agenda-libre-ruby/app/views/events/show.ics.haml

:ruby
  require 'icalendar/tzinfo'

  # Create a calendar with an event (standard method)
  cal = Icalendar::Calendar.new
  tzid = @event.region.tzid
  use_timezone = true
  if cal.timezones.none? { |t| tzid == t.tzid }
    # Only add this zone once
    begin
      tz = TZInfo::Timezone.get tzid
      timezone = tz.ical_timezone @event.start_time
      cal.add_timezone timezone
    rescue TZInfo::InvalidTimezoneIdentifier
      # No need to add this tz
      use_timezone = false
    end
  end

  cal.event do |e|
    e.uid         = "#{@event.id}@#{request.domain}"
    if use_timezone
      e.dtstamp   = Icalendar::Values::DateTime.new @event.decision_time, tzid: tzid
      e.dtstart   = Icalendar::Values::DateTime.new @event.start_time, tzid: tzid
      e.dtend     = Icalendar::Values::DateTime.new @event.end_time, tzid: tzid
    else
      e.dtstamp   = Icalendar::Values::DateTime.new @event.decision_time.localtime
      e.dtstart   = Icalendar::Values::DateTime.new @event.start_time.localtime
      e.dtend     = Icalendar::Values::DateTime.new @event.end_time.localtime
    end
    e.summary     = @event.title
    e.description = to_markdown @event.description.tr '\'', '’'
    e.location    = @event.full_address
    e.organizer   = "mailto:#{@event.contact}"
    e.x_alt_desc  = Icalendar::Values::Text.new @event.description, FMTTYPE: 'text/html'
  end

  cal.publish

= cal.to_ical