#!/usr/bin/perl -w
#
# Takes three arguments and automatically creates an RSS feed for you. It should be added
# to a cronjob, and run once daily (running multiple times a day will just give you the 
# same output, and burn extra cpu cycles.
#
# Arguments:
# First is the text of the RSS. The text can be plain, or contain html markup if you want.
# Each block of text should be followed by a single line containing <breakX>. 'X' is the 
# day of the year that the preceding text should appear on.
#
# The Second argument is the file containing the 'channel' information. It should be in
# proper RSS format, and need not contain the <doc>declaration, as the program will do
# that for you. 
#
# The third argument is the name of the file to output to, such as rss.xml
#
# All of these arguments are required, but this may change in the future to have decent
# defaults. Full pathnames should be given, unless running directly from the command line.
#
# One variable in this line should be changed: $rssurl

$rssurl = 'http://www.shanebishop.net/nau/rss.xml';
use DateTime;
# grab the current date and initialize lots of variables for display in various places
$date = DateTime->now;
# if you want to test particular dates, modify the following line appropriately
#$date = DateTime->new( year => 2008, month => 1, day => 5, hour => 2, minute => 12, second => 2);
$doy = $date->day_of_year;
$month_name = $date->month_name;
$mday = $date->mday;
$year = $date->year;
$short_month = $date->month_abbr;
$short_day = $date->day_abbr;
$pubtime = $date->hms;

# grab yesterdays date and initialize more variables prefixed with a 'y'
$ydate = $date->subtract( days => 1 );
$yesterday = $ydate->day_of_year;
$ymonth_name = $ydate->month_name;
$ymday = $ydate->mday;
$yyear = $ydate->year;
$yshort_month = $ydate->month_abbr;
$yshort_day = $ydate->day_abbr;

# open a file to store the day of the year substituted on leapday

# find out if it is a leap year, and if so, check to see if today is also leap day
$leap = $date->is_leap_year;
if ($leap and ($doy == 60)) {
   $doy = int(rand(364)) + 1;
   $leapday = 1;
   open LEAP, "> leap.day" or die $!;
   print LEAP $doy;
}

# if it is past leapday, we need to decrease the $doy and $yesterday values to keep on schedule
if ($leap and ($doy > 61) and not $leapday) {
   $doy--;
   $yesterday--;
} elsif ($leap and ($doy == 61) and not $leapday) {
   $doy--;
   open LEAP, "leap.day" or die $!;
   $yesterday = <LEAP>;
}

# if it is the first day of the year after a leap year, we need to make a special condition to decrease $yesterday
if (($ydate->is_leap_year) and ($doy == 1)) {
   $yesterday--;
}

open FEED, "> $ARGV[2]" or die $!;
open CHANNEL, $ARGV[1] or die $!;
open TEXT, $ARGV[0] or die $!;

print FEED '<?xml version="1.0" encoding="UTF-8"?>' . "\n" . 
'<rss version="2.0" xmlns:atom="http://www.w3.org/2005/Atom">' . "\n" . '<channel>' . "\n";
while (<CHANNEL>) {
   print FEED $_;
}

print FEED '<pubDate>' . "$short_day, $mday $short_month $year 00:00:01 GMT" . '</pubDate>' 
. "\n" . '<lastBuildDate>' . "$short_day, $mday $short_month $year $pubtime GMT" . 
'</lastBuildDate>'. "\n" . '<docs>http://blogs.law.harvard.edu/tech/rss</docs>' . "\n" . 
'<atom:link href="' . $rssurl . '" rel="self" type="application/rss+xml" />' . "\n" . 
'<item>' . "\n" . '<title>' . "$month_name $mday" . '</title>' . "\n" . '<pubDate>' . 
"$short_day, $mday $short_month $year $pubtime GMT" . '</pubDate>' . "\n" . 
'<guid isPermaLink="false">' . "$month_name $mday, $year" . '</guid>' . "\n" . 
'<description>' . "\n";

if ($leapday) {
   print FEED '&lt;p&gt;Today is leap day (February 29). To make my life easier, I have opted not to create a completely separate set of readings for leap years. As a result, you have been given a random reading from a different day of the year. The normal schedule will resume tomorrow.&lt;/p&gt;';
}

if ($doy == 1) {
   $spit = 1;
}
$prior = $doy - 1;

while (<TEXT>) {
   if ($_ =~ /<break$doy>/) {
      $spit = 0;
   }
   if ($spit) {
      print FEED $_;
   }
   if ($_ =~ /<break$prior>/) {
      $spit = 1;
   }
}
close TEXT;

open TEXT, $ARGV[0] or die $!;

print FEED '</description>' . "\n" . '</item>' . "\n" . '<item>' . "\n" . '<title>' . 
"$ymonth_name $ymday" . '</title>' . "\n" . '<pubDate>' . 
"$yshort_day, $ymday $yshort_month $yyear $pubtime GMT" . '</pubDate>' . "\n" . 
'<guid isPermaLink="false">' . "$ymonth_name $ymday, $yyear" . '</guid>' . "\n" . 
'<description>' . "\n";

if ($leap and ($doy == 60) and not $leapday) {
   print FEED '&lt;p&gt;Today is leap day (February 29). To make my life easier, I have opted not to create a completely separate set of readings for leap years. As a result, you have been given a random reading from a different day of the year. The normal schedule will resume tomorrow.&lt;/p&gt;';
}

if ($yesterday == 1) {
   $spit = 1;
}
$prior = $yesterday - 1;

while (<TEXT>) {
   if ($_ =~ /<break$yesterday>/) {
      $spit = 0;
   }
   if ($spit) {
      print FEED $_;
   }   
   if ($_ =~ /<break$prior>/) {
      $spit = 1;
   }
}

print FEED '</description>' . "\n" . '</item>' . "\n" . '</channel>' . "\n" . '</rss>';

close TEXT;