function Validate_String(string, return_invalid_chars) 
{
  valid_chars = '1234567890-_.^~abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ';
  invalid_chars = '';
  if(string == null || string == '') return true;

  //For every character on the string.   
  for(index = 0; index < string.length; index++) 
  {
    char = string.substr(index, 1);                        
     
    //Is it a valid character?
    if(valid_chars.indexOf(char) == -1) {
      //If not, is it already on the list of invalid characters?
      if(invalid_chars.indexOf(char) == -1) {
        //If it's not, add it.
        if(invalid_chars == '')
          invalid_chars += char;
        else
          invalid_chars += ', ' + char;
      }
    }
  }
            
  //If the string does not contain invalid characters, the function will return true.
  //If it does, it will either return false or a list of the invalid characters used
  //in the string, depending on the value of the second parameter.
  if(return_invalid_chars == true && invalid_chars != '') {
    last_comma = invalid_chars.lastIndexOf(',');
    if(last_comma != -1)
      invalid_chars = invalid_chars.substr(0, $last_comma) + 
      ' and ' + invalid_chars.substr(last_comma + 1, invalid_chars.length);
    return invalid_chars;
    }
  else
    return invalid_chars == ''; 
}


function Validate_Email_Address(email_address) 
{
  at = email_address.indexOf('@');
  dot = email_address.indexOf('.');

  if(at == -1 || 
    dot == -1 || 
    dot <= at + 1 ||
    dot == 0 || 
    dot == email_address.length - 1)
    return false;
     
  user_name = email_address.substr(0, at);
  domain_name = email_address.substr(at + 1, email_address.length);                  

  if(Validate_String(user_name) === false || Validate_String(domain_name) === false) return false;                     

  return true;
}


function trim(s)
{
  return s.replace(/^\s+|\s+$/, '');
}

function validateEmail(fld) 
{
    var error="";
    var tfld = trim(fld.value);                        // value of field with whitespace trimmed off
    var emailFilter = /^[^@]+@[^@.]+\.[^@]*\w\w$/ ;
    var illegalChars= /[\(\)\<\>\,\;\:\\\"\[\]]/ ;
   
    if (fld.value == "") {
        fld.style.background = 'Yellow';
        error = "You didn't enter an email address. \n";
    } else if (!emailFilter.test(tfld)) {              //test email for illegal characters
        fld.style.background = 'Yellow';
        error = "Please enter a valid email address. \n";
    } else if (fld.value.match(illegalChars)) {
        fld.style.background = 'Yellow';
        error = "The email address contains illegal characters. \n";
    } else {
        fld.style.background = 'White';
    }
    return error;
}

function validatePhone(fld) {
    var error = "";
    var stripped = fld.value.replace(/[\(\)\.\-\ ]/g, '');    

   if (fld.value == "") {
        error = "You didn't enter a phone number. \n";
        fld.style.background = 'Yellow';
    } else if (isNaN(parseInt(stripped))) {
        error = "The phone number contains illegal characters. \n";
        fld.style.background = 'Yellow';
    } else if (!(stripped.length == 10)) {
        error = "The phone number is the wrong length. Make sure you included an area code. \n";
        fld.style.background = 'Yellow';
    }
    return error;
}

function validatePassword(fld) {
    var error = "";
    var illegalChars = /[\W_]/; // allow only letters and numbers 
 
    if (fld.value == "") {
        fld.style.background = 'Yellow';
        error = "You didn't enter a password.\n";
    } else if ((fld.value.length < 7) || (fld.value.length > 15)) {
        error = "The password is the wrong length. \n";
        fld.style.background = 'Yellow';
    } else if (illegalChars.test(fld.value)) {
        error = "The password contains illegal characters.\n";
        fld.style.background = 'Yellow';
    } else if (!((fld.value.search(/(a-z)+/)) && (fld.value.search(/(0-9)+/)))) {
        error = "The password must contain at least one numeral.\n";
        fld.style.background = 'Yellow';
    } else {
        fld.style.background = 'White';
    }
   return error;
}  

function validateUsername(fld) {
    var error = "";
    var illegalChars = /\W/; // allow letters, numbers, and underscores
 
    if (fld.value == "") 
    {
        fld.style.background = 'Yellow'; 
        error = "You didn't enter a username.\n";
    } else if ((fld.value.length < 5) || (fld.value.length > 15)) {
        fld.style.background = 'Yellow'; 
        error = "The username is the wrong length.\n";
    } else if (illegalChars.test(fld.value)) {
        fld.style.background = 'Yellow'; 
        error = "The username contains illegal characters.\n";
    } else {
        fld.style.background = 'White';
    }
    return error;
}

function validateEmpty(fld) 
{
    var error = "";
 
    if (fld.value.length == 0) {
        fld.style.background = 'Yellow'; 
        error = "The required field has not been filled in.\n"       
    } else {
        fld.style.background = 'White';
    }
    return error;  
}

function validateFormOnSubmit(theForm) {
	var reason = "";
var reason2 = "";
	try{
	  reason += validateEmpty(theForm.first_name);
reason += validateEmpty(theForm.last_name);
	  	reason += validatePhone(theForm.phone);
	  	reason += validateEmail(theForm.email);
	  	reason += validateEmpty(theForm.forDate);
	  	reason += validateEmpty(theForm.guests);
	  	reason += validateEmpty(theForm.location);
	  	reason += validateEmpty(theForm.description);
		
		if (reason != "") 
	  	{
	    	alert("Please correct the following errors:   \n"  + reason);
	    	return false;
	  	}
	 	
	  	return true;
	}
	catch(e)
	{
		return false;
	}
}

function isString(textObj) 
{
   var newValue = textObj.value;
   var newLength = newValue.length;
   var extraChars=". -,";

   var search;
   for(var i = 0; i != newLength; i++) 
	{
      aChar = newValue.substring(i,i+1);
      aChar = aChar.toUpperCase();
      search = extraChars.indexOf(aChar);
      if(search == -1 && (aChar < "A" || aChar > "Z") ) {
         return false;
      }
   }
   return true;
}