URLSession+Combine.swift

//
//  URLSessionHelpers.swift
//
//  Created by Mauricio Cousillas on 6/17/19.
//  Copyright © 2019 Mauricio Cousillas. All rights reserved.
//

import Foundation
import Combine

enum APIError: Error {
  case invalidUrl
  case unknown(error: Error?)
  case decoding(error: Error?)
  case request(statusCode: Int, error: Error?)
}

extension URLSession {
  func send(request: URLRequest) -> AnyPublisher<Data, APIError> {
    Publishers.Future { promise in
      let task = self.dataTask(with: request) { [weak self] data, response, error in
        guard let self = self else {
          promise(.failure(.unknown(error: error)))
          return
        }
        DispatchQueue.main.async {
          self.handleResponse(data, response, error, promise)
        }
      }
      task.resume()
    }.eraseToAnyPublisher()
  }

  private func handleResponse(_ data: Data?, _ response: URLResponse?, _ error: Error?, _ promise: @escaping (Result<Data, APIError>) -> Void) {
    guard let httpReponse = response as? HTTPURLResponse else {
      promise(.failure(.unknown(error: error)))
      return
    }

    guard let data = data, 200..<300 ~= httpReponse.statusCode else {
      promise(.failure(.request(statusCode: httpReponse.statusCode, error: error)))
      return
    }

    promise(.success(data))
  }
}