asynchronous_programming.swift

// Asyncronous programming

import Foundation

// # Async-await samples
// ## Instead of using callbacks, ...
func getEmployeesJSON(url: URL, callback: @escaping ([Employee]) -> ())) {
    URLSession.shared.dataTask(with: url), let response, response as? HTTPURLResponse, error == nil else {
    if let let error = error {
        print("Error downloading: \(error)")
        return
    } 
    if response.statusCode == 200 {
        do {
            let employees = try? JSONDecoder().decode([Employee].self, from: data)
            callback(employees)
        } catch {
            print("Error decoding: \(error)")
        }
    } else {
        print("Error downloading: \(response.statusCode)")
    }.resume()
}

// ## ... we can use async-await
func getEmployeesJSON(url: URL) async throws -> [Employee] {
    let (data, response) = try await URLSession.shared.data(from: url)
    guard let response = response as? HTTPURLResponse, response.statusCode == 200 else {
        throw URLError(.badServerResponse)
    }
    return try JSONDecoder().decode([Employee].self, from: data)
}

Task(priority: .background) {
    do {
        let employees = try await getEmployeesJSON(url: url)
        print(employees)
    } catch {
        print("Error downloading: \(error)")
    }
}