<?php

/**
 * Array object. You can access it as a regular array using [index].
 * General idea is to get data from DB as fast as possible and return them to the end user.
 * In memory is stored only one chunk of array but you can iterate through whole array
 * even if there is thousends of items.
 * 
 * @author		Marcin Zbijowski
 * @version		1.0
 */

class ExpandableArray extends ArrayObject implements Iterator {

	/**
	 * SQL query to retrieve data from DB.
	 * @var string
	 */
	private $_query = '';

	/**
	 * SQL query offset, used in LIMIT
	 * @var int
	 */
	private $_offset = 0;
	
	/**
	 * SQL query limit, used in LIMIT
	 * @var integer
	 */
	private $_limit = 100;
	
	/**
	 * Actual array size
	 * @var integer
	 */
	private $_count = 0;
	
	/**
	 * Column specified object id, specific for DataEntity classes
	 * @var string
	 */
	private $_remoteId = 'id';
	
	/**
	 * Class name for stored / returned objects
	 * @var string
	 */
	private $_objectType = 'stdClass';
	
	/**
	 * Flag if we want to write something to debug.log
	 * @var boolean
	 */
	private $_debug = false;
	
	/**
	 * Iterator position, basically it's index of an array
	 * @var integer
	 */
	private $_iteratorPos = 0;

	/**
	 * Constructor of the object.
	 * One can pass array or string as a param. Array will be treated as something
	 * already built and passed to parent (ArrayObject::__constructor). String will
	 * be treated as SQL and passed to setQuery() method.
	 * 
	 * @see setQuery
	 * @param $param array | string
	 * @return void
	 * @access public
	 */
	public function __construct($param) {
		
		if(is_array($param)) {
			parent::__construct($param);
		}
		elseif(is_string($param)) {
			parent::__construct();
			$this->setQuery($param);
		}
		else {
			throw Exception('Incorrect or missing param');
		}

	}

	/**
	 * Get item from the array on specified index. This method may trigger
	 * DB query if index is not existing.
	 * 
	 * @param $index integer
	 * @return mixed depending on the objectType
	 * @access public
	 */
	public function offsetGet($index) {
		if($this->_debug) {
			$logger = Registry::get('logger');
			$logger->debug('offset: ' . $index , ', count: ' . $this->count());
		}

		if(Validate::isInteger($index)) {
			if(!$this->offsetExists($index)) {
				$this->_offset = $this->_getQueryOffset($index);
				$this->_executeQuery();
			}
			
			return parent::offsetGet($index);
		}
		else {
			throw Exception('Incorrect or missing param, must be integer');
		}

	}

	/**
	 * Sets the SQL query to retrieve data from DB. MUST BE CORRECT!
	 * 
	 * @param $sql string
	 * @return void
	 * @access public
	 */
	public function setQuery($sql) {
		$this->_query = $sql;
		$this->_countQuery = '';
	}

	/**
	 * Sets query limit.
	 * 
	 * @param $limit integer
	 * @return void
	 * @access public
	 */
	public function setQueryLimit($limit) {
		if(Validate::isInteger($limit)) {
			$this->_limit = $limit;
		}
		else {
			throw Exception('Invalid parameter (' . $limit . '), should be integer');
		}
	}
	
	/**
	 * Sets remote id column name. DataEntity specific
	 * 
	 * @param $remoteId string
	 * @return void
	 * @access public
	 */
	public function setRemoteId($remoteId) {
		$this->_remoteId = $remoteId;
	}
	
	/**
	 * Sets class name of stored / returned objects. Class should extend DataEntity.
	 * 
	 * @param $type string
	 * @return void
	 * @access public
	 */
	public function setObjectType($type) {
		$this->_objectType = $type;
	}
	
	/**
	 * Sets if to write queries to debug.log
	 * 
	 * @param $value boolean
	 * @return void
	 */
	public function setDebug($value) {
		$this->_debug = $value;
	}

	/**
	 * Magic function, used in echo or similar functions. Prevents us from getting fatals
	 * 
	 * @see http://www.php.net/manual/en/language.oop5.magic.php#language.oop5.magic.tostring
	 * @return string
	 * @access public
	 */
	public function __toString() {
		return get_class($this);
	}

	/**
	 * Returns iterator. Used in foreach loop
	 * 
	 * @return ExpandableArray
	 */
	public function getIterator() {
		return $this;
	}
	
	public function count() {
		if(!$this->_count) {
			$q = preg_replace('|^select.*from|i', 'select count(*) c from', $this->_query);
			$db = Registry::get('db');
			$result = $db->Execute($q);
			if($result) {
				$this->_count = $result->fields[0];
			}
			
		}
		
		return $this->_count;
	}

	/**
	 * Runs query on DB and replaces stored array. It calls registry to get db object.
	 * 
	 * @return void
	 */
	private function _executeQuery() {
		$q = $this->_query . ' LIMIT ' . $this->_offset . ', ' . $this->_limit;
		$db = Registry::get('db');
		$result = $db->Execute($q);

		if($result) {
			
			if($this->_debug) {
				Registry::get('logger')->debug($q);
			}

			$index = $this->_offset;
			$arrObjects = array();
			foreach ($result as $row) {
				$obj = new $this->_objectType($row[$this->_remoteId]);
				if($obj->exists()) {
					$arrObjects[$index++] = $obj;
				}
			}
			$this->exchangeArray($arrObjects);
		}
	}
	
	/**
	 * Counts offset that should be used in query. It will allow us to randomly access
	 * items stored in the array.
	 * 
	 * @param $requestedIndex
	 * @return integer
	 */
	private function _getQueryOffset($requestedIndex) {
		return floor($requestedIndex / $this->_limit) * $this->_limit;
	}

	
	/***** Iterator Methods from here *****/
	
	/**
	 * Return current element
	 * 
	 * @return mixed
	 * @access public
	 */
	public function current() {
		return $this->offsetGet($this->_iteratorPos);
	}
	
	/**
	 * Returns array key
	 * 
	 * @return integer
	 * @access public
	 */
	public function key() {
		return $this->_iteratorPos;
	}
	
	/**
	 * Moves iterator to next element
	 * 
	 * @return mixed
	 * @access public
	 */
	public function next() {
		return $this->offsetGet(++$this->_iteratorPos);
	}
	
	/**
	 * Points iterator to the first element of array
	 * 
	 * @return void
	 * @access public
	 */
	public function rewind() {
		$this->_iteratorPos = 0;		
	}
	
	/**
	 * Checks if there is object at that index
	 * 
	 * @return boolean
	 * @access public
	 */
	public function valid() {
		return is_object($this->offsetGet($this->_iteratorPos));
	}
}