From cc1d1f49134cdb5c95a04e8e395a6b3ae0c70eaa Mon Sep 17 00:00:00 2001
From: Justin Beckwith <justin.beckwith@gmail.com>
Date: Thu, 15 Nov 2018 13:30:19 -0800
Subject: [PATCH] refactor: drop usage of _.flatMap

---
 .../grpc-native-core/src/client_interceptors.js |  4 ++--
 packages/grpc-native-core/src/common.js         | 17 ++++++++++++++++-
 2 files changed, 18 insertions(+), 3 deletions(-)

diff --git a/packages/grpc-native-core/src/client_interceptors.js b/packages/grpc-native-core/src/client_interceptors.js
index 5ad6f254..992cb480 100644
--- a/packages/grpc-native-core/src/client_interceptors.js
+++ b/packages/grpc-native-core/src/client_interceptors.js
@@ -716,7 +716,7 @@ function _getStreamReadCallback(emitter, call, get_listener, deserialize) {
  * @return {boolean}
  */
 function _areBatchRequirementsMet(batch_ops, completed_ops) {
-  var dependencies = _.flatMap(batch_ops, function(op) {
+  var dependencies = common.flatMap(batch_ops, function(op) {
     return OP_DEPENDENCIES[op] || [];
   });
   for (var i = 0; i < dependencies.length; i++) {
@@ -752,7 +752,7 @@ function _startBatchIfReady(call, batch, batch_state, callback) {
     // dependencies are met as a result.
     call.startBatch(batch, callback);
     completed_ops = _.union(completed_ops, batch_ops);
-    deferred_batches = _.flatMap(deferred_batches, function(deferred_batch) {
+    deferred_batches = common.flatMap(deferred_batches, function(deferred_batch) {
       var deferred_batch_ops = Object.keys(deferred_batch).map(Number);
       if (_areBatchRequirementsMet(deferred_batch_ops, completed_ops)) {
         call.startBatch(deferred_batch.batch, deferred_batch.callback);
diff --git a/packages/grpc-native-core/src/common.js b/packages/grpc-native-core/src/common.js
index 187dd3eb..834c5f95 100644
--- a/packages/grpc-native-core/src/common.js
+++ b/packages/grpc-native-core/src/common.js
@@ -112,11 +112,26 @@ exports.getMethodType = function(method_definition) {
   }
 };
 
+/**
+ * Iterate over a collection of items, and run the given handler.
+ * Return the results as a flattened array of values.
+ *
+ * @private
+ *
+ * @param {Array} collection Array of items to process
+ * @param {Function} handler The function to call on each element in the array
+ * @return {Array} A flattened array of results.
+ */
+exports.flatMap = function(collection, handler) {
+  const mapped = collection.map(handler);
+  return mapped.reduce((acc, curr) => acc.concat(curr), []);
+}
+
 /**
  * Given an array of property names and an array of values,
  * combine the two into an object map.
  * Equivalent to _.zipObject.
- * 
+ *
  * @private
  *
  * @param props {Array<String>} Array of property names