(function($){
  
  $.fn.newInvoiceForm = function(options) {
    // Extend our default options with those provided.
    var opts = $.extend({}, $.fn.newInvoiceForm.defaults, options);
    this.find('input[type=radio]').change(function() {
      updateStates();
    });
    
    updateStates();
  };
  
  function updateStates() {
    if ($('input[name=invoice_type]:checked').val() == 'fraction') {
      $('#shipment_fieldset select').attr('disabled', 'disabled');
      $('#fraction_fieldset input[type=text]').attr('disabled', '');
      $('#fraction_fieldset input[type=text]').get(1).focus();
    } else {
      $('#shipment_fieldset select').attr('disabled', '');
      $('#fraction_fieldset input[type=text]').attr('disabled', 'disabled');
      $('#shipment_fieldset select').get(0).focus();
    }
  };
  
  $.fn.newInvoiceForm.defaults = {
  };
  
})(jQuery);