using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace TransportGame.Model
{
    public struct LineSegment
    {
        public float X0 { get; private set; }
        public float Y0 { get; private set; }
        public float X1 { get; private set; }
        public float Y1 { get; private set; }

        public Vector2 P0
        {
            get
            {
                return new Vector2(X0, Y0);
            }
        }
        public Vector2 P1
        {
            get
            {
                return new Vector2(X1, Y1);
            }
        }

        public float Length
        {
            get
            {
                return (P1 - P0).Length;
            }
        }

        public float LengthSq
        {
            get
            {
                return (P1 - P0).LengthSq;
            }
        }

        public LineSegment(Vector2 p0, Vector2 p1)
            : this()
        {
            X0 = p0.X; Y0 = p0.Y;
            X1 = p1.X; Y1 = p1.Y;
        }

        public LineSegment(float x0, float y0, float x1, float y1)
            : this()
        {
            X0 = x0; Y0 = y0;
            X1 = x1; Y1 = y1;
        }

        public static Vector2? Intersect(LineSegment a, LineSegment b)
        {
            float s1x = a.X1 - a.X0, s1y = a.Y1 - a.Y0;
            float s2x = b.X1 - b.X0, s2y = b.Y1 - b.Y0;

            float det = (-s2x * s1y + s1x * s2y);

            // Avoid division by zero
            // Note: this is an edge case, the vectors might be parallel or colliniar
            if (det == 0) return null;

            float s = (-s1y * (a.X0 - b.X0) + s1x * (a.Y0 - b.Y0)) / det;
            float t = (s2x * (a.Y0 - b.Y0) - s2y * (a.X0 - b.X0)) / det;

            // Collision detected
            if (s >= 0 && s <= 1 && t >= 0 && t <= 1)
                return new Vector2(a.X0 + t * s1x, a.Y0 + t * s1y);

            // No collision
            return null;
        }

        /// <summary>
        /// Calculates the distance from point p to line segment
        /// </summary>
        /// <param name="line">Line</param>
        /// <param name="p">Point</param>
        /// <returns>Distance</returns>
        public static float Distance(LineSegment line, Vector2 p)
        {
            float det = (line.Y1 - line.Y0) * p.X - (line.X1 - line.X0) * p.Y 
                + line.X1 * line.Y0 - line.Y1 * line.X0;
            return Math.Abs(det) / line.Length;
        }

        public override string ToString()
        {
            return string.Format("({0}, {1})->({2}, {3})", X0, Y0, X1, Y1);
        }
    }
}