Combine Exercise Solution

combine_exercise.swift

// One solution to the class exercise

import UIKit
import Combine
import PlaygroundSupport

// This playground will execute indefinetly in order to give our
// async operations enough time to execute.
PlaygroundPage.current.needsIndefiniteExecution = true


// --- Creating a publisher for performing a network request ---
//     Note: set a retry automatically (3x) if request fails

let url = URL(string: "https://api.github.com/search/repositories?q=language:swift&sort=stars&order=desc")!
let publisher = URLSession.shared
  .dataTaskPublisher(for: url)
  .retry(3)


// --- Bringing back our old friends ---

struct Repositories: Codable {
  let items: [Repository]
  
  enum CodingKeys: String, CodingKey {
    case items
  }
}

struct Repository: Codable, Identifiable {
  let id: Int
  let name: String
  let htmlURL: String
  let itemDescription: String?
  
  enum CodingKeys: String, CodingKey {
    case id
    case name
    case htmlURL = "html_url"
    case itemDescription = "description"
  }
}


// --- Constructing a reactive chain of operators ---

let repoPublisher = publisher
    .map(\.data)
    .decode(
        type: Repositories.self,
        decoder: JSONDecoder()
    )
    .receive(on: DispatchQueue.main)


// --- Updating our UI based on our reactive chain ---

// Some UI labels that we want to render our data using:
  let nameLabel = UILabel()
  let urlLabel = UILabel()
  let errorLabel = UILabel()

let cancellableRepoSubscriber = repoPublisher.sink(
    receiveCompletion: { completion in
        switch completion {
        case .failure(let error):
            // Rendering a description of the error that was encountered:
            print("ErrorMsg: \(error.localizedDescription)")
        case .finished:
            break
        }
    },
    receiveValue: { repos in
        // Rendering each repository's name and url:
        _ = repos.items.map { repo in
          print("Name: \(repo.name)")
          print("URL:  \(repo.htmlURL)")
          print("-----")
        }
    }
)