using Friflo.Engine.ECS;
using Microsoft.Xna.Framework;

namespace MrGameEng.Collisions;

/// <summary>Shape of a <see cref="Collider"/>.</summary>
public enum ColliderShape : byte
{
    /// <summary>Circle of <see cref="Collider.Radius"/>.</summary>
    Circle,

    /// <summary>Axis-aligned box of <see cref="Collider.HalfExtents"/>. Does not rotate with the entity.</summary>
    Box,
}

/// <summary>
/// Collision shape component. Create via <see cref="Circle"/> or <see cref="Box"/> —
/// the struct default has no size and collides with nothing.
/// Positions come from <c>Transform2D</c>; <see cref="Offset"/> shifts the shape
/// relative to it (entity scale and rotation are not applied to collider shapes).
/// </summary>
public struct Collider : IComponent
{
    /// <summary>Shape kind.</summary>
    public ColliderShape Shape;

    /// <summary>Circle radius in world units (<see cref="ColliderShape.Circle"/> only).</summary>
    public float Radius;

    /// <summary>Half extents of the box (<see cref="ColliderShape.Box"/> only).</summary>
    public Vector2 HalfExtents;

    /// <summary>Shape center offset from the entity's transform position.</summary>
    public Vector2 Offset;

    /// <summary>Bit mask of layers this collider belongs to.</summary>
    public uint Layer;

    /// <summary>Bit mask of layers this collider collides with. A pair is reported only when the masks agree both ways.</summary>
    public uint CollidesWith;

    /// <summary>Creates a circle collider on layer 1 colliding with everything.</summary>
    public static Collider Circle(float radius, Vector2 offset = default) =>
        new()
        {
            Shape = ColliderShape.Circle,
            Radius = radius,
            Offset = offset,
            Layer = 1,
            CollidesWith = uint.MaxValue,
        };

    /// <summary>Creates a box collider on layer 1 colliding with everything.</summary>
    public static Collider Box(float width, float height, Vector2 offset = default) =>
        new()
        {
            Shape = ColliderShape.Box,
            HalfExtents = new Vector2(width / 2f, height / 2f),
            Offset = offset,
            Layer = 1,
            CollidesWith = uint.MaxValue,
        };
}