// Author: Jacek Becela
// Website: http://github.com/ncr/at_intervals
// License: cc-by-sa
(function($) {
    $.fn.at_intervals = function(fn, options) {
        var settings = $.extend({}, $.fn.at_intervals.defaults, options);

        return this.each(function() {
            var e = $(this)
            var name = settings.name
            var delay = settings.delay

            var helper = {
                should_stop: function() { // used to completely remove the interval
                    return !this.element_in_dom() || this.user_wants_to_stop()
                },
                should_work: function() { // used to pause/resume the interval
                    return this.element_visible() && !this.user_wants_to_pause()
                },
                user_wants_to_stop: function() {
                    return e.data(name).should_stop == true
                },
                user_wants_to_pause: function() {
                    return e.data(name).should_pause == true
                },
                element_in_dom: function() {
                    return e.parents("html").length > 0
                },
                element_visible: function() {
                    return e.parents("*").andSelf().not(":visible").length == 0
                },
                stop: function(interval_id) {
                    clearInterval(interval_id)
                    e.removeData(name)
                }
            }

            if (e.data(name)) {
                helper.stop(e.data(name).interval_id) // remove previous executer
            }

            e.data(name, { delay: delay }) // initialize data cache

            if (helper.should_work()) {
                fn() // call fn immediately (setInterval applies the delay before calling fn for the first time)
            }

            var interval_id = setInterval(function() {
                if (helper.should_stop()) {
                    helper.stop(interval_id)
                } else {
                    if (helper.should_work()) {
                        fn()
                    }
                }
            }, delay)

            e.data(name).interval_id = interval_id
        })
    };

    $.fn.at_intervals.defaults = {
        name: "at_intervals",
        delay: 1000 // one second
    }
})(jQuery);