The Plan for the February Meeting
James Gray
for us at the February meeting. This is for the fun and education of
us all. Thanks guys!
Below are the details of their challenge for them to see and for those
of us who wish to follow along.
Tim is going to give a talk for the other half of the meeting, showing
off a few of his favorite libraries.
As you can see, it's shaping up to be a great meeting!
James Edward Gray II
Calendar Code Challenge
=======================
The contestants will complete a simple calendar application with just
two abilities: users should be able to enter events and see what
events will occur on a given day. The primary challenge comes from
the fact that the code is expected to handle multiple types of events.
Your Code
---------
The code you provide really only has to do two things: accept new
event entries and provide a way to list all events occurring on a
given day. No judging will be done on the interface, so you are free
to provide a nice interface for these two action or just build methods
to call in IRb or a testing environment. Whatever is easiest for you
is fine.
No judging will be done on tests, documentation, or any other
ancillary assets to the code itself. However, you will be judged on
how easy it is for others to understand your code as outlined below
and these items may help with that.
You also do not need to worry about the data stressing your code.
You're program doesn't need to handle so much data that it can't all
be stored in memory and event fields will be consistently sane. No
dates will be used that are outside a two year range centered on
today, so you needn't worry about calendar changes or the resolution
of Ruby's built in Time class. You just need to build the core
functionality of the problem.
Event Types
-----------
The main challenge is that your calendar is expected to support
multiple types of events. Users need to be able to create any or all
of the types listed below and searches must check all known events
returning all events that will fall on a given day, regardless of type.
Each event type can have different fields and the types share some
fields. Some fields are optional and some have defaults you need to
account for.
All events have a unique name (a String) and a start date and time (a
Time) that are always provided. All events can also have an end date
and time (also a Time), but this field can also be left nil to
indicate that an event is ongoing and does not end.
You can mostly ignore the time portion of all dates and times for the
purposes of this exercise. We're only interested in which events
appear on a given day and the times don't play into that.
Beyond that, the event types differ as follows:
* Daily events also have no additional fields. They recur each day
between their start date and end date.
* Weekly events have a frequency field (an Integer) that defaults to
one and a list of days (an Array containing one or more Strings from
the set: "Sunday", "Monday", "Tuesday", "Wednesday", "Thursday",
"Friday", and "Saturday"). These events recur each week between their
start date and end date on the days indicated. If frequency is
anything but one, they only appear if the week in question is
divisible by the frequency when counted as an offset from the start
date. For example, a frequency of two means an event occurs every
other week and thus would appear within the first seven days of the
start date, skip the next seven, appear in the next seven, etc.
* Monthly events can be set two ways. The first type of monthly event
has a frequency field (same as the weekly version, but in the scope of
months), an "on the" field (a String from the set: "first", "second",
"third", and "last"), and a day field (a String from the same set
mentioned in the weekly events days field). Again, this date recurs
monthly bounded by the start and end date and as dictated by the
frequency. The difference here is that the "on the" and day fields
indicate which day of the month the event happens on.
* If the "on the" and day fields are omitted, you have the second type
of monthly event. This event just repeats on the same day of the
month as the start date (if present in the current month). These too
can have a frequency to skip months.
* Finally, there are yearly events that just recur on the same day of
the year as their start date. These events have no additional fields.
The Judging
-----------
The spirit of this contest is totally for fun and there will be no
official winner or loser. However, we do have some criteria upon
which entries will be considered, just for friendly bragging rights!
The contestants are expected to make their solutions publicly
available by posting them to the mailing list two days before the
February meeting. That means solutions should be posted on February
10th by 6:30 PM.
At the meeting, each of you will explain the other contestant's
code. You are expected to highlight how it works and point out
things you like about the solution. You will be judged on how well
you understand the code you are showing and on how easy your code was
to understand.
If you notice any problems with the code, like edge case searches it
wouldn't get right, feel free to point those out as well. This shows
an even greater understanding of the code on your part.
John Hornbeck
John Hornbeck
Support Manager
Engine Yard
http://engineyard.com
"Work hard to find something that fascinates you." - Richard Feynman
Grant Schofield
Code is here:
http://github.com/schofield/okcal/tree/master
Grant
Brian Clubb
helping Barack with the economy. In my time away from that I've been
solving this problem here http://github.com/bclubb/calendar/tree/master#.
Brian
James Gray
> Sorry for the delay. Didn't have power till just a little bit ago.
>
> Code is here:
> http://github.com/schofield/okcal/tree/master
Some people wanted to see my solution to the code challenge.
Here's the original MySQL solution:
if not params[:date].blank?
condition[<<-END_DATE_SQL, *([params[:date]] * 14)]
start_date <= ? AND (end_date IS NULL OR ? <= end_date) AND
IF(repeats IS NULL OR TRIM(repeats) = '' OR repeats = 'Daily', 1,
IF(repeats = 'Weekly' AND
#{params[:date].strftime("%A").downcase} = 1 AND FLOOR(DATEDIFF(?,
start_date) / 7) % frequency = 0, 1,
IF(repeats = 'Monthly' AND (((on_the IS NULL AND
DAYOFMONTH(start_date) = DAYOFMONTH(?)) OR
(#{params[:date].strftime("%A").downcase} = 1 AND IF(on_the = 'first'
AND DAYOFMONTH(?) <= 7, 1, IF(on_the = 'second' AND DAYOFMONTH(?) > 7
AND DAYOFMONTH(?) <= 14, 1, IF(on_the = 'third' AND DAYOFMONTH(?) > 14
AND DAYOFMONTH(?) <= 21, 1, IF(on_the = 'last' AND MONTH(?) !=
MONTH(DATE_ADD(?, INTERVAL 8 DAY)), 1, 0)))))) AND PERIOD_DIFF(YEAR(?)
* 100 + MONTH(?), YEAR(start_date) * 100 + MONTH(start_date)) %
frequency = 0), 1,
IF(repeats = 'Yearly' AND DAYOFYEAR(start_date) = DAYOFYEAR(?),
1, 0))))
END_DATE_SQL
if params[:date] == Date.today
condition["start_time IS NULL OR start_time >= TIME(?)",
Time.now]
end
end
I'm pretty sure that one works right.
Here's another on in Ruby that may work, but I admit that I've only
tested it a tiny bit. It likely still has bugs:
#!/usr/bin/env ruby -wKU
class Event
DAY_IN_SECONDS = 24 * 60 * 60
def initialize(name, details)
@name = name
@start_date = details[:start_date]
@end_date = details[:end_date]
end
attr_reader :name, :start_date, :end_date
def on?(on)
start_date <= on and (end_date.nil? or on <= end_date)
end
end
class DailyEvent < Event
end
class WeeklyEvent < Event
def initialize(*args)
super
@days = args.last[:days]
@frequency = args.last[:frequency] || 1
end
attr_reader :days, :frequency
def on?(on)
super and
days.include?(on.strftime("%A")) and
((on - start_date).abs.to_i / (7 * DAY_IN_SECONDS) %
frequency).zero?
end
end
class MonthlyEvent < Event
def initialize(*args)
super
@frequency = args.last[:frequency] || 1
@on_the = args.last[:on_the]
@day = args.last[:day]
end
attr_reader :on_the, :day
def on?(on)
super and
( (on_the.nil? and start_date.mday == on.mday) or
(day == on.strftime("%A") and is_on?(on)) ) and
(month_diff(on) % frequency).zero?
end
private
def is_on?(on)
case on_the.to_sym
when :first
on.mday <= 7
when :second
on.mday.between? 8, 14
when :third
on.mday.between? 15, 21
when :last
on.mon != (on + 8 * DAY_IN_SECONDS).mon
end
end
def month_diff(on)
early, late = [start_date, on].sort
year_diff = (late.year - early.year).abs
if year_diff.nonzero? and late.mon < early.mon
(year_diff - 1) * 12 + (start_date.mon - on.mon).abs
else
year_diff * 12 + (start_date.mon - on.mon).abs
end
end
end
class YearlyEvent < Event
def on?(on)
super and @start_date.yday == on.yday
end
end
class EventList
def initialize
@events = [ ]
end
def all_on(on)
@events.select { |event| event.on? on }
end
def method_missing(meth, *args, &blk)
if meth.to_s =~ /\Aadd_(daily|weekly|monthly|yearly)_event\z/
@events << Object.const_get("#{$1.capitalize}Event").new(*args)
else
super
end
end
end
__END__
Great work guys. I think it was a good learning experience for all!
James Edward Gray II