2014 twenty-four merry days of Perl Feed

Christmas Timekeeping

Data::ICal::DateTime - 2014-12-18

The key to doing Christmas right is proper planning of the day. None of this wishy washy behavior that ends up with your pregnant wife giving birth in a manger. No, no, we need organization! We need a schedule! We need a calendar!

In my normal working day I use a Perl script to create events on my calendar from templates, calculating backwards with DateTime from when known point where operations need to end to work out when the things need to happen. I juggle time zones. I have recurrences of the same event over and over.

It's just these technical skills I need to apply to my Christmas Day calendar if I'm going to make it through in one piece.

The iCal file

The simplest way to put something into my calendar is to use Perl to create a ICal calendar file first, then open it in my calendar application. Luckily there's a Perl module for that.


use strict;
use warnings;
use autodie;

use File::Temp qw(tempfile);
use Data::ICal::DateTime;
use Data::ICal::Entry::Event;

my $cal = Data::ICal->new();


my ($fh, $filename) = tempfile(undef, SUFFIX => ".ics");
print $fh $cal->as_string;
close $fh;

# since my computer is a Mac I can open the calendar file
# in Calendar.app by just using the "open" command on it
system("open", $filename);

Now all we need do is replace the ... with some actual code to add some events to our calendar. We've loaded Data::ICal::DateTime which allows us to use the all powerful DateTime module to construct DateTime object from which we can create events.

Turkey Dinner

Even thought I now live in New York, since I was raised in England each year it's tradition to make sure that we cook a turkey dinner. Let's add a entry for eating that to our calendar straight away:

# Let's eat at 3PM
my $dinnertime = DateTime->new(
   year => 2014,
   month => 12,
   day => 25,
   hour => 15,
   minute => 00,
   second => 00,
   time_zone => 'America/New_York',

# And let's take two hours to eat
my $dinner_duration = DateTime::Duration->new( hours => 2 );

# create the event
my $dinner = Data::ICal::Entry::Event->new();
$dinner->summary("Christmas Dinner");
$dinner->description("Turkey with all the trimmings");
$dinner->start( $dinnertime );
$dinner->duration( $dinner_duration );
$cal->add_entry( $dinner );

Of course, we'll need to cook the Turkey. Let's work out when this should go in by working backwards from the time the dinner was meant to start. Note how the overloaded operators for DateTime and DateTime::Duration allow us to simply use subtraction to create a new DateTime.

# butterball says it'll take 4h for a 20lb Turkey
my $cooking_time = DateTime::Duration->new( hours => 4 );
my $in_the_oven = $dinnertime - $cooking_time;

# and it'll probably take me 45 minutes to prep the turkey
my $prep_time = DateTime::Duration->new( minutes => 45 );
my $prep_start = $in_the_oven - $prep_time;

# create the events
my $cooking = Data::ICal::Entry::Event->new();
$cooking->summary("Cooking Turkey");
$cooking->description("Cook at 325F using open pan method");
$cooking->start( $in_the_oven );
$cooking->end( $dinnertime );
$cal->add_entry( $cooking );

my $prep = Data::ICal::Entry::Event->new();
$prep->summary("Prep Turkey");
$prep->description("Wash, apply rub, stuff turkey, place in pan");
$prep->start( $prep_start );
$prep->end( $in_the_oven );
$cal->add_entry( $prep );

We also need to put in the roast veg. We can use multiplication to work out how long the prep time will be.

my $people = 10;
my $time_per_person = DateTime::Duration->new( minutes => 5 );
my $veg_prep_time = $people * $time_per_person;

my $veg_cook_time = DateTime::Duration->new( minutes => 45 );

my $veg_prep = Data::ICal::Entry::Event->new();
$veg_prep->summary("Prep veg");
$veg_prep->description("Prep veg and then stick in oven");
$veg_prep->start( $dinnertime - ( $veg_cook_time + $veg_prep_time ) );
$veg_prep->duration( $veg_prep_time );
$cal->add_entry( $veg_prep );

Fun with Time Zones

Like any loyal British Citizen I have to watch the Queen's speech (which these days can be found on YouTube for expats like myself.)

There's nothing stopping us adding an event to our calendar that's in another time zone:

# The Queen's speech is broadcast at 3PM in the UK.  When I add
# this to my EST calendar, it shows up as happening at 10am.
my $speech_time = DateTime->new(
   year => 2014,
   month => 12,
   day => 25,
   hour => 15,
   minute => 00,
   second => 00,
   time_zone => 'Europe/London', # note, different to where I live!
my $speech_duration = DateTime::Duration->new( minutes => 15 );

# create the event
my $speech = Data::ICal::Entry::Event->new();
$speech->summary("The Queen's Speech");
$speech->start( $speech_time );
$speech->duration( $speech_duration );
$cal->add_entry( $speech );

Repeating Events

At the end of a long day of celebrating we need each night to remember to turn off the Christmas lights before we go to bed. We'll need to do this each night until twelfth night.

my $ninepm = DateTime->new(
  year => 2014,
  month => 12,
  day => 25,
  hour => 21,
  minute => 00,
  second => 00,
  time_zone => 'America/New_York',

my $turn_off_lights = Data::ICal::Entry::Event->new();
$turn_off_lights->summary("Turn off lights");
$turn_off_lights->duration( DateTime::Duration->new( minutes => 15 ) );
$turn_off_lights->start( $ninepm );
    rrule => "FREQ=DAILY;COUNT=12" # every day for 12 days
$cal->add_entry( $turn_off_lights );

Ready to Go

The final result looks awesome:

Now I'm organized. If only I'd had time with all this preparation to go out and buy presents...

See Also

Gravatar Image This article contributed by: Mark Fowler <mark@twoshortplanks.com>