using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using Microsoft.Xna.Framework;

namespace Aphelion.Entities
{
    [Serializable]
    public abstract class CollisionObject
    {
        public abstract Vector2 Intersects(PhysicsObject physicsObj);

        public static bool PointIntersectsTriangle(Vector2 testPoint, Vector2 trianglePoint1, Vector2 trianglePoint2, Vector2 trianglePoint3) // Thanks to Glenn Slayden of StackOverflow for this solution
        {
            float s = trianglePoint1.Y * trianglePoint3.X - trianglePoint1.X * trianglePoint3.Y + (trianglePoint3.Y - trianglePoint1.Y) * testPoint.X + (trianglePoint1.X - trianglePoint3.X) * testPoint.Y;
            float t = trianglePoint1.X * trianglePoint2.Y - trianglePoint1.Y * trianglePoint2.X + (trianglePoint1.Y - trianglePoint2.Y) * testPoint.X + (trianglePoint2.X - trianglePoint1.X) * testPoint.Y;

            if ((s < 0) != (t < 0))
            {
                return false;
            }

            float A = -trianglePoint2.Y * trianglePoint3.X + trianglePoint1.Y * (trianglePoint3.X - trianglePoint2.X) + trianglePoint1.X * (trianglePoint2.Y - trianglePoint3.Y) + trianglePoint2.X * trianglePoint3.Y;

            if (A < 0.0)
            {
                s = -s;
                t = -t;
                A = -A;
            }

            return s > 0 && t > 0 && (s + t) < A;
        }
    }

    [Serializable]
    public class Point : CollisionObject
    {
        public Vector2 Position;

        public Point(Vector2 position)
        {
            Position = position;
        }

        public bool Intersects(PhysicsObject physicsObj)
        {
            Point point = physicsObj.CollisionObj as Point;
            Triangle triangle = physicsObj.CollisionObj as Triangle;
            ComplexShape complexShape = physicsObj.CollisionObj as ComplexShape;
            Circle circle = physicsObj.CollisionObj as Circle;

            if (point != null)
            {
                return point.Position == Position;
            }
            else if (triangle != null)
            {
                return CollisionObject.PointIntersectsTriangle(Position, triangle.Points[0], triangle.Points[1], triangle.Points[2]);
            }
            else if (complexShape != null)
            {
                foreach (Triangle complexShapeTriangle in complexShape.Triangles)
                {
                    if (CollisionObject.PointIntersectsTriangle(Position, complexShapeTriangle.Points[0], complexShapeTriangle.Points[1], complexShapeTriangle.Points[2]))
                    {
                        return true;
                    }
                }
            }
            else if (circle != null)
            {
                return Vector2.Distance(Position, circle.Position) <= circle.Radius;
            }

            return false;
        }
    }

    [Serializable]
    public class Triangle : CollisionObject
    {
        public Vector2[] Points;

        public Triangle(Vector2 point1, Vector2 point2, Vector2 point3)
        {
            Points = new Vector2[] { point1, point2, point3 };
        }

        public bool Intersects(PhysicsObject physicsObj)
        {
            Point point = physicsObj.CollisionObj as Point;
            Triangle triangle = physicsObj.CollisionObj as Triangle;
            ComplexShape complexShape = physicsObj.CollisionObj as ComplexShape;
            Circle circle = physicsObj.CollisionObj as Circle;

            if (point != null)
            {
            }
            else if (triangle != null)
            {
            }
            else if (complexShape != null)
            {
            }
            else if (circle != null)
            {
            }

            return false;
        }
    }

    [Serializable]
    public class ComplexShape : CollisionObject
    {
        public Triangle[] Triangles;

        public ComplexShape(params Triangle[] triangles)
        {
            Triangles = triangles;
        }
    }

    [Serializable]
    public class Circle : CollisionObject
    {
        public Vector2 Position;
        public float Radius;

        public Circle(Vector2 position, float radius)
        {
            Position = position;
            Radius = radius;
        }
    }

    // To do: Add line segments
}