todoRouter.swift

//1
enum TodoRouter: URLRequestConvertible {
  //2
  static let baseURLString = "https://jsonplaceholder.typicode.com/"
  //3
  case get(Int)
  case create([String: Any])
  case delete(Int)
  
  func asURLRequest() throws -> URLRequest {
    var method: HTTPMethod {
      switch self {
        case .get:
          return .get
        case .create:
          return .post
        case .delete:
          return .delete
      }
    }
    //4
    let params: ([String: Any]?) = {
      switch self {
      case .get, .delete:
        return nil
      case .create(let newTodo):
        return (newTodo)
      }
    }()
    //5
    let url: URL = {
      // build up and return the URL for each endpoint
      let relativePath: String?
      switch self {
        case .get(let number):
          relativePath = "todos/\(number)"
        case .create:
          relativePath = "todos"
        case .delete(let number):
          relativePath = "todos/\(number)"
      }
      //6
      var url = URL(string: TodoRouter.baseURLString)!
      if let relativePath = relativePath {
        url = url.appendingPathComponent(relativePath)
      }
      return url
    }()
    
    //7
    var urlRequest = URLRequest(url: url)
    urlRequest.httpMethod = method.rawValue
    
    //8
    let encoding: ParameterEncoding = {
      switch method {
        case .get:
          return URLEncoding.default
        default:
          return JSONEncoding.default
      }
    }()
    return try encoding.encode(urlRequest, with: params)
  }
}