/*
 * Bittorrent Client using Qt and libtorrent.
 * Copyright (C) 2021  Mike Tzou (Chocobo1)
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * 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 General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
 *
 * In addition, as a special exception, the copyright holders give permission to
 * link this program with the OpenSSL project's "OpenSSL" library (or with
 * modified versions of it that use the same license as the "OpenSSL" library),
 * and distribute the linked executables. You must obey the GNU General Public
 * License in all respects for all of the code used other than "OpenSSL".  If you
 * modify file(s), you may extend this exception to your version of the file(s),
 * but you are not obligated to do so. If you do not wish to do so, delete this
 * exception statement from your version.
 */

#include "compare.h"

#include <QChar>
#include <QString>

int Utils::Compare::naturalCompare(const QString &left, const QString &right, const Qt::CaseSensitivity caseSensitivity)
{
    // Return value <0: `left` is smaller than `right`
    // Return value >0: `left` is greater than `right`
    // Return value =0: both strings are equal

    int posL = 0;
    int posR = 0;
    while (true)
    {
        if ((posL == left.size()) || (posR == right.size()))
            return (left.size() - right.size());  // when a shorter string is another string's prefix, shorter string place before longer string

        const QChar leftChar = (caseSensitivity == Qt::CaseSensitive) ? left[posL] : left[posL].toCaseFolded();
        const QChar rightChar = (caseSensitivity == Qt::CaseSensitive) ? right[posR] : right[posR].toCaseFolded();
        // Compare only non-digits.
        // Numbers should be compared as a whole
        // otherwise the string->int conversion can yield a wrong value
        if ((leftChar == rightChar) && !leftChar.isDigit())
        {
            // compare next character
            ++posL;
            ++posR;
        }
        else if (leftChar.isDigit() && rightChar.isDigit())
        {
            // Both are digits, compare the numbers

            const auto numberView = [](const QStringView str, int &pos) -> QStringView
            {
                const int start = pos;
                while ((pos < str.size()) && str[pos].isDigit())
                    ++pos;
                return str.sliced(start, (pos - start));
            };

            const QStringView numViewL = numberView(left, posL);
            const QStringView numViewR = numberView(right, posR);

            if (numViewL.length() != numViewR.length())
                return (numViewL.length() - numViewR.length());

            // both string/view has the same length
            for (qsizetype i = 0; i < numViewL.length(); ++i)
            {
                const QChar numL = numViewL[i];
                const QChar numR = numViewR[i];

                if (numL != numR)
                    return (numL.unicode() - numR.unicode());
            }

            // String + digits do match and we haven't hit the end of both strings
            // then continue to consume the remainings
        }
        else
        {
            return QString::localeAwareCompare(leftChar, rightChar);
        }
    }
}
