DownloadJSON.swift

// Swift 1.2
// synchronous JSON download

import XCPlayground

// my goodness all this complexity is just for an unconditional synchronous
// get in a playground on HTTP or HTTPS and decoding to JSON. sad.

public func waitUntilTrue(@autoclosure pred:()->Bool, secondsUntilTimeout duration:NSTimeInterval = 25)
{
  let previousPlayGroundRunStatus = XCPExecutionShouldContinueIndefinitely()
  XCPSetExecutionShouldContinueIndefinitely(continueIndefinitely: true)
  
  let start = NSDate()
  while true {
    if pred() {
      NSLog("condition met.")
      break
    }
    else if fabs(start.timeIntervalSinceNow) > duration {
      NSLog("timeout")
      break
    }
    else {
      sleep(1)
    }
  }
  
  XCPSetExecutionShouldContinueIndefinitely(continueIndefinitely: previousPlayGroundRunStatus)
}

public class NSURLSessionAllowBadCertificateDelegate : NSObject, NSURLSessionDelegate
{
  public func URLSession(session: NSURLSession, didReceiveChallenge challenge: NSURLAuthenticationChallenge, completionHandler: (NSURLSessionAuthChallengeDisposition, NSURLCredential!) -> Void)
  {
    if challenge.protectionSpace.authenticationMethod == NSURLAuthenticationMethodServerTrust
    {
      let trustObject = challenge.protectionSpace.serverTrust
      let credential = NSURLCredential(forTrust: challenge.protectionSpace.serverTrust)
      completionHandler(NSURLSessionAuthChallengeDisposition.UseCredential,credential)
    }
    else {
      completionHandler(NSURLSessionAuthChallengeDisposition.PerformDefaultHandling,nil)
    }
  }
}

public func downloadJSON(URLString:String, orTimeoutAfterDuration duration:NSTimeInterval = 10) -> AnyObject?
{
  let url = NSURL(string: URLString)!
  let session = NSURLSession(
    configuration: NSURLSessionConfiguration.ephemeralSessionConfiguration(),
    delegate: NSURLSessionAllowBadCertificateDelegate(),
    delegateQueue: nil)
  
  var result:AnyObject?
  
  let task = session.dataTaskWithURL(url, completionHandler: { (data, response, error) -> Void in
    var JSONError:NSError?
    if let response = response as? NSHTTPURLResponse where response.statusCode == 200,
      let data = data
    {
      result  = NSJSONSerialization.JSONObjectWithData(data, options: NSJSONReadingOptions.allZeros, error: &JSONError)
    }
  })
  task.resume()
  
  // just poll every sec. would be better to use an async NSOperation?
  waitUntilTrue(result != nil, secondsUntilTimeout: duration)
  
  return result
}