function update_countries() {
    el = document.getElementById('id_continent');
    $("#country-p").load('/countries/'+el.options[el.selectedIndex].value+'/', add_event);
    return true;
}

function add_event(response, text, obj) {
    // Re-attach the event.
    el = $('#id_country');
    el.change(update_trips);
}

function update_trips(evt) {
    el = document.getElementById('id_continent');
    el2 = document.getElementById('id_country');

    if (!el || !el2) {
        return false;
    }

    if (el2.selectedIndex > 0) {
        if (el.selectedIndex > 0) {
            $("#trip-p").load('/trips/country/'+el2.options[el2.selectedIndex].value+'/?continent='+el.options[el.selectedIndex].value);
        }
        else {
            $("#trip-p").load('/trips/country/'+el2.options[el2.selectedIndex].value+'/');
        }
    }
    else if (el.selectedIndex > 0) {
        $("#trip-p").load('/trips/continent/'+el.options[el.selectedIndex].value+'/');
    }
    else {
        $("#trip-p").load('/trips/all/');
    }
    return true;
}

 $(document).ready(function() {
    el = $('#id_continent');
    el.change(update_countries);
    el.change(update_trips);

    el = $('#id_country');
    el.change(update_trips);
    return true;
})