implemented ical exports

Signed-off-by: Stephan Richter <s.richter@srsoftware.de>

de.srsoftware.cal.api/src/main/java/de/srsoftware/cal/api/Appointment.java

@@ -38,9 +38,10 @@ public interface Appointment {
 
 	/**
 	 * represent this event as ical entry
+	 * @param calendarIdentifier used to generate a unique id. pass something that is unique, but stable over time, e.g. a hostname
 	 * @return the ical string
 	 */
-	String ical();
+	String ical(String calendarIdentifier);
 
 	/**
 	 * ID of the appointment – unique within this system

de.srsoftware.cal.api/src/main/java/de/srsoftware/cal/api/Coords.java

@@ -10,6 +10,18 @@ import org.json.JSONObject;
  * @param latitude the latitude
  */
 public record Coords(double longitude, double latitude) {
+	/**
+	 * get a string representing this coords in the ICAL format, see <a href="https://datatracker.ietf.org/doc/html/rfc5545#section-3.8.1.6">iCalendar spec</a>
+	 * @return the formatted coords
+	 */
+	public String icalFormat(){
+		return "%s;%s".formatted(latitude,longitude);
+	}
+
+	/**
+	 * create a JSON object containing lat and lon of this coordinate
+	 * @return the json object
+	 */
 	public JSONObject json() {
 		return new JSONObject(Map.of("lon", longitude, "lat", latitude));
 	}