/**
 * Tae Won Ha - http://taewon.de - @hataewon
 * See LICENSE
 */

import Foundation
import RxSwift

public final class RxMessagePortClient {

  public enum Error: Swift.Error {

    case serverInit
    case clientInit
    case portInvalid
    case send(msgid: Int32, response: Int32)

    public static func responseCodeToString(code: Int32) -> String {
      switch code {

      case kCFMessagePortSendTimeout:
        return "kCFMessagePortSendTimeout"

      case kCFMessagePortReceiveTimeout:
        return "kCFMessagePortReceiveTimeout"

      case kCFMessagePortIsInvalid:
        return "kCFMessagePortIsInvalid"

      case kCFMessagePortTransportError:
        return "kCFMessagePortTransportError"

      case kCFMessagePortBecameInvalidError:
        return "kCFMessagePortBecameInvalidError"

      default:
        return "unknown"

      }
    }
  }

  public static let defaultTimeout = CFTimeInterval(5)

  public var timeout = RxMessagePortClient.defaultTimeout

  public var queue = DispatchQueue(
    label: String(reflecting: RxMessagePortClient.self),
    qos: .userInitiated
  )

  public init() {
  }

  public func send(
    msgid: Int32,
    data: Data?,
    expectsReply: Bool
  ) -> Single<Data?> {
    return Single.create { single in
      self.queue.async {
        self.portLock.withReadLock {
          guard self.portIsValid else {
            single(.error(Error.portInvalid))
            return
          }

          let returnDataPtr: UnsafeMutablePointer<Unmanaged<CFData>?>
            = UnsafeMutablePointer.allocate(capacity: 1)
          defer { returnDataPtr.deallocate() }

          let responseCode = CFMessagePortSendRequest(
            self.port,
            msgid,
            data?.cfdata,
            self.timeout,
            self.timeout,
            expectsReply ? CFRunLoopMode.defaultMode.rawValue : nil,
            expectsReply ? returnDataPtr : nil
          )

          guard responseCode == kCFMessagePortSuccess else {
            single(.error(Error.send(msgid: msgid, response: responseCode)))
            return
          }

          guard expectsReply else {
            single(.success(nil))
            return
          }

          // Upon return, [returnData] contains a CFData object
          // containing the reply data. Ownership follows the The Create Rule.
          // From: https://developer.apple.com/documentation/corefoundation/1543076-cfmessageportsendrequest
          // This means that we have to release the returned CFData.
          // Thus, we have to use Unmanaged.takeRetainedValue()
          // See also https://www.mikeash.com/pyblog/friday-qa-2017-08-11-swiftunmanaged.html
          let data: Data? = returnDataPtr.pointee?.takeRetainedValue().data
          single(.success(data))
        }
      }

      return Disposables.create()
    }
  }

  public func connect(to name: String) -> Completable {
    return Completable.create { completable in
      self.queue.async {
        self.portLock.withWriteLock {
          self.port = CFMessagePortCreateRemote(kCFAllocatorDefault, name.cfstr)

          if self.port == nil {
            completable(.error(Error.clientInit))
            return
          }

          self.portIsValid = true
          completable(.completed)
        }
      }
      return Disposables.create()
    }
  }

  public func stop() -> Completable {
    return Completable.create { completable in
      self.queue.async {
        self.portLock.withWriteLock {
          self.portIsValid = false
          if self.port != nil && CFMessagePortIsValid(self.port) {
            CFMessagePortInvalidate(self.port)
          }
          completable(.completed)
        }
      }

      return Disposables.create()
    }
  }

  private var portIsValid = false
  private let portLock = ReadersWriterLock()
  private var port: CFMessagePort?
}

public final class RxMessagePortServer {

  public typealias SyncReplyBody = (Int32, Data?) -> Data?

  public struct Message {

    public let msgid: Int32
    public let data: Data?
  }

  public var syncReplyBody: SyncReplyBody? {
    get {
      return self.messageHandler.syncReplyBody
    }
    set {
      self.messageHandler.syncReplyBody = newValue
    }
  }

  public var stream: Observable<Message> {
    return self.streamSubject.asObservable()
  }

  public var queue = DispatchQueue(
    label: String(reflecting: RxMessagePortServer.self),
    qos: .userInitiated
  )

  public init() {
    self.messageHandler = MessageHandler(subject: self.streamSubject)
  }

  public func run(as name: String) -> Completable {
    return Completable.create { completable in
      self.queue.async {
        var localCtx = CFMessagePortContext(
          version: 0,
          info: Unmanaged.passUnretained(self.messageHandler).toOpaque(),
          retain: nil,
          release: nil,
          copyDescription: nil
        )

        self.port = CFMessagePortCreateLocal(
          kCFAllocatorDefault,
          name.cfstr,
          { _, msgid, data, info in
            guard let infoPtr = UnsafeRawPointer(info) else { return nil }

            let handler = Unmanaged<MessageHandler>
              .fromOpaque(infoPtr).takeUnretainedValue()
            return handler.handleMessage(msgId: msgid, cfdata: data)
          },
          &localCtx,
          nil
        )

        if self.port == nil {
          self.streamSubject.onError(RxMessagePortClient.Error.serverInit)
          completable(.error(RxMessagePortClient.Error.serverInit))
        }

        self.portThread = Thread { self.runServer() }
        self.portThread?.name = String(reflecting: RxMessagePortServer.self)
        self.portThread?.start()

        completable(.completed)
      }

      return Disposables.create()
    }
  }

  public func stop() -> Completable {
    return Completable.create { completable in
      self.queue.async {
        self.messageHandler.syncReplyBody = nil
        self.streamSubject.onCompleted()

        if let portRunLoop = self.portRunLoop {
          CFRunLoopStop(portRunLoop)
        }

        if self.port != nil && CFMessagePortIsValid(self.port) {
          CFMessagePortInvalidate(self.port)
        }

        completable(.completed)
      }

      return Disposables.create()
    }
  }

  private var port: CFMessagePort?
  private var portThread: Thread?
  private var portRunLoop: CFRunLoop?

  private var messageHandler: MessageHandler
  private let streamSubject = PublishSubject<Message>()

  private func runServer() {
    self.portRunLoop = CFRunLoopGetCurrent()
    let runLoopSrc = CFMessagePortCreateRunLoopSource(
      kCFAllocatorDefault,
      self.port,
      0
    )
    CFRunLoopAddSource(self.portRunLoop, runLoopSrc, .defaultMode)
    CFRunLoopRun()
  }
}

private class MessageHandler {

  fileprivate var syncReplyBody: RxMessagePortServer.SyncReplyBody?

  fileprivate init(subject: PublishSubject<RxMessagePortServer.Message>) {
    self.subject = subject
  }

  fileprivate func handleMessage(
    msgId: Int32,
    cfdata: CFData?
  ) -> Unmanaged<CFData>? {
    let d = cfdata?.data

    self.subject.onNext(RxMessagePortServer.Message(msgid: msgId, data: d))

    guard let reply = self.syncReplyBody?(msgId, d) else { return nil }

    // The system releases the returned CFData object.
    // From https://developer.apple.com/documentation/corefoundation/cfmessageportcallback
    // See also https://www.mikeash.com/pyblog/friday-qa-2017-08-11-swiftunmanaged.html
    return Unmanaged.passRetained(reply.cfdata)
  }

  private let subject: PublishSubject<RxMessagePortServer.Message>
}

private extension Data {

  var cfdata: CFData {
    return self as NSData
  }
}

private extension CFData {

  var data: Data {
    return self as NSData as Data
  }
}

private extension String {

  var cfstr: CFString {
    return self as NSString
  }
}