ipx/ios/Sources/Playback.swift

import AVFoundation
import MediaPlayer
import UIKit

/// The phone's player: the one that plays on with the screen locked, and the one the lock screen
/// and a car's buttons reach. Knows nothing of the web view; the bridge drives it.
@MainActor
final class Playback: NSObject {
    /// What is loaded: enough for the lock screen, and to save a position without asking the page.
    struct Item {
        var url: URL
        var enc: Int
        var feedId: String
        var guid: String
        var title: String
        var feedTitle: String
        var artwork: String?
        var duration: Int?
    }

    var onTime: ((Double, Double?) -> Void)?
    var onMeta: ((Double) -> Void)?
    var onState: ((Bool) -> Void)?
    var onEnded: (() -> Void)?
    var onError: ((String) -> Void)?

    private let session: URLSession = {
        let cfg = URLSessionConfiguration.default
        cfg.httpCookieStorage = .shared
        cfg.timeoutIntervalForRequest = 20
        return URLSession(configuration: cfg)
    }()
    private var player: AVPlayer?
    private var item: Item?
    private var timeObserver: Any?
    private var statusObservation: NSKeyValueObservation?
    private var endObserver: NSObjectProtocol?
    private var lastSaved: Double = 0
    private var markedRead = false
    private var rate: Float = 1
    private var volume: Float = 1

    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
    }

    override init() {
        super.init()
        // spokenAudio is what tells the system this is speech, so navigation's voice ducks it
        // properly, and longFormAudio is what routes it as a podcast does.
        do {
            try AVAudioSession.sharedInstance().setCategory(.playback, mode: .spokenAudio,
                                                            policy: .longFormAudio)
        } catch {
            NSLog("ipx: audio session: %@", error.localizedDescription)
        }
        wireRemoteCommands()
    }

    // MARK: - what the page asks for

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

        // An AVURLAsset does not read the shared cookie store by itself, and the cookie is how
        // ipx knows whose file this is.
        let asset = AVURLAsset(url: item.url, options: [
            AVURLAssetHTTPCookiesKey: HTTPCookieStorage.shared.cookies(for: item.url) ?? [],
        ])
        let playerItem = AVPlayerItem(asset: asset)
        let player = AVPlayer(playerItem: playerItem)
        player.volume = volume
        player.defaultRate = rate
        self.player = player

        // Where to start is the page's to decide, on loadedmetadata, so one piece of code owns it.
        // Here only the length is reported.
        statusObservation = playerItem.observe(\.status, options: [.new]) { [weak self] pi, _ in
            Task { @MainActor in
                guard let self else { return }
                switch pi.status {
                case .readyToPlay:
                    if let d = self.duration { self.onMeta?(d) }
                case .failed:
                    // A file that will not play, or a session that went while it played: only the
                    // second has something to do about it.
                    let msg = pi.error?.localizedDescription ?? "the file could not be played"
                    let status = await self.request("GET", "/api/me")
                    self.onError?(status == 401 ? "Sign in again" : msg)
                default: break
                }
            }
        }
        timeObserver = player.addPeriodicTimeObserver(
            forInterval: CMTime(seconds: 0.5, preferredTimescale: 600), queue: .main
        ) { [weak self] t in
            MainActor.assumeIsolated { self?.tick(t.seconds) }
        }
        endObserver = NotificationCenter.default.addObserver(
            forName: .AVPlayerItemDidPlayToEndTime, object: playerItem, queue: .main
        ) { [weak self] _ in
            MainActor.assumeIsolated { self?.didEnd() }
        }
        updateNowPlaying()
    }

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

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

    func seek(to secs: Double) {
        // Exact, not the default tolerance, which snaps to a keyframe minutes from where the
        // scrubber was let go on a long episode.
        player?.seek(to: CMTime(seconds: max(0, secs), preferredTimescale: 600),
                     toleranceBefore: .zero, toleranceAfter: .zero)
        updateNowPlaying()
    }

    func setRate(_ r: Float) {
        rate = r
        player?.defaultRate = r
        // Setting rate on a paused player starts it, which changing the speed should not do.
        if isPlaying { player?.rate = r }
        updateNowPlaying()
    }

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

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

    /// Where we are, saved from this clock. The page asks for it too, and sends no time of its
    /// own: a web view frozen in the background holds a time from minutes ago, and writing that
    /// over where you got to is the stale write player.ts guards against.
    func savePosition() {
        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)
        var body: [String: Any] = ["secs": secs]
        if let d = duration { body["duration"] = Int(d.rounded()) }
        // DeadAir's copy runs on a shorter clock; the server has to know which one this is.
        if item.url.path.contains("/deadair") { body["deadair"] = item.enc }
        Task { await request("POST", entryPath(item, "position"), body) }
    }

    // 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() }
        // Heard, not just started: the same 90% the page uses, so an item does not leave Unread
        // the moment it is pressed. The page does the same while it runs; this is for when it
        // does not.
        if let d = duration, secs / d >= 0.9 { markRead() }
    }

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

    private func markRead() {
        guard !markedRead, let item else { return }
        markedRead = true
        Task { await request("POST", entryPath(item, "flags"), ["read": true]) }
    }

    // MARK: - the lock screen and the car

    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 page's 15 back and 30 forward, 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 ? rate : 0,
            MPNowPlayingInfoPropertyElapsedPlaybackTime: currentTime,
        ]
        if let d = duration ?? item.duration.map(Double.init) {
            info[MPMediaItemPropertyPlaybackDuration] = d
        }
        let centre = MPNowPlayingInfoCenter.default()
        centre.nowPlayingInfo = info

        guard let art = item.artwork, let url = Server.resolve(art) else { return }
        Task {
            guard let (data, _) = try? await session.data(from: url),
                  let image = UIImage(data: data), self.item?.guid == item.guid else { return }
            // Read back, not `info`: by the time the picture arrives that elapsed time is stale,
            // and writing it would jerk the progress bar back.
            var latest = centre.nowPlayingInfo ?? [:]
            latest[MPMediaItemPropertyArtwork] = Self.artwork(image)
            centre.nowPlayingInfo = latest
        }
    }

    /// Made outside the main actor: the system asks for the picture on a thread of its own.
    nonisolated private static func artwork(_ image: UIImage) -> MPMediaItemArtwork {
        MPMediaItemArtwork(boundsSize: image.size) { _ in image }
    }

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

    // MARK: - ipx

    private func entryPath(_ item: Item, _ what: String) -> String {
        let esc = { (s: String) in s.addingPercentEncoding(withAllowedCharacters: .alphanumerics) ?? s }
        return "/api/entries/\(esc(item.feedId))/\(esc(item.guid))/\(what)"
    }

    /// One call to ipx, signed in by the web view's cookies; its status, or nil if it never
    /// arrived. A position that does not save is saved again ten seconds on.
    @discardableResult
    private func request(_ method: String, _ path: String, _ json: [String: Any]? = nil) async -> Int? {
        guard let url = Server.resolve(path) else { return nil }
        var req = URLRequest(url: url)
        req.httpMethod = method
        if let json {
            req.setValue("application/json", forHTTPHeaderField: "Content-Type")
            req.httpBody = try? JSONSerialization.data(withJSONObject: json)
        }
        guard let (_, resp) = try? await session.data(for: req) else { return nil }
        return (resp as? HTTPURLResponse)?.statusCode
    }
}