dimebt

    fetchJSON(fromURL: "http://api.json") { (json, error) in
    
    }

dimebt

        fetchJSON(fromURL: "someURL") { (response, results, error) in
            switch response {
            case .success:
                fetchUserData(for: results) { (response, results, error) in
                    switch response {
                    case .success:
                        loginUser(user: results) { (response, results, error) in
                            switch response {
                            case .success:
                                // finialy all of the callbacks are finished

dimebt

fetchJSON(fromURL: "someURL") { (response, results, error) in
    
}

dimebt

func promiseFetchJSON() -> Promise<[String: Any]> {
        return Promise<[String: Any]> { seal in
            fetchJSON(fromURL: "someURL", completion: { (response, results, error) in
                switch response {
                case .success:
                    seal.fulfill(results)
                case .fail:
                    seal.reject(error)
                }
            })

dimebt

func promiseFetchJSON() -> Promise<[String: Any]> {
        return Promise<[String: Any]> { seal in
            fetchJSON(fromURL: "someURL", completion: { (response, results, error) in
                switch response {
                case .success:
                    seal.fulfill(results)
                case .fail:
                    seal.reject(error)
                }
            })

dimebt

func promiseFetchUserData(user: [String: Any]) -> Promise<User> {
        return Promise<User> { seal in
            fetchUserData(for: user, completion: { (response, results, error) in
                switch response {
                case .success:
                    seal.fulfill(results)
                case .fail:
                    seal.reject(error)
                }
            })

dimebt

firstly {
    promise1()
}.then {
    promise2()
}.then {
    promise3()
}.ensure {
    // something that should happen whatever the outcome
}.done {
    // all promises are resolved

dimebt

firstly {
    promiseFetchJSON()
}.then { (json)  in
    promiseFetchUserData(user: json)
}.then { (user) in
    promiseLoginUser(user: user)
}.ensure {
    // something that should happen whatever the outcome        
}.done { (success) in
    // all promises are resolved

dimebt

private func downloadPhotos() {
        //  1. Show preloading animation
        self.activityIndicator.startAnimating()
        //  2. Fetch and serialize json response
        Alamofire.request(photosURL, method: .get).validate().responseData { (data) in
            guard let data = data.result.value else { return }
            guard let photos = try? JSONDecoder().decode([Photo].self, from: data) else { return }
            //  3. Download photos
            for photo in photos {
                guard let photoUrl = URL(string: photo.url) else { return }

dimebt

private func function() -> Promise<T> {
    return Promise<T> { seal in
         
    }
}