private void rerunTransactionQueue()

in src/main/java/com/google/firebase/database/core/Repo.java [936:1074]
106 lines of code
12 McCabe index (conditional complexity)

  private void rerunTransactionQueue(List<TransactionData> queue, Path path) {
    if (queue.isEmpty()) {
      return; // Nothing to do!
    }

    // Queue up the callbacks and fire them after cleaning up all of our transaction state, since
    // the callback could trigger more transactions or sets
    List<Runnable> callbacks = new ArrayList<>();

    // Ignore, by default, all of the sets in this queue, since we're re-running all of them.
    // However, we want to include the results of new sets triggered as part of this re-run, so we
    // don't want to ignore a range, just these specific sets.
    List<Long> setsToIgnore = new ArrayList<>();
    for (TransactionData transaction : queue) {
      setsToIgnore.add(transaction.currentWriteId);
    }

    for (final TransactionData transaction : queue) {
      Path relativePath = Path.getRelative(path, transaction.path);
      boolean abortTransaction = false;
      DatabaseError abortReason = null;
      List<Event> events = new ArrayList<>();

      assert relativePath != null; // rerunTransactionQueue: relativePath should not be null.

      if (transaction.status == TransactionStatus.NEEDS_ABORT) {
        abortTransaction = true;
        abortReason = transaction.abortReason;
        if (abortReason.getCode() != DatabaseError.WRITE_CANCELED) {
          events.addAll(
              serverSyncTree.ackUserWrite(
                  transaction.currentWriteId, /*revert=*/ true, /*persist=*/ false, serverClock));
        }
      } else if (transaction.status == TransactionStatus.RUN) {
        if (transaction.retryCount >= TRANSACTION_MAX_RETRIES) {
          abortTransaction = true;
          abortReason = DatabaseError.fromStatus(TRANSACTION_TOO_MANY_RETRIES);
          events.addAll(
              serverSyncTree.ackUserWrite(
                  transaction.currentWriteId, /*revert=*/ true, /*persist=*/ false, serverClock));
        } else {
          // This code reruns a transaction
          Node currentNode = this.getLatestState(transaction.path, setsToIgnore);
          transaction.currentInputSnapshot = currentNode;
          MutableData mutableCurrent = InternalHelpers.createMutableData(currentNode);
          DatabaseError error = null;
          Transaction.Result result;
          try {
            result = transaction.handler.doTransaction(mutableCurrent);
          } catch (Throwable e) {
            error = DatabaseError.fromException(e);
            result = Transaction.abort();
          }
          if (result.isSuccess()) {
            final Long oldWriteId = transaction.currentWriteId;
            Map<String, Object> serverValues = ServerValues.generateServerValues(serverClock);

            Node newDataNode = result.getNode();
            Node newNodeResolved =
                ServerValues.resolveDeferredValueSnapshot(newDataNode, serverValues);

            transaction.currentOutputSnapshotRaw = newDataNode;
            transaction.currentOutputSnapshotResolved = newNodeResolved;
            transaction.currentWriteId = this.getNextWriteId();

            // Mutates setsToIgnore in place
            setsToIgnore.remove(oldWriteId);
            events.addAll(
                serverSyncTree.applyUserOverwrite(
                    transaction.path,
                    newDataNode,
                    newNodeResolved,
                    transaction.currentWriteId,
                    transaction.applyLocally, /*persist=*/
                    false));
            events.addAll(
                serverSyncTree.ackUserWrite(
                    oldWriteId, /*revert=*/ true, /*persist=*/ false, serverClock));
          } else {
            // The user aborted the transaction. It's not an error, so we don't need to send them
            // one
            abortTransaction = true;
            abortReason = error;
            events.addAll(
                serverSyncTree.ackUserWrite(
                    transaction.currentWriteId, /*revert=*/ true, /*persist=*/ false, serverClock));
          }
        }
      }

      this.postEvents(events);

      if (abortTransaction) {
        // Abort
        transaction.status = TransactionStatus.COMPLETED;
        final DatabaseReference ref = InternalHelpers.createReference(this, transaction.path);

        // We set this field immediately, so it's safe to cast to an actual snapshot
        Node lastInput = transaction.currentInputSnapshot;
        // TODO: In the future, perhaps this should just be KeyIndex?
        final DataSnapshot snapshot =
            InternalHelpers.createDataSnapshot(ref, IndexedNode.from(lastInput));

        // Removing a callback can trigger pruning which can muck with mergedData/visibleData (as it
        // prunes data). So defer removing the callback until later.
        this.scheduleNow(
            new Runnable() {
              @Override
              public void run() {
                removeEventCallback(
                    new ValueEventRegistration(
                        Repo.this,
                        transaction.outstandingListener,
                        QuerySpec.defaultQueryAtPath(transaction.path)));
              }
            });

        final DatabaseError callbackError = abortReason;
        callbacks.add(
            new Runnable() {
              @Override
              public void run() {
                runTransactionOnComplete(transaction.handler, callbackError, false, snapshot);
              }
            });
      }
    }

    // Clean up completed transactions.
    pruneCompletedTransactions(transactionQueueTree);

    // Now fire callbacks, now that we're in a good, known state.
    for (Runnable callback : callbacks) {
      postEvent(callback);
    }

    // Try to send the transaction result to the server.
    sendAllReadyTransactions();
  }