using System;

using System.Windows;

using System.Windows.Media;

using System.Windows.Media.Media3D;



namespace HelixToolkit

{

    /// <summary>

    /// 3D Polygon

    /// </summary>

    public class Polygon3D

    {

        internal Point3DCollection points;



        public Polygon3D()

        {            

        }



        public Polygon3D(Point3DCollection pts)

        {

            points = pts;

        }



        public Point3DCollection Points

        {

            get { return points ?? (points = new Point3DCollection()); }

            set { points = value; }

        }



        // http://en.wikipedia.org/wiki/Polygon_triangulation

        // http://en.wikipedia.org/wiki/Monotone_polygon

        // http://www.codeproject.com/KB/recipes/hgrd.aspx LGPL

        // http://www.springerlink.com/content/g805787811vr1v9v/



        public bool IsPlanar()

        {

            Vector3D v1 = Points[1] - Points[0];

            var normal = new Vector3D();

            for (int i = 2; i < Points.Count; i++)

            {

                var n = Vector3D.CrossProduct(v1, Points[i] - Points[0]);

                n.Normalize();

                if (i == 2)

                    normal = n;

                else

                    if (Math.Abs(Vector3D.DotProduct(n, normal) - 1) > 1e-8)

                    {

                        return false;

                    }

            }

            return true;

        }



        public Vector3D GetNormal()

        {

            if (Points.Count < 3)

                throw new InvalidOperationException("At least three points required in the polygon to find a normal.");

            Vector3D v1 = Points[1] - Points[0];

            for (int i = 2; i < Points.Count; i++)

            {

                var n = Vector3D.CrossProduct(v1, Points[i] - Points[0]);

                if (n.LengthSquared > 1e-8)

                {

                    n.Normalize();

                    return n;

                }

            }

            throw new InvalidOperationException("Invalid polygon.");

        }



        public Polygon Flatten()

        {

            // http://forums.xna.com/forums/p/16529/86802.aspx

            // http://stackoverflow.com/questions/1023948/rotate-normal-vector-onto-axis-plane

            var up = GetNormal();

            up.Normalize();

            var right = Vector3D.CrossProduct(up, Math.Abs(up.X) > Math.Abs(up.Z) ? new Vector3D(0, 0, 1) : new Vector3D(1, 0, 0));

            var backward = Vector3D.CrossProduct(right, up);

            var m = new Matrix3D(backward.X, right.X, up.X, 0, backward.Y, right.Y, up.Y, 0, backward.Z, right.Z, up.Z, 0, 0, 0, 0, 1);

            

            // make first point origin

            var offs = m.Transform(Points[0]);

            m.OffsetX = -offs.X;

            m.OffsetY = -offs.Y;



            var polygon = new Polygon { Points = new PointCollection(Points.Count) };

            foreach (Point3D p in Points)

            {

                var pp = m.Transform(p);

                polygon.Points.Add(new Point(pp.X, pp.Y));

            }

            return polygon;

        }

    }

}