Port transform operations to C++ (#1020)

* port FieldMask to C++

* address changes

* address changes

* fix test

* address change

* Port transform operations (FSTTransformOperation, FSTServerTimestampTransform) to C++

* address changes

* address changes

* address changes

* address change

2 files changed, 98 insertions, 0 deletions

diff --git a/Firestore/core/src/firebase/firestore/model/CMakeLists.txt b/Firestore/core/src/firebase/firestore/model/CMakeLists.txt
index f6c5efe..d83c0aa 100644
--- a/Firestore/core/src/firebase/firestore/model/CMakeLists.txt
+++ b/Firestore/core/src/firebase/firestore/model/CMakeLists.txt
@@ -35,6 +35,7 @@ cc_library(
     resource_path.h
     snapshot_version.cc
     snapshot_version.h
+    transform_operations.h
     types.h
   DEPENDS
     absl_strings
diff --git a/Firestore/core/src/firebase/firestore/model/transform_operations.h b/Firestore/core/src/firebase/firestore/model/transform_operations.h
new file mode 100644
index 0000000..6ff4dbc
--- /dev/null
+++ b/Firestore/core/src/firebase/firestore/model/transform_operations.h
@@ -0,0 +1,97 @@
+/*
+ * 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.
+ */
+
+#ifndef FIRESTORE_CORE_SRC_FIREBASE_FIRESTORE_MODEL_TRANSFORM_OPERATIONS_H_
+#define FIRESTORE_CORE_SRC_FIREBASE_FIRESTORE_MODEL_TRANSFORM_OPERATIONS_H_
+
+namespace firebase {
+namespace firestore {
+namespace model {
+
+// TODO(zxu123): We might want to refactor transform_operations.h into several
+// files when the number of different types of operations grows gigantically.
+// For now, put the interface and the only operation here.
+
+/** Represents a transform within a TransformMutation. */
+class TransformOperation {
+ public:
+  /** All the different kinds to TransformOperation. */
+  enum class Type {
+    ServerTimestamp,
+    Test,  // Purely for test purpose.
+  };
+
+  virtual ~TransformOperation() {
+  }
+
+  /** Returns the actual type. */
+  virtual Type type() const = 0;
+
+  /** Returns whether the two are equal. */
+  virtual bool operator==(const TransformOperation& other) const = 0;
+
+  /** Returns whether the two are not equal. */
+  bool operator!=(const TransformOperation& other) const {
+    return !operator==(other);
+  }
+
+#if defined(__OBJC__)
+  // For Objective-C++ hash; to be removed after migration.
+  // Do NOT use in C++ code.
+  virtual NSUInteger Hash() const = 0;
+#endif  // defined(__OBJC__)
+};
+
+/** Transforms a value into a server-generated timestamp. */
+class ServerTimestampTransform : public TransformOperation {
+ public:
+  ~ServerTimestampTransform() override {
+  }
+
+  Type type() const override {
+    return Type::ServerTimestamp;
+  }
+
+  bool operator==(const TransformOperation& other) const override {
+    // All ServerTimestampTransform objects are equal.
+    return other.type() == Type::ServerTimestamp;
+  }
+
+  static const ServerTimestampTransform& Get() {
+    static ServerTimestampTransform shared_instance;
+    return shared_instance;
+  }
+
+#if defined(__OBJC__)
+  // For Objective-C++ hash; to be removed after migration.
+  // Do NOT use in C++ code.
+  NSUInteger Hash() const override {
+    // arbitrary number, the same as used in ObjC implementation, since all
+    // instances are equal.
+    return 37;
+  }
+#endif  // defined(__OBJC__)
+
+ private:
+  ServerTimestampTransform() {
+  }
+};
+
+}  // namespace model
+}  // namespace firestore
+}  // namespace firebase
+
+#endif  // FIRESTORE_CORE_SRC_FIREBASE_FIRESTORE_MODEL_TRANSFORM_OPERATIONS_H_