AudioDeviceNotifier.swift

//
//  AudioDeviceNotifier.swift

//
//  Created by Rob Jonson on 20/01/2017.
//  Copyright © 2017 HobbyistSoftware. All rights reserved.
//

import Foundation
import CoreAudio

/// Provides notification when the default audio device changes, or when the stream settings of the default audio device change
class AudioDeviceNotifier {
    var active = true
    var handler:(()->(Void))?
    
    private var listenerBlock:AudioObjectPropertyListenerBlock?
    private var streamBlock:AudioObjectPropertyListenerBlock?
    
    private var audioDevicesAddress = AudioObjectPropertyAddress.init(mSelector: kAudioHardwarePropertyDefaultOutputDevice,
                                                                      mScope: kAudioObjectPropertyScopeGlobal,
                                                                      mElement: kAudioObjectPropertyElementMaster)
    private var currentAudioDevice:AudioDevice?  {
        didSet {
            if oldValue != currentAudioDevice {
                moveStreamNotifier(from: oldValue, to:currentAudioDevice )
            }
        }
    }
    
    init() {

        listenerBlock =  {
            [weak self] (numberOfElements, pointerToArrayOfAddresses) in
            print("Default device changed")
            self?.deviceChanged()
        }

        streamBlock = {
            [weak self] (numberOfElements, pointerToArrayOfAddresses) in
            print("Stream details changed")
            self?.deviceChanged()
        }

        let err = AudioObjectAddPropertyListenerBlock(AudioObjectID(kAudioObjectSystemObject), &audioDevicesAddress, DispatchQueue.main,listenerBlock!)
        currentAudioDevice = AudioDevice.defaultOutputDevice()
        moveStreamNotifier(from: nil, to: currentAudioDevice)

        if err != noErr {
            print("Failed to register audio block")
        }
    }
    
    deinit {
        AudioObjectRemovePropertyListenerBlock(AudioObjectID(kAudioObjectSystemObject),
                                               &audioDevicesAddress,
                                               DispatchQueue.main,listenerBlock!)
        
        moveStreamNotifier(from: currentAudioDevice, to: nil)
    }
    
    func deviceChanged() {
        currentAudioDevice = AudioDevice.defaultOutputDevice()
        
        if active {
            handler?()
        }
    }
    
    func moveStreamNotifier(from:AudioDevice?, to:AudioDevice?) {
        
        var audioDeviceStreamsAddress = AudioObjectPropertyAddress.init(mSelector: kAudioDevicePropertyStreamFormat,
                                                                        mScope: kAudioObjectPropertyScopeOutput,
                                                                        mElement: kAudioObjectPropertyElementMaster)
        
        if let streamBlock = streamBlock {
            if let from = from {
                let err = AudioObjectRemovePropertyListenerBlock(from.id,
                                                       &audioDeviceStreamsAddress,
                                                       DispatchQueue.main,streamBlock)
                if err != noErr {
                    print("Error removing listening block")
                }
            }
            
            if let to = to {
                print("moving notifier to \(String(describing: to.name())))")
                let err = AudioObjectAddPropertyListenerBlock(to.id,
                                                    &audioDeviceStreamsAddress,
                                                    DispatchQueue.main,streamBlock)
                if err != noErr {
                    print("Error adding listening block")
                }
            }
        }

    }
}