292 lines
13 KiB
Swift
292 lines
13 KiB
Swift
//
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// ThreadViewModel+Diffable.swift
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// Mastodon
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//
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// Created by MainasuK Cirno on 2021-4-12.
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//
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import UIKit
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import Combine
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import CoreData
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import CoreDataStack
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import MastodonCore
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import MastodonUI
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import MastodonSDK
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extension ThreadViewModel {
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@MainActor
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func setupDiffableDataSource(
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tableView: UITableView,
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statusTableViewCellDelegate: StatusTableViewCellDelegate
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) {
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diffableDataSource = StatusSection.diffableDataSource(
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tableView: tableView,
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context: context,
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configuration: StatusSection.Configuration(
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context: context,
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authContext: authContext,
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statusTableViewCellDelegate: statusTableViewCellDelegate,
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timelineMiddleLoaderTableViewCellDelegate: nil,
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filterContext: .thread,
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activeFilters: context.statusFilterService.$activeFilters
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)
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)
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// make initial snapshot animation smooth
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var snapshot = NSDiffableDataSourceSnapshot<StatusSection, StatusItem>()
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snapshot.appendSections([.main])
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if let root = self.root {
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if case let .root(threadContext) = root,
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let status = threadContext.status.object(in: context.managedObjectContext),
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status.inReplyToID != nil
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{
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snapshot.appendItems([.topLoader], toSection: .main)
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}
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snapshot.appendItems([.thread(root)], toSection: .main)
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} else {
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}
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diffableDataSource?.apply(snapshot, animatingDifferences: false)
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$threadContext
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.receive(on: DispatchQueue.main)
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.sink { [weak self] threadContext in
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guard let self = self else { return }
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guard let _ = threadContext else {
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return
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}
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self.loadThreadStateMachine.enter(LoadThreadState.Loading.self)
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}
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.store(in: &disposeBag)
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Publishers.CombineLatest3(
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$root,
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mastodonStatusThreadViewModel.$ancestors,
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mastodonStatusThreadViewModel.$descendants
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)
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.throttle(for: 1, scheduler: DispatchQueue.main, latest: true)
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.sink { [weak self] root, ancestors, descendants in
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guard let self = self else { return }
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guard let diffableDataSource = self.diffableDataSource else { return }
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Task { @MainActor in
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let oldSnapshot = diffableDataSource.snapshot()
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var newSnapshot = NSDiffableDataSourceSnapshot<StatusSection, StatusItem>()
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newSnapshot.appendSections([.main])
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// top loader
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let _hasReplyTo: Bool? = try? await self.context.managedObjectContext.perform {
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guard case let .root(threadContext) = root else { return nil }
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guard let status = threadContext.status.object(in: self.context.managedObjectContext) else { return nil }
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return status.inReplyToID != nil
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}
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if let hasReplyTo = _hasReplyTo, hasReplyTo {
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let state = self.loadThreadStateMachine.currentState
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if state is LoadThreadState.NoMore {
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// do nothing
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} else {
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newSnapshot.appendItems([.topLoader], toSection: .main)
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}
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}
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// replies
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newSnapshot.appendItems(ancestors.reversed(), toSection: .main)
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// root
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if let root = root {
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let item = StatusItem.thread(root)
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newSnapshot.appendItems([item], toSection: .main)
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}
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// leafs
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newSnapshot.appendItems(descendants, toSection: .main)
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// bottom loader
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if let currentState = self.loadThreadStateMachine.currentState {
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switch currentState {
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case is LoadThreadState.Initial,
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is LoadThreadState.Loading,
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is LoadThreadState.Fail:
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newSnapshot.appendItems([.bottomLoader], toSection: .main)
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default:
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break
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}
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}
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let hasChanges = newSnapshot.itemIdentifiers != oldSnapshot.itemIdentifiers
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if !hasChanges {
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self.logger.log(level: .debug, "\((#file as NSString).lastPathComponent, privacy: .public)[\(#line, privacy: .public)], \(#function, privacy: .public): snapshot not changes")
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return
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} else {
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self.logger.log(level: .debug, "\((#file as NSString).lastPathComponent, privacy: .public)[\(#line, privacy: .public)], \(#function, privacy: .public): snapshot has changes")
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}
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guard let difference = self.calculateReloadSnapshotDifference(
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tableView: tableView,
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oldSnapshot: oldSnapshot,
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newSnapshot: newSnapshot
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) else {
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await self.updateDataSource(snapshot: newSnapshot, animatingDifferences: false)
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self.logger.log(level: .debug, "\((#file as NSString).lastPathComponent, privacy: .public)[\(#line, privacy: .public)], \(#function, privacy: .public): applied new snapshot without tweak")
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return
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}
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self.logger.log(level: .debug, "\((#file as NSString).lastPathComponent, privacy: .public)[\(#line, privacy: .public)], \(#function, privacy: .public): [Snapshot] oldSnapshot: \(oldSnapshot.itemIdentifiers.debugDescription)")
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self.logger.log(level: .debug, "\((#file as NSString).lastPathComponent, privacy: .public)[\(#line, privacy: .public)], \(#function, privacy: .public): [Snapshot] newSnapshot: \(newSnapshot.itemIdentifiers.debugDescription)")
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await self.updateSnapshotUsingReloadData(
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tableView: tableView,
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oldSnapshot: oldSnapshot,
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newSnapshot: newSnapshot,
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difference: difference
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)
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} // end Task
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}
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.store(in: &disposeBag)
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}
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}
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extension ThreadViewModel {
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@MainActor func updateDataSource(
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snapshot: NSDiffableDataSourceSnapshot<StatusSection, StatusItem>,
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animatingDifferences: Bool
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) async {
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diffableDataSource?.apply(snapshot, animatingDifferences: animatingDifferences)
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}
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@MainActor func updateSnapshotUsingReloadData(
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snapshot: NSDiffableDataSourceSnapshot<StatusSection, StatusItem>
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) async {
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if #available(iOS 15.0, *) {
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await self.diffableDataSource?.applySnapshotUsingReloadData(snapshot)
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} else {
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diffableDataSource?.applySnapshot(snapshot, animated: false, completion: nil)
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}
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}
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// Some UI tweaks to present replies and conversation smoothly
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@MainActor private func updateSnapshotUsingReloadData(
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tableView: UITableView,
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oldSnapshot: NSDiffableDataSourceSnapshot<StatusSection, StatusItem>,
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newSnapshot: NSDiffableDataSourceSnapshot<StatusSection, StatusItem>,
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difference: ThreadViewModel.Difference // <StatusItem>
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) async {
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let replies: [StatusItem] = {
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newSnapshot.itemIdentifiers.filter { item in
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guard case let .thread(thread) = item else { return false }
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guard case .reply = thread else { return false }
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return true
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}
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}()
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// additional margin for .topLoader
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let oldTopMargin: CGFloat = {
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let marginHeight = TimelineTopLoaderTableViewCell.cellHeight
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if oldSnapshot.itemIdentifiers.contains(.topLoader) || !replies.isEmpty {
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return marginHeight
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}
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return .zero
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}()
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await self.updateSnapshotUsingReloadData(snapshot: newSnapshot)
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// note:
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// tweak the content offset and bottom inset
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// make the table view stable when data reload
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// the keypoint is set the bottom inset to make the root padding with "TopLoaderHeight" to top edge
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// and restore the "TopLoaderHeight" when bottom inset adjusted
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// set bottom inset. Make root item pin to top.
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if let item = root.flatMap({ StatusItem.thread($0) }),
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let index = newSnapshot.indexOfItem(item),
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let cell = tableView.cellForRow(at: IndexPath(row: index, section: 0))
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{
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// always set bottom inset due to lazy reply loading
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// otherwise tableView will jump when insert replies
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let bottomSpacing = tableView.safeAreaLayoutGuide.layoutFrame.height - cell.frame.height - oldTopMargin
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let additionalInset = round(tableView.contentSize.height - cell.frame.maxY)
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tableView.contentInset.bottom = max(0, bottomSpacing - additionalInset)
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self.logger.log(level: .debug, "\((#file as NSString).lastPathComponent, privacy: .public)[\(#line, privacy: .public)], \(#function, privacy: .public): content inset bottom: \(tableView.contentInset.bottom)")
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}
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// set scroll position
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tableView.scrollToRow(at: difference.targetIndexPath, at: .top, animated: false)
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tableView.contentOffset.y = {
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var offset: CGFloat = tableView.contentOffset.y - difference.sourceDistanceToTableViewTopEdge
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if tableView.contentInset.bottom != 0.0 {
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// needs restore top margin if bottom inset adjusted
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offset += oldTopMargin
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}
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return offset
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}()
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self.logger.log(level: .debug, "\((#file as NSString).lastPathComponent, privacy: .public)[\(#line, privacy: .public)], \(#function, privacy: .public): applied new snapshot")
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}
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}
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extension ThreadViewModel {
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struct Difference {
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let item: StatusItem
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let sourceIndexPath: IndexPath
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let sourceDistanceToTableViewTopEdge: CGFloat
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let targetIndexPath: IndexPath
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}
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@MainActor private func calculateReloadSnapshotDifference(
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tableView: UITableView,
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oldSnapshot: NSDiffableDataSourceSnapshot<StatusSection, StatusItem>,
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newSnapshot: NSDiffableDataSourceSnapshot<StatusSection, StatusItem>
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) -> Difference? {
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guard oldSnapshot.numberOfItems != 0 else { return nil }
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guard let indexPathsForVisibleRows = tableView.indexPathsForVisibleRows?.sorted() else { return nil }
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// find index of the first visible item in both old and new snapshot
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var _index: Int?
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let items = oldSnapshot.itemIdentifiers(inSection: .main)
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for (i, item) in items.enumerated() {
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guard let indexPath = indexPathsForVisibleRows.first(where: { $0.row == i }) else { continue }
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guard newSnapshot.indexOfItem(item) != nil else { continue }
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let rectForCell = tableView.rectForRow(at: indexPath)
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let distanceToTableViewTopEdge = tableView.convert(rectForCell, to: nil).origin.y - tableView.safeAreaInsets.top
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guard distanceToTableViewTopEdge >= 0 else { continue }
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_index = i
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break
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}
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guard let index = _index else { return nil }
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let sourceIndexPath = IndexPath(row: index, section: 0)
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let rectForSourceItemCell = tableView.rectForRow(at: sourceIndexPath)
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let sourceDistanceToTableViewTopEdge: CGFloat = {
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if tableView.window != nil {
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return tableView.convert(rectForSourceItemCell, to: nil).origin.y - tableView.safeAreaInsets.top
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} else {
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return rectForSourceItemCell.origin.y - tableView.contentOffset.y - tableView.safeAreaInsets.top
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}
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}()
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guard sourceIndexPath.section < oldSnapshot.numberOfSections,
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sourceIndexPath.row < oldSnapshot.numberOfItems(inSection: oldSnapshot.sectionIdentifiers[sourceIndexPath.section])
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else { return nil }
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let sectionIdentifier = oldSnapshot.sectionIdentifiers[sourceIndexPath.section]
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let item = oldSnapshot.itemIdentifiers(inSection: sectionIdentifier)[sourceIndexPath.row]
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guard let targetIndexPathRow = newSnapshot.indexOfItem(item),
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let newSectionIdentifier = newSnapshot.sectionIdentifier(containingItem: item),
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let targetIndexPathSection = newSnapshot.indexOfSection(newSectionIdentifier)
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else { return nil }
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let targetIndexPath = IndexPath(row: targetIndexPathRow, section: targetIndexPathSection)
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return Difference(
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item: item,
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sourceIndexPath: sourceIndexPath,
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sourceDistanceToTableViewTopEdge: sourceDistanceToTableViewTopEdge,
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targetIndexPath: targetIndexPath
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)
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}
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}
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