, 'redis.password' );
		$this->_set_if_exists( $file_data, 'fragmentcache.redis.dbid', 'fragmentcache', 'redis.dbid' );
		$this->_set_if_exists( $file_data, 'fragmentcache.lifetime', 'fragmentcache', 'lifetime' );

		// new options, separated old one. implemented in 0.9.5.3.
		if ( isset( $file_data['browsercache.cssjs.replace'] ) && ! isset( $file_data['browsercache.cssjs.querystring'] ) ) {
			$file_data['browsercache.cssjs.querystring'] = $file_data['browsercache.cssjs.replace'];
		}
		if ( isset( $file_data['browsercache.other.replace'] ) && ! isset( $file_data['browsercache.other.querystring'] ) ) {
			$file_data['browsercache.other.querystring'] = $file_data['browsercache.other.replace'];
		}

		// changes in 0.9.5.4.
		if ( isset( $file_data['cdn.engine'] ) ) {
			if ( 'cloudfront_fsd' === $file_data['cdn.engine'] ) {
				$file_data['cdnfsd.engine']  = 'cloudfront';
				$file_data['cdnfsd.enabled'] = $file_data['cdn.enabled'];

				if ( isset( $file_data['cdn.cloudfront_fsd.access_key'] ) ) {
					$file_data['cdnfsd.cloudfront.access_key']          = $file_data['cdn.cloudfront_fsd.access_key'];
					$file_data['cdnfsd.cloudfront.distribution_domain'] = $file_data['cdn.cloudfront_fsd.distribution_domain'];
					$file_data['cdnfsd.cloudfront.secret_key']          = $file_data['cdn.cloudfront_fsd.secret_key'];
					$file_data['cdnfsd.cloudfront.distribution_id']     = $file_data['cdn.cloudfront_fsd.distribution_id'];
				}
			}
		}

		$file_data['version'] = W3TC_VERSION;

		return $file_data;
	}

	/**
	 * Sets an extension configuration if it exists in the provided data array.
	 *
	 * This method migrates extension-specific settings to the proper structure
	 * within the configuration data.
	 *
	 * @param array  $w3tc_a         Reference to the configuration data array.
	 * @param string $w3tc_extension The extension key to check and migrate.
	 *
	 * @return void
	 */
	private function _set_if_exists_extension( &$w3tc_a, $w3tc_extension ) {
		if ( isset( $w3tc_a['extensions.settings'] ) && isset( $w3tc_a['extensions.settings'][ $w3tc_extension ] ) ) {
			$w3tc_a[ $w3tc_extension ] = $w3tc_a['extensions.settings'][ $w3tc_extension ];
			unset( $w3tc_a['extensions.settings'][ $w3tc_extension ] );
		}
	}

	/**
	 * Migrates an existing key to a nested configuration structure.
	 *
	 * This method checks if the specified key exists in the data array and, if so,
	 * moves its value to the designated nested configuration structure.
	 *
	 * @param array  $w3tc_a        Reference to the configuration data array.
	 * @param string $old_key  The existing key to check in the data array.
	 * @param string $new_key0 The primary key for the new nested structure.
	 * @param string $new_key1 The secondary key for the new nested structure.
	 *
	 * @return void
	 */
	private function _set_if_exists( &$w3tc_a, $old_key, $new_key0, $new_key1 ) {
		if ( isset( $w3tc_a[ $old_key ] ) ) {
			$w3tc_a[ $new_key0 ][ $new_key1 ] = $w3tc_a[ $old_key ];
			unset( $w3tc_a[ $old_key ] );
		}
	}
}