<?php
namespace W3TC;

/**
 * Base cache class
 */

/**
 * class Cache_Base
 */
class Cache_Base {
	/*
     * Blog id
     *
     * @var integer
     */
	protected  $_blog_id = 0;

	/**
	 * To separate the caching for different modules
	 *
	 * @var string
	 */
	protected $_module = '';

	/**
	 * Host
	 *
	 * @var string
	 */
	protected $_host = '';

	/**
	 * Host
	 *
	 * @var int
	 */
	protected $_instance_id = 0;

	/*
     * If we are going to return expired data when some other process
     * is working on new data calculation
     *
     * @var boolean
     */
	protected $_use_expired_data = false;

	/**
	 * Constructor
	 *
	 * @param array   $config
	 */
	public function __construct( $config = array() ) {
		$this->_blog_id = $config['blog_id'];
		$this->_use_expired_data = isset( $config['use_expired_data'] )?$config['use_expired_data']:false;
		$this->_module = isset( $config['module'] ) ? $config['module'] : 'default';
		$this->_host = isset( $config['host'] ) ? $config['host'] : '';
		$this->_instance_id = isset( $config['instance_id'] ) ? $config['instance_id'] : 0;
	}
	/**
	 * Adds data
	 *
	 * @abstract
	 * @param string  $key
	 * @param mixed   $data
	 * @param integer $expire
	 * @param string  $group  Used to differentiate between groups of cache values
	 * @return boolean
	 */
	function add( $key, &$data, $expire = 0, $group = '' ) {
		return false;
	}

	/**
	 * Sets data
	 *
	 * @abstract
	 * @param string  $key
	 * @param mixed   $data
	 * @param integer $expire
	 * @param string  $group  Used to differentiate between groups of cache values
	 * @return boolean
	 */
	function set( $key, $data, $expire = 0, $group = '' ) {
		return false;
	}

	/**
	 * Returns data
	 *
	 * @param string  $key
	 * @param string  $group Used to differentiate between groups of cache values
	 * @return mixed
	 */
	function get( $key, $group = '' ) {
		list( $data, $has_old ) = $this->get_with_old( $key, $group );
		return $data;
	}

	/**
	 * Return primary data and if old exists
	 *
	 * @abstract
	 * @param string  $key
	 * @param string  $group Used to differentiate between groups of cache values
	 * @return array|mixed
	 */
	function get_with_old( $key, $group = '' ) {
		return array( null, false );
	}

	/**
	 * Alias for get for minify cache
	 *
	 * @param string  $key
	 * @param string  $group Used to differentiate between groups of cache values
	 * @return mixed
	 */
	function fetch( $key, $group = '' ) {
		return $this->get( $key, $group = '' );
	}

	/**
	 * Replaces data
	 *
	 * @abstract
	 * @param string  $key
	 * @param mixed   $data
	 * @param integer $expire
	 * @param string  $group  Used to differentiate between groups of cache values
	 * @return boolean
	 */
	function replace( $key, &$data, $expire = 0, $group = '' ) {
		return false;
	}

	/**
	 * Deletes data
	 *
	 * @abstract
	 * @param string  $key
	 * @param string  $group Used to differentiate between groups of cache values
	 * @return boolean
	 */
	function delete( $key, $group = '' ) {
		return false;
	}

	/**
	 * Deletes primary data and old data
	 *
	 * @abstract
	 * @param string  $key
	 * @return boolean
	 */
	function hard_delete( $key ) {
		return false;
	}

	/**
	 * Flushes all data
	 *
	 * @abstract
	 * @param string  $group Used to differentiate between groups of cache values
	 * @return boolean
	 */
	function flush( $group = '' ) {
		return false;
	}

	/**
	 * Checks if engine can function properly in this environment
	 *
	 * @return bool
	 */
	public function available() {
		return true;
	}

	/**
	 * Constructs key version key
	 *
	 * @param unknown $group
	 * @return string
	 */
	protected function _get_key_version_key( $group = '' ) {
		return sprintf( 'w3tc_%d_%s_%s_%d_key_version', $this->_blog_id, $this->_module, $group, $this->_instance_id );
	}

	/**
	 * Constructs item key
	 *
	 * @param unknown $name
	 * @return string
	 */
	public function get_item_key( $name ) {
		$key = sprintf( 'w3tc_%s_%d_%s_%s', $this->_host, $this->_blog_id, $this->_module, $name );
		return $key;
	}


	/**
	 * Use key as a counter and add integet value to it
	 */
	public function counter_add( $key, $value ) {
		return false;
	}

	/**
	 * Use key as a counter and add integet value to it
	 */
	public function counter_set( $key, $value ) {
		return false;
	}

	/**
	 * Get counter's value
	 */
	public function counter_get( $key ) {
		return false;
	}
}