session-ios/SignalMessaging/environment/OWSAudioSession.swift

//
//  Copyright (c) 2018 Open Whisper Systems. All rights reserved.
//

import Foundation
import WebRTC

@objc
public class AudioActivity: NSObject {
    let audioDescription: String

    override public var description: String {
        return "<\(self.logTag) audioDescription: \"\(audioDescription)\">"
    }

    public
    init(audioDescription: String) {
        self.audioDescription = audioDescription
    }

    deinit {
        OWSAudioSession.shared.ensureAudioSessionActivationState()
    }
}

@objc
public class OWSAudioSession: NSObject {

    // Force singleton access
    public static let shared = OWSAudioSession()
    private override init() {}
    private let avAudioSession = AVAudioSession.sharedInstance()

    private var currentActivities: [Weak<AudioActivity>] = []

    // Ignores hardware mute switch, plays through external speaker
    public func setPlaybackCategory(audioActivity: AudioActivity) {
        Logger.debug("\(logTag) in \(#function)")

        // In general, we should have put the audio session back to it's default
        // category when we were done with whatever activity required it to be modified
        assert(avAudioSession.category == AVAudioSessionCategorySoloAmbient)

        startAudioActivity(audioActivity)

        do {
            try avAudioSession.setCategory(AVAudioSessionCategoryPlayback)
        } catch {
            owsFail("\(logTag) in \(#function) failed with error: \(error)")
        }
    }

    public func setRecordCategory(audioActivity: AudioActivity) -> Bool {
        Logger.debug("\(logTag) in \(#function)")

        // In general, we should have put the audio session back to it's default
        // category when we were done with whatever activity required it to be modified
        assert(avAudioSession.category == AVAudioSessionCategorySoloAmbient)

        assert(avAudioSession.recordPermission() == .granted)

        startAudioActivity(audioActivity)

        do {
            try avAudioSession.setCategory(AVAudioSessionCategoryRecord)
            return true
        } catch {
            owsFail("\(logTag) in \(#function) failed with error: \(error)")
            return false
        }
    }

    private func startAudioActivity(_ audioActivity: AudioActivity) {
        Logger.debug("\(logTag) in \(#function) with \(audioActivity)")

        self.currentActivities.append(Weak(value: audioActivity))
    }

    public func endAudioActivity(_ audioActivity: AudioActivity) {
        Logger.debug("\(logTag) in \(#function) with audioActivity: \(audioActivity)")

        currentActivities = currentActivities.filter { return $0.value != audioActivity }
        ensureAudioSessionActivationState()
    }

    fileprivate func ensureAudioSessionActivationState() {
        // Cull any stale activities
        currentActivities = currentActivities.flatMap { oldActivity in
            guard oldActivity.value != nil else {
                // Normally we should be explicitly stopping an audio activity, but this allows
                // for recovery if the owner of the AudioAcivity was GC'd without ending it's
                // audio activity
                Logger.warn("\(logTag) an old activity has been gc'd")
                return nil
            }

            // return any still-active activities
            return oldActivity
        }

        guard currentActivities.count == 0 else {
            Logger.debug("\(logTag) not deactivating due to currentActivities: \(currentActivities)")
            return
        }

        do {
            try avAudioSession.setCategory(AVAudioSessionCategorySoloAmbient)

            // When playing audio in Signal, other apps audio (e.g. Music) is paused.
            // By notifying when we deactivate, the other app can resume playback.
            try avAudioSession.setActive(false, with: [.notifyOthersOnDeactivation])
        } catch {
            owsFail("\(logTag) in \(#function) failed with error: \(error)")
        }
    }

    // MARK: - WebRTC Audio

    /**
     * By default WebRTC starts the audio session (PlayAndRecord) immediately upon creating the peer connection
     * but we want to create the peer connection and set up all the signaling channels before we prompt the user
     * for an incoming call. Without manually handling the session, this would result in the user seeing a recording
     * permission requested (and recording banner) before they even know they have an incoming call.
     *
     * By using the `useManualAudio` and `isAudioEnabled` attributes of the RTCAudioSession we can delay recording until
     * it makes sense.
     */

    /**
     * The private class that manages AVAudioSession for WebRTC
     */
    private let rtcAudioSession = RTCAudioSession.sharedInstance()

    /**
     * This must be called before any audio tracks are added to the peerConnection, else we'll start recording before all
     * our signaling is set up.
     */
    public func configureRTCAudio() {
        Logger.info("\(logTag) in \(#function)")
        rtcAudioSession.useManualAudio = true
    }

    /**
     * Because we useManualAudio with our RTCAudioSession, we have to start/stop the recording audio session ourselves.
     * See "WebRTC Audio" comment for details on manual audio.
     */
    public func enableRTCAudio(audioActivity: AudioActivity) {
        startAudioActivity(audioActivity)
        rtcAudioSession.isAudioEnabled = true
    }

    public func disableRTCAudio(audioActivity: AudioActivity) {
        rtcAudioSession.isAudioEnabled = false
        endAudioActivity(audioActivity)
    }
}