User script to struggle against procrastination

self-control.user.js

(function(){

    var hosts = [
        'vk.com',
        'last.fm',
        'lastfm.ru',
        'wikipedia.org',
        'lurkmore.to',
        'habrahabr.ru',
        'lenta.ru',
        'facebook.com',
        'youtube.com'
    ];
    var message = 'Self-control';
    var interval = 20 * 60 * 1000; // 20 minutes
    var localStorageInitializedPrefix = '__selfControl__';

    function getCurrentHost(){
        var host = location.hostname.split('.');
        return host[host.length-2] + '.' + host[host.length-1];
    };

    function initialize(){

        function showMessage(){
            alert(message);
            localStorage.setItem(localStorageTimePrefix, +new Date());
        }

        var localStorageTimePrefix = '__selfControlTime__';

        var startTime;
        var currentTime = +new Date();
        var previousTime = +localStorage.getItem(localStorageTimePrefix);

        var timeShift = currentTime - previousTime;

        if ( previousTime && timeShift < interval ) {
            startTime = previousTime;
            setTimeout(function(){
                showMessage();
                setInterval(showMessage, interval);
            }, interval - timeShift)
        }
        else {
            startTime = currentTime;
            localStorage.setItem(localStorageTimePrefix, startTime);
            setInterval(showMessage, interval);
        }

        onbeforeunload = function(){
            localStorage.removeItem(localStorageInitializedPrefix);
        };
        localStorage.setItem(localStorageInitializedPrefix, true);

    };

    function isInitialized(){
        return localStorage.getItem(localStorageInitializedPrefix);
    };

    if ( window.top === window.self ) {

        var currentHost = getCurrentHost();

        for ( var i = 0, l = hosts.length; i < l; i++ ) {
            if ( hosts[i] === currentHost ) {
                if ( isInitialized() ) {
                    var tempInterval = setInterval(function(){
                        if ( !isInitialized() ) {
                            clearInterval(tempInterval);
                            initialize();
                        }
                    }, 1000);
                }
                else {
                    initialize();
                }
                break;
            }
        }
    }

}());