#!/usr/bin/perl -w

use strict;
use LWP::Simple;

# file to store the update time 
my $speaker_prev_mod_time = '/home/qiang/bin/speaker_prev_mod';
# webpage to watch
my $speaker_url = 'http://cs.senecac.on.ca/speakers/speakersFlash.html
+';

# file to store the update time 
my $cherry_prev_mod_time = '/home/qiang/bin/cherrypick_prev_mod';
# another webpage to watch
my $cherry_url = 'http://cherryavenuefarms.org/';

# update is sent to this email box.
my $email = 'your@email.com';

# build the webpage hash
my %checks = ( 'seneca speaker series' => 
                { 'time_stamp' =>   $speaker_prev_mod_time,
                  'url_to_check' => $speaker_url 
                },
               'cherry picking opening' =>
                { 'time_stamp' =>   $cherry_prev_mod_time,
                  'url_to_check' => $cherry_url }
             );

foreach (my ($k,$v)=each %checks) {
    my $prev_mod_time = &get_prev($v->{time_stamp});
    my $cur_mod_time  = &get_current($v->{url_to_check});

    if ($cur_mod_time ne $prev_mod_time) {
       &update_mod_time($cur_mod_time, $v->{time_stamp});
       my $t = 
`/bin/echo "$v->{url_to_check} modified on $cur_mod_time\n" |
            /bin/mail -s "$k page just updated" $email`;
    }
}

# get current update time for the page
sub get_current {
    my $url = shift;
    my @headers = head($url);
    scalar localtime($headers[2]);
}

# get prev update time for the page
sub get_prev {
    my $file_timestamp = shift;
    unless (-e $file_timestamp) {
        open F,">$file_timestamp" or die $!;
        close F;
        return "bla bla";
    }
    open F,$file_timestamp or die $!;
    my $mod_time = <F>;
    close F;
    return $mod_time;
}

# record the update time for the page
sub update_mod_time {
    my ($mod_time,$file_timestamp) = @_;
    open F,">$file_timestamp" or die $!;
    print F $mod_time;
    close F;
}