Musubi/Packages/MusubiKit/Sources/AudioMatrix/AudioDevices.swift

import CoreAudio
import Foundation

/// A Core Audio device as shown in the UI.
public struct AudioDevice: Identifiable, Hashable, Sendable {
    public var id: String { uid }
    public let deviceID: AudioDeviceID
    public let uid: String
    public let name: String
    public let inputChannels: Int
    public let outputChannels: Int
    public let sampleRate: Double
}

public enum AudioDevices {
    public static func all() -> [AudioDevice] {
        var address = AudioObjectPropertyAddress(
            mSelector: kAudioHardwarePropertyDevices,
            mScope: kAudioObjectPropertyScopeGlobal,
            mElement: kAudioObjectPropertyElementMain
        )
        var size: UInt32 = 0
        guard AudioObjectGetPropertyDataSize(AudioObjectID(kAudioObjectSystemObject), &address, 0, nil, &size) == noErr else { return [] }
        var ids = [AudioDeviceID](repeating: 0, count: Int(size) / MemoryLayout<AudioDeviceID>.size)
        guard AudioObjectGetPropertyData(AudioObjectID(kAudioObjectSystemObject), &address, 0, nil, &size, &ids) == noErr else { return [] }
        return ids.compactMap(device(for:))
    }

    /// The input device selected in System Settings › Sound.
    public static func defaultInput() -> AudioDevice? {
        var address = AudioObjectPropertyAddress(mSelector: kAudioHardwarePropertyDefaultInputDevice,
                                                  mScope: kAudioObjectPropertyScopeGlobal, mElement: kAudioObjectPropertyElementMain)
        var id = AudioDeviceID(0)
        var size = UInt32(MemoryLayout<AudioDeviceID>.size)
        guard AudioObjectGetPropertyData(AudioObjectID(kAudioObjectSystemObject), &address, 0, nil, &size, &id) == noErr else { return nil }
        return device(for: id)
    }

    public static func device(uid: String) -> AudioDevice? {
        all().first { $0.uid == uid }
    }

    static func device(for id: AudioDeviceID) -> AudioDevice? {
        guard let uid = string(id, kAudioDevicePropertyDeviceUID),
              let name = string(id, kAudioObjectPropertyName)
        else { return nil }
        return AudioDevice(
            deviceID: id, uid: uid, name: name,
            inputChannels: channelCount(id, scope: kAudioObjectPropertyScopeInput),
            outputChannels: channelCount(id, scope: kAudioObjectPropertyScopeOutput),
            sampleRate: nominalSampleRate(id)
        )
    }

    static func nominalSampleRate(_ id: AudioDeviceID) -> Double {
        var address = AudioObjectPropertyAddress(mSelector: kAudioDevicePropertyNominalSampleRate,
                                                  mScope: kAudioObjectPropertyScopeGlobal, mElement: kAudioObjectPropertyElementMain)
        var rate: Float64 = 0
        var size = UInt32(MemoryLayout<Float64>.size)
        return AudioObjectGetPropertyData(id, &address, 0, nil, &size, &rate) == noErr ? rate : 0
    }

    /// Calls `handler` on the main queue whenever devices are added or removed.
    /// Keep the returned token alive as long as you want notifications.
    public static func observeChanges(_ handler: @escaping @MainActor @Sendable () -> Void) -> AnyObject {
        DeviceListObserver(handler: handler)
    }

    private static func string(_ id: AudioDeviceID, _ selector: AudioObjectPropertySelector) -> String? {
        var address = AudioObjectPropertyAddress(mSelector: selector, mScope: kAudioObjectPropertyScopeGlobal,
                                                  mElement: kAudioObjectPropertyElementMain)
        var value: Unmanaged<CFString>?
        var size = UInt32(MemoryLayout<Unmanaged<CFString>?>.size)
        guard AudioObjectGetPropertyData(id, &address, 0, nil, &size, &value) == noErr, let value else { return nil }
        return value.takeRetainedValue() as String
    }

    private static func channelCount(_ id: AudioDeviceID, scope: AudioObjectPropertyScope) -> Int {
        var address = AudioObjectPropertyAddress(mSelector: kAudioDevicePropertyStreamConfiguration,
                                                  mScope: scope, mElement: kAudioObjectPropertyElementMain)
        var size: UInt32 = 0
        guard AudioObjectGetPropertyDataSize(id, &address, 0, nil, &size) == noErr, size > 0 else { return 0 }
        let raw = UnsafeMutableRawPointer.allocate(byteCount: Int(size), alignment: MemoryLayout<AudioBufferList>.alignment)
        defer { raw.deallocate() }
        guard AudioObjectGetPropertyData(id, &address, 0, nil, &size, raw) == noErr else { return 0 }
        let list = UnsafeMutableAudioBufferListPointer(raw.assumingMemoryBound(to: AudioBufferList.self))
        return list.reduce(0) { $0 + Int($1.mNumberChannels) }
    }
}

private final class DeviceListObserver {
    private var address = AudioObjectPropertyAddress(mSelector: kAudioHardwarePropertyDevices,
                                                      mScope: kAudioObjectPropertyScopeGlobal, mElement: kAudioObjectPropertyElementMain)
    private let block: AudioObjectPropertyListenerBlock

    init(handler: @escaping @MainActor @Sendable () -> Void) {
        block = { _, _ in MainActor.assumeIsolated { handler() } }
        AudioObjectAddPropertyListenerBlock(AudioObjectID(kAudioObjectSystemObject), &address, .main, block)
    }

    deinit {
        AudioObjectRemovePropertyListenerBlock(AudioObjectID(kAudioObjectSystemObject), &address, .main, block)
    }
}