NetworkManager.swift

import Alamofire
import SwiftyJSON

class APIManager {
    
    private init(){}
    
    class func request(
        _ url: URLConvertible,
        method: HTTPMethod,
        parameters: Parameters?,
        completionHandler: @escaping (JSON) -> Void)
    {
        var parameters = parameters
        if method == .get {
            parameters = nil
        }
        
        let parameterEncoding: ParameterEncoding = JSONEncoding.default
        
        var httpHeaders: HTTPHeaders = HTTPHeaders()
        httpHeaders["Content-Type"] = "application/json"
  
        
        
        Alamofire
            .request(url,
                     method     : method,
                     parameters : parameters,
                     encoding   : parameterEncoding,
                     headers    : httpHeaders)
            .responseJSON(completionHandler: { (response) in
                
                func handleSuccess(_ responseJSON: Any) {
                    let json = JSON(responseJSON)
                    completionHandler(json)
                }
                
                func handleNetworkError(_ error: Error) {
                    let alertController = UIAlertController(title: "Network Error",
                                                            message: error.localizedDescription,
                                                            preferredStyle: .alert)
                    
                    let btnRetry = UIAlertAction(title: "Retry",
                                                 style: .default,
                                                 handler: { (action) in
                                                    request(url,
                                                            method: method,
                                                            parameters: parameters,
                                                            completionHandler: completionHandler)
                    })
                    alertController.addAction(btnRetry)
                    
                    let btnCancel = UIAlertAction(title: "Cancel",
                                                  style: .cancel,
                                                  handler: { (action) in
                                                    let customError: [String: Any] = ["success": false,
                                                                                      "error_id": error._code,
                                                                                      "message": error.localizedDescription]
                                                    let json = JSON(customError)
                                                    completionHandler(json)
                    })
                    alertController.addAction(btnCancel)
                    
                    
                    let vc  = APIManager.getTopMostViewController()
                    
                    if !(vc is UIAlertController) {
                        vc?.present(alertController,
                                    animated: true,
                                    completion: nil)
                    }
                }
                
                switch(response.result) {
                case .success(let responseJSON):
                    handleSuccess(responseJSON)
                    
                case .failure(let error):
                    //Network related error
                    handleNetworkError(error)
                }
            })
    }
    
    class func getTopMostViewController() -> UIViewController? {
        var topMostViewController = UIApplication.shared.keyWindow?.rootViewController
        
        while let presentedViewController = topMostViewController?.presentedViewController {
            topMostViewController = presentedViewController
        }
        
        return topMostViewController
    }
    
}