chanora/apps/chanora_flutter/ios/Runner/AppDelegate.swift

import UIKit
import Flutter
import AVFoundation

@main
@objc class AppDelegate: FlutterAppDelegate, FlutterImplicitEngineDelegate {
  override func application(
    _ application: UIApplication,
    didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?
  ) -> Bool {
    // Configure the iOS AVAudioSession **category + mode** at
    // app-launch time, but DEFER setActive(true) until the scene
    // is foregrounded. Calling setActive in didFinishLaunching is
    // racy on iOS 17+ devices: if the user launches the app from a
    // cold state, the UIApplication isn't yet `.active` and
    // setActive returns `AVAudioSessionErrorCodeCannotStartPlaying`
    // (561017449) — the iOS audio policy server refuses to grant
    // the audio session because the app is not yet considered the
    // foreground priority owner. Symptom in production builds:
    // 'AVAudioSession setup failed: Error 561017449 "Session
    // activation failed"' in NSLog, after which the audio engine
    // is unusable until the user backgrounds + foregrounds the
    // app.
    //
    // The category itself can be set whenever; only the active
    // state needs to be deferred. We listen for
    // didBecomeActiveNotification and activate then. Most
    // production iOS voice apps (Discord, Zoom, FaceTime) follow
    // this same shape.
    do {
      let session = AVAudioSession.sharedInstance()
      try session.setCategory(
        .playAndRecord,
        mode: .voiceChat,
        // Mode rationale (revisited after the iOS VPIO migration):
        //
        // We previously tried .default mode to fix the
        // "speaker/receiver toggle is silent" bug \u2014 that bug was
        // ultimately caused by cpal's iOS RemoteIO unit binding to
        // a stale physical transducer, not by .voiceChat itself.
        // After migrating to coreaudio-rs + kAudioUnitSubType_VoiceProcessingIO
        // (see crates/chanora_audio/src/ios_voice_unit.rs) the
        // route binding is correct under either mode because VPIO
        // is the canonical voice unit and natively re-binds on
        // overrideOutputAudioPort. So .default lost its only
        // benefit.
        //
        // Under .default mode, VPIO's output-side voice processing
        // chain (echo subtraction, noise gating) interprets low-
        // amplitude playback signal as "no farend audio" and
        // aggressively gates inter-phoneme content. Symptom in
        // testing: musicbot (loud, continuous signal) plays fine,
        // human voice (peaks ~-6 dB, average ~-40 dB, classic
        // 20 dB peak-to-average ratio) sounds broken and
        // unintelligible \u2014 the quiet samples between phonemes
        // get gated out, destroying intelligibility.
        //
        // Apple's documentation explicitly pairs VPIO with
        // AVAudioSessionModeVoiceChat. WebRTC's reference iOS
        // ADM implementation uses the same pair. Under
        // .voiceChat mode VPIO's internal AGC/AEC/NS thresholds
        // are tuned for telephony-style speech and pass quiet
        // inter-phoneme content through cleanly.
        //
        // Category options unchanged \u2014 .allowBluetoothHFP +
        // .allowBluetoothA2DP permit BT headsets in both
        // directions regardless of mode.
        options: [.allowBluetoothHFP, .allowBluetoothA2DP]
      )
      NSLog("chanora_flutter: AVAudioSession category set (playAndRecord/voiceChat)")
    } catch {
      NSLog("chanora_flutter: AVAudioSession setCategory failed: \(error)")
    }

    // Activate the session once the app is actually foreground. The
    // notification fires immediately after the cold-launch settles,
    // and again on every resume-from-background — both safe
    // moments to call setActive(true). Repeated activation while
    // already-active is a no-op per the docs.
    NotificationCenter.default.addObserver(
      self,
      selector: #selector(activateAudioSession),
      name: UIApplication.didBecomeActiveNotification,
      object: nil
    )

    // Request microphone access on first launch rather than waiting
    // for the user's first voice-channel join. The latter is
    // surprising: the user has only tapped "connect to server" and
    // suddenly iOS pops the permission prompt because joining a
    // text channel happens to trigger audio engine startup. Asking
    // up-front matches user expectations for a voice-chat client.
    //
    // The request is asynchronous and non-blocking. If the user
    // denies, voice_join will surface a clearer error later when
    // the audio engine fails to open the input device. The
    // permission state is cached by iOS so subsequent launches
    // skip the prompt.
    //
    // Deferred ~1 s so iOS finishes initialising the keyboard /
    // text-input subsystem before the permission alert appears.
    // Firing the alert too early steals focus from the not-yet-
    // ready text-input layer, with the symptom that the first tap
    // on a TextField does nothing (the second tap works because
    // by then iOS has caught up). DispatchQueue.main.asyncAfter
    // keeps everything on the main thread; the permission API
    // itself must be called there too.
    DispatchQueue.main.asyncAfter(deadline: .now() + 1.0) {
      AVAudioSession.sharedInstance().requestRecordPermission { granted in
        NSLog("chanora_flutter: microphone permission granted=\(granted)")
      }
    }

    return super.application(application, didFinishLaunchingWithOptions: launchOptions)
  }

  /// Called by `didBecomeActiveNotification` (cold-launch settle +
  /// every resume-from-background). Activates the AVAudioSession.
  /// Repeated activation is a no-op when the session is already
  /// active so this is safe to call on every foreground.
  @objc private func activateAudioSession() {
    do {
      try AVAudioSession.sharedInstance().setActive(true, options: [])
      NSLog("chanora_flutter: AVAudioSession activated on foreground")
    } catch {
      NSLog("chanora_flutter: AVAudioSession setActive failed: \(error)")
    }
  }

  func didInitializeImplicitFlutterEngine(_ engineBridge: FlutterImplicitEngineBridge) {
    GeneratedPluginRegistrant.register(with: engineBridge.pluginRegistry)
  }
}