<?php

/**
 * Dataset class providing the results of a select operation on a kolab_storage_folder.
 *
 * Can be used as a normal array as well as an iterator in foreach() loops.
 *
 * @version @package_version@
 * @author Thomas Bruederli <bruederli@kolabsys.com>
 *
 * Copyright (C) 2014, Kolab Systems AG <contact@kolabsys.com>
 *
 * 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 <http://www.gnu.org/licenses/>.
 */

class kolab_storage_dataset implements Iterator, ArrayAccess, Countable
{
    private $cache;  // kolab_storage_cache instance to use for fetching data
    private $memlimit = 0;
    private $buffer = false;
    private $index = array();
    private $data = array();
    private $iteratorkey = 0;
    private $error = null;

    /**
     * Default constructor
     *
     * @param object kolab_storage_cache instance to be used for fetching objects upon access
     */
    public function __construct($cache)
    {
        $this->cache = $cache;

        // enable in-memory buffering up until 1/5 of the available memory
        if (function_exists('memory_get_usage')) {
            $this->memlimit = parse_bytes(ini_get('memory_limit')) / 5;
            $this->buffer = true;
        }
    }

    /**
     * Return error state
     */
    public function is_error()
    {
        return !empty($this->error);
    }

    /**
     * Set error state
     */
    public function set_error($err)
    {
        $this->error = $err;
    }


    /*** Implement PHP Countable interface ***/

    public function count()
    {
        return count($this->index);
    }


    /*** Implement PHP ArrayAccess interface ***/

    public function offsetSet($offset, $value)
    {
        $uid = $value['_msguid'];

        if (is_null($offset)) {
            $offset = count($this->index);
            $this->index[] = $uid;
        }
        else {
            $this->index[$offset] = $uid;
        }

        // keep full payload data in memory if possible
        if ($this->memlimit && $this->buffer && isset($value['_mailbox'])) {
            $this->data[$offset] = $value;

            // check memory usage and stop buffering
            if ($offset % 10 == 0) {
                $this->buffer = memory_get_usage() < $this->memlimit;
            }
        }
    }

    public function offsetExists($offset)
    {
        return isset($this->index[$offset]);
    }

    public function offsetUnset($offset)
    {
        unset($this->index[$offset]);
    }

    public function offsetGet($offset)
    {
        if (isset($this->data[$offset])) {
            return $this->data[$offset];
        }
        else if ($msguid = $this->index[$offset]) {
            return $this->cache->get($msguid);
        }

        return null;
    }


    /*** Implement PHP Iterator interface ***/

    public function current()
    {
        return $this->offsetGet($this->iteratorkey);
    }

    public function key()
    {
        return $this->iteratorkey;
    }

    public function next()
    {
        $this->iteratorkey++;
        return $this->valid();
    }

    public function rewind()
    {
        $this->iteratorkey = 0;
    }

    public function valid()
    {
        return !empty($this->index[$this->iteratorkey]);
    }

}