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Problem Solving Library for Java

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package org.psjava.formula.geometry;

import java.util.Comparator;

import org.psjava.ds.geometry.Point2D;
import org.psjava.ds.numbersystrem.MultipliableNumberSystem;

public class DirectionComparator {

	public static  Comparator> create(final MultipliableNumberSystem ns, final Point2D center, final Point2D basis) {
		return new Comparator>() {
			@Override
			public int compare(Point2D p1, Point2D p2) {
				int z1 = calcZoneOrder(p1);
				int z2 = calcZoneOrder(p2);
				if (z1 != z2) {
					return z1 - z2;
				} else { // same zone case
					if (z1 == 0 || z1 == 2) {
						return 0;
					} else {
						T ccw = CCW.ccw(ns, p1, center, p2);
						if (RightTurnFromCCW.is(ns, ccw))
							return -1;
						else if (LeftTurnFromCCW.is(ns, ccw))
							return 1;
						else
							return 0;
					}
				}
			}

			int calcZoneOrder(Point2D p) {
				T ccw = CCW.ccw(ns, basis, center, p);
				if (StraightOrderFromCCW.is(ns, basis, center, p, ccw))
					return 2; // directly opposite from basis.
				else if (RightTurnFromCCW.is(ns, ccw))
					return 1; // right side from basis
				else if (LeftTurnFromCCW.is(ns, ccw))
					return 3; // left side from basis
				else
					return 0; // same direction with basis's
			}

		};
	}

}