MicroWebservice.swift

import UIKit
import Foundation
import PlaygroundSupport

PlaygroundPage.current.needsIndefiniteExecution = true

let endpoint = "https://api.punkapi.com/v2/beers/1"
let url = URL(string: endpoint)!

typealias JSONDictionary = [String: Any]

struct Beer: Codable {
    let id: Int
    let name: String
}

extension Beer {
    init?(json: JSONDictionary) {
        guard let id = json["id"] as? Int,
            let name = json["name"] as? String else {
                return nil
        }
        self.id = id
        self.name = name
    }
}


struct Resource<A> {
    let url: URL
    let parse: (Data) -> A?
}

extension Resource {
    init(url: URL, parseJSON: @escaping (Any) -> A?) {
        self.url = url
        self.parse = { data in
            let json = try? JSONSerialization.jsonObject(with: data, options: [])
            return json.flatMap(parseJSON)
        }
    }
}

extension Beer {
    static let all = Resource<[Beer]>(url: url, parseJSON: { json in
        guard let dictionaries = json as? [JSONDictionary] else { return nil }
        return dictionaries.flatMap(Beer.init)
    })
}

final class Webservice {
    func load<A>(resource: Resource<A>, completion: @escaping (A?) -> ()) {
        URLSession.shared.dataTask(with: resource.url) { data, response, error in
            guard let data = data else {
                completion(nil)
                return
            }
            completion(resource.parse(data))
            }.resume()
    }
}


Webservice().load(resource: Beer.all) { result in
    if let result = result as [Beer]! {
        if let beer = result.first as! Beer! {
            print(beer)
        }
    }
}