Implement ruby holiday api instead of iCalender feed

With the help of ChatGPT I found a solution for using the Ruby holidays library as a kind of web service that gives back a ICS feed.

First, I login on my Zammad Debian VM as root.

Install some libraries:

sudo apt install rubygems
gem install sinatra holidays icalendar rackup

Check, if you’re in the folder /root with pwd.

nano holiday.rb

Paste the following code:

# Little webservice based on Webframework Sinatra
# Call webservice with some paramters and get an iCal-File back

# Description:

# Germany 2025-2026:
# http://localhost:4567/holidays.ics?region=de&from=2025&to=2026

# Germany, Bavaria, catholic communites, current year with informal holidays (e.g. New Year's Eve and Christmas Eve):
# http://localhost:4567/holidays.ics?region=de_by_cath&from=current_year&to=current_year&type=informal

# Germany, Bavaria, City of Augsburg, previous year to following year:
# http://localhost:4567/holidays.ics?region=de_by_augsburg&from=last_year&to=next_year

# Hamburg plus company-specific holidays. To do this, save a company.yaml file in /root. Enter the company abbreviation under [regions] and pass it as a parameter
# http://localhost:4567/holidays.ics?region=de_hh+company&from=last_year&to=next_year&custom=company.yaml

# Holidays for a Bodensee based company regions Baden-Württemberg, Austria and Kanton Thurgau
# http://localhost:4567/holidays.ics?region=at+ch_tg+de_bw&from=last_year&to=next_year



require 'sinatra'
require 'holidays'
require 'icalendar'

# Method to generate iCal file from holiday data
def generate_ics(holidays)
  cal = Icalendar::Calendar.new

  holidays.each do |holiday|
    event = Icalendar::Event.new
    event.dtstart = holiday[:date]
    event.summary = holiday[:name]
    cal.add_event(event)
	puts "#{holiday[:date]}: #{holiday[:name]}"
  end

  cal.to_ical
end

# Method for determining the current year
def current_year
  Date.today.year
end

# Method for determining next year
def next_year
  Date.today.year + 1
end

# Method for determining last year
def last_year
  Date.today.year - 1
end

# Method to check and convert the year variable
def parse_year(year)
  case year.upcase
  when 'CURRENT_YEAR'
    current_year
  when 'NEXT_YEAR'
    next_year
  when 'LAST_YEAR'
    last_year
  else
    if year.match?(/\A\d{4}\z/)
      year.to_i
    else
      puts "Unrecognized year variable, defaulting to current year: #{year}"
      current_year
    end
  end
end

get '/holidays.ics' do
  content_type 'text/calendar'

  from = Date.new(parse_year(params['from'] || 'CURRENT_YEAR'), 1, 1)
  to = Date.new(parse_year(params['to'] || 'NEXT_YEAR'), 12, 31)

  options = {}
  options[:informal] = true if params['type'] == 'informal'
  custom_file = params['custom']

  if custom_file
    custom_path = File.join(settings.root, custom_file)
    Holidays.load_custom(custom_path)
  end

  # Split region and save in array
  regions = params['region'].split(' ')

  # Convert regions to symbols and save in array parameters
  parameters = regions.map(&:to_sym)

  # Add :informal to parameters if type is informal
  parameters << :informal if params['type'] == 'informal'

  puts "parameters: #{parameters}"

  holidays = Holidays.between(from, to, *parameters)

  ics = generate_ics(holidays)

  ics
end

Now add a service (Debian, you may need to adjust the paths):

nano /etc/systemd/system/holiday.service

And paste the following:

[Unit]
Description=Holiday Web Server
After=network.target

[Service]
Type=simple
WorkingDirectory=/root
ExecStart=/usr/bin/ruby /root/holiday.rb
Restart=always

[Install]
WantedBy=multi-user.target

Save this file with Ctrl+X

sudo systemctl daemon-reload
sudo systemctl status holiday
sudo systemctl enable holiday

Now create a new calendar in Zammad and try some of the examples provided at the top of the programm code.

Here are the region codes for the DACH countries. A complete list you can get by Ruby Holidays.available_regions or at Github Holidays:

at
ch
ch_ag
ch_ai
ch_ar
ch_be
ch_bl
ch_bs
ch_fr
ch_ge
ch_gl
ch_gr
ch_ju
ch_lu
ch_ne
ch_nw
ch_ow
ch_sg
ch_sh
ch_so
ch_sz
ch_tg
ch_ti
ch_ur
ch_vd
ch_vs
ch_zg
ch_zh
de
de_bb
de_be
de_bw
de_by
de_by_augsburg
de_by_cath
de_hb
de_he
de_hh
de_mv
de_ni
de_nw
de_rp
de_sh
de_sl
de_sn
de_sn_sorbian
de_st
de_th
de_th_cath