene();
        Spawn(scene, new Vector2(0f, 0f), Collider.Box(20f, 20f));
        Spawn(scene, new Vector2(20f, 0f), Collider.Box(20f, 20f)); // грани соприкасаются ровно

        Tick(context);

        Assert.Equal(1, scene.World.Pairs.Length); // как и у касающихся кругов
    }
}