Swiftgram/TelegramUI/ScreenCaptureDetection.swift

import Foundation
import SwiftSignalKit
import UIKit

enum ScreenCaptureEvent {
    case still
    case video
}

private final class ScreenRecordingObserver: NSObject {
    let f: (Bool) -> Void
    
    init(_ f: @escaping (Bool) -> Void) {
        self.f = f
        
        super.init()
        
        UIScreen.main.addObserver(self, forKeyPath: "captured", options: [.new], context: nil)
    }
    
    func clear() {
        UIScreen.main.removeObserver(self, forKeyPath: "captured")
    }
    
    override func observeValue(forKeyPath keyPath: String?, of object: Any?, change: [NSKeyValueChangeKey : Any]?, context: UnsafeMutableRawPointer?) {
        if keyPath == "captured" {
            if let value = change?[.newKey] as? Bool {
                self.f(value)
            }
        }
    }
}

private func screenRecordingActive() -> Signal<Bool, NoError> {
    return Signal { subscriber in
        if #available(iOSApplicationExtension 11.0, *) {
            subscriber.putNext(UIScreen.main.isCaptured)
            let observer = ScreenRecordingObserver({ value in
                subscriber.putNext(value)
            })
            return ActionDisposable {
                Queue.mainQueue().async {
                    observer.clear()
                }
            }
        } else {
            subscriber.putNext(false)
            return EmptyDisposable
        }
    } |> runOn(Queue.mainQueue())
}

func screenCaptureEvents() -> Signal<ScreenCaptureEvent, NoError> {
    return Signal { subscriber in
        let observer = NotificationCenter.default.addObserver(forName: NSNotification.Name.UIApplicationUserDidTakeScreenshot, object: nil, queue: .main, using: { _ in
            subscriber.putNext(.still)
        })
        
        var previous = false
        let screenRecordingDisposable = screenRecordingActive().start(next: { value in
            if value != previous {
                previous = value
                if value {
                    subscriber.putNext(.video)
                }
            }
        })
        
        return ActionDisposable {
            Queue.mainQueue().async {
                NotificationCenter.default.removeObserver(observer)
                screenRecordingDisposable.dispose()
            }
        }
    } |> runOn(Queue.mainQueue())
}