/*
 * The contents of this file are subject to the terms
 * of the Common Development and Distribution License
 * (the "License").  You may not use this file except
 * in compliance with the License.
 *
 * You can obtain a copy of the license at
 * http://java.net/projects/metro/
 * See the License for the specific language governing
 * permissions and limitations under the License.
 *
 * When distributing Covered Code, include this CDDL
 * HEADER in each file and include the License file at
 * https://jwsdp.java.net/CDDLv1.0.html  If applicable,
 * add the following below this CDDL HEADER, with the
 * fields enclosed by brackets "[]" replaced with your
 * own identifying information: Portions Copyright [yyyy]
 * [name of copyright owner]
 */
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()];
    }
}