halkyon/apps/todo/halkyon_todo_flutter/macos/Runner/MainFlutterWindow.swift

import Cocoa
import FlutterMacOS

class MainFlutterWindow: NSWindow {
  /// The channel halkyon_app's SecretScreen asks to keep the window out of
  /// screenshots and screen recordings while something secret shows (the
  /// recovery phrase, recovery codes, an authenticator's key), and how many
  /// show: counted, as several may at once.
  private var screenGuard: FlutterMethodChannel?
  private var secretsShown = 0

  override func awakeFromNib() {
    let flutterViewController = FlutterViewController()
    let windowFrame = self.frame
    self.contentViewController = flutterViewController
    self.setFrame(windowFrame, display: true)

    RegisterGeneratedPlugins(registry: flutterViewController)
    guardScreen(messenger: flutterViewController.engine.binaryMessenger)

    super.awakeFromNib()
  }

  private func guardScreen(messenger: FlutterBinaryMessenger) {
    let channel = FlutterMethodChannel(
      name: "app.halkyon/screen_guard", binaryMessenger: messenger)
    channel.setMethodCallHandler { [weak self] call, result in
      guard let self = self else {
        result(nil)
        return
      }
      switch call.method {
      case "hold":
        self.secretsShown += 1
        self.sharingType = .none
        result(nil)
      case "release":
        self.secretsShown = max(0, self.secretsShown - 1)
        if self.secretsShown == 0 {
          self.sharingType = .readOnly
        }
        result(nil)
      default:
        result(FlutterMethodNotImplemented)
      }
    }
    screenGuard = channel
  }
}