Amphlify/Packages/AmphlifyKit/Sources/Playback/OutputDevice.swift

#if os(macOS)
    import CoreAudio
    import Foundation

    public enum OutputDeviceError: Error {
        case noDevice, unsupportedRate, writeFailed, timedOut
    }

    public enum OutputDevice {
        private static let pollStep: Duration = .milliseconds(20)
        private static let pollLimit = 50
        private static let settle: Duration = .milliseconds(100)

        public static func current() -> OutputDeviceInfo? {
            guard let id = defaultDevice() else { return nil }
            return OutputDeviceInfo(
                id: id,
                name: read(kAudioObjectPropertyName, from: id, as: CFString.self).map { $0 as String } ?? "",
                nominalRate: read(kAudioDevicePropertyNominalSampleRate, from: id, as: Float64.self) ?? 0,
                availableRates: availableRates(of: id)
            )
        }

        public static func setNominalRate(_ rate: Double) async throws {
            guard let device = current() else { throw OutputDeviceError.noDevice }
            guard device.nominalRate != rate else { return }
            guard device.availableRates.contains(rate) else { throw OutputDeviceError.unsupportedRate }
            var address = address(kAudioDevicePropertyNominalSampleRate)
            var value = rate
            let size = UInt32(MemoryLayout<Float64>.size)
            guard AudioObjectSetPropertyData(device.id, &address, 0, nil, size, &value) == noErr else {
                throw OutputDeviceError.writeFailed
            }
            for _ in 0 ..< pollLimit {
                if read(kAudioDevicePropertyNominalSampleRate, from: device.id, as: Float64.self) == rate {
                    try await Task.sleep(for: settle)
                    return
                }
                try await Task.sleep(for: pollStep)
            }
            throw OutputDeviceError.timedOut
        }

        public static func changes() -> AsyncStream<OutputDeviceInfo?> {
            AsyncStream { continuation in
                continuation.yield(current())
                let listener = Listener { continuation.yield(current()) }
                continuation.onTermination = { _ in listener.stop() }
            }
        }

        fileprivate static func defaultDevice() -> AudioDeviceID? {
            let system = AudioObjectID(kAudioObjectSystemObject)
            let id = read(kAudioHardwarePropertyDefaultOutputDevice, from: system, as: AudioDeviceID.self)
            return id.flatMap { $0 == kAudioObjectUnknown ? nil : $0 }
        }

        fileprivate static func address(_ selector: AudioObjectPropertySelector) -> AudioObjectPropertyAddress {
            AudioObjectPropertyAddress(
                mSelector: selector,
                mScope: kAudioObjectPropertyScopeGlobal,
                mElement: kAudioObjectPropertyElementMain
            )
        }

        private static func read<T>(_ selector: AudioObjectPropertySelector, from object: AudioObjectID, as _: T.Type) -> T? {
            var address = address(selector)
            var size = UInt32(MemoryLayout<T>.size)
            let buffer = UnsafeMutablePointer<T>.allocate(capacity: 1)
            defer { buffer.deallocate() }
            guard AudioObjectGetPropertyData(object, &address, 0, nil, &size, buffer) == noErr else { return nil }
            return buffer.move()
        }

        private static func availableRates(of device: AudioDeviceID) -> [Double] {
            var address = address(kAudioDevicePropertyAvailableNominalSampleRates)
            var size: UInt32 = 0
            guard AudioObjectGetPropertyDataSize(device, &address, 0, nil, &size) == noErr else { return [] }
            let count = Int(size) / MemoryLayout<AudioValueRange>.stride
            var ranges = [AudioValueRange](repeating: AudioValueRange(), count: count)
            guard AudioObjectGetPropertyData(device, &address, 0, nil, &size, &ranges) == noErr else { return [] }
            return Array(Set(ranges.flatMap { [$0.mMinimum, $0.mMaximum] })).sorted()
        }
    }

    private final class Listener: @unchecked Sendable {
        private let queue = DispatchQueue(label: "Amphlify.OutputDevice")
        private let system = AudioObjectID(kAudioObjectSystemObject)
        private var device: AudioDeviceID = kAudioObjectUnknown
        private var systemAddress = OutputDevice.address(kAudioHardwarePropertyDefaultOutputDevice)
        private var rateAddress = OutputDevice.address(kAudioDevicePropertyNominalSampleRate)
        private var onSystemChange: AudioObjectPropertyListenerBlock = { _, _ in }
        private var onRateChange: AudioObjectPropertyListenerBlock = { _, _ in }

        init(onChange: @escaping @Sendable () -> Void) {
            onRateChange = { _, _ in onChange() }
            onSystemChange = { [weak self] _, _ in
                self?.follow()
                onChange()
            }
            queue.sync {
                AudioObjectAddPropertyListenerBlock(system, &systemAddress, queue, onSystemChange)
                follow()
            }
        }

        func stop() {
            queue.sync {
                AudioObjectRemovePropertyListenerBlock(system, &systemAddress, queue, onSystemChange)
                unfollow()
            }
        }

        private func follow() {
            unfollow()
            device = OutputDevice.defaultDevice() ?? kAudioObjectUnknown
            guard device != kAudioObjectUnknown else { return }
            AudioObjectAddPropertyListenerBlock(device, &rateAddress, queue, onRateChange)
        }

        private func unfollow() {
            guard device != kAudioObjectUnknown else { return }
            AudioObjectRemovePropertyListenerBlock(device, &rateAddress, queue, onRateChange)
            device = kAudioObjectUnknown
        }
    }
#endif