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/*
 * Copyright (C) 2020 Graylog, Inc.
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the Server Side Public License, version 1,
 * as published by MongoDB, Inc.
 *
 * This program 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
 * Server Side Public License for more details.
 *
 * You should have received a copy of the Server Side Public License
 * along with this program. If not, see
 * .
 */
package org.graylog2.indexer.indices.util;

import java.util.Comparator;

/**
 * Compares Strings in format [index_prefix][separator][number], i.e. graylog_12.
 * Tries to compare by index_prefix first (ascending), if prefixes are the same, uses number to compare(descending).
 */
public class NumberBasedIndexNameComparator implements Comparator {

    private final String separator;

    public NumberBasedIndexNameComparator(final String separator) {
        this.separator = separator;
    }

    @Override
    public int compare(String indexName1, String indexName2) {
        int separatorPosition = indexName1.lastIndexOf(separator);
        int index1Number;
        final String indexPrefix1 = separatorPosition != -1 ? indexName1.substring(0, separatorPosition) : indexName1;
        try {
            index1Number = Integer.parseInt(indexName1.substring(separatorPosition + 1));
        } catch (Exception e) {
            index1Number = Integer.MIN_VALUE; //wrongly formatted index names go last
        }

        separatorPosition = indexName2.lastIndexOf(separator);
        int index2Number;
        final String indexPrefix2 = separatorPosition != -1 ? indexName2.substring(0, separatorPosition) : indexName2;
        try {
            index2Number = Integer.parseInt(indexName2.substring(separatorPosition + 1));
        } catch (NumberFormatException e) {
            index2Number = Integer.MIN_VALUE; //wrongly formatted index names go last
        }

        final int prefixComparisonResult = indexPrefix1.compareTo(indexPrefix2);
        if (prefixComparisonResult == 0) {
            return -Integer.compare(index1Number, index2Number);
        } else {
            return prefixComparisonResult;
        }
    }
}