/*******************************************************************************
 *
 * Copyright (c) 2004-2011 Oracle Corporation
 *
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 *       Kohsuke Kawaguchi 
 *
 *******************************************************************************/ 

package hudson.util;

import java.util.Collection;
import java.util.Arrays;

/**
 * Computes the string edit distance.
 *
 * <p> Refer to a computer science text book for the definition of the "string
 * edit distance".
 *
 * @author Kohsuke Kawaguchi (kohsuke.kawaguchi@sun.com)
 */
public class EditDistance {

    /**
     * Computes the edit distance between two strings.
     *
     * <p> The complexity is O(nm) where n=a.length() and m=b.length().
     */
    public static int editDistance(String a, String b) {
        return new EditDistance(a, b).calc();
    }

    /**
     * Finds the string in the
     * <code>group</code> closest to
     * <code>key</code> and returns it.
     *
     * @return null if group.length==0.
     */
    public static String findNearest(String key, String[] group) {
        return findNearest(key, Arrays.asList(group));
    }

    public static String findNearest(String key, Collection<String> group) {
        int c = Integer.MAX_VALUE;
        String r = null;

        for (String g : group) {
            int ed = editDistance(key, g);
            if (c > ed) {
                c = ed;
                r = g;
            }
        }
        return r;
    }
    /**
     * cost vector.
     */
    private int[] cost;
    /**
     * back buffer.
     */
    private int[] back;
    /**
     * Two strings to be compared.
     */
    private final String a, b;

    private EditDistance(String a, String b) {
        this.a = a;
        this.b = b;
        cost = new int[a.length() + 1];
        back = new int[a.length() + 1]; // back buffer

        for (int i = 0; i <= a.length(); i++) {
            cost[i] = i;
        }
    }

    /**
     * Swaps two buffers.
     */
    private void flip() {
        int[] t = cost;
        cost = back;
        back = t;
    }

    private int min(int a, int b, int c) {
        return Math.min(a, Math.min(b, c));
    }

    private int calc() {
        for (int j = 0; j < b.length(); j++) {
            flip();
            cost[0] = j + 1;
            for (int i = 0; i < a.length(); i++) {
                int match = (a.charAt(i) == b.charAt(j)) ? 0 : 1;
                cost[i + 1] = min(back[i] + match, cost[i] + 1, back[i + 1] + 1);
            }
        }
        return cost[a.length()];
    }
}