function validate(form)
{
  var first_element = null;
  var not_all_required = false, not_valid_email = false;
  var elemnt;
  
  if (!form) return false;
  
  for (var i=0; i<form.elements.length; i++)
  {
    element = form.elements[i];
    attribs = element.lang.split('_');
  
    if (attribs.find('req') && element.value=='') {
      not_all_required = true;
      if (first_element==null) first_element = element;
      element.style.backgroundColor = '#FFC0C0';
    }
    
    if (attribs.find('email') && element.value!='' && !is_email(element.value)) {
      not_valid_email = true;
      if (first_element==null) first_element = element;
    }
  }
  
  if (not_all_required) {
    first_element.focus();
    alert('Prosím vyplňte všetky povinné údaje.')
    return false;
  }
  
  if (not_valid_email) {
    first_element.style.backgroundColor = '#FFC0C0';
    first_element.focus();
    alert('Nesprávny email.')
    return false;
  }

  return true;
}

function is_email(str)
{
  var objRegExp = /^([a-zA-Z0-9_\.\-])+\@(([a-zA-Z0-9\-])+\.)+([a-zA-Z0-9]{2,4})+$/;
  return objRegExp.test(str);
}

Array.prototype.find = function (str)
{
  for (var i=0; i<this.length; i++)
    if (this[i]==str) return true; 
  
  return false;
}

function calc_diff() {
  var date1 = document.getElementsByName("r_date_arrival")[0].value;
  var date2 = document.getElementsByName("r_date_depart")[0].value;
  var n_count = document.getElementById('date_diff');
  var n_count_display = document.getElementById('n_count_display');
  var one_day = 1000*60*60*24;
  
  if (date1!=undefined && date2!=undefined && n_count!=undefined) {
    var diff = Math.round((parseDate(date2)-parseDate(date1))/one_day);
    
    if (diff<1) {
      n_count.value = -1;
      n_count_display.innerHTML = '<span style="color:#cc0000">zadané dátumy sú neprípustné</span>';
    } else {
      n_count.value = diff;
      n_count_display.innerHTML = diff;
    }
  }
  
  check_send_button();
}

function check_send_button() {
  document.getElementById('doreservation').disabled = !(document.getElementById('r_accept').checked && document.getElementById('date_diff').value>0);
}