function rotateTopContainer(classList) {
    var index = Math.floor( Math.random() * classList.length );
    var selectedClass = classList[index];
    var topContainerNode = document.getElementById("topcontainer");
    topContainerNode.className = selectedClass;

}
function rotateHomePanel(classList) {
    var index = Math.floor( Math.random() * classList.length );
    var selectedClass = classList[index];
    var bubbles = document.getElementById("bubbles");
    bubbles.className = selectedClass;
}

// online services pop up app windows

function isUndefined(v) {
    var undef;
    return v===undef;
} 

function raw_popup(url, target, features) {
    // pops up a window containing url optionally named target, optionally having features
    if (isUndefined(features)) features = _POPUP_FEATURES;
    if (isUndefined(target  )) target   = '_blank';
    var theWindow = window.open(url, target, features);
    theWindow.focus();
    return theWindow;
}

function link_popup(src, features) {
    // to be used in an html event handler as in: <a href="..." onclick="link_popup(this,...)" ...
    // pops up a window grabbing the url from the event source's href
    return raw_popup(src.getAttribute('href'), src.getAttribute('target') || '_blank', features);
}

function event_popup(e) {
    // to be passed as an event listener
    // pops up a window grabbing the url from the event source's href
    link_popup(e.currentTarget);
    e.preventDefault();
}

function event_popup_features(features) {
    // generates an event listener similar to event_popup, but allowing window features
    return function(e) { link_popup(e.currentTarget, features); e.preventDefault() }
}

// redefining default features
var _POPUP_FEATURES = 'location=0,statusbar=0,menubar=0,width=1024,height=600';