SpotifyAPI helper in Swift

SpotifyApi.swift

import Foundation
import Alamofire
import RxSwift
import SwiftyJSON

class SpotifyAPI {
    let accessToken:String
    let url:String
    let params:[String:AnyObject]
    
    var items:[JSON] = []
    var offset = 0
    var limit = 30
    
    
    init(accessToken:String, url:String, params:[String:AnyObject]) {
        self.accessToken = accessToken
        self.url = url
        self.params = params
    }
    
    func getAll(offset:Int = 0) -> Observable<JSON> {
        let headers = [
            "Accept": "application/json; charset=utf-8",
            "Authorization": "Bearer \(self.accessToken)"
        ]
        var params = self.params
        params["offset"] = offset
        params["limit"] = self.limit
        
        DLOG("Getting `\(url)`: params: \(params)")
        return Observable.create({ (subscriber) -> Disposable in
            delay(0.5, closure: {
                Alamofire.request(.GET, self.url, parameters: params, headers: headers).validate().responseJSON { (response) in
                    switch(response.result) {
                    case .Success:
                        let data = JSON(response.result.value!)
                        self.items.append(data)
                        subscriber.onNext(data)
                        subscriber.onCompleted()
                    case .Failure(let error):
                        let data = String(data: response.data!, encoding: NSUTF8StringEncoding)
                        DLOG("Got error from Spotify API: \(data)")
                        subscriber.onError(error)
                        subscriber.onCompleted()
                        return
                        
                    }
                }
            })
            
            return AnonymousDisposable {
                
            }
        }).flatMap({ (data:JSON) -> Observable<JSON> in
            let totalItems = self.items.count * self.limit
            if data["total"].intValue > totalItems && data["items"].array!.count > 0 {
                return self.getAll(totalItems)
            }
            return Observable.empty()
        })
    }
    
    
}

// And here example usage
let api = SpotifyAPI(accessToken: SpotifyAuth.sharedInstance.session!.accessToken, url: "https://api.spotify.com/v1/me/tracks", params: [:])
        let observableApi = api.getAll()
        _ = observableApi.subscribe(onNext: nil, onError: { (error) in
            DLOG("Got error on Spotify API: \(error)")
            self.delegate?.playlist(self, gotError: error as NSError)
            done()
            }, onCompleted: {
                self.tracks = api.items.flatMap({ (data) -> [JSON] in
                    let items = data["items"].array!
                    return items
                }).flatMap({ (track) -> Track? in
                    guard let trackId = track["track"]["id"].string else {
                        return nil
                    }
                    return Track(id: trackId, name: track["track"]["name"].string!, album: track["track"]["album"]["name"].string!, artist: track["track"]["artists"][0]["name"].string!)
                })
                done()
            }, onDisposed: nil)