module DateExtensions
  def rest_of_days_in_week
    (0...(7 - wday)).map { |i| self + i }
  end
  
  def rest_of_days_in_month
    (0..(days_in_month - day)).map { |i| self + i }
  end
  
  def rest_of_days_in_year
    (0..((leap? ? 366 : 365) - yday)).map { |i| self + i }
  end
  
  def start_of_week
    self - wday
  end
  
  def start_of_next_week(interval = 1)
    self + (7 * interval) - wday
  end
  
  def start_of_month
    Date.new(year, month, 1)
  end
  
  def start_of_next_month(interval = 1)
    new_month, new_year = month + interval, year
    
    until new_month <= 12 do
      new_month -= 12
      new_year += 1
    end
    
    Date.new(new_year, new_month, 1)
  end
  
  def start_of_next_year(interval = 1)
    Date.new(year + interval, 1, 1)
  end
  
  def occurrence_in_month?(type)
    case type.to_s
      when 'first'
        (1..7).include?(day)
      when 'second'
        (8..14).include?(day)
      when 'third'
        (15..21).include?(day)
      when 'fourth'
        (22..28).include?(day)
      when 'last'
        day > days_in_month - 7
    end
  end
  
  def weekday?
    (1..5).include?(wday)
  end
  
  def days_in_month
    self.class.days_in_month(year, month)
  end
end

# Compatibility with Ruby < 1.8.6
unless Date.const_defined?(:Format)
  module Date::Format
    Date.constants.each do |constant|
      const_set(constant, Date.const_get(constant))
    end
  end
end

class Date
  NORMAL_MONTH_LENGTHS = {
    1 => 31, 2 => 28, 3 => 31, 4 => 30, 5 => 31, 6 => 30,
    7 => 31, 8 => 31, 9 => 30, 10 => 31, 11 => 30, 12 => 31
  } unless const_defined? :NORMAL_MONTH_LENGTHS
  
  def self.days_in_month(year, month)
    days = NORMAL_MONTH_LENGTHS[month]
    days += 1 if new(year, month, 1).leap? && month == 2
    days
  end
  
  include DateExtensions
end