Port `SnapshotVersion` for the rest Firestore modulo (#1185)

* remove conversions in `Local` and `Remote`

* replace `FSTSnapshotVersion` in `Model`

* replace `FSTSnapshotVersion` in the rest

* let test check equal with C++ equal

* fix newly added code

* address changes

2 files changed, 9 insertions, 9 deletions

diff --git a/Firestore/Source/Core/FSTSyncEngine.mm b/Firestore/Source/Core/FSTSyncEngine.mm
index 775f865..8ec98e8 100644
--- a/Firestore/Source/Core/FSTSyncEngine.mm
+++ b/Firestore/Source/Core/FSTSyncEngine.mm
@@ -24,7 +24,6 @@
 
 #import "FIRFirestoreErrors.h"
 #import "Firestore/Source/Core/FSTQuery.h"
-#import "Firestore/Source/Core/FSTSnapshotVersion.h"
 #import "Firestore/Source/Core/FSTTransaction.h"
 #import "Firestore/Source/Core/FSTView.h"
 #import "Firestore/Source/Core/FSTViewSnapshot.h"
@@ -347,7 +346,7 @@ static const FSTListenSequenceNumber kIrrelevantSequenceNumber = -1;
     NSMutableDictionary<NSNumber *, FSTTargetChange *> *targetChanges =
         [NSMutableDictionary dictionary];
     FSTDeletedDocument *doc =
-        [FSTDeletedDocument documentWithKey:limboKey version:[FSTSnapshotVersion noVersion]];
+        [FSTDeletedDocument documentWithKey:limboKey version:SnapshotVersion::None()];
     FSTDocumentKeySet *limboDocuments = [[FSTDocumentKeySet keySet] setByAddingObject:doc.key];
     FSTRemoteEvent *event = [[FSTRemoteEvent alloc] initWithSnapshotVersion:SnapshotVersion::None()
                                                               targetChanges:targetChanges
diff --git a/Firestore/Source/Core/FSTTransaction.mm b/Firestore/Source/Core/FSTTransaction.mm
index 4aabd5a..57dcc48 100644
--- a/Firestore/Source/Core/FSTTransaction.mm
+++ b/Firestore/Source/Core/FSTTransaction.mm
@@ -23,7 +23,6 @@
 
 #import "FIRFirestoreErrors.h"
 #import "Firestore/Source/API/FSTUserDataConverter.h"
-#import "Firestore/Source/Core/FSTSnapshotVersion.h"
 #import "Firestore/Source/Model/FSTDocument.h"
 #import "Firestore/Source/Model/FSTDocumentKeySet.h"
 #import "Firestore/Source/Model/FSTMutation.h"
@@ -33,9 +32,11 @@
 
 #include "Firestore/core/src/firebase/firestore/model/document_key.h"
 #include "Firestore/core/src/firebase/firestore/model/precondition.h"
+#include "Firestore/core/src/firebase/firestore/model/snapshot_version.h"
 
 using firebase::firestore::model::DocumentKey;
 using firebase::firestore::model::Precondition;
+using firebase::firestore::model::SnapshotVersion;
 
 NS_ASSUME_NONNULL_BEGIN
 
@@ -53,7 +54,7 @@ NS_ASSUME_NONNULL_BEGIN
 @end
 
 @implementation FSTTransaction {
-  std::map<DocumentKey, FSTSnapshotVersion *> _readVersions;
+  std::map<DocumentKey, SnapshotVersion> _readVersions;
 }
 
 + (instancetype)transactionWithDatastore:(FSTDatastore *)datastore {
@@ -79,11 +80,11 @@ NS_ASSUME_NONNULL_BEGIN
 - (BOOL)recordVersionForDocument:(FSTMaybeDocument *)doc error:(NSError **)error {
   FSTAssert(error != nil, @"nil error parameter");
   *error = nil;
-  FSTSnapshotVersion *docVersion = doc.version;
+  SnapshotVersion docVersion = doc.version;
   if ([doc isKindOfClass:[FSTDeletedDocument class]]) {
     // For deleted docs, we must record an explicit no version to build the right precondition
     // when writing.
-    docVersion = [FSTSnapshotVersion noVersion];
+    docVersion = SnapshotVersion::None();
   }
   if (_readVersions.find(doc.key) == _readVersions.end()) {
     _readVersions[doc.key] = docVersion;
@@ -159,8 +160,8 @@ NS_ASSUME_NONNULL_BEGIN
     return Precondition::Exists(true);
   }
 
-  FSTSnapshotVersion *version = iter->second;
-  if ([version isEqual:[FSTSnapshotVersion noVersion]]) {
+  const SnapshotVersion &version = iter->second;
+  if (version == SnapshotVersion::None()) {
     // The document was read, but doesn't exist.
     // Return an error because the precondition is impossible
     if (error) {
@@ -200,7 +201,7 @@ NS_ASSUME_NONNULL_BEGIN
                            precondition:[self preconditionForDocumentKey:key]] ]];
   // Since the delete will be applied before all following writes, we need to ensure that the
   // precondition for the next write will be exists without timestamp.
-  _readVersions[key] = [FSTSnapshotVersion noVersion];
+  _readVersions[key] = SnapshotVersion::None();
 }
 
 - (void)commitWithCompletion:(FSTVoidErrorBlock)completion {