/*
 * @(#)NaturalOrderComparator.java
 *
 * Copyright 2010 Instituto Superior Tecnico
 * Founding Authors: Anil Kassamali
 * 
 *      https://fenix-ashes.ist.utl.pt/
 * 
 *   This file is part of the Correspondence Registry Module.
 *
 *   The Correspondence Registry Module 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 
 *   3 of the License, or (at your option) any later version.
 *
 *   The Correspondence Registry Module 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 the Correspondence Registry Module. If not, see <http://www.gnu.org/licenses/>.
 * 
 */
package module.mailtracking.utilities;

import java.util.Comparator;

/**
 * 
 * @author Anil Kassamali
 * 
 */
public class NaturalOrderComparator implements Comparator<String> {

    int compareRight(String a, String b) {
        int bias = 0;
        int ia = 0;
        int ib = 0;

        // The longest run of digits wins. That aside, the greatest
        // value wins, but we can't know that it will until we've scanned
        // both numbers to know that they have the same magnitude, so we
        // remember it in BIAS.
        for (;; ia++, ib++) {
            char ca = charAt(a, ia);
            char cb = charAt(b, ib);

            if (!Character.isDigit(ca) && !Character.isDigit(cb)) {
                return bias;
            } else if (!Character.isDigit(ca)) {
                return -1;
            } else if (!Character.isDigit(cb)) {
                return +1;
            } else if (ca < cb) {
                if (bias == 0) {
                    bias = -1;
                }
            } else if (ca > cb) {
                if (bias == 0) {
                    bias = +1;
                }
            } else if (ca == 0 && cb == 0) {
                return bias;
            }
        }
    }

    @Override
    public int compare(String o1, String o2) {
        String a = o1;
        String b = o2;

        int ia = 0, ib = 0;
        int nza = 0, nzb = 0;
        char ca, cb;
        int result;

        while (true) {
            // only count the number of zeroes leading the last number compared
            nza = nzb = 0;

            ca = charAt(a, ia);
            cb = charAt(b, ib);

            // skip over leading spaces or zeros
            while (Character.isSpaceChar(ca) || ca == '0') {
                if (ca == '0') {
                    nza++;
                } else {
                    // only count consecutive zeroes
                    nza = 0;
                }

                ca = charAt(a, ++ia);
            }

            while (Character.isSpaceChar(cb) || cb == '0') {
                if (cb == '0') {
                    nzb++;
                } else {
                    // only count consecutive zeroes
                    nzb = 0;
                }

                cb = charAt(b, ++ib);
            }

            // process run of digits
            if (Character.isDigit(ca) && Character.isDigit(cb)) {
                if ((result = compareRight(a.substring(ia), b.substring(ib))) != 0) {
                    return result;
                }
            }

            if (ca == 0 && cb == 0) {
                // The strings compare the same. Perhaps the caller
                // will want to call strcmp to break the tie.
                return nza - nzb;
            }

            if (ca < cb) {
                return -1;
            } else if (ca > cb) {
                return +1;
            }

            ++ia;
            ++ib;
        }
    }

    static char charAt(String s, int i) {
        if (i >= s.length()) {
            return 0;
        } else {
            return s.charAt(i);
        }
    }

}