Port FieldTransform to C++ (#1033)

* 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

* implement `FieldTransform` in C++

* port `FieldTransform`

* make `fieldTransforms` shared inside `context`

* address changes

* fix lint

* address changes

2 files changed, 71 insertions, 0 deletions

diff --git a/Firestore/core/src/firebase/firestore/model/CMakeLists.txt b/Firestore/core/src/firebase/firestore/model/CMakeLists.txt
index d83c0aa..de783ad 100644
--- a/Firestore/core/src/firebase/firestore/model/CMakeLists.txt
+++ b/Firestore/core/src/firebase/firestore/model/CMakeLists.txt
@@ -25,6 +25,7 @@ cc_library(
     field_mask.h
     field_path.cc
     field_path.h
+    field_transform.h
     field_value.cc
     field_value.h
     maybe_document.cc
diff --git a/Firestore/core/src/firebase/firestore/model/field_transform.h b/Firestore/core/src/firebase/firestore/model/field_transform.h
new file mode 100644
index 0000000..a1dd96c
--- /dev/null
+++ b/Firestore/core/src/firebase/firestore/model/field_transform.h
@@ -0,0 +1,70 @@
+/*
+ * 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_FIELD_TRANSFORM_H_
+#define FIRESTORE_CORE_SRC_FIREBASE_FIRESTORE_MODEL_FIELD_TRANSFORM_H_
+
+#include <memory>
+#include <utility>
+
+#include "Firestore/core/src/firebase/firestore/model/field_path.h"
+#include "Firestore/core/src/firebase/firestore/model/transform_operations.h"
+
+namespace firebase {
+namespace firestore {
+namespace model {
+
+/** A field path and the TransformOperation to perform upon it. */
+class FieldTransform {
+ public:
+  FieldTransform(FieldPath path,
+                 std::unique_ptr<TransformOperation> transformation) noexcept
+      : path_{std::move(path)}, transformation_{std::move(transformation)} {
+  }
+
+  const FieldPath& path() const {
+    return path_;
+  }
+
+  const TransformOperation& transformation() const {
+    return *transformation_.get();
+  }
+
+  bool operator==(const FieldTransform& other) const {
+    return path_ == other.path_ && *transformation_ == *other.transformation_;
+  }
+
+#if defined(__OBJC__)
+  // For Objective-C++ hash; to be removed after migration.
+  // Do NOT use in C++ code.
+  NSUInteger Hash() const {
+    NSUInteger hash = path_.Hash();
+    hash = hash * 31 + transformation_->Hash();
+    return hash;
+  }
+#endif  // defined(__OBJC__)
+
+ private:
+  FieldPath path_;
+  // Shared by copies of the same FieldTransform.
+  std::shared_ptr<const TransformOperation> transformation_;
+};
+
+}  // namespace model
+}  // namespace firestore
+}  // namespace firebase
+
+#endif  // FIRESTORE_CORE_SRC_FIREBASE_FIRESTORE_MODEL_FIELD_TRANSFORM_H_