=begin
  Copyright (C) 2008 Sean Dague

  This library is free software; you can redistribute it and/or modify it
  under the same terms as the ruby language itself, see the file COPYING for
  details.
=end

# The following adds a bunch of mixins to the tzinfo class, with the
# intent on making it very easy to load in tzinfo data for generating
# ical events.  With this you can do the following:
#
#   require "icalendar/tzinfo"
#
#   estart = DateTime.new(2008, 12, 29, 8, 0, 0)
#   eend = DateTime.new(2008, 12, 29, 11, 0, 0)
#   tstring = "America/Chicago"
#
#   tz = TZInfo::Timezone.get(tstring)
#   cal = Calendar.new
#   # the mixins now generate all the timezone info for the date in question
#   timezone = tz.ical_timezone(estart)
#   cal.add(timezone)
#  
#   cal.event do
#       dtstart       estart
#       dtend        eend
#       summary     "Meeting with the man."
#       description "Have a long lunch meeting and decide nothing..."
#       klass       "PRIVATE"
#   end
#
#   puts cal.to_ical
#
# The recurance rule calculations are hacky, and only start at the
# beginning of the current dst transition.  I doubt this works for non
# dst areas yet.  However, for a standard dst flipping zone, this
# seems to work fine (tested in Mozilla Thunderbird + Lightning).
# Future goal would be making this better.

# require "rubygems"
# require "tzinfo"

module TZInfo
    class Timezone
        def ical_timezone(date)
            period = period_for_local(date)
            timezone = Icalendar::Timezone.new
            timezone.timezone_id = identifier
            timezone.add(period.daylight)
            timezone.add(period.standard)
            return timezone
        end
    end
    
    class TimezoneTransitionInfo
        def offset_from
            a = previous_offset.utc_total_offset
            sprintf("%2.2d%2.2d", (a / 3600).to_i, ((a / 60) % 60).to_i)
        end
        
        def offset_to
            a = offset.utc_total_offset
            sprintf("%2.2d%2.2d", (a / 3600).to_i, ((a / 60) % 60).to_i)
        end
        
        def rrule 
            start = local_start.to_datetime
            # this is somewhat of a hack, but seems to work ok
            [sprintf(
                    "FREQ=YEARLY;BYMONTH=%d;BYDAY=%d%s",
                    start.month, 
                    ((start.day - 1)/ 7).to_i + 1,
                    start.strftime("%a").upcase[0,2]
                    )]
        end
        
        def dtstart
            local_start.to_datetime.strftime("%Y%m%dT%H%M%S")
        end

    end
    
    class TimezonePeriod
        def daylight
            day = Icalendar::Daylight.new
            if dst?
                day.timezone_name = abbreviation.to_s
                day.timezone_offset_from = start_transition.offset_from
                day.timezone_offset_to = start_transition.offset_to
                day.dtstart = start_transition.dtstart
                day.recurrence_rules = start_transition.rrule
            else
                day.timezone_name = abbreviation.to_s.sub("ST","DT")
                day.timezone_offset_from = end_transition.offset_from
                day.timezone_offset_to = end_transition.offset_to
                day.dtstart = end_transition.dtstart
                day.recurrence_rules = end_transition.rrule
            end
            return day
        end
        
        def standard
            std = Icalendar::Standard.new
            if dst?
                std.timezone_name = abbreviation.to_s.sub("DT","ST")
                std.timezone_offset_from = end_transition.offset_from
                std.timezone_offset_to = end_transition.offset_to
                std.dtstart = end_transition.dtstart
                std.recurrence_rules = end_transition.rrule
            else
                std.timezone_name = abbreviation.to_s
                std.timezone_offset_from = start_transition.offset_from
                std.timezone_offset_to = start_transition.offset_to
                std.dtstart = start_transition.dtstart
                std.recurrence_rules = start_transition.rrule
            end
            return std
        end
    end
end