Revert "Adopt diffable data source for tracks"

This reverts commit 9015ce7.

App/Sources/Controllers/SearchController.swift

@@ -68,6 +68,7 @@ final class SearchController: UISplitViewController {
     tracksViewController.favoritesDelegate = self
     tracksViewController.indexDataSource = self
     tracksViewController.indexDelegate = self
+    tracksViewController.dataSource = self
     tracksViewController.delegate = self
     self.tracksViewController = tracksViewController
 
@@ -79,17 +80,56 @@ final class SearchController: UISplitViewController {
       viewControllers.append(makeWelcomeViewController())
     }
 
-    reloadTracks(animated: false)
+    reloadTracks()
     observer = dependencies.favoritesService.addObserverForTracks { [weak self] in
-      self?.reloadTracks(animated: true)
+      self?.reloadTracks()
     }
   }
 
-  private func reloadTracks(animated: Bool) {
+  private func reloadTracks() {
     dependencies.tracksService.loadConfiguration { [weak self] tracksConfiguration in
-      guard let self else { return }
+      self?.tracksLoadingDidSucceed(tracksConfiguration)
+    }
+  }
+
+  private func tracksLoadingDidSucceed(_ tracksConfiguration: TracksConfiguration) {
+    guard let currentTracksConfiguration = self.tracksConfiguration else {
+      self.tracksConfiguration = tracksConfiguration
+      tracksViewController?.reloadData()
+      return
+    }
+
+    let oldNonFavoriteTracks = currentTracksConfiguration.filteredTracks[selectedFilter]?.map(\.name) ?? []
+    let newNonFavoriteTracks = tracksConfiguration.filteredTracks[selectedFilter]?.map(\.name) ?? []
+    guard oldNonFavoriteTracks == newNonFavoriteTracks else {
+      self.tracksConfiguration = tracksConfiguration
+      tracksViewController?.reloadData()
+      return
+    }
+
+    var oldIdentifiers = currentTracksConfiguration.filteredFavoriteTracks[selectedFilter]?.map(\.name) ?? []
+    let newIdentifiers = tracksConfiguration.filteredFavoriteTracks[selectedFilter]?.map(\.name) ?? []
+    let deletesIdentifiers = Set(oldIdentifiers).subtracting(Set(newIdentifiers))
+    let insertsIdentifiers = Set(newIdentifiers).subtracting(Set(oldIdentifiers))
+
+    tracksViewController?.performBatchUpdates {
+      switch (oldIdentifiers.isEmpty, newIdentifiers.isEmpty) {
+      case (true, false): tracksViewController?.insertFavoritesSection()
+      case (false, true): tracksViewController?.deleteFavoritesSection()
+      default: break
+      }
+
+      for (index, track) in oldIdentifiers.enumerated().reversed() where deletesIdentifiers.contains(track) {
+        tracksViewController?.deleteFavorite(at: index)
+        oldIdentifiers.remove(at: index)
+      }
+
+      for (index, track) in newIdentifiers.enumerated() where insertsIdentifiers.contains(track) {
+        tracksViewController?.insertFavorite(at: index)
+        oldIdentifiers.insert(track, at: index)
+      }
+
       self.tracksConfiguration = tracksConfiguration
-      self.tracksViewController?.setSections(tracksSections, animatingDifferences: animated)
     }
   }
 }
@@ -105,7 +145,7 @@ extension SearchController: UISplitViewControllerDelegate {
   }
 }
 
-extension SearchController: TracksViewControllerDelegate {
+extension SearchController: TracksViewControllerDataSource, TracksViewControllerDelegate {
   private var filteredTracks: [Track] {
     tracksConfiguration?.filteredTracks[selectedFilter] ?? []
   }
@@ -118,25 +158,28 @@ extension SearchController: TracksViewControllerDelegate {
     !filteredFavoriteTracks.isEmpty
   }
 
-  var tracksSections: [TracksSection] {
-    var sections: [TracksSection] = []
-    if hasFavoriteTracks {
-      sections.append(
-        .init(
-          title: L10n.Search.Filter.favorites,
-          accessibilityIdentifier: "favorites",
-          tracks: filteredFavoriteTracks
-        )
-      )
-    }
-    sections.append(
-      .init(
-        title: selectedFilter.title,
-        accessibilityIdentifier: selectedFilter.accessibilityIdentifier,
-        tracks: filteredTracks
-      )
-    )
-    return sections
+  private func isFavoriteSection(_ section: Int) -> Bool {
+    section == 0 && hasFavoriteTracks
+  }
+
+  func numberOfSections(in _: TracksViewController) -> Int {
+    hasFavoriteTracks ? 2 : 1
+  }
+
+  func tracksViewController(_: TracksViewController, titleForSectionAt section: Int) -> String? {
+    isFavoriteSection(section) ? L10n.Search.Filter.favorites : selectedFilter.title
+  }
+
+  func tracksViewController(_: TracksViewController, accessibilityIdentifierForSectionAt section: Int) -> String? {
+    isFavoriteSection(section) ? "favorites" : selectedFilter.accessibilityIdentifier
+  }
+
+  func tracksViewController(_: TracksViewController, numberOfTracksIn section: Int) -> Int {
+    isFavoriteSection(section) ? filteredFavoriteTracks.count : filteredTracks.count
+  }
+
+  func tracksViewController(_: TracksViewController, trackAt indexPath: IndexPath) -> Track {
+    isFavoriteSection(indexPath.section) ? filteredFavoriteTracks[indexPath.row] : filteredTracks[indexPath.row]
   }
 
   func tracksViewController(_ tracksViewController: TracksViewController, didSelect track: Track) {
@@ -174,9 +217,8 @@ extension SearchController: TracksViewControllerDelegate {
     let filters = tracksConfiguration?.filters ?? []
     for filter in filters where filter != selectedFilter {
       let actionHandler: (UIAlertAction) -> Void = { [weak self] _ in
-        guard let self else { return }
-        self.selectedFilter = filter
-        self.tracksViewController?.setSections(tracksSections, animatingDifferences: false)
+        self?.selectedFilter = filter
+        self?.tracksViewController?.reloadData()
       }
       let action = UIAlertAction(title: filter.title, style: .default, handler: actionHandler)
       alertController.addAction(action)

App/Sources/Controllers/YearController.swift

@@ -9,6 +9,7 @@ final class YearController: TracksViewController {
   private weak var eventsViewController: EventsViewController?
   private var searchController: UISearchController?
 
+  private var tracks: [Track] = []
   private var events: [Event] = []
   var results: [Event] = []
 
@@ -32,6 +33,7 @@ final class YearController: TracksViewController {
     view.backgroundColor = .systemGroupedBackground
 
     delegate = self
+    dataSource = self
     definesPresentationContext = true
 
     let resultsViewController = EventsViewController(style: .grouped)
@@ -52,14 +54,27 @@ final class YearController: TracksViewController {
         case let .failure(error):
           self.didError?(self, error)
         case let .success(tracks):
-          self.setSections([.init(tracks: tracks)])
+          self.tracks = tracks
+          self.reloadData()
         }
       }
     }
   }
 }
 
-extension YearController: TracksViewControllerDelegate {
+extension YearController: TracksViewControllerDataSource, TracksViewControllerDelegate {
+  func numberOfSections(in _: TracksViewController) -> Int {
+    1
+  }
+
+  func tracksViewController(_: TracksViewController, numberOfTracksIn _: Int) -> Int {
+    tracks.count
+  }
+
+  func tracksViewController(_: TracksViewController, trackAt indexPath: IndexPath) -> Track {
+    tracks[indexPath.row]
+  }
+
   func tracksViewController(_ tracksViewController: TracksViewController, didSelect track: Track) {
     let eventsViewController = EventsViewController(style: .grouped)
     eventsViewController.title = track.formattedName

App/Sources/Models/Track.swift

@@ -10,12 +10,6 @@ extension Track: Equatable {
   }
 }
 
-extension Track: Hashable {
-  func hash(into hasher: inout Hasher) {
-    hasher.combine(name)
-  }
-}
-
 extension Track {
   var formattedName: String {
     TrackFormatter().formattedName(from: name)