An extension enabling global access to settings scene of a macOS SwiftUI application.

NSApplication+openSettings.swift

//
//  NSApplication+openSettings.swift
//
//  Created by Stephan Casas on 12/3/23.
//

import SwiftUI;

extension NSApplication {
    
    /// Open the application settings/preferences window.
    func openSettings() {
        // macOS 14 Sonoma
        if let internalItemAction = NSApp.mainMenu?.item(
            withInternalIdentifier: "app"
        )?.submenu?.item(
            withAction: Selector(("menuAction:"))
        )?.internalItemAction {
            internalItemAction();
            return;
        }
        
        guard let delegate = NSApp.delegate else { return }
        
        // macOS 13 Ventura
        var selector = Selector(("showSettingsWindow:"));
        if delegate.responds(to: selector) {
            delegate.perform(selector, with: nil, with: nil);
            return;
        }
        
        // macOS 12 Monterrey
        selector = Selector(("showPreferencesWindow:"));
        if delegate.responds(to: selector) {
            delegate.perform(selector, with: nil, with: nil);
            return;
        }
    }
    
}

// MARK: - NSMenuItem (Private)

extension NSMenuItem {
    
    /// An internal SwiftUI menu item identifier that should be a public property on `NSMenuItem`.
    var internalIdentifier: String? {
        guard let id = Mirror.firstChild(
            withLabel: "id", in: self
        )?.value else {
            return nil;
        }
        
        return "\(id)";
    }
    
    /// A callback which is associated directly with this `NSMenuItem`.
    var internalItemAction: (() -> Void)? {
        guard 
            let platformItemAction = Mirror.firstChild(
                withLabel: "platformItemAction", in: self)?.value,
            let typeErasedCallback = Mirror.firstChild(
                in: platformItemAction)?.value
        else {
            return nil;
        }
            
        return Mirror.firstChild(
            in: typeErasedCallback
        )?.value as? () -> Void;
    }
    
}

// MARK: - NSMenu (Private)

extension NSMenu {
    
    /// Get the first `NSMenuItem` whose internal identifier string matches the given value.
    func item(withInternalIdentifier identifier: String) -> NSMenuItem? {
        self.items.first(where: {
            $0.internalIdentifier?.elementsEqual(identifier) ?? false
        })
    }
    
    /// Get the first `NSMenuItem` whose action matches the given selector.
    func item(withAction action: Selector) -> NSMenuItem? {
        self.items.first(where: {
            $0.action == action
        })
    }
    
}

// MARK: - Mirror (Helper)

fileprivate extension Mirror {
    
    /// The unconditional first child of the reflection subject.
    var firstChild: Child? { self.children.first }
    
    /// The first child of the reflection subject whose label matches the given string.
    func firstChild(withLabel label: String) -> Child? {
        self.children.first(where: {
            $0.label?.elementsEqual(label) ?? false
        })
    }
    
    /// The unconditional first child of the given subject.
    static func firstChild(in subject: Any) -> Child? {
        Mirror(reflecting: subject).firstChild
    }
    
    /// The first child of the given subject whose label matches the given string.
    static func firstChild(
        withLabel label: String, in subject: Any
    ) -> Child? {
        Mirror(reflecting: subject).firstChild(withLabel: label)
    }
    
}