/*
 * jQuery appear plugin
 *
 * Copyright (c) 2012 Andrey Sidorov
 * licensed under MIT license.
 *
 * https://github.com/morr/jquery.appear/
 *
 * Version: 0.3.6
 */
(function($) {
    var selectors = [];

    var check_binded = false;
    var check_lock = false;
    var defaults = {
        interval: 250,
        force_process: false
    };
    var $window = $(window);

    var $prior_appeared = [];

    function appeared(selector) {
        return $(selector).filter(function() {
            return $(this).is(':appeared');
        });
    }

    function process() {
        check_lock = false;
        for (var index = 0, selectorsLength = selectors.length; index < selectorsLength; index++) {
            var $appeared = appeared(selectors[index]);

            $appeared.trigger('appear', [$appeared]);

            if ($prior_appeared[index]) {
                var $disappeared = $prior_appeared[index].not($appeared);
                $disappeared.trigger('disappear', [$disappeared]);
            }
            $prior_appeared[index] = $appeared;
        }
    }

    function add_selector(selector) {
        selectors.push(selector);
        $prior_appeared.push();
    }

    // "appeared" custom filter
    $.expr[':'].appeared = function(element) {
        var $element = $(element);
        if (!$element.is(':visible')) {
            return false;
        }

        var window_left = $window.scrollLeft();
        var window_top = $window.scrollTop();
        var offset = $element.offset();
        var left = offset.left;
        var top = offset.top;

        if (top + $element.height() >= window_top &&
            top - ($element.data('appear-top-offset') || 0) <= window_top + $window.height() &&
            left + $element.width() >= window_left &&
            left - ($element.data('appear-left-offset') || 0) <= window_left + $window.width()) {
            return true;
        } else {
            return false;
        }
    };

    $.fn.extend({
        // watching for element's appearance in browser viewport
        appear: function(options) {
            var opts = $.extend({}, defaults, options || {});
            var selector = this.selector || this;
            if (!check_binded) {
                var on_check = function() {
                    if (check_lock) {
                        return;
                    }
                    check_lock = true;

                    setTimeout(process, opts.interval);
                };

                $(window).scroll(on_check).resize(on_check);
                check_binded = true;
            }

            if (opts.force_process) {
                setTimeout(process, opts.interval);
            }
            add_selector(selector);
            return $(selector);
        }
    });

    $.extend({
        // force elements's appearance check
        force_appear: function() {
            if (check_binded) {
                process();
                return true;
            }
            return false;
        }
    });
})(function() {
    if (typeof module !== 'undefined') {
        // Node
        return require('jquery');
    } else {
        return jQuery;
    }
}());