$(function () {
    function check() {
        var checkedNum = 0;
        langs.map(function (i) {
            if(langs[i].checked) checkedNum++;
        });
        if (checkedNum === langs.size()) {
            selectAll.prop('checked',true);
            selectAllLabel.hide();
            deselectAllLabel.show();
        } else {
            selectAll.prop('checked',false);
            selectAllLabel.toggle(true);
            deselectAllLabel.toggle(false); 
        } 
    }
    selectAll.change(function () {
        langs.prop('checked',this.checked);
        selectAllLabel.toggle(!this.checked);
        deselectAllLabel.toggle(this.checked);
    });
    invertSelect.click(function () {
        langs.map(function(i) {
            langs[i].checked = !langs[i].checked;
        });
        check();
    });
    langs.change(function () {
        check();       
    });
});