#!/usr/bin/perl -w

=head1 NAME

who_likes.pl

=head1 DESCRIPTION

Compile a list of vegetables with the names of the people
who like them.

=head1 INPUT

A list of people and (at most) three vegetables they like.

Each line in the input consists of the person's name followed
by a colon, a space, then a list of the vegetables they like.
The vegetables are separated by comma + space.

The string "--" is used instead of a list of vegetables when
a person doesn't like B<any> vegetables.

Sample:

    Paul: onions, rutabagas, beets
    Xerxes: --
    Yolanda: squash, peas, beets
    Zainab: beets, broccoli, Brussels sprouts

=head1 OUTPUT

Like the input, but the other way around: each line consists of
the name of a vegetable followed by a colon, a single space, and
a list of the vegetables they like.

The vegetables are listed in alphabetical order.

Sample:

    beets: Paul, Yolanda, Zainab
    broccoli: Zainab
    Brussels sprouts: Zainab
    onions: Paul
    peas: Yolanda
    rutabagas: Paul
    squash: Yolanda

=cut

use strict;
use warnings;

# Get command-line arguments
# Usage:
#   perl who_likes.pl rutabagas input/vegetables.txt output/likes.txt
my ($vegetable, $input_file, $output_file) = @ARGV;

# Here's where we'll keep the information on who likes what
my $what_they_like;

my ($input_handle, $output_handle);

# Open the input and output files
open $input_handle, '<', $input_file
    or die "Can't open input file '$input_file': $!";

# Ask everyone what they like
$what_they_like = collect_information($input_handle);

# Answer questions about who likes what
report_information(%$what_they_like);

# Answer questions about who likes what
answer_questions($what_they_like);

sub collect_information {
    print STDERR "Collecting information...\n";
    my %who_likes_what;
    while (defined(my $line = <$input_handle>)) {
        # For each line in the input file...
        
        # *** FILL THIS IN ***
        
        # Remember the information
        $who_likes_what{$name} = $vegetables;
    }
    return \%who_likes_what;
}

sub report_information {
    my (%name2veggies) = @_;
    my %veggie2names;
    my @names = keys %name2veggies;
    foreach my $name (@names) {
        
        # *** FILL THIS IN ***
        
    }
    my @veggies = keys %veggie2names;
    foreach my $veggie (@veggies) {
        
        # *** FILL THIS IN ***
        
    }
}

sub answer_questions {
    my ($likes) = @_;
    print "Answering questions...\n";
    while (1) {
        print "Name? ";
        my $name = <STDIN>;
        last unless defined $name;
        chomp $name;
        if (exists ) {
            my $vegetables = $likes->{$name};
            if ($vegetables eq '') {
                print "$name doesn't like any vegetables!\n";
            }
            else {
                print "$name likes $vegetables.\n";
            }
        }
        else {
            print "Sorry, I don't what $name likes.\n";
        }
    }
}