introduce TailableCursor interface

Author: jmoghisi

core/src/main/java/de/bwaldvogel/mongo/backend/EmptyCursor.java

@@ -4,8 +4,9 @@
 import java.util.NoSuchElementException;
 
 import de.bwaldvogel.mongo.bson.Document;
+import de.bwaldvogel.mongo.oplog.OplogPosition;
 
-public class EmptyCursor extends AbstractCursor {
+public class EmptyCursor extends AbstractCursor implements TailableCursor {
 
     private static final long EMPTY_CURSOR_ID = 0L;
 
@@ -33,4 +34,9 @@ public List<Document> takeDocuments(int numberToReturn) {
     public String toString() {
         return getClass().getSimpleName() + "()";
     }
+
+    @Override
+    public OplogPosition getPosition() {
+        return null;
+    }
 }

core/src/main/java/de/bwaldvogel/mongo/backend/TailableCursor.java

@@ -0,0 +1,9 @@
+package de.bwaldvogel.mongo.backend;
+
+import de.bwaldvogel.mongo.oplog.OplogPosition;
+
+public interface TailableCursor extends Cursor {
+
+    OplogPosition getPosition();
+
+}

core/src/main/java/de/bwaldvogel/mongo/oplog/InvalidateOplogCursor.java

@@ -4,9 +4,10 @@
 import java.util.List;
 
 import de.bwaldvogel.mongo.backend.AbstractCursor;
+import de.bwaldvogel.mongo.backend.TailableCursor;
 import de.bwaldvogel.mongo.bson.Document;
 
-class InvalidateOplogCursor extends AbstractCursor {
+class InvalidateOplogCursor extends AbstractCursor implements TailableCursor {
     private final OplogPosition position;
 
     InvalidateOplogCursor(OplogPosition position) {
@@ -27,4 +28,8 @@ public List<Document> takeDocuments(int numberToReturn) {
         return Collections.singletonList(result);
     }
 
+    @Override
+    public OplogPosition getPosition() {
+        return null;
+    }
 }

core/src/main/java/de/bwaldvogel/mongo/oplog/OplogCursor.java

@@ -8,9 +8,10 @@
 
 import de.bwaldvogel.mongo.backend.CollectionUtils;
 import de.bwaldvogel.mongo.backend.AbstractCursor;
+import de.bwaldvogel.mongo.backend.TailableCursor;
 import de.bwaldvogel.mongo.bson.Document;
 
-public class OplogCursor extends AbstractCursor {
+public class OplogCursor extends AbstractCursor implements TailableCursor {
 
     private final Function<OplogPosition, Stream<Document>> oplogStream;
     private OplogPosition position;
@@ -51,7 +52,8 @@ private void emulateWaitingForAllShards() {
         }
     }
 
-    OplogPosition getPosition() {
+    @Override
+    public OplogPosition getPosition() {
         return position;
     }