file.
	 *
	 * @param string $w3tc_key An MD5 of the DB query.
	 * @param string $w3tc_group Cache group.
	 * @param string $mode File mode.  For example: 'wb' for write binary.
	 *
	 * @return resource|false File pointer on success, false on failure.
	 */
	private function fopen_write( $w3tc_key, $w3tc_group, $mode ) {
		// Get the storage key (format: "w3tc_INSTANCEID_HOST_BLOGID_dbcache_$w3tc_key").
		$storage_key = $this->get_item_key( $w3tc_key );

		// Get the subpath for the cache file (format: [0-9a-f]{3}/[0-9a-f]{3}/[0-9a-f]{32}).
		$sub_path = $this->_get_path( $storage_key, $w3tc_group );

		// Ge the entire path of the cache file.
		$path = $this->_cache_dir . DIRECTORY_SEPARATOR . $sub_path;

		// Create the directory if it does not exist.
		$dir = dirname( $path );

		if ( ! @is_dir( $dir ) ) {
			if ( ! Util_File::mkdir_from( $dir, dirname( W3TC_CACHE_DIR ) ) ) {
				return false;
			}
		}

		// Open the cache file for writing.
		return @fopen( $path, $mode );
	}

	/**
	 * Flushes cache files matching a specific regex pattern.
	 *
	 * This method scans a directory and removes cache files that match the provided regular expression. Supports multisite setups.
	 *
	 * @since 2.7.1
	 *
	 * @param string $regex The regular expression pattern to match file names.
	 *
	 * @return void
	 */
	private function _flush_based_on_regex( $regex ) {
		if ( Util_Environment::is_wpmu() && ! Util_Environment::is_wpmu_subdomain() ) {
			$domain    = get_home_url();
			$parsed    = parse_url( $domain );
			$host      = $parsed['host'];
			$path      = isset( $parsed['path'] ) ? '/' . trim( $parsed['path'], '/' ) : '';
			$flush_dir = W3TC_CACHE_PAGE_ENHANCED_DIR . DIRECTORY_SEPARATOR . $host . $path;
		} else {
			$flush_dir = W3TC_CACHE_PAGE_ENHANCED_DIR . DIRECTORY_SEPARATOR . Util_Environment::host();
		}

		$dir = @opendir( $flush_dir );
		if ( $dir ) {
			$w3tc_entry = @readdir( $dir );
			while ( false !== $w3tc_entry ) {
				if ( '.' === $w3tc_entry || '..' === $w3tc_entry ) {
					$w3tc_entry = @readdir( $dir );
					continue;
				}

				if ( preg_match( '~' . $regex . '~', basename( $w3tc_entry ) ) ) {
					Util_File::rmdir( $flush_dir . DIRECTORY_SEPARATOR . $w3tc_entry );
				}

				$w3tc_entry = @readdir( $dir );
			}

			@closedir( $dir );
		}
	}
}
file.
	 *
	 * @param string $w3tc_key An MD5 of the DB query.
	 * @param string $w3tc_group Cache group.
	 * @param string $mode File mode.  For example: 'wb' for write binary.
	 *
	 * @return resource|false File pointer on success, false on failure.
	 */
	private function fopen_write( $w3tc_key, $w3tc_group, $mode ) {
		// Get the storage key (format: "w3tc_INSTANCEID_HOST_BLOGID_dbcache_$w3tc_key").
		$storage_key = $this->get_item_key( $w3tc_key );

		// Get the subpath for the cache file (format: [0-9a-f]{3}/[0-9a-f]{3}/[0-9a-f]{32}).
		$sub_path = $this->_get_path( $storage_key, $w3tc_group );

		// Ge the entire path of the cache file.
		$path = $this->_cache_dir . DIRECTORY_SEPARATOR . $sub_path;

		// Create the directory if it does not exist.
		$dir = dirname( $path );

		if ( ! @is_dir( $dir ) ) {
			if ( ! Util_File::mkdir_from( $dir, dirname( W3TC_CACHE_DIR ) ) ) {
				return false;
			}
		}

		// Open the cache file for writing.
		return @fopen( $path, $mode );
	}

	/**
	 * Flushes cache files matching a specific regex pattern.
	 *
	 * This method scans a directory and removes cache files that match the provided regular expression. Supports multisite setups.
	 *
	 * @since 2.7.1
	 *
	 * @param string $regex The regular expression pattern to match file names.
	 *
	 * @return void
	 */
	private function _flush_based_on_regex( $regex ) {
		if ( Util_Environment::is_wpmu() && ! Util_Environment::is_wpmu_subdomain() ) {
			$domain    = get_home_url();
			$parsed    = parse_url( $domain );
			$host      = $parsed['host'];
			$path      = isset( $parsed['path'] ) ? '/' . trim( $parsed['path'], '/' ) : '';
			$flush_dir = W3TC_CACHE_PAGE_ENHANCED_DIR . DIRECTORY_SEPARATOR . $host . $path;
		} else {
			$flush_dir = W3TC_CACHE_PAGE_ENHANCED_DIR . DIRECTORY_SEPARATOR . Util_Environment::host();
		}

		$dir = @opendir( $flush_dir );
		if ( $dir ) {
			$w3tc_entry = @readdir( $dir );
			while ( false !== $w3tc_entry ) {
				if ( '.' === $w3tc_entry || '..' === $w3tc_entry ) {
					$w3tc_entry = @readdir( $dir );
					continue;
				}

				if ( preg_match( '~' . $regex . '~', basename( $w3tc_entry ) ) ) {
					Util_File::rmdir( $flush_dir . DIRECTORY_SEPARATOR . $w3tc_entry );
				}

				$w3tc_entry = @readdir( $dir );
			}

			@closedir( $dir );
		}
	}
}