com.teradata.benchto.driver.utils.NaturalOrderComparator Maven / Gradle / Ivy

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/*
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.teradata.benchto.driver.utils;

import java.nio.file.Path;
import java.util.Comparator;

/**
 * https://raw.githubusercontent.com/paour/natorder/master/NaturalOrderComparator.java
 */
public class NaturalOrderComparator
        implements Comparator
{
    private static final Comparator FOR_STRINGS = new NaturalOrderComparator();

    private static final Comparator FOR_PATHS = (o1, o2) -> forStrings().compare(o1.toString(), o2.toString());

    public static Comparator forStrings()
    {
        return FOR_STRINGS;
    }

    public static Comparator forPaths()
    {
        return FOR_PATHS;
    }

    public int compare(String a, String b)
    {
        int ia = 0;
        int ib = 0;
        int nza;
        int nzb;
        char ca;
        char cb;
        int result;

        while (true) {
            // only count the number of zeroes leading the last number compared
            nza = 0;
            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)) {
                result = compareRight(a.substring(ia), b.substring(ib));
                if (result != 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;
        }
    }

    private 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;
            }
        }
    }

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

    private NaturalOrderComparator() {}
}