mastodon-ios/Mastodon/Scene/Notification/NotificationViewModel+diffa...

128 lines
5.6 KiB
Swift

//
// NotificationViewModel+diffable.swift
// Mastodon
//
// Created by sxiaojian on 2021/4/13.
//
import CoreData
import CoreDataStack
import os.log
import UIKit
extension NotificationViewModel {
func setupDiffableDataSource(
for tableView: UITableView,
delegate: NotificationTableViewCellDelegate,
dependency: NeedsDependency
) {
let timestampUpdatePublisher = Timer.publish(every: 30.0, on: .main, in: .common)
.autoconnect()
.share()
.eraseToAnyPublisher()
guard let userid = activeMastodonAuthenticationBox.value?.userID else {
return
}
diffableDataSource = NotificationSection.tableViewDiffableDataSource(
for: tableView,
timestampUpdatePublisher: timestampUpdatePublisher,
managedObjectContext: context.managedObjectContext,
delegate: delegate,
dependency: dependency,
requestUserID: userid
)
}
}
extension NotificationViewModel: NSFetchedResultsControllerDelegate {
func controllerWillChangeContent(_ controller: NSFetchedResultsController<NSFetchRequestResult>) {
os_log("%{public}s[%{public}ld], %{public}s", (#file as NSString).lastPathComponent, #line, #function)
}
func controller(_ controller: NSFetchedResultsController<NSFetchRequestResult>, didChangeContentWith snapshot: NSDiffableDataSourceSnapshotReference) {
os_log("%{public}s[%{public}ld], %{public}s", (#file as NSString).lastPathComponent, #line, #function)
guard let tableView = self.tableView else { return }
guard let navigationBar = contentOffsetAdjustableTimelineViewControllerDelegate?.navigationBar() else { return }
guard let diffableDataSource = self.diffableDataSource else { return }
let oldSnapshot = diffableDataSource.snapshot()
let predicate = fetchedResultsController.fetchRequest.predicate
let parentManagedObjectContext = fetchedResultsController.managedObjectContext
let managedObjectContext = NSManagedObjectContext(concurrencyType: .privateQueueConcurrencyType)
managedObjectContext.parent = parentManagedObjectContext
managedObjectContext.perform {
let notifications: [MastodonNotification] = {
let request = MastodonNotification.sortedFetchRequest
request.returnsObjectsAsFaults = false
request.predicate = predicate
do {
return try managedObjectContext.fetch(request)
} catch {
assertionFailure(error.localizedDescription)
return []
}
}()
var newSnapshot = NSDiffableDataSourceSnapshot<NotificationSection, NotificationItem>()
newSnapshot.appendSections([.main])
newSnapshot.appendItems(notifications.map { NotificationItem.notification(objectID: $0.objectID) }, toSection: .main)
if !notifications.isEmpty, self.noMoreNotification.value == false {
newSnapshot.appendItems([.bottomLoader], toSection: .main)
}
DispatchQueue.main.async {
guard let difference = self.calculateReloadSnapshotDifference(navigationBar: navigationBar, tableView: tableView, oldSnapshot: oldSnapshot, newSnapshot: newSnapshot) else {
diffableDataSource.apply(newSnapshot)
self.isFetchingLatestNotification.value = false
return
}
diffableDataSource.apply(newSnapshot, animatingDifferences: false) {
tableView.scrollToRow(at: difference.targetIndexPath, at: .top, animated: false)
tableView.contentOffset.y = tableView.contentOffset.y - difference.offset
self.isFetchingLatestNotification.value = false
}
}
}
}
private struct Difference<T> {
let item: T
let sourceIndexPath: IndexPath
let targetIndexPath: IndexPath
let offset: CGFloat
}
private func calculateReloadSnapshotDifference<T: Hashable>(
navigationBar: UINavigationBar,
tableView: UITableView,
oldSnapshot: NSDiffableDataSourceSnapshot<NotificationSection, T>,
newSnapshot: NSDiffableDataSourceSnapshot<NotificationSection, T>
) -> Difference<T>? {
guard oldSnapshot.numberOfItems != 0 else { return nil }
// old snapshot not empty. set source index path to first item if not match
let sourceIndexPath = UIViewController.topVisibleTableViewCellIndexPath(in: tableView, navigationBar: navigationBar) ?? IndexPath(row: 0, section: 0)
guard sourceIndexPath.row < oldSnapshot.itemIdentifiers(inSection: .main).count else { return nil }
if oldSnapshot.itemIdentifiers.elementsEqual(newSnapshot.itemIdentifiers) {
return nil
}
let timelineItem = oldSnapshot.itemIdentifiers(inSection: .main)[sourceIndexPath.row]
guard let itemIndex = newSnapshot.itemIdentifiers(inSection: .main).firstIndex(of: timelineItem) else { return nil }
let targetIndexPath = IndexPath(row: itemIndex, section: 0)
let offset = UIViewController.tableViewCellOriginOffsetToWindowTop(in: tableView, at: sourceIndexPath, navigationBar: navigationBar)
return Difference(
item: timelineItem,
sourceIndexPath: sourceIndexPath,
targetIndexPath: targetIndexPath,
offset: offset
)
}
}