implement `TargetIdGenerator` in C++ for Firestore (#701)

* implement `TargetIdGenerator`

* address changes

2 files changed, 101 insertions, 0 deletions

diff --git a/Firestore/core/test/firebase/firestore/core/CMakeLists.txt b/Firestore/core/test/firebase/firestore/core/CMakeLists.txt
new file mode 100644
index 0000000..34993aa
--- /dev/null
+++ b/Firestore/core/test/firebase/firestore/core/CMakeLists.txt
@@ -0,0 +1,21 @@
+# Copyright 2018 Google
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+cc_test(
+  firebase_firestore_core_test
+  SOURCES
+    target_id_generator_test.cc
+  DEPENDS
+    firebase_firestore_core
+)
diff --git a/Firestore/core/test/firebase/firestore/core/target_id_generator_test.cc b/Firestore/core/test/firebase/firestore/core/target_id_generator_test.cc
new file mode 100644
index 0000000..c98bfd3
--- /dev/null
+++ b/Firestore/core/test/firebase/firestore/core/target_id_generator_test.cc
@@ -0,0 +1,80 @@
+/*
+ * Copyright 2018 Google
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "Firestore/core/src/firebase/firestore/core/target_id_generator.h"
+
+#include "gtest/gtest.h"
+
+namespace firebase {
+namespace firestore {
+namespace core {
+
+TEST(TargetIdGenerator, Constructor) {
+  TargetIdGenerator local_store_generator =
+      TargetIdGenerator::LocalStoreTargetIdGenerator(0);
+  TargetIdGenerator sync_engine_generator =
+      TargetIdGenerator::SyncEngineTargetIdGenerator(0);
+  EXPECT_EQ(TargetIdGeneratorId::LocalStore,
+            local_store_generator.generator_id());
+  EXPECT_EQ(2, local_store_generator.NextId());
+  EXPECT_EQ(TargetIdGeneratorId::SyncEngine,
+            sync_engine_generator.generator_id());
+  EXPECT_EQ(1, sync_engine_generator.NextId());
+}
+
+TEST(TargetIdGenerator, SkipPast) {
+  EXPECT_EQ(1, TargetIdGenerator::SyncEngineTargetIdGenerator(-1).NextId());
+  EXPECT_EQ(3, TargetIdGenerator::SyncEngineTargetIdGenerator(2).NextId());
+  EXPECT_EQ(5, TargetIdGenerator::SyncEngineTargetIdGenerator(4).NextId());
+
+  for (int i = 4; i < 12; ++i) {
+    TargetIdGenerator a = TargetIdGenerator::LocalStoreTargetIdGenerator(i);
+    TargetIdGenerator b = TargetIdGenerator::SyncEngineTargetIdGenerator(i);
+    EXPECT_EQ(i + 2 & ~1, a.NextId());
+    EXPECT_EQ(i + 1 | 1, b.NextId());
+  }
+
+  EXPECT_EQ(13, TargetIdGenerator::SyncEngineTargetIdGenerator(12).NextId());
+  EXPECT_EQ(24, TargetIdGenerator::LocalStoreTargetIdGenerator(22).NextId());
+}
+
+TEST(TargetIdGenerator, Increment) {
+  TargetIdGenerator a = TargetIdGenerator::LocalStoreTargetIdGenerator(0);
+  EXPECT_EQ(2, a.NextId());
+  EXPECT_EQ(4, a.NextId());
+  EXPECT_EQ(6, a.NextId());
+
+  TargetIdGenerator b = TargetIdGenerator::LocalStoreTargetIdGenerator(46);
+  EXPECT_EQ(48, b.NextId());
+  EXPECT_EQ(50, b.NextId());
+  EXPECT_EQ(52, b.NextId());
+  EXPECT_EQ(54, b.NextId());
+
+  TargetIdGenerator c = TargetIdGenerator::SyncEngineTargetIdGenerator(0);
+  EXPECT_EQ(1, c.NextId());
+  EXPECT_EQ(3, c.NextId());
+  EXPECT_EQ(5, c.NextId());
+
+  TargetIdGenerator d = TargetIdGenerator::SyncEngineTargetIdGenerator(46);
+  EXPECT_EQ(47, d.NextId());
+  EXPECT_EQ(49, d.NextId());
+  EXPECT_EQ(51, d.NextId());
+  EXPECT_EQ(53, d.NextId());
+}
+
+}  //  namespace core
+}  //  namespace firestore
+}  //  namespace firebase