Simple RxSwift like Throttle functionality added to UISearchBar and UISearchController

ThrottledSearchController.swift

//  ThrottledSearchController.swift
//  Created by Daniele Margutti on 10/19/2017
//  Updated by RAFAT TOUQIR RAFSUN.
import UIKit

class ThrottledSearchController: UISearchController{
    // Mark this property as lazy to defer initialization until
    // the searchBar property is called.
    private lazy var customSearchBar = ThrottledSearchBar()

    // Override this property to return your custom implementation.
    override var searchBar: UISearchBar { customSearchBar }
    
}

class ThrottledSearchBar: UISearchBar, UISearchBarDelegate {
    
    /// Throttle engine
    private var throttler: Throttler? = nil
    
    /// Throttling interval
    var throttlingInterval: Double? = 0 {
        didSet {
            guard let interval = throttlingInterval else {
                self.throttler = nil
                return
            }
            self.throttler = Throttler(seconds: interval)
        }
    }
    
    /// Event received when cancel is pressed
    var onCancel: (() -> (Void))? = nil
    
    /// Event received when a change into the search box is occurred
    var onSearch: ((String) -> (Void))? = nil
    
    override init(frame: CGRect) {
        super.init(frame: frame)
        self.delegate = self
    }
    
    required init?(coder: NSCoder) {
        super.init(coder: coder)
        self.delegate = self
    }
    
    // Events for UISearchBarDelegate
    
    func searchBarCancelButtonClicked(_ searchBar: UISearchBar) {
        self.onCancel?()
    }
    
    func searchBarSearchButtonClicked(_ searchBar: UISearchBar) {
        self.onSearch?(self.text ?? "")
    }
    
    func searchBar(_ searchBar: UISearchBar, textDidChange searchText: String) {
        guard let throttler = self.throttler else {
            self.onSearch?(searchText)
            return
        }
        throttler.throttle {
            DispatchQueue.main.async {
                self.onSearch?(self.text ?? "")
            }
        }
    }
    
}

class Throttler {
    
    private let queue: DispatchQueue = DispatchQueue.global(qos: .background)
    private var job: DispatchWorkItem = DispatchWorkItem(block: {})
    private var previousRun: Date = Date.distantPast
    private var maxInterval: Double
    
    init(seconds: Double) {
        self.maxInterval = seconds
    }
    
    func throttle(block: @escaping () -> ()) {
        job.cancel()
        job = DispatchWorkItem(){ [weak self] in
            self?.previousRun = Date()
            block()
        }
        let delay = Date.second(from: previousRun) > maxInterval ? 0 : maxInterval
        queue.asyncAfter(deadline: .now() + Double(delay), execute: job)
    }
}

private extension Date {
    static func second(from referenceDate: Date) -> Double {
        return Date().timeIntervalSince(referenceDate).rounded()
    }
}

ViewController.swift

//  ViewController.swift
//  Created by RAFAT TOUQIR RAFSUN.
import UIKit

class ViewController: UIViewController {
    
    fileprivate let searchController: UISearchController = {
        let searchController = ThrottledSearchController(searchResultsController: nil)
        (searchController.searchBar as? ThrottledSearchBar)?.throttlingInterval = 0.5
        return searchController
    }()
    
    override func viewDidLoad() {
        super.viewDidLoad()

        // Do any additional setup after loading the view.
        self.setupSearchBar()
        
    }
    
    private func setupSearchBar(){
        searchController.searchResultsUpdater = self
        searchController.obscuresBackgroundDuringPresentation = false
        searchController.searchBar.placeholder = "Search Here..."
        self.navigationItem.searchController = searchController
        self.definesPresentationContext = true
        
        (searchController.searchBar as? ThrottledSearchBar)?.onSearch = {(searchText) in
            if searchText.trimmingCharacters(in: .whitespacesAndNewlines).isEmpty{
                print(searchText)
            }else {
                // A valid search (where searchText.count > MIN_CHARS_TO_SEARCH) could be used
                print(searchText)
                
            }
        }
    }
    
}

extension ViewController: UISearchResultsUpdating {
    func updateSearchResults(for searchController: UISearchController) { }
}