function call_ajax(method, params, callback) {
    var jsonRequest = new Request.JSON({url: '/ajax/' + method, onSuccess: function(response){
        for(i=0; i< response.messages.length; i++) {
            show_message(response.messages[i].type, response.messages[i].data);
            }
        callback(response);
    }}).post(params);
}

function display_error_message(response) {
    var error_content = new Element('div');
    var error_dialog = new Dialog("Entschuldigung, ein Fehler ist aufgetreten! (" + response.error.code + ")", error_content);
    var error_message = new Element('p');
    error_message.set('html', response.error.message);
    error_message.inject(error_content);
    
    // Buttons
    var button_box = new Element('div');
    button_box.set('class', 'button-container-box');
    button_box.inject(error_content);

    var button_close = new Element('a');
    button_close.set('html', 'Schließen')
    button_close.set('href', '#')
    button_close.set('class', 'button float_right red')
    button_close.inject(button_box);
    
    button_close.addEvent('click', function(event) {
        error_dialog.hide()
    });
}