Add reference counting for accounts

Closes #97

Tusker/Controllers/MastodonController.swift

@@ -84,11 +84,19 @@ class MastodonController {
             run(request) { response in
                 guard case let .success(account, _) = response else { fatalError() }
                 self.account = account
-                self.persistentContainer.addOrUpdate(account: account)
+                self.persistentContainer.backgroundContext.perform {
+                    if let accountMO = self.persistentContainer.account(for: account.id, in: self.persistentContainer.backgroundContext) {
+                        accountMO.updateFrom(apiAccount: account, container: self.persistentContainer)
+                    } else {
+                        // the first time the user's account is added to the store,
+                        // increment its reference count so that it's never removed
+                        self.persistentContainer.addOrUpdate(account: account, incrementReferenceCount: true)
+                    }
                     completion?(account)
                 }
             }
         }
+    }
     
     func getOwnInstance(completion: ((Instance) -> Void)? = nil) {
         if let instance = self.instance {

Tusker/CoreData/AccountMO.swift

@@ -32,6 +32,7 @@ public final class AccountMO: NSManagedObject, AccountProtocol {
     @NSManaged public var locked: Bool
     @NSManaged public var movedCD: Bool
     @NSManaged public var note: String
+    @NSManaged public var referenceCount: Int
     @NSManaged public var statusesCount: Int
     @NSManaged public var url: URL
     @NSManaged public var username: String
@@ -46,12 +47,30 @@ public final class AccountMO: NSManagedObject, AccountProtocol {
     public var bot: Bool? { botCD }
     public var moved: Bool? { movedCD }
     
+    func incrementReferenceCount() {
+        referenceCount += 1
+    }
+    
+    func decrementReferenceCount() {
+        referenceCount -= 1
+        if referenceCount <= 0 {
+            managedObjectContext!.delete(self)
+        }
+    }
+    
+    public override func prepareForDeletion() {
+        super.prepareForDeletion()
+        movedTo?.decrementReferenceCount()
+    }
+
 }
 
 extension AccountMO {
     convenience init(apiAccount account: Pachyderm.Account, container: MastodonCachePersistentStore, context: NSManagedObjectContext) {
         self.init(context: context)
         self.updateFrom(apiAccount: account, container: container)
+        
+        movedTo?.incrementReferenceCount()
     }
     
     func updateFrom(apiAccount account: Pachyderm.Account, container: MastodonCachePersistentStore) {

Tusker/CoreData/MastodonCachePersistentStore.swift

@@ -105,18 +105,25 @@ class MastodonCachePersistentStore: NSPersistentContainer {
     }
     
     @discardableResult
-    private func upsert(account: Account) -> AccountMO {
+    private func upsert(account: Account, incrementReferenceCount: Bool) -> AccountMO {
         if let accountMO = self.account(for: account.id, in: self.backgroundContext) {
             accountMO.updateFrom(apiAccount: account, container: self)
+            if incrementReferenceCount {
+                accountMO.incrementReferenceCount()
+            }
             return accountMO
         } else {
-            return AccountMO(apiAccount: account, container: self, context: self.backgroundContext)
+            let accountMO = AccountMO(apiAccount: account, container: self, context: self.backgroundContext)
+            if incrementReferenceCount {
+                accountMO.incrementReferenceCount()
+            }
+            return accountMO
         }
     }
     
-    func addOrUpdate(account: Account, completion: ((AccountMO) -> Void)? = nil) {
+    func addOrUpdate(account: Account, incrementReferenceCount: Bool, completion: ((AccountMO) -> Void)? = nil) {
         backgroundContext.perform {
-            let accountMO = self.upsert(account: account)
+            let accountMO = self.upsert(account: account, incrementReferenceCount: incrementReferenceCount)
             if self.backgroundContext.hasChanges {
                 try! self.backgroundContext.save()
             }
@@ -127,7 +134,7 @@ class MastodonCachePersistentStore: NSPersistentContainer {
     
     func addAll(accounts: [Account], completion: (() -> Void)? = nil) {
         backgroundContext.perform {
-            accounts.forEach { self.upsert(account: $0) }
+            accounts.forEach { self.upsert(account: $0, incrementReferenceCount: true) }
             if self.backgroundContext.hasChanges {
                 try! self.backgroundContext.save()
             }
@@ -139,9 +146,11 @@ class MastodonCachePersistentStore: NSPersistentContainer {
     func addAll(notifications: [Pachyderm.Notification], completion: (() -> Void)? = nil) {
         backgroundContext.perform {
             let statuses = notifications.compactMap { $0.status }
-            let accounts = notifications.map { $0.account }
+            // filter out mentions, otherwise we would double increment the reference count of those accounts
+            // since the status has the same account as the notification
+            let accounts = notifications.filter { $0.kind != .mention }.map { $0.account }
             statuses.forEach { self.upsert(status: $0, incrementReferenceCount: true) }
-            accounts.forEach { self.upsert(account: $0) }
+            accounts.forEach { self.upsert(account: $0, incrementReferenceCount: true) }
             if self.backgroundContext.hasChanges {
                 try! self.backgroundContext.save()
             }
@@ -157,7 +166,7 @@ class MastodonCachePersistentStore: NSPersistentContainer {
             var updatedStatuses = [String]()
             
             block(self.backgroundContext, { (accounts) in
-                accounts.forEach { self.upsert(account: $0) }
+                accounts.forEach { self.upsert(account: $0, incrementReferenceCount: true) }
                 updatedAccounts.append(contentsOf: accounts.map { $0.id })
             }, { (statuses) in
                 statuses.forEach { self.upsert(status: $0, incrementReferenceCount: true) }

Tusker/CoreData/StatusMO.swift

@@ -82,6 +82,7 @@ public final class StatusMO: NSManagedObject, StatusProtocol {
     public override func prepareForDeletion() {
         super.prepareForDeletion()
         reblog?.decrementReferenceCount()
+        account.decrementReferenceCount()
     }
 
 }
@@ -92,6 +93,7 @@ extension StatusMO {
         self.updateFrom(apiStatus: status, container: container)
         
         reblog?.incrementReferenceCount()
+        account.incrementReferenceCount()
     }
     
     func updateFrom(apiStatus status: Pachyderm.Status, container: MastodonCachePersistentStore) {

Tusker/CoreData/Tusker.xcdatamodeld/Tusker.xcdatamodel/contents

@@ -15,6 +15,7 @@
         <attribute name="locked" attributeType="Boolean" usesScalarValueType="YES"/>
         <attribute name="movedCD" optional="YES" attributeType="Boolean" usesScalarValueType="YES"/>
         <attribute name="note" attributeType="String"/>
+        <attribute name="referenceCount" optional="YES" attributeType="Integer 64" defaultValueString="0" usesScalarValueType="YES"/>
         <attribute name="statusesCount" attributeType="Integer 64" defaultValueString="0" usesScalarValueType="YES"/>
         <attribute name="url" attributeType="URI"/>
         <attribute name="username" attributeType="String"/>
@@ -49,7 +50,6 @@
         <attribute name="uri" attributeType="String"/>
         <attribute name="url" optional="YES" attributeType="URI"/>
         <attribute name="visibilityString" attributeType="String"/>
-
         <relationship name="account" maxCount="1" deletionRule="Nullify" destinationEntity="Account"/>
         <relationship name="reblog" optional="YES" maxCount="1" deletionRule="Nullify" destinationEntity="Status"/>
         <uniquenessConstraints>
@@ -59,7 +59,7 @@
         </uniquenessConstraints>
     </entity>
     <elements>
-        <element name="Account" positionX="169.21875" positionY="78.9609375" width="128" height="313"/>
+        <element name="Account" positionX="169.21875" positionY="78.9609375" width="128" height="328"/>
         <element name="Status" positionX="-63" positionY="-18" width="128" height="418"/>
     </elements>
 </model>

Tusker/Screens/Profile/ProfileTableViewController.swift

@@ -61,6 +61,15 @@ class ProfileTableViewController: EnhancedTableViewController {
         fatalError("init(coder:) has not been implemeneted")
     }
     
+    deinit {
+        if let id = accountID {
+            let container = mastodonController.persistentContainer
+            container.backgroundContext.perform {
+                container.account(for: id, in: container.backgroundContext)?.decrementReferenceCount()
+            }
+        }
+    }
+    
     override func viewDidLoad() {
         super.viewDidLoad()
 
@@ -90,7 +99,7 @@ class ProfileTableViewController: EnhancedTableViewController {
                         }
                         return
                     }
-                    self.mastodonController.persistentContainer.addOrUpdate(account: account) { (_) in
+                    self.mastodonController.persistentContainer.addOrUpdate(account: account, incrementReferenceCount: true) { (_) in
                         DispatchQueue.main.async {
                             self.updateAccountUI()
                             self.tableView.reloadData()

Tusker/Screens/Search/SearchResultsViewController.swift

@@ -134,11 +134,10 @@ class SearchResultsViewController: EnhancedTableViewController {
             var snapshot = NSDiffableDataSourceSnapshot<Section, Item>()
             
             self.mastodonController.persistentContainer.performBatchUpdates({ (context, addAccounts, addStatuses) in
-                // todo: reference count accounts
+                oldSnapshot.itemIdentifiers(inSection: .accounts).forEach { (item) in
-//                oldSnapshot.itemIdentifiers(inSection: .accounts).forEach { (item) in
+                    guard case let .account(id) = item else { return }
-//                    guard case let .account(id) = item else { return }
+                    self.mastodonController.persistentContainer.account(for: id, in: context)?.decrementReferenceCount()
-//                    self.mastodonController.persistentContainer.account(for: id, in: context)?.decrementReferenceCount()
+                }
-//                }
                 
                 oldSnapshot.itemIdentifiers(inSection: .statuses).forEach { (item) in
                     guard case let .status(id, _) = item else { return }

Tusker/Screens/Status Action Account List/StatusActionAccountListTableViewController.swift

@@ -58,6 +58,17 @@ class StatusActionAccountListTableViewController: EnhancedTableViewController {
         fatalError("init(coder:) has not been implemented")
     }
     
+    deinit {
+        if let accountIDs = self.accountIDs {
+            let container = self.mastodonController.persistentContainer
+            container.backgroundContext.perform {
+                for id in accountIDs {
+                    container.account(for: id, in: container.backgroundContext)?.decrementReferenceCount()
+                }
+            }
+        }
+    }
+    
     override func viewDidLoad() {
         super.viewDidLoad()
 
@@ -71,7 +82,11 @@ class StatusActionAccountListTableViewController: EnhancedTableViewController {
         
         tableView.tableHeaderView = UIView(frame: CGRect(x: 0, y: 0, width: 0, height: CGFloat.leastNormalMagnitude))
         
-        if accountIDs == nil {
+        if let accountIDs = accountIDs {
+            accountIDs.forEach { (id) in
+                self.mastodonController.persistentContainer.account(for: id)?.incrementReferenceCount()
+            }
+        } else {
             // account IDs haven't been set, so perform a request to load them
             guard let status = mastodonController.persistentContainer.status(for: statusID) else {
                 fatalError("Missing cached status \(statusID)")