( function ( mw, $ ) {

	/**
	 * Creates the link element and appends it to the footer element.
	 *
	 * The following elements are considered to be the footer element (highest
	 * priority to lowest):
	 *
	 * # `#footer-places`
	 * # `#f-list`
	 * # The parent element of `#footer li`, which is either an `ol` or `ul`.
	 *
	 * @return {jQuery} The link element
	 */
	function createFooterLink() {
		var $link = $( '<li>' ).append(
				$( '<a>' )
					.attr( 'href', '#' )
					.text( mw.message( 'popups-settings-enable' ).text() )
			),
			$footer;

		// As yet, we don't know whether the link should be visible.
		$link.hide();

		// From https://en.wikipedia.org/wiki/MediaWiki:Gadget-ReferenceTooltips.js,
		// which was written by Yair rand <https://en.wikipedia.org/wiki/User:Yair_rand>.
		$footer = $( '#footer-places, #f-list' );

		if ( $footer.length === 0 ) {
			$footer = $( '#footer li' ).parent();
		}

		$footer.append( $link );

		return $link;
	}

	/**
	 * Creates an instance of the footer link change listener.
	 *
	 * The change listener covers the following behaviour:
	 *
	 * * The "Enable previews" link (the "link") is appended to the footer menu
	 *   (see `createFooterLink` above).
	 * * When Page Previews are disabled, then the link is shown; otherwise, the
	 *   link is hidden.
	 * * When the user clicks the link, then the `showSettings` bound action
	 *   creator is called.
	 *
	 * @param {Object} boundActions
	 * @return {ext.popups.ChangeListener}
	 */
	mw.popups.changeListeners.footerLink = function ( boundActions ) {
		var $footerLink;

		return function ( prevState, state ) {
			if ( $footerLink === undefined ) {
				$footerLink = createFooterLink();
				$footerLink.click( boundActions.showSettings );
			}

			if ( state.preview.enabled ) {
				$footerLink.hide();
			} else {
				$footerLink.show();
			}
		};
	};

}( mediaWiki, jQuery ) );