/*
 * SPDX-License-Identifier: Apache-2.0
 *
 * The OpenSearch Contributors require contributions made to
 * this file be licensed under the Apache-2.0 license or a
 * compatible open source license.
 */

package org.opensearch.index.remote;

import java.util.Arrays;

/**
 * Utils for remote store
 *
 * @opensearch.internal
 */
public class RemoteStoreUtils {
    public static final int LONG_MAX_LENGTH = String.valueOf(Long.MAX_VALUE).length();

    /**
     * This method subtracts given numbers from Long.MAX_VALUE and returns a string representation of the result.
     * The resultant string is guaranteed to be of the same length that of Long.MAX_VALUE. If shorter, we add left padding
     * of 0s to the string.
     * @param num number to get the inverted long string for
     * @return String value of Long.MAX_VALUE - num
     */
    public static String invertLong(long num) {
        if (num < 0) {
            throw new IllegalArgumentException("Negative long values are not allowed");
        }
        String invertedLong = String.valueOf(Long.MAX_VALUE - num);
        char[] characterArray = new char[LONG_MAX_LENGTH - invertedLong.length()];
        Arrays.fill(characterArray, '0');

        return new String(characterArray) + invertedLong;
    }

    /**
     * This method converts the given string into long and subtracts it from Long.MAX_VALUE
     * @param str long in string format to be inverted
     * @return long value of the invert result
     */
    public static long invertLong(String str) {
        long num = Long.parseLong(str);
        if (num < 0) {
            throw new IllegalArgumentException("Strings representing negative long values are not allowed");
        }
        return Long.MAX_VALUE - num;
    }

    /**
     * Extracts the segment name from the provided segment file name
     * @param filename Segment file name to parse
     * @return Name of the segment that the segment file belongs to
     */
    public static String getSegmentName(String filename) {
        // Segment file names follow patterns like "_0.cfe" or "_0_1_Lucene90_0.dvm".
        // Here, the segment name is "_0", which is the set of characters
        // starting with "_" until the next "_" or first ".".
        int endIdx = filename.indexOf('_', 1);
        if (endIdx == -1) {
            endIdx = filename.indexOf('.');
        }

        if (endIdx == -1) {
            throw new IllegalArgumentException("Unable to infer segment name for segment file " + filename);
        }

        return filename.substring(0, endIdx);
    }
}