/** jQuery.bsf_appear
 * https://github.com/bas2k/jquery.bsf_appear/
 * http://code.google.com/p/jquery-bsf_appear/
 *
 * Copyright (c) 2009 Michael Hixson
 * Copyright (c) 2012 Alexander Brovikov
 * Licensed under the MIT license (http://www.opensource.org/licenses/mit-license.php)
 */
(function($) {
	"use strict";
    $.fn.bsf_appear = function(fn, options) {
        var settings = $.extend({
            //arbitrary data to pass to fn
            data: undefined,
            //call fn only on the first bsf_appear?
            one: true,
            // X & Y accuracy
            accX: 0,
            accY: 0
        }, options);
        return this.each(function() {
            var t = $(this);
            //whether the element is currently visible
            t.bsf_appeared = false;
            if (!fn) {
                //trigger the custom event
                t.trigger('bsf_appear', settings.data);
                return;
            }
            var w = $(window);
            //fires the bsf_appear event when appropriate
            var check = function() {
                //is the element hidden?
                if (!t.is(':visible')) {
                    //it became hidden
                    t.bsf_appeared = false;
                    return;
                }
                //is the element inside the visible window?
                var a = w.scrollLeft();
                var b = w.scrollTop();
                var o = t.offset();
                var x = o.left;
                var y = o.top;
                var ax = settings.accX;
                var ay = settings.accY;
                var th = t.height();
                var wh = w.height();
                var tw = t.width();
                var ww = w.width();
                if (y + th + ay >= b &&
                    y <= b + wh + ay &&
                    x + tw + ax >= a &&
                    x <= a + ww + ax) {
                    //trigger the custom event
                    if (!t.bsf_appeared) t.trigger('bsf_appear', settings.data);
                } else {
                    //it scrolled out of view
                    t.bsf_appeared = false;
                }
            };
            //create a modified fn with some additional logic
            var modifiedFn = function() {
                //mark the element as visible
                t.bsf_appeared = true;
                //is this supposed to happen only once?
                if (settings.one) {
                    //remove the check
                    w.unbind('scroll', check);
                    var i = $.inArray(check, $.fn.bsf_appear.checks);
                    if (i >= 0) $.fn.bsf_appear.checks.splice(i, 1);
                }
                //trigger the original fn
                fn.apply(this, arguments);
            };
            //bind the modified fn to the element
            if (settings.one) t.one('bsf_appear', settings.data, modifiedFn);
            else t.bind('bsf_appear', settings.data, modifiedFn);
            //check whenever the window scrolls
            w.scroll(check);
            //check whenever the dom changes
            $.fn.bsf_appear.checks.push(check);
            //check now
            (check)();
        });
    };
    //keep a queue of bsf_appearance checks
    $.extend($.fn.bsf_appear, {
        checks: [],
        timeout: null,
        //process the queue
        checkAll: function() {
            var length = $.fn.bsf_appear.checks.length;
            if (length > 0) while (length--) ($.fn.bsf_appear.checks[length])();
        },
        //check the queue asynchronously
        run: function() {
            if ($.fn.bsf_appear.timeout) clearTimeout($.fn.bsf_appear.timeout);
            $.fn.bsf_appear.timeout = setTimeout($.fn.bsf_appear.checkAll, 20);
        }
    });
    //run checks when these methods are called
    $.each(['append', 'prepend', 'after', 'before', 'attr',
        'removeAttr', 'addClass', 'removeClass', 'toggleClass',
        'remove', 'css', 'show', 'hide'], function(i, n) {
        var old = $.fn[n];
        if (old) {
            $.fn[n] = function() {
                var r = old.apply(this, arguments);
                $.fn.bsf_appear.run();
                return r;
            }
        }
    });
})(jQuery);