hudini/Sources/HUDini/VolumeMonitor.swift

import CoreAudio
import AudioToolbox
import Foundation

class VolumeMonitor {
    typealias VolumeCallback = (Float, Bool) -> Void

    private let callback: VolumeCallback
    private var deviceID: AudioDeviceID = kAudioObjectUnknown
    private var isListening = false
    private var lastVolume: Float = -1
    private var lastMuted: Bool = false

    init(callback: @escaping VolumeCallback) {
        self.callback = callback
    }

    func start() {
        guard !isListening else { return }
        deviceID = getDefaultOutputDevice()
        guard deviceID != kAudioObjectUnknown else { return }

        addDeviceChangeListener()
        addVolumeListener(for: deviceID)
        addMuteListener(for: deviceID)
        isListening = true
    }

    func stop() {
        guard isListening else { return }
        removeVolumeListener(for: deviceID)
        removeMuteListener(for: deviceID)
        removeDeviceChangeListener()
        isListening = false
    }

    // MARK: - Default Output Device

    private func getDefaultOutputDevice() -> AudioDeviceID {
        var deviceID = AudioDeviceID(0)
        var size = UInt32(MemoryLayout<AudioDeviceID>.size)
        var address = AudioObjectPropertyAddress(
            mSelector: kAudioHardwarePropertyDefaultOutputDevice,
            mScope: kAudioObjectPropertyScopeGlobal,
            mElement: kAudioObjectPropertyElementMain
        )
        let status = AudioObjectGetPropertyData(
            AudioObjectID(kAudioObjectSystemObject), &address, 0, nil, &size, &deviceID
        )
        return status == noErr ? deviceID : kAudioObjectUnknown
    }

    // MARK: - Volume

    func getVolume() -> Float {
        guard deviceID != kAudioObjectUnknown else { return 0 }
        var volume: Float32 = 0
        var size = UInt32(MemoryLayout<Float32>.size)

        // Try master channel first
        var address = AudioObjectPropertyAddress(
            mSelector: kAudioDevicePropertyVolumeScalar,
            mScope: kAudioDevicePropertyScopeOutput,
            mElement: kAudioObjectPropertyElementMain
        )

        var status = AudioObjectGetPropertyData(deviceID, &address, 0, nil, &size, &volume)
        if status == noErr { return volume }

        // Fallback to channel 1 (left)
        address.mElement = 1
        status = AudioObjectGetPropertyData(deviceID, &address, 0, nil, &size, &volume)
        return status == noErr ? volume : 0
    }

    func isMuted() -> Bool {
        guard deviceID != kAudioObjectUnknown else { return false }
        var muted: UInt32 = 0
        var size = UInt32(MemoryLayout<UInt32>.size)
        var address = AudioObjectPropertyAddress(
            mSelector: kAudioDevicePropertyMute,
            mScope: kAudioDevicePropertyScopeOutput,
            mElement: kAudioObjectPropertyElementMain
        )
        let status = AudioObjectGetPropertyData(deviceID, &address, 0, nil, &size, &muted)
        return status == noErr ? muted != 0 : false
    }

    // MARK: - Listeners

    private func addVolumeListener(for device: AudioDeviceID) {
        var address = AudioObjectPropertyAddress(
            mSelector: kAudioDevicePropertyVolumeScalar,
            mScope: kAudioDevicePropertyScopeOutput,
            mElement: kAudioObjectPropertyElementMain
        )

        // Try master first
        let status = AudioObjectAddPropertyListener(device, &address, volumeChanged, Unmanaged.passUnretained(self).toOpaque())
        if status != noErr {
            // Fallback: listen on channel 1
            address.mElement = 1
            AudioObjectAddPropertyListener(device, &address, volumeChanged, Unmanaged.passUnretained(self).toOpaque())
        }
    }

    private func removeVolumeListener(for device: AudioDeviceID) {
        var address = AudioObjectPropertyAddress(
            mSelector: kAudioDevicePropertyVolumeScalar,
            mScope: kAudioDevicePropertyScopeOutput,
            mElement: kAudioObjectPropertyElementMain
        )
        AudioObjectRemovePropertyListener(device, &address, volumeChanged, Unmanaged.passUnretained(self).toOpaque())
        address.mElement = 1
        AudioObjectRemovePropertyListener(device, &address, volumeChanged, Unmanaged.passUnretained(self).toOpaque())
    }

    private func addMuteListener(for device: AudioDeviceID) {
        var address = AudioObjectPropertyAddress(
            mSelector: kAudioDevicePropertyMute,
            mScope: kAudioDevicePropertyScopeOutput,
            mElement: kAudioObjectPropertyElementMain
        )
        AudioObjectAddPropertyListener(device, &address, muteChanged, Unmanaged.passUnretained(self).toOpaque())
    }

    private func removeMuteListener(for device: AudioDeviceID) {
        var address = AudioObjectPropertyAddress(
            mSelector: kAudioDevicePropertyMute,
            mScope: kAudioDevicePropertyScopeOutput,
            mElement: kAudioObjectPropertyElementMain
        )
        AudioObjectRemovePropertyListener(device, &address, muteChanged, Unmanaged.passUnretained(self).toOpaque())
    }

    private func addDeviceChangeListener() {
        var address = AudioObjectPropertyAddress(
            mSelector: kAudioHardwarePropertyDefaultOutputDevice,
            mScope: kAudioObjectPropertyScopeGlobal,
            mElement: kAudioObjectPropertyElementMain
        )
        AudioObjectAddPropertyListener(
            AudioObjectID(kAudioObjectSystemObject), &address, deviceChanged,
            Unmanaged.passUnretained(self).toOpaque()
        )
    }

    private func removeDeviceChangeListener() {
        var address = AudioObjectPropertyAddress(
            mSelector: kAudioHardwarePropertyDefaultOutputDevice,
            mScope: kAudioObjectPropertyScopeGlobal,
            mElement: kAudioObjectPropertyElementMain
        )
        AudioObjectRemovePropertyListener(
            AudioObjectID(kAudioObjectSystemObject), &address, deviceChanged,
            Unmanaged.passUnretained(self).toOpaque()
        )
    }

    // MARK: - Callbacks

    fileprivate func handleVolumeChange() {
        let vol = getVolume()
        let muted = isMuted()
        callback(vol, muted)
    }

    fileprivate func handleMuteChange() {
        let vol = getVolume()
        let muted = isMuted()
        callback(vol, muted)
    }

    fileprivate func handleDeviceChange() {
        // Remove old listeners
        if deviceID != kAudioObjectUnknown {
            removeVolumeListener(for: deviceID)
            removeMuteListener(for: deviceID)
        }
        // Switch to new device
        deviceID = getDefaultOutputDevice()
        if deviceID != kAudioObjectUnknown {
            addVolumeListener(for: deviceID)
            addMuteListener(for: deviceID)
        }
    }
}

// C-style callbacks that bridge to the class methods
private func volumeChanged(
    _ objectID: AudioObjectID,
    _ numberAddresses: UInt32,
    _ addresses: UnsafePointer<AudioObjectPropertyAddress>,
    _ clientData: UnsafeMutableRawPointer?
) -> OSStatus {
    guard let clientData = clientData else { return noErr }
    let monitor = Unmanaged<VolumeMonitor>.fromOpaque(clientData).takeUnretainedValue()
    monitor.handleVolumeChange()
    return noErr
}

private func muteChanged(
    _ objectID: AudioObjectID,
    _ numberAddresses: UInt32,
    _ addresses: UnsafePointer<AudioObjectPropertyAddress>,
    _ clientData: UnsafeMutableRawPointer?
) -> OSStatus {
    guard let clientData = clientData else { return noErr }
    let monitor = Unmanaged<VolumeMonitor>.fromOpaque(clientData).takeUnretainedValue()
    monitor.handleMuteChange()
    return noErr
}

private func deviceChanged(
    _ objectID: AudioObjectID,
    _ numberAddresses: UInt32,
    _ addresses: UnsafePointer<AudioObjectPropertyAddress>,
    _ clientData: UnsafeMutableRawPointer?
) -> OSStatus {
    guard let clientData = clientData else { return noErr }
    let monitor = Unmanaged<VolumeMonitor>.fromOpaque(clientData).takeUnretainedValue()
    DispatchQueue.main.async {
        monitor.handleDeviceChange()
    }
    return noErr
}