/* emailcheck.js */

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 represents the range of characters allowed as the first character in a valid username or domain.  I just made it the same as above, but if you want to add a different constraint, you would change it here. */
	var firstChars=validChars
	/* 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=/^\[(\d{1,3})\.(\d{1,3})\.(\d{1,3})\.(\d{1,3})\]$/
	/* The following string represents at atom (basically a series of non-special characters.) */
	var atom="(" + firstChars + validChars + "*" + ")"
	/* The following string represents one word in the typical username. For example, in john.doe@somewhere.com, john and doe are words. Basically, a word is either an atom or quoted string. */
	var word="(" + atom + "|" + quotedUser + ")"
	// The following pattern describes the structure of the user
	var userPat=new RegExp("^" + word + "(\\." + word + ")*$")
	/* 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 course 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 problem : 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("Email Address problem : 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("Email Address problem : Destination IP address is invalid!")
			return false
		    }
	    }
	    return true
	}
	
	// Domain is symbolic name
	/*
	var domainArray=domain.match(domainPat)
	if (domainArray==null) {
		alert("Email Address problem : 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). If there's a country code at the end of the address, the full domain
	   must include a hostname and category (e.g. host.co.uk or host.pub.nl). If it ends in a .com or something, make sure there's a hostname.*/
	
	/* 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>3) {
	   // the address must end in a two letter or three letter word.
	   alert("Email Address problem : The address must end in a three-letter domain, " +
		    "or two letter country.")
	   return false
	}
	
	/* If it ends in a country code, we want to make sure there are at least 2 atoms preceding it (representing host and category (i.e. com, gov, etc.)) 
	   Note: The check for a category has been disabled, since there are apparently e-mail addressed without the category now. 
	*/
	if (domArr[domArr.length-1].length==2 && len<2) {
	   var errStr="Email Address problem : " + 
			  "This address ends in two characters, which is a country"
	   errStr+=" code.  Country codes must be preceded by "
	   errStr+="a hostname and, preferably, a category (like com, net, org, edu etc.)"
	   alert(errStr)
	   return false
	}
	
	/* If it just ends in .com, .gov, etc., make sure there's a host name. This case can never actually happen because earlier checks take care of this implicitly, but we'll do it anyway. */
	if (domArr[domArr.length-1].length==3 && len<2) {
	   var errStr="Email Address problem : This address is missing a hostname!"
	   alert(errStr)
	   return false
	}
	// If we've gotten this far, everything's valid!
	return true;
}
//  End -->