$keys  Array of keys to be deleted.
	 * @param string $group Optional. Where the cache contents are grouped. Default empty.
	 *
	 * @return bool[] Array of return values, grouped by key. Each value is either
	 *                true on success, or false if the contents were not deleted.
	 */
	public function delete_multiple( $keys, $group = 'default' ) {
		$cache = $this->_get_engine( $group );
		return $cache->delete_multiple( $keys, $group );
	}

	/**
	 * Add to the cache
	 *
	 * @param string  $id     ID.
	 * @param mixed   $data   Data.
	 * @param string  $group  Group.
	 * @param integer $expire Expire.
	 *
	 * @return boolean
	 */
	public function add( $id, $data, $group = 'default', $expire = 0 ) {
		$cache = $this->_get_engine( $group );
		return $cache->add( $id, $data, $group, $expire );
	}

	/**
	 * Adds multiple values to the cache in one call.
	 *
	 * @since 2.2.8
	 *
	 * @param array  $data   Array of keys and values to be added.
	 * @param string $group  Optional. Where the cache contents are grouped. Default empty.
	 * @param int    $expire Optional. When to expire the cache contents, in seconds.
	 *                       Default 0 (no expiration).
	 *
	 * @return bool[] Array of return values, grouped by key. Each value is either
	 *                true on success, or false if cache key and group already exist.
	 */
	public function add_multiple( array $data, $group = '', $expire = 0 ) {
		$cache = $this->_get_engine( $group );
		return $cache->add_multiple( $data, $group, $expire );
	}

	/**
	 * Replace in the cache
	 *
	 * @param string  $id     ID.
	 * @param mixed   $data   Data.
	 * @param string  $group  Group.
	 * @param integer $expire Expire.
	 *
	 * @return boolean
	 */
	public function replace( $id, $data, $group = 'default', $expire = 0 ) {
		$cache = $this->_get_engine( $group );
		return $cache->replace( $id, $data, $group, $expire );
	}

	/**
	 * Reset keys
	 *
	 * @return boolean
	 */
	public function reset() {
		$result = true;

		foreach ( $this->_caches as $engine ) {
			$result = $result && $engine->reset();
		}

		return $result;
	}

	/**
	 * Flush cache
	 *
	 * @return boolean
	 */
	public function flush() {
		$result = true;

		foreach ( $this->_caches as $engine ) {
			$result = $result && $engine->flush();
		}

		return $result;
	}

	/**
	 * Flush group.
	 *
	 * @param string $group Group.
	 *
	 * @return boolean
	 */
	public function flush_group( $group ) {
		$result = true;

		foreach ( $this->_caches as $engine ) {
			$result = $result && $engine->flush_group( $group );
		}

		return $result;
	}

	/**
	 * Flush runtime.
	 *
	 * @return boolean
	 */
	public function flush_runtime() {
		$result = true;

		foreach ( $this->_caches as $engine ) {
			$result = $result && $engine->flush_runtime();
		}

		return $result;
	}

	/**
	 * Check supported features.
	 *
	 * @param string $feature Feature.
	 *
	 * @return boolean
	 */
	public function supports( string $feature ) {
		return in_array( $feature, $this->supported_features, true );
	}

	/**
	 * Add global groups
	 *
	 * @param array $groups Groups.
	 *
	 * @return void
	 */
	public function add_global_groups( $groups ) {
		if ( ! is_array( $groups ) ) {
			$groups = array( $groups );
		}

		foreach ( $groups as $group ) {
			$cache = $this->_get_engine( $group );
			$cache->add_global_groups( array( $group ) );
		}
	}

	/**
	 * Add non-persistent groups
	 *
	 * @param array $groups Groups.
	 *
	 * @return void
	 */
	public function add_nonpersistent_groups( $groups ) {
		if ( ! is_array( $groups ) ) {
			$groups = array( $groups );
		}

		foreach ( $groups as $group ) {
			$cache = $this->_get_engine( $group );
			$cache->add_nonpersistent_groups( array( $group ) );
		}
	}

	/**
	 * Return engine based on which group the OC value belongs to.
	 *
	 * @param string $group Group.
	 *
	 * @return mixed
	 */
	private function _get_engine( $group = '' ) {
		if ( isset( $this->_cache_by_group[ $group ] ) ) {
			return $this->_cache_by_group[ $group ];
		}

		return $this->_default_cache;
	}

	/**
	 * Decrement numeric cache item's value
	 *
	 * @param int|string $id     The cache key to increment.
	 * @param int        $offset The amount by which to decrement the item's value. Default is 1.
	 * @param string     $group  The group the key is in.
	 *
	 * @return bool|int False on failure, the item's new value on success.
	 */
	public function decr( $id, $offset = 1, $group = 'default' ) {
		$cache = $this->_get_engine( $group );
		return $cache->decr( $id, $offset, $group );
	}

	/**
	 * Increment numeric cache item's value
	 *
	 * @param int|string $id     The cache key to increment.
	 * @param int        $offset The amount by which to increment the item's value. Default is 1.
	 * @param string     $group  The group the key is in.
	 *
	 * @return false|int False on failure, the item's new value on success.
	 */
	public function incr( $id, $offset = 1, $group = 'default' ) {
		$cache = $this->_get_engine( $group );
		return $cache->incr( $id, $offset, $group );
	}

	/**
	 * Switch to blog
	 *
	 * @param int $blog_id Blog ID.
	 *
	 * @return void
	 */
	public function switch_to_blog( $blog_id ) {
		foreach ( $this->_caches as $cache ) {
			$cache->switch_blog( $blog_id );
		}
	}
}