Theme_Upgrader::bulk_upgrade()

	public function bulk_upgrade( $themes, $args = array() ) {
		$defaults    = array(
			'clear_update_cache' => true,
		);
		$parsed_args = gc_parse_args( $args, $defaults );

		$this->init();
		$this->bulk = true;
		$this->upgrade_strings();

		$current = get_site_transient( 'update_themes' );

		add_filter( 'upgrader_pre_install', array( $this, 'current_before' ), 10, 2 );
		add_filter( 'upgrader_post_install', array( $this, 'current_after' ), 10, 2 );
		add_filter( 'upgrader_clear_destination', array( $this, 'delete_old_theme' ), 10, 4 );

		$this->skin->header();

		// Connect to the filesystem first.
		$res = $this->fs_connect( array( GC_CONTENT_DIR ) );
		if ( ! $res ) {
			$this->skin->footer();
			return false;
		}

		$this->skin->bulk_header();

		/*
		 * Only start maintenance mode if:
		 * - running Multisite and there are one or more themes specified, OR
		 * - a theme with an update available is currently in use.
		 * @todo For multisite, maintenance mode should only kick in for individual sites if at all possible.
		 */
		$maintenance = ( is_multisite() && ! empty( $themes ) );
		foreach ( $themes as $theme ) {
			$maintenance = $maintenance || get_stylesheet() === $theme || get_template() === $theme;
		}
		if ( $maintenance ) {
			$this->maintenance_mode( true );
		}

		$results = array();

		$this->update_count   = count( $themes );
		$this->update_current = 0;
		foreach ( $themes as $theme ) {
			$this->update_current++;

			$this->skin->theme_info = $this->theme_info( $theme );

			if ( ! isset( $current->response[ $theme ] ) ) {
				$this->skin->set_result( true );
				$this->skin->before();
				$this->skin->feedback( 'up_to_date' );
				$this->skin->after();
				$results[ $theme ] = true;
				continue;
			}

			// Get the URL to the zip file.
			$r = $current->response[ $theme ];

			$result = $this->run(
				array(
					'package'           => $r['package'],
					'destination'       => get_theme_root( $theme ),
					'clear_destination' => true,
					'clear_working'     => true,
					'is_multi'          => true,
					'hook_extra'        => array(
						'theme' => $theme,
					),
				)
			);

			$results[ $theme ] = $this->result;

			// Prevent credentials auth screen from displaying multiple times.
			if ( false === $result ) {
				break;
			}
		} // End foreach $themes.

		$this->maintenance_mode( false );

		// Refresh the Theme Update information.
		gc_clean_themes_cache( $parsed_args['clear_update_cache'] );

		/** This action is documented in gc-admin/includes/class-gc-upgrader.php */
		do_action(
			'upgrader_process_complete',
			$this,
			array(
				'action' => 'update',
				'type'   => 'theme',
				'bulk'   => true,
				'themes' => $themes,
			)
		);

		$this->skin->bulk_footer();

		$this->skin->footer();

		// Cleanup our hooks, in case something else does a upgrade on this connection.
		remove_filter( 'upgrader_pre_install', array( $this, 'current_before' ) );
		remove_filter( 'upgrader_post_install', array( $this, 'current_after' ) );
		remove_filter( 'upgrader_clear_destination', array( $this, 'delete_old_theme' ) );

		// Ensure any future auto-update failures trigger a failure email by removing
		// the last failure notification from the list when themes update successfully.
		$past_failure_emails = get_option( 'auto_plugin_theme_update_emails', array() );

		foreach ( $results as $theme => $result ) {
			// Maintain last failure notification when themes failed to update manually.
			if ( ! $result || is_gc_error( $result ) || ! isset( $past_failure_emails[ $theme ] ) ) {
				continue;
			}

			unset( $past_failure_emails[ $theme ] );
		}

		update_option( 'auto_plugin_theme_update_emails', $past_failure_emails );

		return $results;
	}