ensure that all recovered Timestamps are done in Ticks format (#174)

* ensure that all recovered Timestamps are done in Ticks format

* fixed timestamp conversion

* updated comment

Author: Aaronontheweb

src/Akka.Persistence.MongoDb/Journal/MongoDbJournal.cs

@@ -347,8 +347,25 @@ private JournalEntry ToJournalEntry(IPersistentRepresentation message)
             };
         }
 
+        private static long ToTicks(BsonTimestamp bson)
+        {
+
+
+            // BSON Timestamps are stored natively as Unix epoch seconds + an ordinal value
+
+            // need to use BsonTimestamp.Timestamp because the ordinal value doesn't actually have any
+            // bearing on the time - it's used to try to somewhat order the events that all occurred concurrently
+            // according to the MongoDb clock. No need to include that data in the EventEnvelope.Timestamp field
+            // which is used entirely for end-user purposes.
+            //
+            // See https://docs.mongodb.com/manual/reference/bson-types/#timestamps
+
+            return DateTimeOffset.FromUnixTimeSeconds(bson.Timestamp).Ticks;
+        }
+
         private Persistent ToPersistenceRepresentation(JournalEntry entry, IActorRef sender)
         {
+
             if (_settings.LegacySerialization)
             {
                 var manifest = string.IsNullOrEmpty(entry.Manifest) ? entry.Payload.GetType().TypeQualifiedName() : entry.Manifest;
@@ -360,7 +377,7 @@ private Persistent ToPersistenceRepresentation(JournalEntry entry, IActorRef sen
                     manifest,
                     entry.IsDeleted,
                     sender,
-                    timestamp: entry.Ordering.Timestamp);
+                    timestamp: ToTicks(entry.Ordering)); // MongoDb timestamps are stored as Unix Epoch
             }
 
             var legacy = entry.SerializerId.HasValue || !string.IsNullOrEmpty(entry.Manifest);
@@ -373,7 +390,7 @@ private Persistent ToPersistenceRepresentation(JournalEntry entry, IActorRef sen
                 // it the timestamp is not defined in the binary payload
                 if (output.Timestamp == 0L)
                 {
-                    output = (Persistent)output.WithTimestamp(entry.Ordering.Timestamp);
+                    output = (Persistent)output.WithTimestamp(ToTicks(entry.Ordering));
                 }
 
                 return output;
@@ -402,14 +419,14 @@ private Persistent ToPersistenceRepresentation(JournalEntry entry, IActorRef sen
                 }
 
                 if (deserialized is Persistent p)
-                    return (Persistent)p.WithTimestamp(entry.Ordering.Timestamp);
+                    return (Persistent)p.WithTimestamp(ToTicks(entry.Ordering));
 
-                return new Persistent(deserialized, entry.SequenceNr, entry.PersistenceId, entry.Manifest, entry.IsDeleted, sender, timestamp: entry.Ordering.Timestamp);
+                return new Persistent(deserialized, entry.SequenceNr, entry.PersistenceId, entry.Manifest, entry.IsDeleted, sender, timestamp: ToTicks(entry.Ordering));
             }
             else // backwards compat for object serialization - Payload was already deserialized by BSON
             {
                 return new Persistent(entry.Payload, entry.SequenceNr, entry.PersistenceId, entry.Manifest,
-                    entry.IsDeleted, sender, timestamp: entry.Ordering.Timestamp);
+                    entry.IsDeleted, sender, timestamp: ToTicks(entry.Ordering));
             }
 
         }