ipodderx-app/ios/Sources/Playback.swift

import AVFoundation
import Foundation
import MediaPlayer

/// The host's player: the one CarPlay and a car's own buttons can reach, and the one that keeps
/// going when the screen locks. Knows nothing about the web view -- the bridge drives it, and so
/// will a CarPlay scene.
final class Playback: NSObject {
    /// What is loaded, enough to keep the car's screen right and to save a position without
    /// asking anyone.
    struct Item {
        var url: URL
        var feedId: String
        var guid: String
        var title: String
        var feedTitle: String
        var artwork: String?
        var position: Int
        var duration: Int?
    }

    /// Where playback state goes: the web page, through the bridge. A CarPlay scene would take
    /// the same callbacks.
    var onTime: ((Double, Double?) -> Void)?
    var onMeta: ((Double) -> Void)?
    var onState: ((Bool) -> Void)?
    var onEnded: (() -> Void)?
    var onError: ((String) -> Void)?

    private let cookies: CookieBridge
    private let library: Library
    private var player: AVPlayer?
    private var item: Item?
    private var timeObserver: Any?
    private var statusObservation: NSKeyValueObservation?
    private var lastSaved: Double = 0
    private var markedRead = false

    var isPlaying: Bool { player?.timeControlStatus == .playing }
    var currentTime: Double { player?.currentTime().seconds ?? 0 }
    var duration: Double? {
        guard let d = player?.currentItem?.duration.seconds, d.isFinite, d > 0 else { return nil }
        return d
    }

    init(cookies: CookieBridge, library: Library) {
        self.cookies = cookies
        self.library = library
        super.init()
        configureSession()
        wireRemoteCommands()
    }

    /// `.spokenAudio` is the podcast mode: it is what tells the system this is speech, so the
    /// right thing happens when navigation talks over it.
    private func configureSession() {
        do {
            try AVAudioSession.sharedInstance().setCategory(.playback, mode: .spokenAudio, policy: .longFormAudio)
        } catch {
            NSLog("ipx: audio session: %@", error.localizedDescription)
        }
    }

    // MARK: - what the page asks for

    func load(_ item: Item) {
        stop(notify: false)
        self.item = item
        self.markedRead = false
        self.lastSaved = 0

        // The session cookie is how ipx knows who is asking, and an AVURLAsset does not read the
        // shared store on its own.
        let asset = AVURLAsset(url: item.url, options: [
            AVURLAssetHTTPCookiesKey: cookies.cookies(for: item.url),
        ])
        let playerItem = AVPlayerItem(asset: asset)
        let player = AVPlayer(playerItem: playerItem)
        // Seeking has to land where it was asked to: the default tolerance snaps to keyframes,
        // which on a long episode is minutes away from where you let go of the scrubber.
        player.automaticallyWaitsToMinimizeStalling = true
        self.player = player

        // Whose position this is belongs to the page, on loadedmetadata, so one piece of code
        // decides it. Here we only report that the length is known.
        statusObservation = playerItem.observe(\.status, options: [.new]) { [weak self] pi, _ in
            guard let self else { return }
            switch pi.status {
            case .readyToPlay:
                if let d = self.duration { self.onMeta?(d) }
            case .failed:
                let msg = pi.error?.localizedDescription ?? "the file could not be played"
                self.library.check { good in
                    DispatchQueue.main.async { self.onError?(good ? msg : "sign in again") }
                }
            default: break
            }
        }

        timeObserver = player.addPeriodicTimeObserver(
            forInterval: CMTime(seconds: 0.5, preferredTimescale: 600), queue: .main
        ) { [weak self] t in self?.tick(t.seconds) }

        NotificationCenter.default.addObserver(
            self, selector: #selector(didEnd),
            name: .AVPlayerItemDidPlayToEndTime, object: playerItem)

        updateNowPlaying()
    }

    func play() {
        guard let player else { return }
        try? AVAudioSession.sharedInstance().setActive(true)
        player.play()
        onState?(true)
        updateNowPlaying()
    }

    func pause() {
        player?.pause()
        onState?(false)
        savePosition()
        updateNowPlaying()
    }

    func seek(to secs: Double) {
        guard let player else { return }
        player.seek(to: CMTime(seconds: max(0, secs), preferredTimescale: 600),
                    toleranceBefore: .zero, toleranceAfter: .zero)
        updateNowPlaying()
    }

    func setRate(_ r: Float) {
        // Assigning to `rate` also starts playback, which is not what changing the speed of a
        // paused episode should do.
        player?.defaultRate = r
        if isPlaying { player?.rate = r }
        updateNowPlaying()
    }

    func setVolume(_ v: Float) { player?.volume = v }

    func stop(notify: Bool = true) {
        savePosition()
        if let timeObserver { player?.removeTimeObserver(timeObserver) }
        timeObserver = nil
        statusObservation = nil
        NotificationCenter.default.removeObserver(self, name: .AVPlayerItemDidPlayToEndTime, object: nil)
        player?.pause()
        player = nil
        item = nil
        MPNowPlayingInfoCenter.default().nowPlayingInfo = nil
        try? AVAudioSession.sharedInstance().setActive(false, options: .notifyOthersOnDeactivation)
        if notify { onState?(false) }
    }

    /// The page asking us to save, because its own beacon is ours now. It sends the path rather
    /// than a time: the time it has may be minutes old if it has been frozen in the background.
    func savePosition(path: String? = nil) {
        guard let item, let player, player.currentItem?.status == .readyToPlay else { return }
        let secs = Int(player.currentTime().seconds.rounded())
        guard secs > 0 else { return }
        lastSaved = Double(secs)
        let dur = duration.map { Int($0.rounded()) }
        if let path {
            library.savePosition(path: path, secs: secs, duration: dur)
        } else {
            library.savePosition(feedId: item.feedId, guid: item.guid, secs: secs, duration: dur)
        }
    }

    // MARK: - as it plays

    private func tick(_ secs: Double) {
        guard secs.isFinite else { return }
        onTime?(secs, duration)
        updateElapsed(secs)
        if abs(secs - lastSaved) > 10 { savePosition() }
        // Listened to, not merely started -- the same 90% the page uses. Doing it on play made an
        // item vanish from Unread the instant you pressed it.
        if let d = duration, d > 0, secs / d >= 0.9 { markRead() }
    }

    @objc private func didEnd() {
        savePosition()
        markRead()
        onState?(false)
        onEnded?()
        updateNowPlaying()
    }

    private func markRead() {
        guard !markedRead, let item else { return }
        markedRead = true
        library.markRead(feedId: item.feedId, guid: item.guid)
    }

    // MARK: - the car and the lock screen

    private func wireRemoteCommands() {
        let c = MPRemoteCommandCenter.shared()
        c.playCommand.addTarget { [weak self] _ in self?.play(); return .success }
        c.pauseCommand.addTarget { [weak self] _ in self?.pause(); return .success }
        c.togglePlayPauseCommand.addTarget { [weak self] _ in
            guard let self else { return .commandFailed }
            self.isPlaying ? self.pause() : self.play()
            return .success
        }
        // The same 15 and 30 the page uses, so a steering wheel and the keyboard agree.
        c.skipBackwardCommand.preferredIntervals = [15]
        c.skipForwardCommand.preferredIntervals = [30]
        c.skipBackwardCommand.addTarget { [weak self] _ in
            guard let self else { return .commandFailed }
            self.seek(to: self.currentTime - 15); return .success
        }
        c.skipForwardCommand.addTarget { [weak self] _ in
            guard let self else { return .commandFailed }
            self.seek(to: self.currentTime + 30); return .success
        }
        c.changePlaybackPositionCommand.addTarget { [weak self] ev in
            guard let self, let e = ev as? MPChangePlaybackPositionCommandEvent else { return .commandFailed }
            self.seek(to: e.positionTime); return .success
        }
    }

    private func updateNowPlaying() {
        guard let item else { return }
        var info: [String: Any] = [
            MPMediaItemPropertyTitle: item.title,
            MPMediaItemPropertyArtist: item.feedTitle,
            MPMediaItemPropertyAlbumTitle: item.feedTitle,
            MPNowPlayingInfoPropertyMediaType: MPNowPlayingInfoMediaType.audio.rawValue,
            MPNowPlayingInfoPropertyPlaybackRate: isPlaying ? (player?.rate ?? 1) : 0,
            MPNowPlayingInfoPropertyElapsedPlaybackTime: currentTime,
        ]
        if let d = duration ?? item.duration.map(Double.init) {
            info[MPMediaItemPropertyPlaybackDuration] = d
        }
        let centre = MPNowPlayingInfoCenter.default()
        centre.nowPlayingInfo = info

        if let art = item.artwork {
            library.artwork(art) { image in
                guard let image else { return }
                DispatchQueue.main.async {
                    // Read back rather than reusing `info`: by the time the picture arrives the
                    // elapsed time in it is stale, and writing it would jerk the car's progress bar.
                    var latest = centre.nowPlayingInfo ?? [:]
                    latest[MPMediaItemPropertyArtwork] =
                        MPMediaItemArtwork(boundsSize: image.size) { _ in image }
                    centre.nowPlayingInfo = latest
                }
            }
        }
    }

    /// Just the clock, every tick. Rewriting the whole dictionary that often makes the car's
    /// progress bar stutter.
    private func updateElapsed(_ secs: Double) {
        guard var info = MPNowPlayingInfoCenter.default().nowPlayingInfo else { return }
        info[MPNowPlayingInfoPropertyElapsedPlaybackTime] = secs
        info[MPNowPlayingInfoPropertyPlaybackRate] = isPlaying ? (player?.rate ?? 1) : 0
        MPNowPlayingInfoCenter.default().nowPlayingInfo = info
    }
}