#!/usr/local/bin/perl -w

use strict;
use Carp;

my %Commands = ('who'      => \&do_who,
                'what'     => \&do_what,
                'why'      => \&do_why,
                'never'    => \&do_never,
                'again'    => \&do_again,
                'answer'   => \&do_answer);

{
   my $userinput = $ARGV[0];

   my ($errmsg, $command) = check_commands (\%Commands, $userinput);

   if ($errmsg)
   {
      print "$errmsg\n";
      exit;
   }

   &{$Commands {$command}};
}

sub check_commands
{
   @_ == 2 or croak "Incorrect number of parameters";
   
   my ($cmdhash, $command) = @_;
   
   my @matches = grep /^$command/i, sort keys %$cmdhash;
   
   if (scalar @matches == 0)
   {
      return ("I don't know what '$command' means", undef);
   }
   elsif (scalar @matches > 1)
   {
      my $lastcmd = pop @matches;

      return ("'$command' is ambigous.  It could mean " . join (', ', @matches) . " or $lastcmd", undef);
   }
   
   return (undef, $matches [0]);
}

sub do_who     {print "Who\n"};
sub do_what    {print "What\n"};
sub do_why     {print "Why\n"};
sub do_never   {print "Never\n"};
sub do_again   {print "Again\n"};
sub do_answer  {print "Answer\n"};