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Binding

In order to start using the "icalendar" binding, it must be installed. In my case that's a job for Ansible:

- name: Get list of available and installed extensions
  uri:
    url: "http://{{ ansible_host }}:8080/rest/extensions"
  register: oh2_extensions
  changed_when: false

- name: Install extensions
  uri:
    url: "http://{{ ansible_host }}:8080/rest/extensions/{{ item }}/install"
    method: POST
  when: "not (oh2_extensions.json|byattr('id', item))[0].installed"
  with_items:
    - binding-icalendar
  register: oh2_install_extensions

More about this is described here.

iCal Calendar

Next comes the calendar data. Go to your Google calendar, click on the three dots next to the calendar you want to use.

And then click on "Settings and sharing". In the next window, scroll down to "Integrate calendar" and copy the URL from the "Private address in iCal format" field. That is the URL which needs to be added to the openHAB configuration.

openHAB configuration

The configuration needs a "Thing" and "Items". Let's start with the "Thing", which in my case is placed in "calendar.things". Since I deploy everything with Ansible, the file is a template:

Thing icalendar:calendar:entries "Calendar" @ "openHAB" [ url="{{ lookup('file', playbook_dir + '/credentials/reminders-calendar-ical.txt') }}", refreshTime=15 ]

The file "credentials/reminders-calendar-ical.txt" holds the iCal URL which was copied from the calendar earlier. The result in "/etc/openhab2/things/calendar.things":

Thing icalendar:calendar:entries "Calendar" @ "openHAB" [ url="https://calendar.google.com/calendar/ical/...", refreshTime=15 ]

Once the "Thing" is loaded, "Items" can be deployed. No templating here, the file "/etc/openhab2/items/calendar.items" has only a couple lines:

Switch		Event_current_event_present	"current event present"					<calendar> { channel="icalendar:calendar:events:current_presence" }

String		Event_current_event_name	"current event [%s]"					<calendar> { channel="icalendar:calendar:events:current_title" }
DateTime	Event_current_event_start	"current event start [%1$tT, %1$tY-%1$tm-%1$td]"	<calendar> { channel="icalendar:calendar:events:current_start" }
DateTime	Event_current_event_until	"current event until [%1$tT, %1$tY-%1$tm-%1$td]"	<calendar> { channel="icalendar:calendar:events:current_end" }

String		Event_next_event_name		"next event [%s]"					<calendar> { channel="icalendar:calendar:events:next_title" }
DateTime	Event_next_event_start		"next event start [%1$tT, %1$tY-%1$tm-%1$td]"		<calendar> { channel="icalendar:calendar:events:next_start" }
DateTime	Event_next_event_until		"next event until [%1$tT, %1$tY-%1$tm-%1$td]"		<calendar> { channel="icalendar:calendar:events:next_end" }

This defines a Presence switch, which indicates if one event is currently going on. And then the title, start time and end time of the current and next upcoming event. In my case I'm only interested in the presence switch, but I defined the other items anyway.