Prevent Mac Catalyst apps from running in the background for a long time, after user explicitly quit it.

MacCatalystFastQuitHelper.swift

//
//  MacCatalystFastQuitHelper
//
//  Copyright © 2022 Jonny Kuang. MIT
//

import UIKit

enum MacCatalystFastQuitHelper {
    
    /// Enforces a maximum 3 seconds of execution time on all background tasks.
    /// The app will be terminated within 3 seconds once user clicks the Quit App button.
    static let setup: Void = {
#if targetEnvironment(macCatalyst)
        swizzleInstanceMethod(
            class: UIApplication.self,
            originalSelector: #selector(UIApplication.beginBackgroundTask(expirationHandler:)),
            swizzledSelector: #selector(UIApplication.kjy_swizzle_disable_beginBackgroundTask(expirationHandler:))
        )
        swizzleInstanceMethod(
            class: UIApplication.self,
            originalSelector: #selector(UIApplication.beginBackgroundTask(withName:expirationHandler:)),
            swizzledSelector: #selector(UIApplication.kjy_swizzle_disable_beginBackgroundTask(withName:expirationHandler:))
        )
#endif
    }()
}

#if targetEnvironment(macCatalyst)
private extension UIApplication {
    
    typealias Closure = () -> Void
    
    @objc func kjy_swizzle_disable_beginBackgroundTask(expirationHandler: Closure?) -> UIBackgroundTaskIdentifier {
        kjy_swizzle_disable_beginBackgroundTask(
            expirationHandler: _resolved(expirationHandler: expirationHandler, taskName: nil)
        )
    }
    
    @objc func kjy_swizzle_disable_beginBackgroundTask(withName taskName: String?, expirationHandler: Closure?) -> UIBackgroundTaskIdentifier {
        kjy_swizzle_disable_beginBackgroundTask(
            withName: taskName,
            expirationHandler: _resolved(expirationHandler: expirationHandler, taskName: taskName)
        )
    }
    
    func _resolved(expirationHandler: Closure?, taskName: String?) -> Closure {
        var expirationHandler = expirationHandler
        let endTask = {
            let handler = expirationHandler
            expirationHandler = nil
            handler?()
        }
        if let taskName = taskName, taskName.contains("CoreData") {
            // don't mess with CoreData
        } else {
            DispatchQueue.main.asyncAfter(deadline: .now() + 3, execute: endTask)
        }
        return endTask
    }
}
#endif

Swizzle.swift

//
//  Swizzle.swift
//
//  Copyright © 2022 Jonny Kuang. MIT
//

import Foundation

@discardableResult
public func swizzleInstanceMethod(class aClass: AnyClass?, originalSelector: Selector, swizzledSelector: Selector) -> Bool {
    swizzleMethod(class: aClass, originalSelector: originalSelector, swizzledSelector: swizzledSelector, isClassMethod: false)
}

@discardableResult
public func swizzleClassMethod(class aClass: AnyClass?, originalSelector: Selector, swizzledSelector: Selector) -> Bool {
    swizzleMethod(class: aClass, originalSelector: originalSelector, swizzledSelector: swizzledSelector, isClassMethod: true)
}

private func swizzleMethod(class aClass: AnyClass?, originalSelector: Selector, swizzledSelector: Selector, isClassMethod: Bool) -> Bool {
    
    guard var aClass = aClass else {
        assertionFailure("class not exist.")
        return false
    }
    
    if isClassMethod {
        if let _class = NSStringFromClass(aClass).withCString(objc_getMetaClass) as? AnyClass {
            aClass = _class
        } else {
            assertionFailure("meta class not found.")
        }
    }
    
    guard let originalMethod = isClassMethod ? class_getClassMethod(aClass, originalSelector) : class_getInstanceMethod(aClass, originalSelector),
          let swizzledMethod = isClassMethod ? class_getClassMethod(aClass, swizzledSelector) : class_getInstanceMethod(aClass, swizzledSelector)
    else {
        assertionFailure("\(isClassMethod ? "class" : "instance") method unavailable. class: \(aClass) originalSelector: \(originalSelector) swizzledSelector: \(swizzledSelector)")
        return false
    }
    
    if class_addMethod(aClass, originalSelector, method_getImplementation(swizzledMethod), method_getTypeEncoding(swizzledMethod)) {
        class_replaceMethod(aClass, swizzledSelector, method_getImplementation(originalMethod), method_getTypeEncoding(originalMethod))
    } else {
        method_exchangeImplementations(originalMethod, swizzledMethod)
    }
    return true
}