<?php
/**
 * SeekQuarry/Yioop --
 * Open Source Pure PHP Search Engine, Crawler, and Indexer
 *
 * Copyright (C) 2009 - 2026  Chris Pollett chris@pollett.org
 *
 * LICENSE:
 *
 * 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 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 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/>.
 *
 * END LICENSE
 *
 * @author Chris Pollett chris@pollett.org
 * @license https://www.gnu.org/licenses/ GPL3
 * @link https://www.seekquarry.com/
 * @copyright 2009 - 2026
 * @filesource
 */
namespace seekquarry\yioop\tests;

use seekquarry\yioop\library\av_processing\Pvq;

/**
 * Works out which number stands for a given band shape, which is the
 * definition the reader has to agree with.
 *
 * The Opus specification fixes the order the shapes are numbered in by
 * giving this calculation: a short walk from the last slot back to the
 * first, adding a count at each step. Going that way is simple. Going
 * the other way, from a number back to a shape, is what the reader has
 * to do, and is where a mistake could hide. Having both means every
 * shape of a small band can be checked, which is what the test beside
 * this does.
 *
 * Only the reading direction is needed to play a recording, so this
 * sits here rather than in the library.
 */
class PvqIndexer
{
    /**
     * Works out which number stands for a shape
     *
     * @param array $pattern how many pulses fall in each slot,
     *      negative where they point the other way
     * @return int the number standing for that shape
     */
    public static function numberFor($pattern)
    {
        $slots = count($pattern);
        if ($slots < 2) {
            throw new \Exception("This needs a band of at least two slots");
        }
        $at = $slots - 1;
        $number = ($pattern[$at] < 0) ? 1 : 0;
        $running = abs($pattern[$at]);
        do {
            $at--;
            $number += Pvq::helperCount($slots - $at, $running);
            $running += abs($pattern[$at]);
            if ($pattern[$at] < 0) {
                $number += Pvq::helperCount($slots - $at, $running + 1);
            }
        } while ($at > 0);
        return $number;
    }
}
