How to handle keyDown in NSResponder

import AppKit
import Omnia

class MyWindow: NSWindow {
    override func keyDown(with event: NSEvent) {
        super.keyDown(with: event)

        if isKey(NSDeleteCharacter, event: event) {
            NotificationCenter.default.post(Notification(name: .didKeyboardDeleteItem))
        } else if isKey(NSUpArrowFunctionKey, event: event) {
            print("up")
        } else if isKey(NSDownArrowFunctionKey, event: event) {
            print("down")
        } else if isKey(NSLeftArrowFunctionKey, event: event) {
            print("left")
        } else if isKey(NSRightArrowFunctionKey, event: event) {
            print("right")
        }
    }

    private func isKey(_ key: Int, event: NSEvent) -> Bool {
        if let scalar = UnicodeScalar(key) {
            return event.characters == String(scalar)
        } else {
            return false
        }
    }
}

NSEvent.addLocalMonitorForEvents(matching: .keyDown) { event in
       if handled(with: $0) {
          return nil
       }
       return event
    }

class MyWindow: NSWindow {
    override func keyDown(with event: NSEvent) {
        if !EventService.shared.inspect(event) {
            super.keyDown(with: event)
        }
    }

    override var canBecomeKey: Bool  { true }
    override var canBecomeMain: Bool { true }
    override var acceptsFirstResponder: Bool { true }
    override func becomeFirstResponder() -> Bool { true }
}

import AppKit
import Omnia
import KeyboardShortcuts

final class EventService {
    static let shared = EventService()

    private var combos: [Combo] = []
    private let debouncer = Debouncer(delay: 0.1)

    func register(_ combo: Combo) {
        combos.append(combo)
    }

    func inspect(_ event: NSEvent) -> Bool {
        for combo in combos {
            if combo.match(event) {
                self.debouncer.run {
                    combo.action()
                }
                return true
            }
        }

        return false
    }
}

extension EventService {
    struct Combo {
        let modifier: NSEvent.ModifierFlags?
        let keyCode: KeyboardShortcuts.Key
        let action: () -> Void

        func match(_ event: NSEvent) -> Bool {
            if let modifier = modifier,
               !event.modifierFlags.contains(modifier) {
                return false
            }

            if event.keyCode != keyCode.rawValue {
                return false
            }

            return true
        }
    }
}