/*
 * FindBugs - Find Bugs in Java programs
 * Copyright (C) 2003-2008 University of Maryland
 * 
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 * 
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 * 
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */

package edu.umd.cs.findbugs.util;

/**
 * @author pwilliam
 */
public class EditDistance {
	/**
     * 
     */
	private static final int INSERT_OR_DELETE_COST = 2;

	private static int minimum(int a, int b, int c) {
		if (a > b)
			return Math.min(b, c);
		return Math.min(a, c);
	}

	private static int distance(char a, char b) {
		if (a == b)
			return 0;
		if (Character.toLowerCase(a) == Character.toLowerCase(b))
			return 1;
		return 2;
	}

	public static double editDistanceRatio(String str1, String str2) {
		double distance = editDistance(str1, str2);
		int maxDistance = INSERT_OR_DELETE_COST * Math.max(str1.length(), str2.length());
		return Math.min(distance / maxDistance, distance / 4);
	}

	public static int editDistance(String str1, String str2) {
		int n1 = str1.length();
		int n2 = str2.length();
		int diff = Math.abs(n1 - n2);
		if (diff > 6)
			return INSERT_OR_DELETE_COST * Math.max(n1, n2);
		return editDistance1(str1, str2);

	}

	public static int editDistance0(String str1, String str2) {
		int n1 = str1.length();
		int n2 = str2.length();

		int[][] distance = new int[n1 + 1][];

		for (int i = 0; i <= n1; i++) {
			distance[i] = new int[n2 + 1];
			distance[i][0] = INSERT_OR_DELETE_COST * i;
		}
		for (int j = 1; j <= n2; j++)
			distance[0][j] = INSERT_OR_DELETE_COST * j;

		for (int i = 1; i <= n1; i++)
			for (int j = 1; j <= n2; j++)
				distance[i][j] = minimum(distance[i - 1][j] + INSERT_OR_DELETE_COST, distance[i][j - 1] + INSERT_OR_DELETE_COST,
				        distance[i - 1][j - 1] + distance(str1.charAt(i - 1), str2.charAt(j - 1)));

		return distance[n1][n2];
	}

	public static int editDistance1(String str1, String str2) {
		int n1 = str1.length();
		int n2 = str2.length();

		int[] distance = new int[n2 + 1];
		int[] oldDistance = new int[n2 + 1];

		for (int j = 1; j <= n2; j++)
			oldDistance[j] = INSERT_OR_DELETE_COST * j;

		for (int i = 1; i <= n1; i++) {
			distance[0] = INSERT_OR_DELETE_COST * i;
			for (int j = 1; j <= n2; j++)
				distance[j] = minimum(oldDistance[j] + INSERT_OR_DELETE_COST, distance[j - 1] + INSERT_OR_DELETE_COST,
				        oldDistance[j - 1] + distance(str1.charAt(i - 1), str2.charAt(j - 1)));
			int[] tmp = oldDistance;
			oldDistance = distance;
			distance = tmp;
		}

		int result = oldDistance[n2];
		assert result == editDistance0(str1, str2);
		return result;
	}
}