var daysInMonth = new Array(12);
daysInMonth[1] = 31;
daysInMonth[2] = 29;   // must programmatically check this
daysInMonth[3] = 31;
daysInMonth[4] = 30;
daysInMonth[5] = 31;
daysInMonth[6] = 30;
daysInMonth[7] = 31;
daysInMonth[8] = 31;
daysInMonth[9] = 30;
daysInMonth[10] = 31;
daysInMonth[11] = 30;
daysInMonth[12] = 31;

var digits = "0123456789";

// whitespace characters
var whitespace = " \t\n\r";

function isDigit (c)
{   return ((c >= "0") && (c <= "9"))
}

// Check whether string s is empty.

function isEmpty(s)
{   return ((s == null) || (s.length == 0))
}



// Returns true if string s is empty or 
// whitespace characters only.

function isWhitespace (s)

{   var i;

    // Is s empty?
    if (isEmpty(s)) return true;

    // Search through string's characters one by one
    // until we find a non-whitespace character.
    // When we do, return false; if we don't, return true.

    for (i = 0; i < s.length; i++)
    {   
        // Check that current character isn't whitespace.
        var c = s.charAt(i);

        if (whitespace.indexOf(c) == -1) return false;
    }

    // All characters are whitespace.
    return true;
}

// Removes initial (leading) whitespace characters from s.
// Global variable whitespace (see above)
// defines which characters are considered whitespace.

function stripInitialWhitespace (s)

{   var i = 0;

    while ((i < s.length) && (whitespace.indexOf(s.charAt(i)) != -1))
       i++;
    
    return s.substring (i, s.length);
}

// isNumber (STRING s [,BOOLEAN emptyOK])
// 
// Returns true if all characters in string s are numbers.
//
// Accepts non-signed integers only. Does not accept floating 
// point, exponential notation, etc.
//
// We don't use parseInt because that would accept a string
// with trailing non-numeric characters.
//
// If emptyOK is false (or any value other than true), 
//      the function will return false if s is empty.
// If emptyOK is true, the function will return true if s is empty.
//
function isNumber (s)

{   var i;

    if (isEmpty(s) || isWhitespace(s)) 
       if (isNumber.arguments.length == 1) return false; // cannot be empty
       else return (isNumber.arguments[1] == true);
    // Search through string's characters one by one
    // until we find a non-numeric character.
    // When we do, return false; if we don't, return true.

    s = stripInitialWhitespace (s);
    for (i = 0; i < s.length; i++)
    {   
        // Check that current character is number.
        var c = s.charAt(i);

        if (!isDigit(c)) return false;
    }
    // All characters are numbers -- no negative or positive sign
    return true;
}


// isYear (STRING s [, BOOLEAN emptyOK])
// 
// isYear returns true if string s is a valid 
// Year number.  Must be 4 digits only.
// 
// And yes, this function is not Year 10000 compliant, but 
// because I am giving you 8003 years of advance notice,
// I don't feel very guilty about this ...
//
// For B.C. compliance, write your own function. ;->
//
// For explanation of optional argument emptyOK,
// see comments of function isNumber.

function isYear (s)
{ 
if (isEmpty(s) || isWhitespace(s)) 
       if (isYear.arguments.length == 1) return false;
       else return (isYear.arguments[1] == true);
 
   if (!isNumber(s, false)) return false;
    return (s.length == 4);
}

// isMonth (STRING s [, BOOLEAN emptyOK])
// 
// isMonth returns true if string s is a valid 
// month number between 1 and 12.
//
// For explanation of optional argument emptyOK,
// see comments of function isNumber.

function isMonth (s)
{    
 if (isEmpty(s) || isWhitespace(s)) 
       if (isMonth.arguments.length == 1) return false;
       else return (isMonth.arguments[1] == true);

    if (!isNumber(s, false)) return false;

    // Now, explicitly change the type to integer via parseInt
    // so that the comparison code below will work both on 
    // JavaScript 1.2 (which typechecks in equality comparisons)
    // and JavaScript 1.1 and before (which doesn't).
    var num = parseInt (s, 10);
    return ((num >= 1) && (num <= 12));

}



// isDay (STRING s [, BOOLEAN emptyOK])
// 
// isDay returns true if string s is a valid 
// day number between 1 and 31.
// 
// For explanation of optional argument emptyOK,
// see comments of function isNumber.

function isDay (s)
{ 
  	if (isEmpty(s) || isWhitespace(s)) 
       if (isDay.arguments.length == 1) return false;
       else return (isDay.arguments[1] == true);

    if (!isNumber(s, false)) return false;

    // Now, explicitly change the type to integer via parseInt
    // so that the comparison code below will work both on 
    // JavaScript 1.2 (which typechecks in equality comparisons)
    // and JavaScript 1.1 and before (which doesn't).
    var num = parseInt (s, 10);
    return ((num >= 1) && (num <= 31));

}



// daysInFebruary (INTEGER year)
// 
// Given integer argument year,
// returns number of days in February of that year.

function daysInFebruary (year)
{   // February has 29 days in any year evenly divisible by four,
    // EXCEPT for centurial years which are not also divisible by 400.
    return (  ((year % 4 == 0) && ( (!(year % 100 == 0)) || (year % 400 == 0) ) ) ? 29 : 28 );
}



// isDate (STRING year, STRING month, STRING day)
//
// isDate returns true if string arguments year, month, and day 
// form a valid date.
// 

function isDate (year, month, day)

{   // catch invalid years (not 4-digit) and invalid months and days.
    if (! (isYear(year, false) && isMonth(month, false) && isDay(day, false))) return false;

    // Explicitly change type to integer to make code work in both
    // JavaScript 1.1 and JavaScript 1.2.
    var intYear = parseInt(year, 10);
    var intMonth = parseInt(month, 10);
    var intDay = parseInt(day, 10);

    // catch invalid days, except for February
    if (intDay > daysInMonth[intMonth]) return false; 

    if ((intMonth == 2) && (intDay > daysInFebruary(intYear))) return false;

    return true;
}
function isNotEmpty(obj, name) {
	if (obj.value == "") return "You need to fill in the " + name + " field.\n";
	return "";
}

function isInteger(obj, name, mi, ma) {
	if (mi != null) {
		if (parseInt(obj.value) == obj.value){
			if (obj.value < mi) return name + " must be an integer (whole number) greater than or equal to " + mi + ".\n";
		}
	}
	if (ma != null) {
		if (parseInt(obj.value) == obj.value){
			if (obj.value > ma) return name + " must be an integer (whole number) less than or equal to " + ma + ".\n";
		}
	}
	if (parseInt(obj.value) != obj.value) return name + " must be an integer (whole number).\n";
	return "";
}

// isEmail (STRING s [, BOOLEAN emptyOK])
// 
// Email address must be of form a@b.c -- in other words:
// * there must be at least one character before the @
// * there must be at least one character before and after the .
// * the characters @ and . are both required
//
// For explanation of optional argument emptyOK,
// see comments of function isInteger.

function isEmail (s)
{   if (isEmpty(s) || isWhitespace(s)) 
       if (isEmail.arguments.length == 1) return false;
       else return (isEmail.arguments[1] == true);
   
    
    // there must be >= 1 character before @, so we
    // start looking at character position 1 
    // (i.e. second character)
    s = stripInitialWhitespace (s);
    var i = 1;
    var sLength = s.length;

    // look for @
    while ((i < sLength) && (s.charAt(i) != "@"))
    { i++
    }

    if ((i >= sLength) || (s.charAt(i) != "@")) return false;
    else i += 2;

    // look for .
    while ((i < sLength) && (s.charAt(i) != "."))
    { i++
    }

    // there must be at least one character after the .
    if ((i >= sLength - 1) || (s.charAt(i) != ".")) return false;
    else return true;
}