<?php
/** 
 *  SeekQuarry/Yioop --
 *  Open Source Pure PHP Search Engine, Crawler, and Indexer
 *
 *  Copyright (C) 2009, 2010, 2011  Chris Pollett hide@address.com
 *
 *  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 <http://www.gnu.org/licenses/>.
 *
 *  END LICENSE
 *
 * @author Chris Pollett hide@address.com
 * @package seek_quarry
 * @subpackage library
 * @license http://www.gnu.org/licenses/ GPL3
 * @link http://www.seekquarry.com/
 * @copyright 2009, 2010, 2011
 * @filesource
 */

if(!defined('BASE_DIR')) {echo "BAD REQUEST"; exit();}

/**
 * A PersistentStructure is a data structure which every so many operations 
 * will be saved to secondary storage (such as disk).
 * An operation occurs whenever the PersistentStructure's checkSave method is 
 * called. A PersistentStructure also supports the ability to be load 
 * (read in from) secondary storage.
 * 
 * @author Chris Pollett
 *
 * @package seek_quarry
 * @subpackage library
 */ 
 
class PersistentStructure
{
    /** If not specified in the constructor, this will be the number of 
     *  operations between saves
     *  @var int  
     */
    const DEFAULT_SAVE_FREQUENCY = 50000;
    /** Name of the file in which to store the PersistentStructure 
     *  @var string
     */
    var $filename;
    /** Number of operations since the last save 
     *  @var int
     */
    var $unsaved_operations;
    /** Number of operation between saves. If == -1 never save using checkSave
     *  @var int
     */
    var $save_frequency;

    /**
     * Sets up the file name and save frequency for the PersistentStructure, 
     * initializes the oepration count
     *
     * @param string $fname the name of the file to store the 
     *      PersistentStructure in
     * @param int $save_frequency the number of operation before a save If 
     *      <= 0 never check save
     */
    public function __construct($fname, 
        $save_frequency = self::DEFAULT_SAVE_FREQUENCY)
    {
        $this->filename = $fname;
        $this->save_frequency = $save_frequency;
        $this->unsaved_operations = 0;
    }

    /**
     *  Load a PersistentStructure from a file
     *
     *  @param string the name of the file to load the PersistentStructure from
     *  @return object the PersistentStructure loaded
     */
    public static function load($fname)
    {
        return unserialize(file_get_contents($fname));
    }

    /**
     *  Save the PersistentStructure to its filename 
     *  This method is generic but super memory inefficient, so reimplement
     *  for subclasses is needed
     */
    public function save()
    {
        file_put_contents($this->filename, serialize($this));
    }

    /**
     * Add one to the unsaved_operations count. If this goes above the 
     * save_frquency then save the PersistentStructure to secondary storage
     */
    function checkSave()
    {
        $this->unsaved_operations++;
        if($this->save_frequency > 0 && 
            $this->unsaved_operations >= $this->save_frequency) {
            $this->save();
            $this->unsaved_operations = 0;
        }
    }
}

 ?>