clarion/app/views/api/events/index.ics.erb

<%
cal = Icalendar::Calendar.new
cal.add_timezone(Time.zone.tzinfo.ical_timezone(Time.now))

@events.each do |event|
    next unless event&.slot&.starts_at

    cal.event do |ical_event|
        ical_event.dtstart       = Icalendar::Values::DateTime.new(event.slot.starts_at, 'tzid' => event.slot.starts_at.time_zone.tzinfo.identifier)
        ical_event.dtend         = Icalendar::Values::DateTime.new(event.slot.ends_at, 'tzid' => event.slot.ends_at.time_zone.tzinfo.identifier)
        ical_event.summary       = event.title
        ical_event.description   = event.description
        ical_event.created       = Icalendar::Values::DateTime.new(event.created_at, 'tzid' => event.created_at.time_zone.tzinfo.identifier)
        ical_event.last_modified = Icalendar::Values::DateTime.new(event.updated_at, 'tzid' => event.updated_at.time_zone.tzinfo.identifier)
        ical_event.location      = event.slot.hall.name
        ical_event.url           = "https://www.openfest.org/2019/bg/full-schedule-bg/#lecture-#{event.id}"
        ical_event.alarm do |alarm|
            alarm.summary = event.title
            alarm.trigger = "-PT15M"
        end
    end
end
cal.publish
-%>
<%= raw cal.to_ical %>