Generic NetworkService

NetworkService.swift

import Foundation

public enum Result<Value> {
    case success(Value)
    case failure(Error)
}

public protocol Resource {
    associatedtype Response
    func makeRequest() -> URLRequest
    func parseResponse(_ data: Data) throws -> Response
}

public final class NetworkService {

    private let session: URLSession

    public init(session: URLSession = .shared) {
        self.session = session
    }

    @discardableResult
    public func fetch<R: Resource>(_ resource: R, completion: @escaping (Result<R.Response>) -> Void) -> URLSessionTask {
        let task = session.dataTask(with: resource.makeRequest()) { data, _, error in
            if let error = error {
                completion(.failure(error))
            } else if let data = data {
                do {
                    let response = try resource.parseResponse(data)
                    completion(.success(response))
                } catch {
                    completion(.failure(error))
                }
            } else {
                assertionFailure()
            }
        }
        task.resume()
        return task
    }
}