auth.swift

//: Playground - noun: a place where people can play

import UIKit

typealias JSON = [String: AnyObject]

protocol Authable {
    static func login(params: JSON?, completion: (ResultType<User>) -> Void)
    static func logout()
}

enum ResultType<T> {
    case success(T)
    case error(String)
}

struct User {
    
}

struct EmailAuth: Authable {
    static func login(params: JSON?, completion: (ResultType<User>) -> Void) {
        guard let params = params,
            email = params["email"] as? String,
            password = params["password"] as? String else {
                completion(.error("enter a username and password"))
                return
        }
        
        // do some login stuff
    }
    
    static func logout() {
        // remove stuff
    }
}

struct FacebookAuth: Authable {
    static func login(params: JSON? = nil, completion: (ResultType<User>) -> Void) {
        // do the fb auth flow
    }
    
    static func logout() {
        // remove stuff
    }
}

enum Auth {
    
    case email(String, String)
    case facebook
    
    func login(completion: (ResultType<User>) -> Void) {
        switch self {
        case .email(let email, let password):
            EmailAuth.login(["email":email, "password":password], completion: completion)
        case .facebook:
            FacebookAuth.login(completion: completion)
        }
    }
}

Auth.email("", "").login { result in
    
}

Auth.facebook.login { result in
    
}