Remote.swift

//
//  Remote.swift
//
//  Created by BJ Miller on 3/7/20.
//  Copyright © 2020 BJ Miller. All rights reserved.
//

import Foundation
import Combine

class AbstractRemote<T>: ObservableObject {
  @Published var result: Result<T, Error>? = nil
  fileprivate var transform: (Data) -> T?
  private var cancellable: AnyCancellable?

  var value: T? {
    guard let result = result else { return nil }
    switch result {
    case .failure(_): return nil
    case .success(let item): return item
    }
  }

  fileprivate var url: URL

  init() {
    self.url = URL(string: "http://foo.com")!
    self.transform = { _ in return nil }
  }

  func fetch() {
    cancellable = URLSession.shared.dataTaskPublisher(for: url)
      .map { $0.data }
      .compactMap(self.transform)
      .sink(receiveCompletion: { (completion: Subscribers.Completion<URLError>) in
        switch completion {
        case .failure(let err):
          print("error: \(err.localizedDescription)")
          DispatchQueue.main.async { self.result = .failure(err) }
        case .finished: break
        }
      }, receiveValue: { (item: T) in
        DispatchQueue.main.async { self.result = .success(item) }
      })
  }
}

class Remote<T: Decodable>: AbstractRemote<T> {
  init(url: URL) {
    super.init()
    self.url = url
    self.transform = { try? Decoders.defaultDecoder.decode(T.self, from: $0) }
  }
}

class RemoteData<T>: AbstractRemote<T> {
  init(url: URL, transform: @escaping (Data) -> T?) {
    super.init()
    self.url = url
    self.transform = transform
  }
}