feature: add event sourcing microservice init

src/main/java/com/eventsourcing/es/AggregateRoot.java

@@ -0,0 +1,96 @@
+package com.eventsourcing.es;
+
+import com.eventsourcing.es.exceptions.InvalidEventException;
+import lombok.Data;
+import lombok.NoArgsConstructor;
+
+import java.time.LocalDateTime;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Objects;
+
+@Data
+@NoArgsConstructor
+public abstract class AggregateRoot {
+
+    protected String id;
+    protected String type;
+    protected long version;
+    protected final List<Event> changes = new ArrayList<>();
+
+    public AggregateRoot(final String id, final String aggregateType) {
+        this.id = id;
+        this.type = aggregateType;
+    }
+
+
+    public abstract void when(final Event event);
+
+    public void load(final List<Event> events) {
+        events.forEach(event -> {
+            this.validateEvent(event);
+            this.raiseEvent(event);
+            this.version++;
+        });
+    }
+
+    public void apply(final Event event) {
+        this.validateEvent(event);
+        event.setAggregateType(this.type);
+
+        when(event);
+        changes.add(event);
+
+        this.version++;
+        event.setVersion(this.version);
+    }
+
+    public void raiseEvent(final Event event) {
+        this.validateEvent(event);
+
+        event.setAggregateType(this.type);
+        when(event);
+
+        this.version++;
+    }
+
+    public void clearChanges() {
+        this.changes.clear();
+    }
+
+    public void toSnapshot() {
+        this.clearChanges();
+    }
+
+    public String string() {
+        return String.format("id: {%s}, type: {%s}, version: {%s}, changes: {%s}", id, type, version, changes.size());
+    }
+
+    private void validateEvent(final Event event) {
+        if (Objects.isNull(event) || !event.getAggregateId().equals(this.id))
+            throw new InvalidEventException(event.toString());
+    }
+
+    protected Event createEvent(String eventType, byte[] data, byte[] metadata) {
+        return Event.builder()
+                .aggregateId(this.getId())
+                .version(this.getVersion())
+                .aggregateType(this.getType())
+                .eventType(eventType)
+                .data(Objects.isNull(data) ? new byte[]{} : data)
+                .metaData(Objects.isNull(metadata) ? new byte[]{} : metadata)
+                .timeStamp(LocalDateTime.now())
+                .build();
+    }
+
+
+    @Override
+    public String toString() {
+        return "AggregateRoot{" +
+                "id='" + id + '\'' +
+                ", type='" + type + '\'' +
+                ", version=" + version +
+                ", changes=" + changes.size() +
+                '}';
+    }
+}