er update.
				if ( $this->isBadDirectoryStructure($remoteSource) ) {
					return new WP_Error(
						'puc-incorrect-directory-structure',
						sprintf(
							'The directory structure of the update is incorrect. All files should be inside ' .
							'a directory named <span class="code">%s</span>, not at the root of the ZIP archive.',
							htmlentities($this->slug)
						)
					);
				}

				/** @var WP_Upgrader_Skin $upgrader ->skin */
				$upgrader->skin->feedback(sprintf(
					'Renaming %s to %s&#8230;',
					'<span class="code">' . basename($source) . '</span>',
					'<span class="code">' . $this->directoryName . '</span>'
				));

				if ( $wp_filesystem->move($source, $correctedSource, true) ) {
					$upgrader->skin->feedback('Directory successfully renamed.');
					return $correctedSource;
				} else {
					return new WP_Error(
						'puc-rename-failed',
						'Unable to rename the update to match the existing directory.'
					);
				}
			}

			return $source;
		}

		/**
		 * Is there an update being installed right now, for this plugin or theme?
		 *
		 * @param WP_Upgrader|null $upgrader The upgrader that's performing the current update.
		 * @return bool
		 */
		abstract public function isBeingUpgraded($upgrader = null);

		/**
		 * Check for incorrect update directory structure. An update must contain a single directory,
		 * all other files should be inside that directory.
		 *
		 * @param string $remoteSource Directory path.
		 * @return bool
		 */
		protected function isBadDirectoryStructure($remoteSource) {
			global $wp_filesystem;
			/** @var WP_Filesystem_Base $wp_filesystem */

			$sourceFiles = $wp_filesystem->dirlist($remoteSource);
			if ( is_array($sourceFiles) ) {
				$sourceFiles = array_keys($sourceFiles);
				$firstFilePath = trailingslashit($remoteSource) . $sourceFiles[0];
				return (count($sourceFiles) > 1) || (!$wp_filesystem->is_dir($firstFilePath));
			}

			//Assume it's fine.
			return false;
		}

		/* -------------------------------------------------------------------
		 * DebugBar integration
		 * -------------------------------------------------------------------
		 */

		/**
		 * Initialize the update checker Debug Bar plugin/add-on thingy.
		 */
		public function maybeInitDebugBar() {
			if ( class_exists('Debug_Bar', false) && file_exists(dirname(__FILE__) . '/DebugBar') ) {
				$this->debugBarExtension = $this->createDebugBarExtension();
			}
		}

		protected function createDebugBarExtension() {
			return new Puc_v4p11_DebugBar_Extension($this);
		}

		/**
		 * Display additional configuration details in the Debug Bar panel.
		 *
		 * @param Puc_v4p11_DebugBar_Panel $panel
		 */
		public function onDisplayConfiguration($panel) {
			//Do nothing. Subclasses can use this to add additional info to the panel.
		}

	}

endif;