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