STITCH-2211 Swift SDK: Create data models and implement local event coalescence

[jsflax]

"Port" the following classes:

InstanceSynchronization:

• InstanceSynchronization now acts as a container for an internal config (InstanceSynchronization.Config). This was due to the fact that the current Java equivalent can exist in a partial state, which is a no-go in Swift. It also cleans up a significant amount of the encoding/decoding code, which was cumbersome. IMO, we should make these changes on Java as well.
• Conformance to Sequence. Can iterate through NamespaceSynchronization.Configs.
• Subscript access. InstanceSynchronization subscript uses a mutating getter to either get existing NamespaceSynchronizations or will create new ones.

  NamespaceSynchronization

• See above for container information.
• Conformance to Sequence. Can iterate through CoreDocumentSynchronization.Configs.
• Subscript access. NamespaceSynchronization subscript will either fetch existing CoreDocumentSynchronization by id or can set new ones by id.

  CoreDocumentSynchronization

• See above for container information. Config properties are now private. The properties are exposed in the outlying struct CoreDocumentSynchronization as computed properties. These getters/setters are synchronized via a ReadWriteLock, with the setters mutating the underlying config.

  ChangeEvent

• OperationType has been moved out to its own enum.
  • The string values of each case are now implicit.
• transform (the method that converts a ChangeEvent with an associated type of Document to a user associated type) now takes on a more Swifty shape.

  UpdateDescription

• UpdateDescription has been moved out to its own class.
• Conversion to a Document is now computed lazily.
• diff is now a method extended to the Document class.

  ConflictHandler

• Uses associated types, which forces us to store locally using type erasure.

  ChangeEventListener

• Uses associated types, which forces us to store locally using type erasure.

  MongoNamespace

• Not sure why this class doesn't exist on MongoMobile. Simple port-over.

  DocumentVersionInfo

• nextVersionDocument is now lazily computed.

  ReadWriteLock

• Swift doesn't have a default RWLock, so this is a simple wrapper above pthread_rwlock_t.

Other additions, notable or otherwise:

• More comments.
• More tests.
• Take advantage of nullability and mutability.
• More Swift.

[jsflax]

Disregard that comment

On Thu 15 Nov 2018, 12:58 Jason Flax, notifications@github.com wrote:

@jsflax commented on this pull request.

In Core/Services/StitchCoreRemoteMongoDBService/Sources/StitchCoreRemoteMongoDBService/Sync/CoreDocumentSynchronizationConfig.swift https://github.com/mongodb/stitch-ios-sdk/pull/103#discussion_r233948518 :

• locally emitted change event. This variant maintains the last version set.
• • parameter atTime: the time at which the write occurred.
• • parameter changeEvent: the description of the write/change.
• */
• mutating func setSomePendingWrites(atTime: TimeInterval,
• changeEvent: ChangeEvent) {
• // if we were frozen
• if (isPaused) {
• // unfreeze the document due to the local write
• isPaused = false
• // and now the unfrozen document is now stale
• isStale = true
• }
• docLock.writeLock()

I ported over what happens on Android and assumed we had a reason for doing it this way. @edaniels https://github.com/edaniels?

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[jsflax]

@adamchel @dkaminsky I think we should kick the versioning changes downfield until we get to that ticket. I've laid down the base model which arguably was in scope for this one.

Otherwise, I've addressed your remarks. PTAL.