// Copyright 2020 Google LLC
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

#ifndef CORE_INTERNAL_MEDIUMS_WEBRTC_H_
#define CORE_INTERNAL_MEDIUMS_WEBRTC_H_

#include <cstddef>
#include <functional>
#include <memory>
#include <string>

#include "absl/container/flat_hash_map.h"
#include "absl/container/flat_hash_set.h"
#include "core/internal/mediums/webrtc/connection_flow.h"
#include "core/internal/mediums/webrtc/data_channel_listener.h"
#include "core/internal/mediums/webrtc/local_ice_candidate_listener.h"
#include "core/internal/mediums/webrtc/peer_id.h"
#include "core/internal/mediums/webrtc/webrtc_socket.h"
#include "core/internal/mediums/webrtc/webrtc_socket_wrapper.h"
#include "platform/base/byte_array.h"
#include "platform/base/cancellation_flag.h"
#include "platform/base/listeners.h"
#include "platform/base/runnable.h"
#include "platform/public/atomic_boolean.h"
#include "platform/public/cancelable_alarm.h"
#include "platform/public/future.h"
#include "platform/public/mutex.h"
#include "platform/public/scheduled_executor.h"
#include "platform/public/single_thread_executor.h"
#include "platform/public/webrtc.h"
#include "proto/connections/offline_wire_formats.pb.h"
#include "proto/mediums/web_rtc_signaling_frames.pb.h"
#include "webrtc/api/data_channel_interface.h"
#include "webrtc/api/jsep.h"
#include "webrtc/api/scoped_refptr.h"

namespace location {
namespace nearby {
namespace connections {
namespace mediums {

// Callback that is invoked when a new connection is accepted.
struct AcceptedConnectionCallback {
  std::function<void(WebRtcSocketWrapper socket)> accepted_cb =
      DefaultCallback<WebRtcSocketWrapper>();
};

// Entry point for connecting a data channel between two devices via WebRtc.
class WebRtc {
 public:
  WebRtc();
  ~WebRtc();

  // Gets the default two-letter country code associated with current locale.
  // For example, en_US locale resolves to "US".
  const std::string GetDefaultCountryCode();

  // Returns if WebRtc is available as a medium for nearby to transport data.
  // Runs on @MainThread.
  bool IsAvailable();

  // Returns if the device is accepting connection with specific service id.
  // Runs on @MainThread.
  bool IsAcceptingConnections(const std::string& service_id)
      ABSL_LOCKS_EXCLUDED(mutex_);

  // Prepares the device to accept incoming WebRtc connections. Returns a
  // boolean value indicating if the device has started accepting connections.
  // Runs on @MainThread.
  bool StartAcceptingConnections(const std::string& service_id,
                                 const PeerId& self_peer_id,
                                 const LocationHint& location_hint,
                                 AcceptedConnectionCallback callback)
      ABSL_LOCKS_EXCLUDED(mutex_);

  // Try to stop (accepting) the specific connection with provided service id.
  // Runs on @MainThread
  void StopAcceptingConnections(const std::string& service_id)
      ABSL_LOCKS_EXCLUDED(mutex_);

  // Initiates a WebRtc connection with peer device identified by |peer_id|
  // with internal retry for maximum attempts of kConnectAttemptsLimit.
  // Runs on @MainThread.
  WebRtcSocketWrapper Connect(const std::string& service_id,
                              const PeerId& peer_id,
                              const LocationHint& location_hint,
                              CancellationFlag* cancellation_flag)
      ABSL_LOCKS_EXCLUDED(mutex_);

 private:
  static constexpr int kConnectAttemptsLimit = 3;
  static constexpr int kRestartAcceptConnectionsLimit = 3;

  enum class Role {
    kNone = 0,
    kOfferer = 1,
    kAnswerer = 2,
  };

  struct AcceptingConnectionsInfo {
    // The self_peer_id is generated from the BT/WiFi advertisements and allows
    // the scanner to message us over Tachyon.
    PeerId self_peer_id;

    // The registered callback. When there's an incoming connection, this
    // callback is notified.
    AcceptedConnectionCallback accepted_connection_callback;

    // Allows us to communicate with the Tachyon web server.
    std::unique_ptr<WebRtcSignalingMessenger> signaling_messenger;

    // Restarts the tachyon inbox receives messages streaming rpc if the
    // streaming rpc times out. The streaming rpc times out after 60s while
    // advertising. Non-null when listening for WebRTC connections as an
    // offerer.
    CancelableAlarm restart_tachyon_receive_messages_alarm;

    // Tracks the number of times we've restarted receiving messages after a
    // failure. We limit the number to prevent endless restarts if we are
    // repeatedly unable to communicate with Tachyon.
    int restart_accept_connections_count = 0;
  };

  struct ConnectionRequestInfo {
    // The self_peer_id is randomly generated and allows the advertiser to
    // message us over Tachyon.
    PeerId self_peer_id;

    // Allows us to communicate with the Tachyon web server.
    std::unique_ptr<WebRtcSignalingMessenger> signaling_messenger;

    // The pending DataChannel future. Our client will be blocked on this while
    // they wait for us to set up the channel over Tachyon.
    Future<WebRtcSocketWrapper> socket_future;
  };

  // Attempt to initiates a WebRtc connection with peer device identified by
  // |peer_id|.
  // Runs on @MainThread.
  WebRtcSocketWrapper AttemptToConnect(const std::string& service_id,
                                       const PeerId& peer_id,
                                       const LocationHint& location_hint,
                                       CancellationFlag* cancellation_flag)
      ABSL_LOCKS_EXCLUDED(mutex_);

  // Returns if the device is accepting connection with specific service id.
  // Runs on @MainThread.
  bool IsAcceptingConnectionsLocked(const std::string& service_id)
      ABSL_EXCLUSIVE_LOCKS_REQUIRED(mutex_);

  // Receives a message from the signaling messenger.
  void OnSignalingMessage(const std::string& service_id,
                          const ByteArray& message);

  // Decides whether to restart receiving messages.
  void OnSignalingComplete(const std::string& service_id, bool success);

  // Runs on |single_thread_executor_|.
  void ProcessTachyonInboxMessage(const std::string& service_id,
                                  const ByteArray& message)
      ABSL_LOCKS_EXCLUDED(mutex_);

  // Runs on |single_thread_executor_|.
  void SendOffer(const std::string& service_id, const PeerId& remote_peer_id)
      ABSL_EXCLUSIVE_LOCKS_REQUIRED(mutex_);

  // Runs on |single_thread_executor_|.
  void ReceiveOffer(const PeerId& remote_peer_id,
                    SessionDescriptionWrapper offer)
      ABSL_EXCLUSIVE_LOCKS_REQUIRED(mutex_);

  // Runs on |single_thread_executor_|.
  void SendAnswer(const PeerId& remote_peer_id)
      ABSL_EXCLUSIVE_LOCKS_REQUIRED(mutex_);

  // Runs on |single_thread_executor_|.
  void ReceiveAnswer(const PeerId& remote_peer_id,
                     SessionDescriptionWrapper answer)
      ABSL_EXCLUSIVE_LOCKS_REQUIRED(mutex_);

  // Runs on |single_thread_executor_|.
  void ReceiveIceCandidates(
      const PeerId& remote_peer_id,
      std::vector<std::unique_ptr<webrtc::IceCandidateInterface>>
          ice_candidates) ABSL_EXCLUSIVE_LOCKS_REQUIRED(mutex_);

  // Runs on |single_thread_executor_|.
  std::unique_ptr<ConnectionFlow> CreateConnectionFlow(
      const std::string& service_id, const PeerId& remote_peer_id)
      ABSL_EXCLUSIVE_LOCKS_REQUIRED(mutex_);

  // Runs on |single_thread_executor_|.
  std::unique_ptr<ConnectionFlow> GetConnectionFlow(
      const PeerId& remote_peer_id) ABSL_EXCLUSIVE_LOCKS_REQUIRED(mutex_);

  // Runs on |single_thread_executor_|.
  void RemoveConnectionFlow(const PeerId& remote_peer_id)
      ABSL_EXCLUSIVE_LOCKS_REQUIRED(mutex_);

  // Runs on |single_thread_executor_|.
  void ProcessDataChannelOpen(const std::string& service_id,
                              const PeerId& remote_peer_id,
                              WebRtcSocketWrapper socket_wrapper)
      ABSL_LOCKS_EXCLUDED(mutex_);

  // Runs on |single_thread_executor_|.
  void ProcessDataChannelClosed(const PeerId& remote_peer_id)
      ABSL_LOCKS_EXCLUDED(mutex_);

  // Runs on |single_thread_executor_|.
  void ProcessLocalIceCandidate(
      const std::string& service_id, const PeerId& remote_peer_id,
      const ::location::nearby::mediums::IceCandidate ice_candidate)
      ABSL_LOCKS_EXCLUDED(mutex_);

  // Runs on |single_thread_executor_|.
  void ProcessRestartTachyonReceiveMessages(const std::string& service_id)
      ABSL_LOCKS_EXCLUDED(mutex_);

  // Runs on |single_thread_executor_|.
  void RestartTachyonReceiveMessages(const std::string& service_id)
      ABSL_EXCLUSIVE_LOCKS_REQUIRED(mutex_);

  void OffloadFromThread(const std::string& name, Runnable runnable);

  Mutex mutex_;

  WebRtcMedium medium_;

  // The single thread we throw the potentially blocking work on to.
  ScheduledExecutor single_thread_executor_;

  // A map of ServiceID -> State for all services that are listening for
  // incoming connections.
  absl::flat_hash_map<std::string, AcceptingConnectionsInfo>
      accepting_connections_info_ ABSL_GUARDED_BY(mutex_);

  // A map of a remote PeerId -> State for pending connection requests. As
  // messages from Tachyon come in, this lets us look up the connection request
  // info to handle the interaction.
  absl::flat_hash_map<std::string, ConnectionRequestInfo>
      requesting_connections_info_ ABSL_GUARDED_BY(mutex_);

  // A map of a remote PeerId -> ConnectionFlow. For each connection, we create
  // a unique ConnectionFlow.
  absl::flat_hash_map<std::string, std::unique_ptr<ConnectionFlow>>
      connection_flows_ ABSL_GUARDED_BY(mutex_);
};

}  // namespace mediums
}  // namespace connections
}  // namespace nearby
}  // namespace location

#endif  // CORE_INTERNAL_MEDIUMS_WEBRTC_H_