bank_holiday.rb

require 'rubygems'
require 'chronic'
require 'activesupport'

class BankHoliday
  def self.include?(date)
    @@holidays.include?(date.utc.beginning_of_day)
  end
  
  def self.next_from(date)
    date = date.utc.beginning_of_day
    @@holidays.each do |day|
      return day if day >= date
    end
  end
  
  def self.next_workday_from(date)
    return date.utc unless include?(date)
    next_workday_from(date.tomorrow)
  end
  
  private
    def self.load_dates!
      @@holidays = [
        Chronic.parse('1st day in January'),                # New Years Day       (1st of January)
        easter - 2.days,                                    # Good Friday         (Easter Sunday - 2)
        easter + 1.days,                                    # Easter Monday       (Easter Sunday + 1)
        Chronic.parse('1st Monday in May'),                 # Easter Bank Holiday (First Monday in May)
        Chronic.parse('1st Monday in June') - 7.days,       # Spring Bank Holiday (Last Monday in May)
        Chronic.parse('1st Monday in September') - 7.days,  # Summer Bank Holiday (Last Monday in August)
        Chronic.parse('25th day in December'),              # Christmas Day       (25th of December)
        Chronic.parse('26th day in December')               # Boxing Day          (26th of December)
      ].map { |day| day.utc.beginning_of_day }.sort
    end
    
    def self.easter(y = Time.now.year)
      c = y / 100
      n = y - 19 * ( y / 19 )
      k = ( c - 17 ) / 25
      i = c - c / 4 - ( c - k ) / 3 + 19 * n + 15
      i = i - 30 * ( i / 30 )
      i = i - ( i / 28 ) * ( 1 - ( i / 28 ) * ( 29 / ( i + 1 ) ) * ( ( 21 - n ) / 11 ) )
      j = y + y / 4 + i + 2 - c + c / 4
      j = j - 7 * ( j / 7 )
      l = i - j
      m = 3 + ( l + 40 ) / 44
      d = l + 28 - 31 * ( m / 4 )
      easter_sunday = Time.gm(y, m, d)
      
      return easter_sunday < Time.now.utc ? easter(y + 1) : easter_sunday
    end
  
  # Here we load up the holiday dates
  load_dates!
end

bank_holiday_test.rb

require 'test/unit'
require 'bank_holiday'

class BankHolidayTests < Test::Unit::TestCase
  def setup
    BankHoliday.cattr_reader(:holidays)
  end
  def test_includes_bank_holidays
    BankHoliday.holidays.each do |holiday|
      assert BankHoliday.include?(holiday)
    end
  end
  def test_next_from_with_holiday_dates
    BankHoliday.holidays.each do |holiday|
      assert_equal BankHoliday.next_from(holiday), holiday
    end
  end
  # Here we test all but the last one, the last one will technically
  # generate a failure as only one years worth (from Time.now) of
  # bank holidays are generated.
  def test_next_from_with_holiday_dates_plus_one_day
    BankHoliday.holidays[0...-1].each_with_index do |holiday, index|
      assert_equal BankHoliday.next_from(holiday + 1.day), BankHoliday.holidays[index + 1]
    end
  end
  def test_next_workday_from_with_holiday_dates
    BankHoliday.holidays.each do |holiday|
      assert BankHoliday.next_workday_from(holiday) > holiday
      assert ! BankHoliday.include?(BankHoliday.next_workday_from(holiday))
    end
  end
end