from Swift Talk 1st episode

Networking.swift

// Check out the talk: https://talk.objc.io/episodes/S01E01-networking (Part 1)
// the talk uses swift 2 and I follow along by writing it in swift 3.

import Foundation
import PlaygroundSupport

//extension Sequence {
//    public func failingFlatMap<T>(_ transform: @noescape(Self.Iterator.Element) throws -> T?) rethrows -> [T]? {
//        var result: [T] = []
//        for element in self {
//            guard let transformed = try transform(element) else { return nil }
//            result.append(transformed)
//        }
//        return result
//    }
//}


typealias JSONDictionary = [String: AnyObject]
struct Episode { let id, title: String }
extension Episode {
    init?(dictionary: JSONDictionary) {
        guard let id = dictionary["id"] as? String,
            title = dictionary["title"] as? String
            else { return nil }
        
        self.id = id; self.title = title
    }
}

struct Media {}

struct Resource<A> { let url: URL, parse: (Data) -> A? }
extension Resource {
    init(_ url: URL, parseJSON: (AnyObject) -> A?) {
        self.url = url
        self.parse = { data in
            let json = try? JSONSerialization.jsonObject(with: data)
            return json.flatMap(parseJSON)
        }
    }
}

extension Episode {
    static let all = Resource<[Episode]> (url) {
        return ($0 as? [JSONDictionary])?.flatMap(Episode.init)
    }
    
    var media: Resource<Media> {
        let url = URL(string: "http://localhost:8000/episodes/\(id).json")!
        // TODO: Retuen the resource...
    }
}

final class WebService {
    func load<A>(resource: Resource<A>, completion: (A?) -> Void) {
        URLSession.shared().dataTask(with: resource.url) { (data, _, _) in
            completion(data.flatMap(resource.parse))
        }.resume()
    }
}

PlaygroundPage.current.needsIndefiniteExecution = true

WebService().load(resource: Episode.all) { print($0) }