module CalInvite::IcalTimezone

# File lib/cal_invite/ical_timezone.rb
102 def fixed_observance_lines(period)
103   [
104     "BEGIN:STANDARD",
105     "DTSTART:16010101T000000",
106     "TZOFFSETFROM:#{format_offset(period.offset.observed_utc_offset)}",
107     "TZOFFSETTO:#{format_offset(period.offset.observed_utc_offset)}",
108     "TZNAME:#{period.offset.abbreviation}",
109     "END:STANDARD"
110   ]
111 end

# File lib/cal_invite/ical_timezone.rb
126 def format_offset(seconds)
127   sign = seconds.negative? ? '-' : '+'
128   abs = seconds.abs
129   format('%<sign>s%<hours>02d%<minutes>02d', sign: sign, hours: abs / 3600, minutes: (abs % 3600) / 60)
130 end

# File lib/cal_invite/ical_timezone.rb
25 def local_time(tzid, utc_time)
26   return nil if tzid.nil? || tzid.to_s.strip.empty? || tzid.to_s.upcase == 'UTC'
27 
28   TZInfo::Timezone.get(tzid.to_s).to_local(utc_time.utc)
29 rescue TZInfo::InvalidTimezoneIdentifier
30   nil
31 end

# File lib/cal_invite/ical_timezone.rb
87 def observance_lines(kind, from_period, to_period)
88   transition_time = from_period.local_ends_at.to_time
89 
90   [
91     "BEGIN:#{kind}",
92     "DTSTART:#{transition_time.strftime('%Y%m%dT%H%M%S')}",
93     "TZOFFSETFROM:#{format_offset(from_period.offset.observed_utc_offset)}",
94     "TZOFFSETTO:#{format_offset(to_period.offset.observed_utc_offset)}",
95     "TZNAME:#{to_period.offset.abbreviation}",
96     rrule_line(transition_time),
97     "END:#{kind}"
98   ]
99 end

# File lib/cal_invite/ical_timezone.rb
80 def period_after(tz, period)
81   return nil unless period&.ends_at
82 
83   tz.period_for(period.ends_at.to_time)
84 end

# File lib/cal_invite/ical_timezone.rb
73 def period_before(tz, period)
74   return nil unless period.starts_at
75 
76   tz.period_for(period.starts_at.to_time - 1)
77 end

# File lib/cal_invite/ical_timezone.rb
116 def rrule_line(time)
117   wday_names = %w[SU MO TU WE TH FR SA]
118   days_in_month = Date.new(time.year, time.month, -1).day
119   nth = (time.day - 1) / 7 + 1
120   nth = -1 if time.day + 7 > days_in_month
121 
122   "RRULE:FREQ=YEARLY;BYMONTH=#{time.month};BYDAY=#{nth}#{wday_names[time.wday]}"
123 end

# File lib/cal_invite/ical_timezone.rb
40 def vtimezone_lines(tzid)
41   return nil if tzid.nil? || tzid.to_s.strip.empty? || tzid.to_s.upcase == 'UTC'
42 
43   tz = TZInfo::Timezone.get(tzid.to_s)
44   current = tz.period_for(Time.now.utc)
45 
46   if current.dst?
47     dst_period = current
48     std_period = period_before(tz, dst_period)
49   else
50     std_period = current
51     dst_period = period_after(tz, std_period)
52     dst_period = nil unless dst_period&.dst?
53   end
54 
55   lines = ["BEGIN:VTIMEZONE", "TZID:#{tzid}"]
56 
57   if std_period && dst_period
58     lines.concat(observance_lines('STANDARD', dst_period, std_period))
59     lines.concat(observance_lines('DAYLIGHT', std_period, dst_period))
60   else
61     lines.concat(fixed_observance_lines(std_period || dst_period || current))
62   end
63 
64   lines << "END:VTIMEZONE"
65   lines
66 rescue StandardError
67   # Never let an exotic/edge-case timezone break calendar generation —
68   # worst case the VEVENT ends up without a VTIMEZONE definition.
69   nil
70 end