#!/usr/bin/perl

# This tells the program to use a 'Class' (set of subroutines/functions/methods) 
# that knows how to read and write the HTTP CGI methods.
use CGI;

# This creates an instance of that class, called an 'object', 
# and its output gets assigned to a variable called 'query'.
# 'query' is now how we can access all of the CGI class's functionality.
$query = new CGI;

# This is the logic/ruleset governing what the page displays.
#   If the script receives data using the HTTP GET method,
#     a subroutine called 'show_form' (that generates the 
#     HTML displaying the form) gets accessed.
#   Otherwise, if something is sent to the script using the 
#     POST method, the 'process_form' subroutine (that 
#     contains the mailing instructions) is run.  How does 
#     the program know it can rely on receiving things from POST?
#   Otherwise, access the 'error' subroutine, which prints an error.
if ($query->request_method eq 'GET') {
  &show_form; 
} elsif ($query->request_method eq 'POST') {
  &process_form; 
} else {
  &error('Unsupported request method.'); 
} 

##########################################################
# Here begin the subroutine definitions.
#   Don't worry about understanding everything that they do.
#   Just understand the template:
#   - logic at the top of the script, makes decisions on 
#     how the page should react given certain user input;
#   - then encapulated lists of actions hold HTML fragments
#     that get pieced together to make the webpage code 
#     seen by the user.
##########################################################
sub error { 
  my ($message) = @_; 
  print $query->header, 
        $query->start_html(-bgcolor=>'white'), 
        qq{ $message }, $query->end_html; 
  exit; 
} 

sub process_form {
  my $email, $message; 
  $message = $query->param('message'); 
  $email = $query->param('email'); 
  $email =~ s/\s//g; 
  if ($email =~ /^[a-zA-Z]+\@indiana.edu$/i) { 
} elsif ($email =~ /^[a-zA-Z]+$/i) {
    $email .= "\@indiana.edu"; 
} else { &error('Unsupported e-mail address format.'); } 
  open MAIL, "| mailx $email jowarren\@indiana.edu "; 
  print MAIL $message; 
  close MAIL; 
  print $query->header,
        $query->start_html(-bgcolor=>'white'),
        qq{ Your message<blockquote>$message</blockquote> has 
            been sent to the webmaster. A copy has been sent  
            to the e-mail address that you indicated. }, 
        $query->end_html;
} 

sub show_form { print 
  $query->header, 
  $query->start_html(-bgcolor=>'white', 
                     -title=>'feedback'),
  $query->start_form(-method=>'POST', 
                     -action=>$query->url),
  qq{ Email address: }, 
  $query->textfield(-name=>'email', 
                    -size=>20,
                    -maxlength=>40),
  $query->p, qq{Message: },
  $query->textarea(-name=>'message', 
                   -rows=>5, 
                   -columns=>60,
                   -default=>'Replace me with your comments...'),
  $query->p, $query->submit(-name=>'Proceed'), $query->end_form, 
  $query->end_html; 
}