ObjectOrientedApproach.swift

/* Object Oriented Approach */

// Conversion of Data to JSONObject

class Deserializer {
    func deserialize(_ data: Data?) -> JSONObject? {
        guard let data = data else {
            return nil
        }
        
        do {
            return try JSONObject(JSONSerialization.jsonObject(with: data, options: .allowFragments))
        } catch {
            return nil
        }
    }
}

// Conversion of JSONObject to Model

protocol ModelDeserializerType {
    associatedtype Deserializable
    
    func model(fromJSONObject json: JSONObject?) -> Deserializable?
}

class ModelDeserializer<T>: ModelDeserializerType {
    typealias Deserializable = T
    
    var deserializer = Deserializer()
    
    /**
     Subclasses must override this method and provide an implementation.
     */
    func model(fromJSONObject json: JSONObject?) -> Deserializable? {
        return nil
    }
}

// Helper for decoding JSON

struct JSONDecoder {
    private let dictionary: [String: Any]
    
    init?(json: JSONObject?) {
        guard let json = json, case .dictionary(let dictionary) = json else { return nil }
        self.dictionary = dictionary
    }
    
    func decode<T>(key: String) -> T? {
        guard let object = dictionary[key] as? T else { return nil }
        return object
    }
}

// Creating a User from a JSONObject

class UserDeserializer: ModelDeserializer<User> {
    override func model(fromJSONObject json: JSONObject?) -> User? {
        guard let decoder = JSONDecoder(json: json) else {
            return nil
        }
        
        guard let firstName: String = decoder.decode(key: "FirstName") else {
            return nil
        }
        
        let url = decoder.decode(key: "AvatarURL").flatMap(URL.init(string:))
        
        return User(avatarURL: url, firstName: firstName)
    }
}

// Example Usage

let userJSON: [String: Any] = [
    "FirstName": "Tyler",
    "AvatarURL": "https://upload.wikimedia.org/wikipedia/commons/thumb/3/3c/William_Howard_Taft_1909b.jpg/1200px-William_Howard_Taft_1909b.jpg"
]
let userData = try JSONSerialization.data(withJSONObject: userJSON, options: [])
let json = Deserializer().deserialize(userData)
let user: User? = UserDeserializer().model(fromJSONObject: json)

let imageData = try Data(contentsOf: user!.avatarURL!)
UIImageView(image: UIImage(data: imageData))