package org.matheclipse.core.patternmatching;

import java.util.Comparator;

import org.matheclipse.core.interfaces.IPatternObject;
import org.matheclipse.core.interfaces.IPatternSequence;

/**
 * Compares two pattern objects.
 * 
 */
public class PatternComparator implements Comparator {
	/**
	 * The only PatternComparator instance.
	 */
	public static PatternComparator CONST = new PatternComparator();

	private PatternComparator() {

	}

	/**
	 * Compares two patterns. Two patterns are considered as equal, if there
	 * associated symbols are equal and not null. If the associated
	 * symbols are null, then the patterns
	 * System#identityHashCode() value is used to compare them.
	 */
	@Override
	public int compare(IPatternObject o1, IPatternObject o2) {
		if (o1 == o2) {
			return 0;
		}
		if (!o1.getClass().equals(o2.getClass())) {
			if (o1 instanceof IPatternSequence) {
				return 1;
			}
			return -1;
		}
		if (o1.getSymbol() == null) {
			if (o2.getSymbol() == null) {
				if (System.identityHashCode(o1) > System.identityHashCode(o2)) {
					return 1;
				} 
			}
			return -1;
		}
		if (o2.getSymbol() == null) {
			return 1;
		}
		return o1.getSymbol().compareTo(o2.getSymbol());
	}

}