private static function is_file_accessible( $filename ) {
		if ( ! $filename || empty( $filename ) || ! is_string( $filename ) ) {
			PUM_Utils_Logging::instance()->log( 'Cannot check if file is accessible. Filename passed: ' . print_r( $filename, true ) );
			return false;
		}
		$cache_url = PUM_Helpers::get_cache_dir_url();
		if ( false === $cache_url ) {
			PUM_Utils_Logging::instance()->log( 'Cannot access cache file when tested. Cache URL returned false.' );
		}
		$protocol  = is_ssl() ? 'https:' : 'http:';
		$file      = $protocol . $cache_url . '/' . $filename;
		$results   = wp_remote_request( $file, array(
			'method'    => 'HEAD',
			'sslverify' => false,
		));

		// If it returned a WP_Error, let's log its error message.
		if ( is_wp_error( $results ) ) {
			$error = $results->get_error_message();
			PUM_Utils_Logging::instance()->log( sprintf( 'Cannot access cache file when tested. Tested file: %s Error given: %s', esc_html( $file ), esc_html( $error ) ) );
		}

		// If it returned valid array...
		if ( is_array( $results ) && isset( $results['response'] ) ) {
			$status_code = $results['response']['code'];

			// ... then, check if it's a valid status code. Only if it is a valid 2XX code, will this method return true.
			if ( false !== $status_code && ( 200 <= $status_code && 300 > $status_code ) ) {
				return true;
			} else {
				PUM_Utils_Logging::instance()->log( sprintf( 'Cannot access cache file when tested. Status code received was: %s', esc_html( $status_code ) ) );
			}
		}
		return false;
	}