how request chaining work with NSUrlSessionDelegate

chainingRequestDelegate.swift

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

import UIKit
import XCPlayground

XCPSetExecutionShouldContinueIndefinitely(continueIndefinitely: true)

class ExampleChainingRequest: NSObject{
    
    private var session: NSURLSession!
    
    private let loginURL = "http://my.server.com/token"
    private let getUserDataURL = "http://my.server.com/user"
    private let getAddressesURL = "http://my.server.com/addresses"
    
    private var token = "76543ab3244ac"
    private var userID = 0
    private var addresses: [String] = []
    
    private var receivedData = NSMutableData()
    
    private var getTokenTask: NSURLSessionTask!
    private var getUserDataTask: NSURLSessionTask!
    private var getAddressesDataTask: NSURLSessionTask!
    
    override init(){
        super.init()
        let configuration = NSURLSessionConfiguration.defaultSessionConfiguration()
        session = NSURLSession(configuration: configuration, delegate: self, delegateQueue: nil)
    }
    
    
    private var loginRequest: NSURLRequest{
        
        let lognRequestURL = NSURL(string: loginURL)!
        let params = "username=admin&password=12345678"
        
        let loginRequest = NSMutableURLRequest()
        loginRequest.HTTPMethod = "POST"
        loginRequest.HTTPBody = params.dataUsingEncoding(NSUTF8StringEncoding)
        loginRequest.URL = lognRequestURL
        
        return loginRequest
    }
    
    // start with this function
    func getAddresses(){
        getTokenTask = session.dataTaskWithRequest(loginRequest)
        getTokenTask.resume()
    }
}

extension ExampleChainingRequest: NSURLSessionDataDelegate{
    
    func URLSession(session: NSURLSession, dataTask: NSURLSessionDataTask, didReceiveData data: NSData) {
        // concat a piece of data
        receivedData.appendData(data)
    }
    
    // handle everything inside delegate
    func URLSession(session: NSURLSession, task: NSURLSessionTask, didCompleteWithError error: NSError?) {
        
        if let error = error{
            return println(error)
        }
        
        if let result = NSString(data: receivedData, encoding: NSUTF8StringEncoding){
            println(result)
        }
        
        // do something with result
        
        // 1.
        if task == getTokenTask{
            
            println("we got token.")
            let getCurrentUserURL = NSURL(string: getUserDataURL + "?token=\(token)")!
            
            getUserDataTask = session.dataTaskWithURL(getCurrentUserURL)
            getUserDataTask.resume()
        
        // 2.
        }else if task == getUserDataTask{
            
            println("we got userData.")
            let getAddressesCurrentUserURL = NSURL(string: getAddressesURL + "?token=\(token)&userID=\(userID)")!
            
            getAddressesDataTask = session.dataTaskWithURL(getAddressesCurrentUserURL)
            getAddressesDataTask.resume()
            
        // 3.
        }else if task == getAddressesDataTask{
            println("we got user's addresses.")
            println("finish")
        }
        
        // clear previous request data
        receivedData = NSMutableData()
    }
    
}



// start here
let getAddresses = ExampleChainingRequest()
getAddresses.getAddresses()