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/*
    This file is part of the iText (R) project.
    Copyright (c) 1998-2023 Apryse Group NV
    Authors: Apryse Software.

    This program is offered under a commercial and under the AGPL license.
    For commercial licensing, contact us at https://itextpdf.com/sales.  For AGPL licensing, see below.

    AGPL licensing:
    This program is free software: you can redistribute it and/or modify
    it under the terms of the GNU Affero General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.

    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
    GNU Affero General Public License for more details.

    You should have received a copy of the GNU Affero General Public License
    along with this program.  If not, see .
 */
package com.itextpdf.kernel.numbering;

/**
 * This is a general class for alphabet numbering.
 * You can specify an alphabet and convert an integer into the corresponding
 * alphabet number representation.
 * E.g.: if the alphabet is English letters 'a' to 'z', then
 * 1 is represented as "a", ..., 26 is represented as "z",
 * 27 is represented as "aa" and so on.
 */
public class AlphabetNumbering {
    /**
     * Translates a positive integer (not equal to zero)
     * into an alphabet number using the letters from the specified alphabet.
     *
     * @param number the number
     * @param alphabet the array containing all possible letters from the alphabet
     * @return a translated number representation
     */
    public static String toAlphabetNumber(int number, char[] alphabet) {
        if (number < 1) {
            throw new IllegalArgumentException("The parameter must be a positive integer");
        }

        int cardinality = alphabet.length;

        number--;
        int bytes = 1;
        long start = 0;
        long symbols = cardinality;

        while (number >= symbols + start) {
            bytes++;
            start += symbols;
            symbols *= cardinality;
        }

        long c = number - start;
        char[] value = new char[bytes];
        while (bytes > 0) {
            value[--bytes] = alphabet[(int) (c % cardinality)];
            c /= cardinality;
        }

        return new String(value);
    }
}