refactoring Events for better journal

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

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

@@ -1,35 +1,70 @@
 /* © SRSoftware 2025 */
 package de.srsoftware.umbrella.messagebus.events;
 
-import static de.srsoftware.umbrella.core.Constants.USER;
+import static de.srsoftware.umbrella.core.Constants.*;
+import static java.text.MessageFormat.format;
+import static java.util.Optional.*;
 
 import de.srsoftware.tools.Mappable;
 import de.srsoftware.umbrella.core.model.UmbrellaUser;
+import java.util.HashMap;
 import java.util.Map;
+import java.util.Optional;
 import org.json.JSONObject;
 
+
 public abstract class Event<Payload extends Mappable> {
 
 	public enum EventType {
 		CREATE,
 		UPDATE,
 		DELETE;
-
 	}
-	private UmbrellaUser initiator;
 
-	private String module;
-	private Payload payload;
-	private EventType eventType;
+	private final UmbrellaUser initiator;
+	private final String module;
+	private final Payload payload;
+	private final EventType eventType;
+	private final Map<String, Object> oldData;
+
 	public Event(UmbrellaUser initiator, String module, Payload payload, EventType type){
 		this.initiator = initiator;
 		this.module    = module;
 		this.payload   = payload;
 		this.eventType = type;
+		this.oldData   = null;
+	}
+
+	public Event(UmbrellaUser initiator, String module, Payload payload, Map<String, Object> oldData){
+		this.initiator = initiator;
+		this.module    = module;
+		this.payload   = payload;
+		this.eventType = EventType.UPDATE;
+		this.oldData   = oldData;
 	}
 
 	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()){
+			var v = entry.getValue();
+			if (v instanceof Map<?,?> m && m.containsKey(RENDERED) && m.get(SOURCE) instanceof String s) v=s;
+			result.put(entry.getKey(),v);
+		}
+		return result;
+	}
+
+	public Optional<String> diff(){
+		return oldData == null ? empty() : of(diff(oldData,payload.toMap()));
+	}
+
+
 	public String eventType(){
 		return eventType.toString();
 	}

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

@@ -5,6 +5,7 @@ import static de.srsoftware.umbrella.core.Constants.PROJECT;
 
 import de.srsoftware.umbrella.core.model.Project;
 import de.srsoftware.umbrella.core.model.UmbrellaUser;
+import java.util.Map;
 
 
 public class ProjectEvent extends Event<Project>{
@@ -12,9 +13,13 @@ public class ProjectEvent extends Event<Project>{
 		super(initiator, PROJECT, project, type);
 	}
 
+	public ProjectEvent(UmbrellaUser initiator, Project project, Map<String, Object> oldData){
+		super(initiator, PROJECT, project, oldData);
+	}
+
 	@Override
 	public String describe() {
-		return "[TODO: ProjectEvent.describe]";
+		return diff().orElse("[TODO: ProjectEvent.describe]");
 	}
 
 	@Override

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

@@ -5,6 +5,7 @@ import static de.srsoftware.umbrella.core.Constants.TASK;
 
 import de.srsoftware.umbrella.core.model.Task;
 import de.srsoftware.umbrella.core.model.UmbrellaUser;
+import java.util.Map;
 
 
 public class TaskEvent extends Event<Task>{
@@ -12,9 +13,13 @@ public class TaskEvent extends Event<Task>{
 		super(initiator, TASK, task, type);
 	}
 
+	public TaskEvent(UmbrellaUser initiator, Task task, Map<String, Object> oldData){
+		super(initiator, TASK, task, oldData);
+	}
+
 	@Override
 	public String describe() {
-		return "[TODO: TaskEvent.describe()]";
+		return diff().orElse("[TODO: TaskEvent.describe()]");
 	}
 
 	@Override