/** @file
 * @brief truncate a utf-8 string, ideally without splitting words.
 */
/* Copyright (C) 2007,2021 Olly Betts
 *
 * 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, see
 * <https://www.gnu.org/licenses/>.
 */

#include <config.h>

#include "utf8truncate.h"
#include <string>

using namespace std;

bool
utf8_truncate(string& value, string::size_type maxlen)
{
    if (value.size() <= maxlen) return false;

    string::size_type len = maxlen + 1;
    // Skip back to (and past) the last whitespace.  We start one past the
    // length we want to correctly handle the case where a word ends exactly
    // maxlen bytes in.
    while (len && static_cast<unsigned char>(value[len - 1]) > 32) --len;
    while (len && static_cast<unsigned char>(value[len - 1]) <= 32) --len;

    // If the first word is too long, truncate it.
    if (!len) {
        len = maxlen;
        // If the bytes of a UTF-8 character span the maxlen position we need
        // to remove some extra bytes to avoid leaving a partial UTF-8
        // character.
        //
        // We start at the byte after the cut point.  If it's a continuation
        // byte we step back until we find the start of the character and
        // truncate right before that.
        while (len && (value[len] & 0xc0) == 0x80) --len;
    }
    value.resize(len);

    return true;
}
