#!/usr/bin/perl

use strict;
use warnings;

use CGI ':cgi';
use Template; # for producing output.

# List of subroutines that handle the different modes
my %modes = (
  mode1 => \&process_mode1,
  mode2 => \&process_mode2,
  default => \&process_default,
);

# Work out which mode we're in
my $mode = param('mode');

# If we have a mode, then call that subroutine
if ($mode && %modes{$mode}) {
  $modes{mode}->();
} else {
  # Otherwise call the default handler
  $modes{default}->();
}

sub process_default {
  # no mode give, display the default form
}

sub process_mode1 {
  # process mode1 and display the next form
}

sub process_mode2 {
  # process mode2 and display the next form
}