== Holiday Gem Definition Syntax

All holidays are defined in YAML files in the <tt>data/</tt> directory.  These  definition files have three main parts: *months*, *methods* and *tests*. Before you start, you may want to look some of the existing files at http://code.dunae.ca/svn/holidays/trunk/data.

=== Months

Holidays are grouped by month from 1 through 12.  Each entry within a month can have several fields.

[<tt>name</tt>]     The name of the holiday.
[<tt>regions</tt>]  One or more region codes.

===== Dates defined by a fixed date (e.g. January 1st) 

[<tt>wday</tt>]  Integer representing day of the month (1 through 31).

For example, the following holiday is on the first of January and available in the <tt>ca</tt>, <tt>us</tt> and <tt>au</tt> regions.

    1:
    - name: New Year's Day
      regions: [ca, us, au]
      mday: 1

===== Dates defined by a week number (e.g. first Monday of a month)

[<tt>wday</tt>]  Integer representing day of the week (0 = Sunday through 6 = Saturday).
[<tt>week</tt>]  Integer representing week number (1 = first week, 3 = third week, -1 = last week),


For example, the following holiday is on the first Monday of September and available in the <tt>ca</tt> region.

    9:
    - name: Labour Day
      regions: [ca]
      week: 1
      wday: 1

=== Calculating dates with methods

In addition to defining holidays by day or week, you can create custom methods to calculate a date.

For example, Canada celebrates Victoria Day, which falls on the Monday on or before May 24.  So, under the <tt>methods</tt> section we could create a custom method that returns a Date object.

  methods:
    ca_victoria_day: |
      def self.ca_victoria_day(year)
        date = Date.civil(year,5,24)
        if date.wday > 1
          date -= (date.wday - 1)
        elsif date.wday == 0
          date -= 6
        end
        date
      end

This would be represented in the <tt>months</tt> section as:

    5:
    - name: Victoria Day
      regions: [ca]
      function: ca_victoria_day(year)

If a holiday can occur in different months (e.g. Easter) it can go in the '0' month.

    0:
    - name: Easter Monday
      regions: [ca]
      function: easter(year)+1

Calculated-date functions take the year (integer) as a parameter and must return either a Date object or an integer representing the day of the month.


=== Calculating observed dates

Several built-in methods are available for holidays that are observed on varying dates.  For example, for a holiday that is observed on Monday if it falls on a weekend you could write:

    7:
    - name: Canada Day
      regions: [ca]
      mday: 1
      observed: to_monday_if_weekend(date)

Methods included in the Holidays module are:

* Holidays#to_monday_if_sunday
* Holidays#to_monday_if_weekend
* Holidays#to_weekday_if_boxing_weekend
* Holidays#to_weekday_if_weekend

Observed-date functions take a Date object as a parameter and must return either a Date object or an integer representing the day of the month.



=== Tests

All definition files should have tests included.  In the YAML file, tests are just a block of Ruby code.

  tests: |
    {Date.civil(2008,1,1) => 'New Year\'s Day', 
     Date.civil(2008,3,21) => 'Good Friday', 
     Date.civil(2008,3,24) => 'Easter Monday',
     Date.civil(2008,9,1) => 'Labour Day',
     Date.civil(2008,12,25) => 'Christmas Day',
     Date.civil(2008,12,26) => 'Boxing Day'}.each do |date, name|
      assert_equal name, Holidays.on(date, :ca, :informal)[0][:name]
    end

    # Victoria Day
    [Date.civil(2004,5,24), Date.civil(2005,5,23), Date.civil(2006,5,22),
     Date.civil(2007,5,21), Date.civil(2008,5,19)].each do |date|
      assert_equal 'Victoria Day', Holidays.on(date, :ca)[0][:name]
    end