/* 1.1.2: Fixed a bug where trailing . in e-mail address was passing
            (the bug is actually in the weak regexp engine of the browser; I
            simplified the regexps to make it work).
   1.1.1: Removed restriction that countries must be preceded by a domain,
            so abc@host.uk is now legal.  However, there's still the 
            restriction that an address must end in a two or three letter
            word.
     1.1: Rewrote most of the function to conform more closely to RFC 822.
     1.0: Original  */

function emailCheck (emailStr)
{
   /* The following pattern is used to check if the entered e-mail address
      fits the user@domain format.  It also is used to separate the username
      from the domain. */
   var emailPat=/^(.+)@(.+)$/
   /* The following string represents the pattern for matching all special
      characters.  We don't want to allow special characters in the address. 
      These characters include ( ) < > @ , ; : \ " . [ ]    */
   var specialChars="\\(\\)<>@,;:\\\\\\\"\\.\\[\\]"
   /* The following string represents the range of characters allowed in a 
      username or domainname.  It really states which chars aren't allowed. */
   var validChars="\[^\\s" + specialChars + "\]"
   /* The following pattern applies if the "user" is a quoted string (in
      which case, there are no rules about which characters are allowed
      and which aren't; anything goes).  E.g. "jiminy cricket"@disney.com
      is a legal e-mail address. */
   var quotedUser="(\"[^\"]*\")"
   /* The following pattern applies for domains that are IP addresses,
      rather than symbolic names.  E.g. joe@[123.124.233.4] is a legal
      e-mail address. NOTE: The square brackets are required. */
   var ipDomainPat=/^\[(\d{1,3})\.(\d{1,3})\.(\d{1,3})\.(\d{1,3})\]$/
   /* The following string represents an atom (basically a series of
      non-special characters.) */
   var atom=validChars + '+'
   /* The following string represents one word in the typical username.
      For example, in john.doe@somewhere.com, john and doe are words.
      Basically, a word is either an atom or quoted string. */
   var word="(" + atom + "|" + quotedUser + ")"
   // The following pattern describes the structure of the user
   var userPat=new RegExp("^" + word + "(\\." + word + ")*$")
   /* The following pattern describes the structure of a normal symbolic
      domain, as opposed to ipDomainPat, shown above. */
   var domainPat=new RegExp("^" + atom + "(\\." + atom +")*$")


   /* Finally, let's start trying to figure out if the supplied address is
      valid. */

   /* Begin with the coarse pattern to simply break up user@domain into
      different pieces that are easy to analyze. */
   var matchArray=emailStr.match(emailPat)
   if (matchArray==null)
   {
     /* Too many/few @'s or something; basically, this address doesn't
        even fit the general mould of a valid e-mail address. */
           //alert("Email address seems incorrect (check @ and .'s)")
           return false
   }
   var user=matchArray[1]
   var domain=matchArray[2]

   // See if "user" is valid 
   if (user.match(userPat)==null)
   {
       // user is not valid
       //alert("The username doesn't seem to be valid.")
       return false
   }

   /* if the e-mail address is at an IP address (as opposed to a symbolic
      host name) make sure the IP address is valid. */
   var IPArray=domain.match(ipDomainPat)
   if (IPArray!=null)
   {
       // this is an IP address
       for (var i=1;i<=4;i++)
       {
           if (IPArray[i]>255)
           {
               //alert("Destination IP address is invalid!")
               return false
           }
       }
       return true
   }

   // Domain is symbolic name
   var domainArray=domain.match(domainPat)
   if (domainArray==null)
   {
           //alert("The domain name doesn't seem to be valid.")
       return false
   }

   /* domain name seems valid, but now make sure that it ends in a
      three-letter word (like com, edu, gov) or a two-letter word,
      representing country (uk, nl), and that there's a hostname preceding 
      the domain or country. */

   /* Now we need to break up the domain to get a count of how many atoms
      it consists of. */
   var atomPat=new RegExp(atom,"g")
   var domArr=domain.match(atomPat)
   var len=domArr.length
   if (domArr[domArr.length-1].length<2 || 
       domArr[domArr.length-1].length>4)
   {
      // the address must end in a two letter or three letter word.
      //alert("The address must end in a three-letter domain, or two letter country.")
      return false
   }

   // Make sure there's a host name preceding the domain.
   if (len<2)
   {
      var errStr="This address is missing a hostname!"
      //alert(errStr)
      return false
   }

   // If we've gotten this far, everything's valid!
   return true;
}