Protocol Oriented Programing [Networking-Error Example]

pop.swift

/****
  Protocol Oriented Programing 
  Networking-Error Example
***/
import Foundation

public protocol NetworkController {
 func fetchCurrentWeatherData(city: String, 
                 completionHandler: @escaping (WeatherData?, NetworkControllerError?) -> Void) -> WeatherData?
}

public struct WeatherData {
 var temperature: Float
 var condition: String
 var unit: TemperatureUnit
}

public enum TemperatureUnit: String {
 case scientific = "scientific"
 case metric = "metric"
 case imperial = "imperial"
}

public enum NetworkControllerError: Error {
 case invalidURL(String)
 case invalidPayload(URL)
 case forwarded(Error) 
}

/// IMPLEMENTATION

func fetchCurrentWeatherData(city: String, 
                 completionHandler: @escaping (WeatherData?, NetworkControllerError?) -> Void) -> WeatherData? {
  
  let session = URLSession(configuration: URLSessionConfiguration.default, delegate: nil, delegateQueue: OperationQueue.main)
  let endpoint = "http://URL/API"
  let safeURLString = endpoint.addingPercentEncoding(withAllowedCharacters: .urlQueryallowed)
  
  guard let endpointURL = URL(string: safeURLString!) else {
   completionHandler(nil, NetworkControllerError.invalidURL(safeURLString!))
    return
  }
  
  let dataTask = session.dataTask(witch: endpointURL) { (data, response, error) in
      guard error == nil else {
        completionHandler(nil, NetworkControllerError.forwarded(error!))
        return 
      }
                                                       
      guard let jsonData = data else {
           completionHandler(nil, NetworkControllerError.invalidPayload(endpointURL))
      }
                                                       
      self.decode(jsonDta: jsonData, endpointURL: URL, completionHandler: completionHandler)
       
  }//end dataTask
  dataTask.resume()
}