feat: add PlaylistViewModel with reactive playlist observation

Music/ViewModels/PlaylistViewModel.swift

@@ -0,0 +1,122 @@
+import Foundation
+import Observation
+import GRDB
+
+@Observable
+final class PlaylistViewModel {
+    var playlists: [Playlist] = []
+    var selectedPlaylist: Playlist?
+    var playlistTracks: [Track] = []
+
+    var lastUsedPlaylistId: Int64? {
+        get { UserDefaults.standard.object(forKey: "lastUsedPlaylistId") as? Int64 }
+        set { UserDefaults.standard.set(newValue, forKey: "lastUsedPlaylistId") }
+    }
+
+    var lastUsedPlaylistName: String? {
+        guard let id = lastUsedPlaylistId else { return nil }
+        return playlists.first(where: { $0.id == id })?.name
+    }
+
+    private let db: DatabaseService
+    private var playlistsCancellable: AnyDatabaseCancellable?
+    private var tracksCancellable: AnyDatabaseCancellable?
+    private var searchTask: Task<Void, Never>?
+    private var searchText = ""
+
+    init(db: DatabaseService) {
+        self.db = db
+        observePlaylists()
+    }
+
+    func createPlaylist(name: String) throws {
+        _ = try db.createPlaylist(name: name)
+    }
+
+    func renamePlaylist(_ playlist: Playlist, to name: String) throws {
+        guard let id = playlist.id else { return }
+        try db.renamePlaylist(id: id, name: name)
+    }
+
+    func deletePlaylist(_ playlist: Playlist) throws {
+        guard let id = playlist.id else { return }
+        if selectedPlaylist?.id == id {
+            deselectPlaylist()
+        }
+        if lastUsedPlaylistId == id {
+            lastUsedPlaylistId = nil
+        }
+        try db.deletePlaylist(id: id)
+    }
+
+    func addTrack(_ track: Track, to playlist: Playlist) throws {
+        guard let trackId = track.id, let playlistId = playlist.id else { return }
+        try db.addTrackToPlaylist(trackId: trackId, playlistId: playlistId)
+        lastUsedPlaylistId = playlistId
+    }
+
+    func addTrackToLastUsedPlaylist(_ track: Track) throws {
+        guard let playlistId = lastUsedPlaylistId,
+              let playlist = playlists.first(where: { $0.id == playlistId }) else { return }
+        try addTrack(track, to: playlist)
+    }
+
+    func removeTrack(_ track: Track, from playlist: Playlist) throws {
+        guard let trackId = track.id, let playlistId = playlist.id else { return }
+        try db.removeTrackFromPlaylist(trackId: trackId, playlistId: playlistId)
+    }
+
+    func moveTrack(in playlist: Playlist, from source: Int, to destination: Int) throws {
+        guard let playlistId = playlist.id else { return }
+        try db.reorderPlaylistTrack(playlistId: playlistId, fromPosition: source, toPosition: destination)
+    }
+
+    func search(_ text: String) {
+        searchText = text
+        searchTask?.cancel()
+        searchTask = Task { @MainActor [weak self] in
+            try? await Task.sleep(for: .milliseconds(150))
+            guard !Task.isCancelled else { return }
+            self?.observePlaylistTracks()
+        }
+    }
+
+    func selectPlaylist(_ playlist: Playlist) {
+        selectedPlaylist = playlist
+        observePlaylistTracks()
+    }
+
+    func deselectPlaylist() {
+        selectedPlaylist = nil
+        tracksCancellable?.cancel()
+        tracksCancellable = nil
+        playlistTracks = []
+        searchText = ""
+    }
+
+    private func observePlaylists() {
+        let observation = ValueObservation.tracking { [db] dbAccess in
+            try db.fetchPlaylists(db: dbAccess)
+        }
+        playlistsCancellable = observation.start(
+            in: db.dbPool,
+            onError: { error in print("Playlists observation error: \(error)") },
+            onChange: { [weak self] playlists in self?.playlists = playlists }
+        )
+    }
+
+    private func observePlaylistTracks() {
+        tracksCancellable?.cancel()
+        guard let playlistId = selectedPlaylist?.id else { return }
+        let search = searchText
+
+        let observation = ValueObservation.tracking { [db] dbAccess in
+            try db.fetchPlaylistTracks(db: dbAccess, playlistId: playlistId, search: search)
+        }
+        tracksCancellable = observation.start(
+            in: db.dbPool,
+            onError: { error in print("Playlist tracks observation error: \(error)") },
+            onChange: { [weak self] tracks in self?.playlistTracks = tracks }
+        )
+    }
+}