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

namespace bbiwarg.Utility
{
    public enum LineSide
    {
        onLine = 0,
        above = 1,
        below = 2
    }

    class Line2D
    {
        public Vector2D P1 { get; private set; }
        public Vector2D P2 { get; private set; }
        public Vector2D Direction { get; private set; }
        public float Length { get { return P1.getDistanceTo(P2); }}

        public Line2D(Vector2D p1, Vector2D p2)
        {
            setPoints(p1, p2);
        }

        private void setPoints(Vector2D p1, Vector2D p2)
        {
            //endpoints
            P1 = p1;
            P2 = p2;

            //direction
            Direction = (P1 - P2).normalize();
        }

        public float getAngleBetween(Line2D line)
        {
            float angle = Direction.getAngleBetween(line.Direction);
            return Math.Min(angle, 180 - angle);
        }

        public float getParallelDistanceTo(Line2D line)
        {
            if (onSide(line.P1) != onSide(line.P2)) return 0;

            Vector2D a1 = projectToLine(line.P1);
            Vector2D a2 = projectToLine(line.P2);

            float distanceA1 = a1.getDistanceTo(line.P1);
            float distanceA2 = a2.getDistanceTo(line.P2);
            return Math.Min(distanceA1, distanceA2);
        }

        public float getVerticalDistanceTo(Line2D line)
        {
            Vector2D a1 = projectToLine(line.P1);
            Vector2D a2 = projectToLine(line.P2);

            if (P1.isInBox(a1, a2) || P2.isInBox(a1, a2)) return 0;

            float distanceP1A1 = P1.getDistanceTo(a1);
            float distanceP1A2 = P1.getDistanceTo(a2);
            float distanceP2A1 = P2.getDistanceTo(a1);
            float distanceP2A2 = P2.getDistanceTo(a2);
            return Math.Min(Math.Min(distanceP1A1, distanceP1A2), Math.Min(distanceP2A1, distanceP2A2));
        }

        public LineSide onSide(Vector2D point)
        {
            float yPerX = Direction.Y / Direction.X;
            float xDiff = point.X - P1.X;
            float newY = P1.Y + yPerX * xDiff;
            if (newY < point.Y) return LineSide.above;
            else if (newY > point.Y) return LineSide.below;
            else return LineSide.onLine;
        }

        public Vector2D projectToLine(Vector2D point)
        {
            float px = point.X, py = point.Y, dx = Direction.X, dy = Direction.Y, ox = P1.X, oy = P1.Y;
            float diffx = px - ox;
            float diffy = py - oy;

            float diff_d = (diffx * dx + diffy * dy);
            float d_d = (dx * dx + dy * dy);
            float q = diff_d / d_d;

            float newX = ox + q * dx;
            float newY = oy + q * dy;

            return new Vector2D(newX, newY);
        }

        public Vector2D intersection(Line2D line)
        {
            Vector2D p = P1;
            Vector2D r = P2 - P1;
            Vector2D q = line.P1;
            Vector2D s = line.P2 - line.P1;

            float r_cross_s = r.cross(s);
            float q_p_cross_s = (q - p).cross(s);

            if (r_cross_s == 0.0)
                return null;

            float t = q_p_cross_s / r_cross_s;
            return p + t * r;
        }

        public override string ToString()
        {
            return (int)P1.X + "|" + (int)P1.Y + " --- " + (int)P2.X + "|" + (int)P2.Y;
        }
    }
}