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

1 files changed, 19 insertions, 18 deletions

diff --git a/Firestore/Source/Remote/FSTSerializerBeta.mm b/Firestore/Source/Remote/FSTSerializerBeta.mm
index 1d9ad30..c8b0fa4 100644
--- a/Firestore/Source/Remote/FSTSerializerBeta.mm
+++ b/Firestore/Source/Remote/FSTSerializerBeta.mm
@@ -50,6 +50,7 @@
 #include "Firestore/core/src/firebase/firestore/model/field_mask.h"
 #include "Firestore/core/src/firebase/firestore/model/field_path.h"
 #include "Firestore/core/src/firebase/firestore/model/field_transform.h"
+#include "Firestore/core/src/firebase/firestore/model/precondition.h"
 #include "Firestore/core/src/firebase/firestore/model/resource_path.h"
 #include "Firestore/core/src/firebase/firestore/model/transform_operations.h"
 #include "Firestore/core/src/firebase/firestore/util/string_apple.h"
@@ -61,8 +62,10 @@ using firebase::firestore::model::DocumentKey;
 using firebase::firestore::model::FieldMask;
 using firebase::firestore::model::FieldPath;
 using firebase::firestore::model::FieldTransform;
+using firebase::firestore::model::Precondition;
 using firebase::firestore::model::ResourcePath;
 using firebase::firestore::model::ServerTimestampTransform;
+using firebase::firestore::model::SnapshotVersion;
 using firebase::firestore::model::TransformOperation;
 
 NS_ASSUME_NONNULL_BEGIN
@@ -475,7 +478,7 @@ NS_ASSUME_NONNULL_BEGIN
     FSTFail(@"Unknown mutation type %@", NSStringFromClass(mutationClass));
   }
 
-  if (!mutation.precondition.isNone) {
+  if (!mutation.precondition.IsNone()) {
     proto.currentDocument = [self encodedPrecondition:mutation.precondition];
   }
 
@@ -483,9 +486,9 @@ NS_ASSUME_NONNULL_BEGIN
 }
 
 - (FSTMutation *)decodedMutation:(GCFSWrite *)mutation {
-  FSTPrecondition *precondition = [mutation hasCurrentDocument]
-                                      ? [self decodedPrecondition:mutation.currentDocument]
-                                      : [FSTPrecondition none];
+  Precondition precondition = [mutation hasCurrentDocument]
+                                  ? [self decodedPrecondition:mutation.currentDocument]
+                                  : Precondition::None();
 
   switch (mutation.operationOneOfCase) {
     case GCFSWrite_Operation_OneOfCase_Update:
@@ -505,8 +508,7 @@ NS_ASSUME_NONNULL_BEGIN
                                        precondition:precondition];
 
     case GCFSWrite_Operation_OneOfCase_Transform: {
-      FSTPreconditionExists exists = precondition.exists;
-      FSTAssert(exists == FSTPreconditionExistsYes,
+      FSTAssert(precondition == Precondition::Exists(true),
                 @"Transforms must have precondition \"exists == true\"");
 
       return [[FSTTransformMutation alloc]
@@ -520,30 +522,29 @@ NS_ASSUME_NONNULL_BEGIN
   }
 }
 
-- (GCFSPrecondition *)encodedPrecondition:(FSTPrecondition *)precondition {
-  FSTAssert(!precondition.isNone, @"Can't serialize an empty precondition");
+- (GCFSPrecondition *)encodedPrecondition:(const Precondition &)precondition {
+  FSTAssert(!precondition.IsNone(), @"Can't serialize an empty precondition");
   GCFSPrecondition *message = [GCFSPrecondition message];
-  if (precondition.updateTime) {
-    message.updateTime = [self encodedVersion:precondition.updateTime];
-  } else if (precondition.exists != FSTPreconditionExistsNotSet) {
-    message.exists = precondition.exists == FSTPreconditionExistsYes;
+  if (precondition.type() == Precondition::Type::UpdateTime) {
+    message.updateTime = [self encodedVersion:precondition.update_time()];
+  } else if (precondition.type() == Precondition::Type::Exists) {
+    message.exists = precondition == Precondition::Exists(true);
   } else {
-    FSTFail(@"Unknown precondition: %@", precondition);
+    FSTFail(@"Unknown precondition: %@", precondition.description());
   }
   return message;
 }
 
-- (FSTPrecondition *)decodedPrecondition:(GCFSPrecondition *)precondition {
+- (Precondition)decodedPrecondition:(GCFSPrecondition *)precondition {
   switch (precondition.conditionTypeOneOfCase) {
     case GCFSPrecondition_ConditionType_OneOfCase_GPBUnsetOneOfCase:
-      return [FSTPrecondition none];
+      return Precondition::None();
 
     case GCFSPrecondition_ConditionType_OneOfCase_Exists:
-      return [FSTPrecondition preconditionWithExists:precondition.exists];
+      return Precondition::Exists(precondition.exists);
 
     case GCFSPrecondition_ConditionType_OneOfCase_UpdateTime:
-      return [FSTPrecondition
-          preconditionWithUpdateTime:[self decodedVersion:precondition.updateTime]];
+      return Precondition::UpdateTime([self decodedVersion:precondition.updateTime]);
 
     default:
       FSTFail(@"Unrecognized Precondition one-of case %@", precondition);