(function( exports, $ ){

	var api = wp.customize,

		debounce;

	debounce = function( fn, delay, context ) {

		var timeout;

		return function() {

			var args = arguments;

			context = context || this;

			clearTimeout( timeout );

			timeout = setTimeout( function() {

				timeout = null;

				fn.apply( context, args );

			}, delay );

		};

	};

	api.Preview = api.Messenger.extend({

		/**

		 * Requires params:

		 *  - url    - the URL of preview frame

		 */

		initialize: function( params, options ) {

			var self = this;

			api.Messenger.prototype.initialize.call( this, params, options );

			this.body = $( document.body );

			this.body.on( 'click.preview', 'a', function( event ) {

				event.preventDefault();

				self.send( 'scroll', 0 );

				self.send( 'url', $(this).prop('href') );

			});

			// You cannot submit forms.

			// @todo: Allow form submissions by mixing $_POST data with the customize setting $_POST data.

			this.body.on( 'submit.preview', 'form', function( event ) {

				event.preventDefault();

			});

			this.window = $( window );

			this.window.on( 'scroll.preview', debounce( function() {

				self.send( 'scroll', self.window.scrollTop() );

			}, 200 ));

			this.bind( 'scroll', function( distance ) {

				self.window.scrollTop( distance );

			});

		}

	});

	$( function() {

		api.settings = window._wpCustomizeSettings;

		if ( ! api.settings )

			return;

		var preview, bg;

		preview = new api.Preview({

			url: window.location.href,

			channel: api.settings.channel

		});

		preview.bind( 'settings', function( values ) {

			$.each( values, function( id, value ) {

				if ( api.has( id ) )

					api( id ).set( value );

				else

					api.create( id, value );

			});

		});

		preview.trigger( 'settings', api.settings.values );

		preview.bind( 'setting', function( args ) {

			var value;

			args = args.slice();

			if ( value = api( args.shift() ) )

				value.set.apply( value, args );

		});

		preview.bind( 'sync', function( events ) {

			$.each( events, function( event, args ) {

				preview.trigger( event, args );

			});

			preview.send( 'synced' );

		});

	 	preview.bind( 'active', function() {

	 		if ( api.settings.nonce )

	 			preview.send( 'nonce', api.settings.nonce );

	 	});

		preview.send( 'ready' );

		/* Custom Backgrounds */

		bg = $.map(['color', 'image', 'position_x', 'repeat', 'attachment'], function( prop ) {

			return 'background_' + prop;

		});

		api.when.apply( api, bg ).done( function( color, image, position_x, repeat, attachment ) {

			var body = $(document.body),

				head = $('head'),

				style = $('#custom-background-css'),

				update;

			// If custom backgrounds are active and we can't find the

			// default output, bail.

			if ( body.hasClass('custom-background') && ! style.length )

				return;

			update = function() {

				var css = '';

				// The body will support custom backgrounds if either

				// the color or image are set.

				//

				// See get_body_class() in /wp-includes/post-template.php

				body.toggleClass( 'custom-background', !! ( color() || image() ) );

				if ( color() )

					css += 'background-color: ' + color() + ';';

				if ( image() ) {

					css += 'background-image: url("' + image() + '");';

					css += 'background-position: top ' + position_x() + ';';

					css += 'background-repeat: ' + repeat() + ';';

					css += 'background-attachment: ' + attachment() + ';';

				}

				// Refresh the stylesheet by removing and recreating it.

				style.remove();

				style = $('<style type="text/css" id="custom-background-css">body.custom-background { ' + css + ' }</style>').appendTo( head );

			};

			$.each( arguments, function() {

				this.bind( update );

			});

		});

	});

})( wp, jQuery );