Implement RetroIndex reducer

src/main/java/com/epita/guereza/RetroIndex.java

@@ -0,0 +1,30 @@
+package com.epita.guereza;
+
+import com.epita.domain.Document;
+import com.epita.domain.Index;
+import com.epita.guereza.eventsourcing.Event;
+import com.epita.guereza.eventsourcing.Reducer;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+public class RetroIndex implements Reducer {
+    private static final Logger LOGGER = LoggerFactory.getLogger(RetroIndex.class);
+
+    private final Index index = new Index();
+
+    @SuppressWarnings("unchecked")
+    @Override
+    public void reduce(final Event<?> event) {
+        switch (event.type) {
+            case "ADD_DOCUMENT":
+                addDocument((Event<Document>) event);
+                break;
+        }
+    }
+
+    private void addDocument(Event<Document> event) {
+        index.docs.add(event.obj);
+        LOGGER.info("added a document to the index");
+    }
+}
+