finnish holiday calendar supporting local file cache

holiday_calendar.rb

require 'date'
require 'tmpdir'
require 'open-uri'
require 'digest'

require 'ri_cal'

class HolidayCalendar
  DEFAULT_CAL_URI = 'https://www.google.com/calendar/ical/fi.finnish%23holiday%40group.v.calendar.google.com/public/basic.ics'
  CACHE_MAX_DAYS = 360

  def initialize(opts={})
    @opts = {}
    @holidays = nil
    @cal_uri = opts[:cal_uri] || DEFAULT_CAL_URI

    @calendar_cache = opts[:cache_file] || cache_path
  end

  def cache_path
    File.join(Dir.tmpdir, cache_basename)
  end

  def parse
    if needs_cache_refresh?(@calendar_cache)
      write_cache(@calendar_cache, read_calendar(@cal_uri))
    end

    @holidays = build_hash RiCal.parse(open(@calendar_cache))
  end

  # read calendar from uri. Can be local file or remote path
  def read_calendar(uri)
    open(uri).read
  end

  def needs_cache_refresh?(fpath)
    !File.exist?(fpath) || cache_age_in_days(fpath) > CACHE_MAX_DAYS
  end

  def cache_age_in_days(fpath)
    (Time.now - File.mtime(fpath)) / 86400
  end

  # return hash keyed by holiday date object, with holiday name as value
  def holidays
    parse unless @holidays
    @holidays
  end

  def weekday?(date)
    !holiday?
  end

  def holiday?(date)
    weekend?(date) || holidays.has_key?(date)
  end

  def weekend?(date)
    [0, 6].include?(date.wday)
  end

  private

  def write_cache(fpath, content)
    STDERR.puts 'creating cache'
    File.open(fpath, 'w') do |f|
      f.write content
    end
  end

  def cache_basename
    [Digest::MD5.hexdigest(@cal_uri), 'calendar_cache.ics'].join('-')
  end

  def build_hash(cal)
    cal.each_with_object({}) do |occ, days|
      occ.events.each do |evt|
        day = evt.dtstart
        days[day] = evt.summary
      end
    end
  end
end

# example usage:
# c = HolidayCalendar.new
# c.holidays.sort.each do |d, v|
#  puts "%s: %s" % [d, v]
# end
# c.holiday?(Date.new(2013, 1, 1)) # => true