Port `Precondition` to C++ (#1040)

* 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`

* Implement Precondition in C++ w/o test yet

* add unit test for `Precondition`

* port `Precondition`

* address changes

* address changes

* fix bugs for integration test

* address changes

* fix lint

* address changes

* address changes

3 files changed, 107 insertions, 0 deletions

diff --git a/Firestore/core/test/firebase/firestore/model/CMakeLists.txt b/Firestore/core/test/firebase/firestore/model/CMakeLists.txt
index 3bac89d..9c94677 100644
--- a/Firestore/core/test/firebase/firestore/model/CMakeLists.txt
+++ b/Firestore/core/test/firebase/firestore/model/CMakeLists.txt
@@ -24,6 +24,7 @@ cc_test(
     field_value_test.cc
     maybe_document_test.cc
     no_document_test.cc
+    precondition_test.cc
     resource_path_test.cc
     snapshot_version_test.cc
     transform_operations_test.cc
diff --git a/Firestore/core/test/firebase/firestore/model/precondition_test.cc b/Firestore/core/test/firebase/firestore/model/precondition_test.cc
new file mode 100644
index 0000000..3ddb2ba
--- /dev/null
+++ b/Firestore/core/test/firebase/firestore/model/precondition_test.cc
@@ -0,0 +1,77 @@
+/*
+ * 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/model/precondition.h"
+
+#include "Firestore/core/src/firebase/firestore/model/document.h"
+#include "Firestore/core/src/firebase/firestore/model/no_document.h"
+#include "Firestore/core/src/firebase/firestore/model/snapshot_version.h"
+#include "Firestore/core/test/firebase/firestore/testutil/testutil.h"
+
+#include "gtest/gtest.h"
+
+namespace firebase {
+namespace firestore {
+namespace model {
+
+TEST(Precondition, None) {
+  const Precondition none = Precondition::None();
+  EXPECT_EQ(Precondition::Type::None, none.type());
+  EXPECT_TRUE(none.IsNone());
+  EXPECT_EQ(SnapshotVersion::None(), none.update_time());
+
+  const NoDocument deleted_doc = testutil::DeletedDoc("foo/doc", 1234567);
+  const Document doc = testutil::Doc("bar/doc", 7654321);
+  EXPECT_TRUE(none.IsValidFor(deleted_doc));
+  EXPECT_TRUE(none.IsValidFor(doc));
+}
+
+TEST(Precondition, Exists) {
+  const Precondition exists = Precondition::Exists(true);
+  const Precondition no_exists = Precondition::Exists(false);
+  EXPECT_EQ(Precondition::Type::Exists, exists.type());
+  EXPECT_EQ(Precondition::Type::Exists, no_exists.type());
+  EXPECT_FALSE(exists.IsNone());
+  EXPECT_FALSE(no_exists.IsNone());
+  EXPECT_EQ(SnapshotVersion::None(), exists.update_time());
+  EXPECT_EQ(SnapshotVersion::None(), no_exists.update_time());
+
+  const NoDocument deleted_doc = testutil::DeletedDoc("foo/doc", 1234567);
+  const Document doc = testutil::Doc("bar/doc", 7654321);
+  EXPECT_FALSE(exists.IsValidFor(deleted_doc));
+  EXPECT_TRUE(exists.IsValidFor(doc));
+  EXPECT_TRUE(no_exists.IsValidFor(deleted_doc));
+  EXPECT_FALSE(no_exists.IsValidFor(doc));
+}
+
+TEST(Precondition, UpdateTime) {
+  const Precondition update_time =
+      Precondition::UpdateTime(testutil::Version(1234567));
+  EXPECT_EQ(Precondition::Type::UpdateTime, update_time.type());
+  EXPECT_FALSE(update_time.IsNone());
+  EXPECT_EQ(testutil::Version(1234567), update_time.update_time());
+
+  const NoDocument deleted_doc = testutil::DeletedDoc("foo/doc", 1234567);
+  const Document not_match = testutil::Doc("bar/doc", 7654321);
+  const Document match = testutil::Doc("baz/doc", 1234567);
+  EXPECT_FALSE(update_time.IsValidFor(deleted_doc));
+  EXPECT_FALSE(update_time.IsValidFor(not_match));
+  EXPECT_TRUE(update_time.IsValidFor(match));
+}
+
+}  // namespace model
+}  // namespace firestore
+}  // namespace firebase
diff --git a/Firestore/core/test/firebase/firestore/testutil/testutil.h b/Firestore/core/test/firebase/firestore/testutil/testutil.h
index 9c69784..9a875f4 100644
--- a/Firestore/core/test/firebase/firestore/testutil/testutil.h
+++ b/Firestore/core/test/firebase/firestore/testutil/testutil.h
@@ -17,9 +17,16 @@
 #ifndef FIRESTORE_CORE_TEST_FIREBASE_FIRESTORE_TESTUTIL_TESTUTIL_H_
 #define FIRESTORE_CORE_TEST_FIREBASE_FIRESTORE_TESTUTIL_TESTUTIL_H_
 
+#include <chrono>  // NOLINT(build/c++11)
+#include <cstdint>
+
+#include "Firestore/core/include/firebase/firestore/timestamp.h"
+#include "Firestore/core/src/firebase/firestore/model/document.h"
 #include "Firestore/core/src/firebase/firestore/model/document_key.h"
 #include "Firestore/core/src/firebase/firestore/model/field_path.h"
+#include "Firestore/core/src/firebase/firestore/model/no_document.h"
 #include "Firestore/core/src/firebase/firestore/model/resource_path.h"
+#include "Firestore/core/src/firebase/firestore/model/snapshot_version.h"
 #include "absl/strings/string_view.h"
 
 namespace firebase {
@@ -40,6 +47,28 @@ inline model::ResourcePath Resource(absl::string_view field) {
   return model::ResourcePath::FromString(field);
 }
 
+/**
+ * Creates a snapshot version from the given version timestamp.
+ *
+ * @param version a timestamp in microseconds since the epoch.
+ */
+inline model::SnapshotVersion Version(int64_t version) {
+  namespace chr = std::chrono;
+  auto timepoint =
+      chr::time_point<chr::system_clock>(chr::microseconds(version));
+  return model::SnapshotVersion{Timestamp::FromTimePoint(timepoint)};
+}
+
+inline model::Document Doc(absl::string_view key, int64_t version) {
+  return model::Document{model::FieldValue::ObjectValueFromMap({}), Key(key),
+                         Version(version),
+                         /* has_local_mutations= */ false};
+}
+
+inline model::NoDocument DeletedDoc(absl::string_view key, int64_t version) {
+  return model::NoDocument{Key(key), Version(version)};
+}
+
 // Add a non-inline function to make this library buildable.
 // TODO(zxu123): remove once there is non-inline function.
 void dummy();