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

:ruby
  require 'icalendar/tzinfo'

  # Create a calendar with an event (standard method)
  cal = Icalendar::Calendar.new
  @events.each do |event|
    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|
      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.uid         = "#{event.id}@#{request.domain}"
      e.summary     = event.title
      e.description = to_markdown event.description.tr '\'', '’'
      e.location    = event.full_address.tr '\'', '’'
      e.organizer   = "mailto:#{event.contact}"
      e.x_alt_desc  = Icalendar::Values::Text.new event.description, FMTTYPE: 'text/html'
    end
  end

  cal.publish

= cal.to_ical