implemented ical exports

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

de.srsoftware.cal.base/src/main/java/de/srsoftware/cal/BaseAppointment.java

@@ -1,6 +1,7 @@
 /* © SRSoftware 2024 */
 package de.srsoftware.cal;
 
+import static de.srsoftware.cal.Util.*;
 import static de.srsoftware.tools.Optionals.nullable;
 
 import de.srsoftware.cal.api.Appointment;
@@ -124,10 +125,24 @@ public class BaseAppointment implements Appointment {
 	}
 
 	@Override
-	public String ical() { // TODO: implement
-		return "converting event (%s) to ical not implemented".formatted(title);
+	public String ical(String calendarIdentifier) { // TODO: implement
+		var sb = new StringBuilder();
+		sb.append(contentLine(BEGIN,VEVENT));
+		if (calendarIdentifier != null) sb.append(contentLine(UID,"%s@%s".formatted(id(),calendarIdentifier)));
+		sb.append(contentLine(DTSTART,start().format(ICAL_DATE_FORMAT).replace(" ","T")));
+		end().map(end -> contentLine(DTEND,end.format(ICAL_DATE_FORMAT).replace(" ","T"))).ifPresent(sb::append);
+		sb.append(contentLine(SUMMARY,title()));
+		sb.append(contentLine(DESCRIPTION,description()));
+		coords().map(Coords::icalFormat).map(geo -> contentLine(GEO,geo)).ifPresent(sb::append);
+		if (!location().isBlank()) sb.append(contentLine(LOCATION,location()));
+		for (var attachment : attachments()) sb.append(contentLine("ATTACH;FMTYPE=%s".formatted(attachment.mime()),attachment.url().toString()));
+		for (var link : links) sb.append(contentLine("ATTACH;TITLE="+paramText(link.desciption()),link.url().toString()));
+		sb.append(contentLine("CLASS","PUBLIC"));
+		sb.append(contentLine(END,VEVENT));
+		return sb.toString();
 	}
 
+
 	@Override
 	public long id() {
 		return id;

de.srsoftware.cal.base/src/main/java/de/srsoftware/cal/Util.java

@@ -6,8 +6,51 @@ import static de.srsoftware.tools.Error.error;
 import de.srsoftware.cal.api.Coords;
 import de.srsoftware.tools.Payload;
 import de.srsoftware.tools.Result;
+import java.time.format.DateTimeFormatter;
+import java.util.ArrayList;
 
 public class Util {
+	public static final String BEGIN = "BEGIN";
+	public static final String END = "END";
+	public static final String DESCRIPTION = "DESCRIPTION";
+	public static final String DTEND = "DTEND";
+	public static final String DTSTAMP = "DTSTAMP";
+	public static final String DTSTART = "DTSTART";
+	public static final String GEO = "GEO";
+	public static final DateTimeFormatter ICAL_DATE_FORMAT = DateTimeFormatter.ofPattern("yyyyMMdd HHmmss");
+	public static final String LOCATION = "LOCATION";
+	public static final String PRODID = "PRODID";
+	public static final String SUMMARY = "SUMMARY";
+	public static final String UID = "UID";
+	public static final String VERSION = "VERSION";
+	public static final String VEVENT = "VEVENT";
+	public static final String VCALENDAR = "VCALENDAR";
+
+	private Util(){}
+
+	/**
+	 * formats a content line as defined in <a href="https://datatracker.ietf.org/doc/html/rfc5545#section-3.1">iCalendar spec</a>
+	 * @param key the content line key
+	 * @param value the content line value
+	 * @return content line formatted as described in the spec
+	 */
+	public static String contentLine(String key, String value){
+		var contentLine = "%s:%s".formatted(key,value).trim();
+		// escape line breaks
+		contentLine = contentLine.replace("\\n","\\\\n").replace("\r\n","\\n").replace("\r","\\n").replace("\n","\\n");
+		var lines = new ArrayList<String>();
+		while (contentLine.length()>70){
+			var pos = contentLine.lastIndexOf(" ",70);
+			if (pos < 10) pos = 70;
+			var dummy = contentLine.substring(0,pos);
+			lines.add(dummy);
+			contentLine = '\t'+contentLine.substring(pos);
+		}
+		lines.add(contentLine);
+		lines.add("");
+		return String.join("\r\n",lines);
+	}
+
 	public static Result<Coords> extractCoords(String coords) {
 		if (coords == null) return error("Argument is null");
 		if (coords.isBlank()) return error("Argument is blank");
@@ -21,4 +64,35 @@ public class Util {
 			return error(nfe, "Failed to parse coords from %s", coords);
 		}
 	}
+
+
+
+	public static String paramText(String param) {
+		return param
+				.replace("\n","\\n")
+				.replace("\"","''")
+				.replace(";","/")
+				.replace(",","/")
+				.replace(":","/");
+	}
+
+
+	/**
+	 * wraps a text (list of vevents in a vcalendar, as described in th <a href="https://datatracker.ietf.org/doc/html/rfc5545#section-3.4">iCalendar spec</a>
+	 * @param ical the vevents list
+	 * @param prodId the producer id of this icalendar
+	 * @return the completed ical string
+	 */
+	public static Result<String> wrapIcal(Result<String> ical, String prodId) {
+		if (ical instanceof Payload<String> payload){
+			var calendar = new StringBuilder();
+			calendar.append(contentLine(BEGIN,VCALENDAR));
+			calendar.append(contentLine(VERSION,"2.0"));
+			calendar.append(contentLine(PRODID,prodId));
+			calendar.append(payload.get());
+			calendar.append(contentLine(END,VCALENDAR));
+			return Payload.of(calendar.toString());
+		}
+		return ical;
+	}
 }

de.srsoftware.cal.base/src/test/java/de/srsoftware/cal/UtilTest.java

@@ -0,0 +1,25 @@
+/* © SRSoftware 2024 */
+package de.srsoftware.cal;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import org.junit.jupiter.api.Test;
+
+public class UtilTest {
+
+	@Test
+	public void testContentLine(){
+		var longText = """
+This text block, spanning several long lines, should be distributed over several lines, when passing it to the contentLine function.
+Let`s see what happens… New line breaks should be introduced at roughly every 70 characters,
+while the existing line breaks should be converted to '\n' escapes.""";
+		var expected = """
+Test:This text block, spanning several long lines, should be\r
+\t distributed over several lines, when passing it to the contentLine\r
+\t function.\\nLet`s see what happens… New line breaks should be\r
+\t introduced at roughly every 70 characters,\\nwhile the existing line\r
+\t breaks should be converted to '\\n' escapes.\r\n""";
+		var result = Util.contentLine("Test",longText);
+		assertEquals(expected,result);
+	}
+}