Handle all CRUD work in updateCollections

app/src/main/kotlin/at/bitfire/davdroid/sync/Syncer.kt

@@ -96,17 +96,13 @@ abstract class Syncer<CollectionType: LocalCollection<*>>(
 
  // Find collections in database and provider which should be synced (are sync-enabled)
  val dbCollections = getSyncEnabledCollections()
- val localCollections = getLocalCollections(provider).toMutableList()
+ val localCollections = getLocalCollections(provider)
 
- // Update/delete local collections and determine new (unknown) remote collections
- val newDbCollections = updateCollections(localCollections, dbCollections)
-
- // Create new local collections for newly found remote collections
- val newProviderCollections = createLocalCollections(provider, newDbCollections)
- localCollections.addAll(newProviderCollections) // Add the newly created collections
+ // Create/update/delete local collections according to DB
+ val updatedLocalCollections = updateCollections(provider, localCollections, dbCollections)
 
  // Sync local collection contents (events, contacts, tasks)
- syncCollectionContents(provider, localCollections, dbCollections)
+ syncCollectionContents(provider, updatedLocalCollections, dbCollections)
  }
 
  /**
@@ -128,53 +124,60 @@ abstract class Syncer<CollectionType: LocalCollection<*>>(
  /**
  * Updates and deletes local collections. Specifically:
  *
- * - Deletes local collections if corresponding database collections are missing. If
- * a local collection is removed because it's not in [dbCollections], **it becomes also removed from [localCollections]!**
- *
+ * - Deletes local collections if corresponding database collections are missing.
  * - Updates local collections with possibly new info from corresponding database collections.
  * - Determines new database collections to be also created as local collections.
  *
- * @param localCollections The local collections to be updated or deleted. May be modified by this method.
+ * @param localCollections The local collections to be updated or deleted.
  * @param dbCollections The database collections possibly containing new information
  *
  * @return New found database collections to be created in provider
  */
  @VisibleForTesting
  internal fun updateCollections(
- localCollections: MutableList<CollectionType>,
+ provider: ContentProviderClient,
+ localCollections: List<CollectionType>,
  dbCollections: Map<HttpUrl, Collection>
- ): HashMap<HttpUrl, Collection> {
- val newDbCollections = HashMap(dbCollections) // create a copy
+ ): List<CollectionType> {
+ // create mutable copies of input
+ val newLocalCollections = localCollections.toMutableList()
+ val newDbCollections = dbCollections.toMutableMap()
+
  for (localCollection in localCollections) {
  val dbCollection = dbCollections[localCollection.collectionUrl?.toHttpUrlOrNull()]
  if (dbCollection == null) {
- // Collection not available in db = on server (anymore), delete obsolete local collection
+ // Collection not available in db = on server (anymore), delete
  logger.info("Deleting local collection ${localCollection.title}")
  localCollection.deleteCollection()
- localCollections -= localCollection
+ newLocalCollections -= localCollection
  } else {
  // Collection exists locally, update local collection and remove it from "to be created" map
  update(localCollection, dbCollection)
  newDbCollections -= dbCollection.url
  }
  }
- return newDbCollections
+
+ // Create local collections which are in DB, but don't exist locally yet
+ val newProviderCollections = createLocalCollections(provider, newDbCollections.values.toList())
+ newLocalCollections.addAll(newProviderCollections) // Add the newly created collections
+
+ return newLocalCollections
  }
 
  /**
  * Creates new local collections from database collections.
  *
  * @param provider Content provider client to access local collections.
  * @param dbCollections Database collections to be created as local collections.
+ *
  * @return Newly created local collections.
  */
  @VisibleForTesting
  internal fun createLocalCollections(
  provider: ContentProviderClient,
- dbCollections: Map<HttpUrl, Collection>
+ dbCollections: List<Collection>
  ): List<CollectionType> =
- dbCollections.map { (_, collection) -> create(provider, collection) }
-
+ dbCollections.map { collection -> create(provider, collection) }
 
  /**
  * Synchronize the actual collection contents.