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

namespace MonoGame.Extended.Triangulation
{
    /// <summary>
	/// A basic triangle structure that holds the three vertices that make up a given triangle.
    /// MIT Licensed: https://github.com/nickgravelyn/Triangulator
	/// </summary>
	struct Triangle
    {
        public readonly Vertex A;
        public readonly Vertex B;
        public readonly Vertex C;

        public Triangle(Vertex a, Vertex b, Vertex c)
        {
            A = a;
            B = b;
            C = c;
        }

        public bool ContainsPoint(Vertex point)
        {
            //return true if the point to test is one of the vertices
            if (point.Equals(A) || point.Equals(B) || point.Equals(C))
                return true;

            bool oddNodes = false;

            if (checkPointToSegment(C, A, point))
                oddNodes = !oddNodes;
            if (checkPointToSegment(A, B, point))
                oddNodes = !oddNodes;
            if (checkPointToSegment(B, C, point))
                oddNodes = !oddNodes;

            return oddNodes;
        }

        public static bool ContainsPoint(Vertex a, Vertex b, Vertex c, Vertex point)
        {
            return new Triangle(a, b, c).ContainsPoint(point);
        }

        static bool checkPointToSegment(Vertex sA, Vertex sB, Vertex point)
        {
            if ((sA.Position.Y < point.Position.Y && sB.Position.Y >= point.Position.Y) ||
                (sB.Position.Y < point.Position.Y && sA.Position.Y >= point.Position.Y))
            {
                float x =
                    sA.Position.X +
                    (point.Position.Y - sA.Position.Y) /
                    (sB.Position.Y - sA.Position.Y) *
                    (sB.Position.X - sA.Position.X);

                if (x < point.Position.X)
                    return true;
            }

            return false;
        }

        public override bool Equals(object obj)
        {
            if (obj.GetType() != typeof(Triangle))
                return false;
            return Equals((Triangle)obj);
        }

        public bool Equals(Triangle obj)
        {
            return obj.A.Equals(A) && obj.B.Equals(B) && obj.C.Equals(C);
        }

        public override int GetHashCode()
        {
            unchecked
            {
                int result = A.GetHashCode();
                result = (result * 397) ^ B.GetHashCode();
                result = (result * 397) ^ C.GetHashCode();
                return result;
            }
        }
    }
}