// ********************************************************
// This function accepts a string variable and verifies if
// it is a proper date or not.  It validates format
// matching either mm-dd-yyyy or mm/dd/yyyy. Then it checks
// to make sure the month has the proper number of days,
// based on which month it is.

// The function returns true if a valid date, false if not.
// ********************************************************

function isDate(dateStr) {

  var datePat = /^(\d{1,2})(\/|-)(\d{1,2})(\/|-)(\d{4})$/;
  var matchArray = dateStr.match(datePat); // is format OK?

  if (matchArray == null) {
    alert("Please enter date as either mm/dd/yyyy or mm-dd-yyyy.");
    return false;
  }

  // parse date into variables
  month = matchArray[1];
  day = matchArray[3];
  year = matchArray[5];

  if (month < 1 || month > 12) { // check month range
    alert("O mes deve estar entre 1 and 12.");
    return false;
  }

  if (day < 1 || day > 31) {
    alert("O dia deve estar entre 1 and 31.");
    return false;
  }

  if ((month==4 || month==6 || month==9 || month==11) && day==31) {
    alert("O mes " + month + " não tem 31 dias!")
    return false;
  }

  if (month == 2) { // check for february 29th
    var isleap = (year % 4 == 0 && (year % 100 != 0 || year % 400 == 0));
    if (day > 29 || (day==29 && !isleap)) {
      alert("Fevereiro " + year + " não tem " + day + " dias!");
      return false;
    }
  }
  return true;  // date is valid
}