// Javascript functions
function form_control() {
	if (document.sendform.email.value=='') { 
	          alert('Please, write your mail adress!');  
			  document.sendform.email.focus(); 
			  return false; 
	}else if(! Validate_Email_Address(document.sendform.email.value) ) {
			alert('This mail adress is not sure!');  document.sendform.email.focus();  return false;
	}else { document.sendform.submit(); }
}

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)    {
         //Assumes that valid email addresses consist of user_name@domain.tld
         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);
 }