iOS-NetworkController.swift

import UIKit
import Foundation

internal let ACCEPT_HEADER_KEY: String = "Accept"
internal let ACCEPT_HEADER_VALUE: String = "application/json"

class NetworkController {
    
    private init() {}
    static let sharedInstance = NetworkController()
    
    func dataRequest<T: Decodable>( url: String,
                                    objectType: T.Type,
                                    method: RequestMethod? = .GET,
                                    parameters: [String : Any]? = nil,
                                    completion: @escaping (Result<T>) -> Void ) {
        var request: URLRequest!
        
        if !Reachability.connectedToNetwork{
            completion(Result.failure(APPError.connectivityError))
            return
        }
        
        /*------------------------------------------
            POST REQUEST
        --------------------------------------------*/

        if method == .POST{
            guard let urlToRequest = URL(string: url) else { return }
            request = URLRequest(url: urlToRequest)
            if parameters != nil {
                guard let postData = try? JSONSerialization.data(withJSONObject: parameters!, options:[]) else { return }
                request.httpBody = postData
            }
            request.httpMethod = "POST"
        }
        
        /*------------------------------------------
            GET REQUEST
         --------------------------------------------*/
        if method == .GET{
            var components = URLComponents(string: url)!
            if parameters != nil{
                var items:[URLQueryItem] = [URLQueryItem]()
                for (key,value) in parameters! {
                    items.append(URLQueryItem(name: key, value: "\(value)"))
                }
                components.queryItems = items
            }
            components.percentEncodedQuery = components.percentEncodedQuery?.replacingOccurrences(of: "+", with: "%2B")
            guard let urlToRequest = components.url else { return }
            request = URLRequest(url: urlToRequest)
            request.httpMethod = "GET"
        }
        
        
        request.addValue(ACCEPT_HEADER_VALUE, forHTTPHeaderField: ACCEPT_HEADER_KEY)
        request.cachePolicy = .reloadIgnoringLocalAndRemoteCacheData
        request.timeoutInterval = 60
        let task = URLSession.shared.dataTask(with: request, completionHandler: { data, response, error in
            
            guard error == nil else {
                completion(Result.failure(APPError.networkError(error!)))
                return
            }
            
            guard let jsonData = data else {
                completion(Result.failure(APPError.dataNotFound))
                return
            }
            
            do {
                let decodedObject = try JSONDecoder().decode(objectType.self, from: jsonData)
                completion(Result.success(decodedObject))
            } catch let error {
                completion(Result.failure(APPError.jsonParsingError(error as! DecodingError)))
            }
        })
        
        task.resume()
    }
    
}


enum APPError: Error {
    case connectivityError
    case networkError(Error)
    case dataNotFound
    case jsonParsingError(Error)
    case invalidStatusCode(Int)
}

enum Result<T> {
    case success(T)
    case failure(APPError)
}

enum RequestMethod {
    case POST
    case GET
}