improved diff for journal

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

bus/src/main/java/de/srsoftware/umbrella/messagebus/events/Event.java

@@ -2,9 +2,9 @@
 package de.srsoftware.umbrella.messagebus.events;
 
 import static de.srsoftware.umbrella.core.Constants.*;
-import static java.text.MessageFormat.format;
 import static java.util.Optional.*;
 
+import de.srsoftware.tools.Diff;
 import de.srsoftware.tools.Mappable;
 import de.srsoftware.umbrella.core.model.UmbrellaUser;
 import java.util.HashMap;
@@ -45,11 +45,6 @@ public abstract class Event<Payload extends Mappable> {
 
 	public abstract String describe();
 
-	private String diff(Map<String, Object> a, Map<String, Object> b){
-		// TODO: replace by better implementation
-		return format("{0}\n→\n{1}",dropMarkdown(a),dropMarkdown(b));
-	}
-
 	private Map<String, Object> dropMarkdown(Map<String, Object> map) {
 		var result = new HashMap<String, Object>();
 		for (var entry : map.entrySet()){
@@ -61,7 +56,7 @@ public abstract class Event<Payload extends Mappable> {
 	}
 
 	public Optional<String> diff(){
-		return oldData == null ? empty() : of(diff(oldData,payload.toMap()));
+		return oldData == null ? empty() : of(Diff.MapDiff.diff(dropMarkdown(oldData),dropMarkdown(payload.toMap())));
 	}