MTMR/MTMR/VolumeViewController.swift

import Cocoa
import AppKit
import AVFoundation
import CoreAudio

class VolumeViewController: NSCustomTouchBarItem {
    private(set) var sliderItem: CustomSlider!
    
    init(identifier: NSTouchBarItem.Identifier, image: NSImage? = nil) {
        super.init(identifier: identifier)
        
        var forPropertyAddress = AudioObjectPropertyAddress(
            mSelector: kAudioHardwareServiceDeviceProperty_VirtualMasterVolume,
            mScope: kAudioDevicePropertyScopeOutput,
            mElement: kAudioObjectPropertyElementMaster)
        
        addListenerBlock(listenerBlock: audioObjectPropertyListenerBlock,
                         onAudioObjectID: defaultDeviceID,
                         forPropertyAddress: &forPropertyAddress)
        
        if (image == nil) {
            sliderItem = CustomSlider()
        } else {
            sliderItem = CustomSlider(knob: image!)
        }
        sliderItem.target = self
        sliderItem.action =  #selector(VolumeViewController.sliderValueChanged(_:))        
        sliderItem.minValue = 0.0
        sliderItem.maxValue = 100.0
        sliderItem.floatValue = getInputGain()*100

        self.view = sliderItem
    }
    
    func addListenerBlock( listenerBlock: @escaping AudioObjectPropertyListenerBlock, onAudioObjectID: AudioObjectID, forPropertyAddress: UnsafePointer<AudioObjectPropertyAddress>) {

        if (kAudioHardwareNoError != AudioObjectAddPropertyListenerBlock(onAudioObjectID, forPropertyAddress, nil, listenerBlock)) {
            print("Error calling: AudioObjectAddPropertyListenerBlock") }
    }
    
    func audioObjectPropertyListenerBlock (numberAddresses: UInt32, addresses: UnsafePointer<AudioObjectPropertyAddress>) {
        var index: UInt32 = 0
        while index < numberAddresses {
            let address: AudioObjectPropertyAddress = addresses[Int(index)]
            switch address.mSelector {
            case kAudioHardwareServiceDeviceProperty_VirtualMasterVolume:
                DispatchQueue.main.async {
                    self.sliderItem.floatValue = self.getInputGain() * 100
                }
            default:
                
                print("We didn't expect this!")
                
            }
            index += 1
        }
    }
    
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

    deinit {
        sliderItem.unbind(NSBindingName.value)
    }
    
    @objc func sliderValueChanged(_ sender: Any) {
        if let sliderItem = sender as? NSSlider {
            _ = setInputGain(Float32(sliderItem.intValue)/100.0)
        }
    }
    
    private var defaultDeviceID: AudioObjectID {
        var deviceID: AudioObjectID = AudioObjectID(0)
        var size: UInt32 = UInt32(MemoryLayout<AudioObjectID>.size)
        var address: AudioObjectPropertyAddress = AudioObjectPropertyAddress()
        address.mSelector = AudioObjectPropertySelector(kAudioHardwarePropertyDefaultOutputDevice)
        address.mScope = AudioObjectPropertyScope(kAudioObjectPropertyScopeGlobal)
        address.mElement = AudioObjectPropertyElement(kAudioObjectPropertyElementMaster)
        AudioObjectGetPropertyData(AudioObjectID(kAudioObjectSystemObject), &address, 0, nil, &size, &deviceID)
        return deviceID
    }
    
    private func getInputGain() -> Float32 {
        var volume: Float32 = 0.5
        var size: UInt32 = UInt32(MemoryLayout.size(ofValue: volume))
        var address: AudioObjectPropertyAddress = AudioObjectPropertyAddress()
        address.mSelector = AudioObjectPropertySelector(kAudioHardwareServiceDeviceProperty_VirtualMasterVolume)
        address.mScope = AudioObjectPropertyScope(kAudioDevicePropertyScopeOutput)
        address.mElement = AudioObjectPropertyElement(kAudioObjectPropertyElementMaster)
        AudioObjectGetPropertyData(defaultDeviceID, &address, 0, nil, &size, &volume)
        return volume
    }
    
    private func setInputGain(_ volume: Float32) -> OSStatus {
        var inputVolume: Float32 = volume
        
        if inputVolume == 0.0 {
           _ = setMute( mute: 1)
        } else {
            _ = setMute( mute: 0)
        }
        
        let size: UInt32 = UInt32(MemoryLayout.size(ofValue: inputVolume))
        var address: AudioObjectPropertyAddress = AudioObjectPropertyAddress()
        address.mScope = AudioObjectPropertyScope(kAudioDevicePropertyScopeOutput)
        address.mElement = AudioObjectPropertyElement(kAudioObjectPropertyElementMaster)
        address.mSelector = AudioObjectPropertySelector(kAudioHardwareServiceDeviceProperty_VirtualMasterVolume)
        return AudioObjectSetPropertyData(defaultDeviceID, &address, 0, nil, size, &inputVolume)
    }
    
    private func setMute( mute: Int) -> OSStatus {
        var muteVal: Int = mute
        var address: AudioObjectPropertyAddress = AudioObjectPropertyAddress()
        address.mSelector = AudioObjectPropertySelector(kAudioDevicePropertyMute)
        let size: UInt32 = UInt32(MemoryLayout.size(ofValue: muteVal))
        address.mScope = AudioObjectPropertyScope(kAudioDevicePropertyScopeOutput)
        address.mElement = AudioObjectPropertyElement(kAudioObjectPropertyElementMaster)
        return AudioObjectSetPropertyData(defaultDeviceID, &address, 0, nil, size, &muteVal)
    }
}