Review

Author: schmidt-sebastian

firebase-database/src/androidTest/java/com/google/firebase/database/DataTest.java

@@ -2749,13 +2749,13 @@ public void onComplete(DatabaseError error, boolean committed, DataSnapshot curr
   @Test
   public void testServerIncrementOverwritesExistingDataOnline()
       throws DatabaseException, TimeoutException, InterruptedException {
-    serverIncrementOverwritesExistingData(true);
+    serverIncrementOverwritesExistingData(/* online= */ true);
   }
 
   @Test
   public void testServerIncrementOverwritesExistingDataOffline()
       throws DatabaseException, TimeoutException, InterruptedException {
-    serverIncrementOverwritesExistingData(false);
+    serverIncrementOverwritesExistingData(/* online= */ false);
   }
 
   public void serverIncrementOverwritesExistingData(boolean online)
@@ -2830,13 +2830,13 @@ public void onCancelled(DatabaseError error) {}
   @Test
   public void testServerIncrementPriorityOnline()
       throws DatabaseException, TimeoutException, InterruptedException {
-    serverIncrementPriority(true);
+    serverIncrementPriority(/* online= */ true);
   }
 
   @Test
   public void testServerIncrementPriorityOffline()
       throws DatabaseException, TimeoutException, InterruptedException {
-    serverIncrementPriority(false);
+    serverIncrementPriority(/* online= */ false);
   }
 
   public void serverIncrementPriority(boolean online)

firebase-database/src/main/java/com/google/firebase/database/core/DeferredValueProvider.java

@@ -14,6 +14,8 @@
 
 package com.google.firebase.database.core;
 
+import com.google.firebase.database.core.ValueProvider.DeferredValueProvider;
+import com.google.firebase.database.core.ValueProvider.ExistingValueProvider;
 import com.google.firebase.database.core.utilities.Clock;
 import com.google.firebase.database.core.utilities.Utilities;
 import com.google.firebase.database.snapshot.ChildKey;

firebase-database/src/main/java/com/google/firebase/database/core/ExistingValueProvider.java

@@ -242,9 +242,6 @@ public List<? extends Event> call() {
             boolean needToReevaluate = pendingWriteTree.removeWrite(writeId);
             if (write.isVisible()) {
               if (!revert) {
-                ArrayList<Long> excludeThis = new ArrayList<>();
-                excludeThis.add(write.getWriteId());
-                Node existing = calcCompleteEventCache(write.getPath(), excludeThis);
                 Map<String, Object> serverValues = ServerValues.generateServerValues(serverClock);
                 if (write.isOverwrite()) {
                   Node resolvedNode =

firebase-database/src/main/java/com/google/firebase/database/core/ServerValues.java

@@ -16,6 +16,7 @@
 
 import com.google.firebase.database.snapshot.ChildKey;
 import com.google.firebase.database.snapshot.Node;
+import java.util.ArrayList;
 
 /**
  * A ValueProvider defers the calculation of a Node's value until needed.
@@ -25,8 +26,54 @@
  * value resolution, we ned a wrapper class that will let us share code {@see
  * https://github.com/firebase/firebase-js-sdk/issues/2487}.
  */
-public interface ValueProvider {
-  ValueProvider getImmediateChild(ChildKey childKey);
+abstract class ValueProvider {
+  public abstract ValueProvider getImmediateChild(ChildKey childKey);
 
-  Node node();
+  public abstract Node node();
+
+  /**
+   * An ExistingValueProvider implements the ValueProvider interface for a Node whose value is
+   * known.
+   */
+  public static class ExistingValueProvider extends ValueProvider {
+    private final Node node;
+
+    ExistingValueProvider(Node node) {
+      this.node = node;
+    }
+
+    @Override
+    public ValueProvider getImmediateChild(ChildKey childKey) {
+      Node child = node.getImmediateChild(childKey);
+      return new ExistingValueProvider(child);
+    }
+
+    @Override
+    public Node node() {
+      return node;
+    }
+  }
+
+  /** A DeferredValueProvider computes the value of a Node only when {@link #node()} is invoked. */
+  public static class DeferredValueProvider extends ValueProvider {
+
+    private final SyncTree syncTree;
+    private final Path path;
+
+    DeferredValueProvider(SyncTree syncTree, Path path) {
+      this.syncTree = syncTree;
+      this.path = path;
+    }
+
+    @Override
+    public ValueProvider getImmediateChild(ChildKey childKey) {
+      Path child = path.child(childKey);
+      return new DeferredValueProvider(syncTree, child);
+    }
+
+    @Override
+    public Node node() {
+      return syncTree.calcCompleteEventCache(path, new ArrayList<>());
+    }
+  }
 }

firebase-database/src/main/java/com/google/firebase/database/core/SyncTree.java

@@ -257,7 +257,7 @@ public void onComplete(DatabaseError error, DatabaseReference ref) {
     }
   }
 
-  /** A nullable-aware equals method . */
+  /** A nullable-aware equals method. */
   public static boolean equals(@Nullable Object left, @Nullable Object right) {
     if (left == right) {
       return true;