/*
 * Copyright 2017 Discord, Inc.
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy of
 * this software and associated documentation files (the "Software"), to deal in
 * the Software without restriction, including without limitation the rights to
 * use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies
 * of the Software, and to permit persons to whom the Software is furnished to do
 * so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in all
 * copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 *
 */

#include <atomic>
#include <chrono>
#include <mutex>
#include <condition_variable>
#include <thread>

#include "discord_rpc.h"
#include "discord_backoff.h"
#include "discord_register.h"
#include "discord_msg_queue.h"
#include "discord_rpc_connection.h"
#include "discord_serialization.h"

using namespace discord_rpc;

static void Discord_UpdateConnection();

namespace {

constexpr size_t MaxMessageSize { 16 * 1024 };
constexpr size_t MessageQueueSize { 8 };
constexpr size_t JoinQueueSize { 8 };

struct QueuedMessage {
  size_t length;
  char buffer[MaxMessageSize];

  void Copy(const QueuedMessage &other) {
    length = other.length;
    if (length) {
      memcpy(buffer, other.buffer, length);
    }
  }
};

struct User {
  // snowflake (64bit int), turned into a ascii decimal string, at most 20 chars +1 null
  // terminator = 21
  char userId[32];
  // 32 unicode glyphs is max name size => 4 bytes per glyph in the worst case, +1 for null
  // terminator = 129
  char username[344];
  // 4 decimal digits + 1 null terminator = 5
  char discriminator[8];
  // optional 'a_' + md5 hex digest (32 bytes) + null terminator = 35
  char avatar[128];
  // Rounded way up because I'm paranoid about games breaking from future changes in these sizes
};

static RpcConnection *Connection { nullptr };
static DiscordEventHandlers QueuedHandlers {};
static DiscordEventHandlers Handlers {};
static std::atomic_bool WasJustConnected { false };
static std::atomic_bool WasJustDisconnected { false };
static std::atomic_bool GotErrorMessage { false };
static std::atomic_bool WasJoinGame { false };
static std::atomic_bool WasSpectateGame { false };
static std::atomic_bool UpdatePresence { false };
static char JoinGameSecret[256];
static char SpectateGameSecret[256];
static int LastErrorCode { 0 };
static char LastErrorMessage[256];
static int LastDisconnectErrorCode { 0 };
static char LastDisconnectErrorMessage[256];
static std::mutex PresenceMutex;
static std::mutex HandlerMutex;
static QueuedMessage QueuedPresence {};
static MsgQueue<QueuedMessage, MessageQueueSize> SendQueue;
static MsgQueue<User, JoinQueueSize> JoinAskQueue;
static User connectedUser;

// We want to auto connect, and retry on failure, but not as fast as possible. This does expoential backoff from 0.5 seconds to 1 minute
static Backoff ReconnectTimeMs(500, 60 * 1000);
static auto NextConnect = std::chrono::system_clock::now();
static int Pid { 0 };
static int Nonce { 1 };

class IoThreadHolder {
 private:
  std::atomic_bool keepRunning { true };
  std::mutex waitForIOMutex;
  std::condition_variable waitForIOActivity;
  std::thread ioThread;

 public:
  void Start() {
    keepRunning.store(true);
    ioThread = std::thread([&]() {
      const std::chrono::duration<int64_t, std::milli> maxWait { 500LL };
      Discord_UpdateConnection();
      while (keepRunning.load()) {
        std::unique_lock<std::mutex> lock(waitForIOMutex);
        waitForIOActivity.wait_for(lock, maxWait);
        Discord_UpdateConnection();
      }
    });
  }

  void Notify() { waitForIOActivity.notify_all(); }

  void Stop() {
    keepRunning.exchange(false);
    Notify();
    if (ioThread.joinable()) {
      ioThread.join();
    }
  }

  ~IoThreadHolder() { Stop(); }
};

static IoThreadHolder *IoThread { nullptr };

static void UpdateReconnectTime() {

  NextConnect = std::chrono::system_clock::now() + std::chrono::duration<int64_t, std::milli> { ReconnectTimeMs.nextDelay() };

}

static void SignalIOActivity() {

  if (IoThread != nullptr) {
    IoThread->Notify();
  }

}

static bool RegisterForEvent(const char *evtName) {

  auto qmessage = SendQueue.GetNextAddMessage();
  if (qmessage) {
    qmessage->length = JsonWriteSubscribeCommand(qmessage->buffer, sizeof(qmessage->buffer), Nonce++, evtName);
    SendQueue.CommitAdd();
    SignalIOActivity();
    return true;
  }

  return false;

}

static bool DeregisterForEvent(const char *evtName) {

  auto qmessage = SendQueue.GetNextAddMessage();
  if (qmessage) {
    qmessage->length = JsonWriteUnsubscribeCommand(qmessage->buffer, sizeof(qmessage->buffer), Nonce++, evtName);
    SendQueue.CommitAdd();
    SignalIOActivity();
    return true;
  }

  return false;

}

} // namespace

static void Discord_UpdateConnection() {

  if (!Connection) {
    return;
  }

  if (!Connection->IsOpen()) {
    if (std::chrono::system_clock::now() >= NextConnect) {
      UpdateReconnectTime();
      Connection->Open();
    }
  }
  else {
    // reads

    for (;;) {
      JsonDocument message;

      if (!Connection->Read(message)) {
        break;
      }

      const char *evtName = GetStrMember(&message, "evt");
      const char *nonce = GetStrMember(&message, "nonce");

      if (nonce) {
        // in responses only -- should use to match up response when needed.

        if (evtName && strcmp(evtName, "ERROR") == 0) {
          auto data = GetObjMember(&message, "data");
          LastErrorCode = GetIntMember(data, "code");
          StringCopy(LastErrorMessage, GetStrMember(data, "message", ""));
          GotErrorMessage.store(true);
        }
      }
      else {
        // should have evt == name of event, optional data
        if (evtName == nullptr) {
          continue;
        }

        auto data = GetObjMember(&message, "data");

        if (strcmp(evtName, "ACTIVITY_JOIN") == 0) {
          auto secret = GetStrMember(data, "secret");
          if (secret) {
            StringCopy(JoinGameSecret, secret);
            WasJoinGame.store(true);
          }
        }
        else if (strcmp(evtName, "ACTIVITY_SPECTATE") == 0) {
          auto secret = GetStrMember(data, "secret");
          if (secret) {
            StringCopy(SpectateGameSecret, secret);
            WasSpectateGame.store(true);
          }
        }
        else if (strcmp(evtName, "ACTIVITY_JOIN_REQUEST") == 0) {
          auto user = GetObjMember(data, "user");
          auto userId = GetStrMember(user, "id");
          auto username = GetStrMember(user, "username");
          auto avatar = GetStrMember(user, "avatar");
          auto joinReq = JoinAskQueue.GetNextAddMessage();
          if (userId && username && joinReq) {
            StringCopy(joinReq->userId, userId);
            StringCopy(joinReq->username, username);
            auto discriminator = GetStrMember(user, "discriminator");
            if (discriminator) {
              StringCopy(joinReq->discriminator, discriminator);
            }
            if (avatar) {
              StringCopy(joinReq->avatar, avatar);
            }
            else {
              joinReq->avatar[0] = 0;
            }
            JoinAskQueue.CommitAdd();
          }
        }
      }
    }

    // writes
    if (UpdatePresence.exchange(false) && QueuedPresence.length) {
      QueuedMessage local;
      {
        std::lock_guard<std::mutex> guard(PresenceMutex);
        local.Copy(QueuedPresence);
      }
      if (!Connection->Write(local.buffer, local.length)) {
        // if we fail to send, requeue
        std::lock_guard<std::mutex> guard(PresenceMutex);
        QueuedPresence.Copy(local);
        UpdatePresence.exchange(true);
      }
    }

    while (SendQueue.HavePendingSends()) {
      auto qmessage = SendQueue.GetNextSendMessage();
      Connection->Write(qmessage->buffer, qmessage->length);
      SendQueue.CommitSend();
    }
  }

}

extern "C" void Discord_Initialize(const char *applicationId, DiscordEventHandlers *handlers, const int autoRegister) {

  IoThread = new (std::nothrow) IoThreadHolder();
  if (IoThread == nullptr) {
    return;
  }

  if (autoRegister) {
    Discord_Register(applicationId, nullptr);
  }

  Pid = GetProcessId();

  {
    std::lock_guard<std::mutex> guard(HandlerMutex);

    if (handlers) {
      QueuedHandlers = *handlers;
    }
    else {
      QueuedHandlers = {};
    }

    Handlers = {};
  }

  if (Connection) {
    return;
  }

  Connection = RpcConnection::Create(applicationId);
  Connection->onConnect = [](JsonDocument &readyMessage) {
    Discord_UpdateHandlers(&QueuedHandlers);
    if (QueuedPresence.length > 0) {
      UpdatePresence.exchange(true);
      SignalIOActivity();
    }
    auto data = GetObjMember(&readyMessage, "data");
    auto user = GetObjMember(data, "user");
    auto userId = GetStrMember(user, "id");
    auto username = GetStrMember(user, "username");
    auto avatar = GetStrMember(user, "avatar");
    if (userId && username) {
      StringCopy(connectedUser.userId, userId);
      StringCopy(connectedUser.username, username);
      auto discriminator = GetStrMember(user, "discriminator");
      if (discriminator) {
        StringCopy(connectedUser.discriminator, discriminator);
      }
      if (avatar) {
        StringCopy(connectedUser.avatar, avatar);
      }
      else {
        connectedUser.avatar[0] = 0;
      }
    }
    WasJustConnected.exchange(true);
    ReconnectTimeMs.reset();
  };
  Connection->onDisconnect = [](int err, const char *message) {
    LastDisconnectErrorCode = err;
    StringCopy(LastDisconnectErrorMessage, message);
    WasJustDisconnected.exchange(true);
    UpdateReconnectTime();
  };

  IoThread->Start();

}

extern "C" void Discord_Shutdown() {

  if (!Connection) {
    return;
  }
  Connection->onConnect = nullptr;
  Connection->onDisconnect = nullptr;
  Handlers = {};
  QueuedPresence.length = 0;
  UpdatePresence.exchange(false);
  if (IoThread != nullptr) {
    IoThread->Stop();
    delete IoThread;
    IoThread = nullptr;
  }

  RpcConnection::Destroy(Connection);

}

extern "C" void Discord_UpdatePresence(const DiscordRichPresence *presence) {

  {
    std::lock_guard<std::mutex> guard(PresenceMutex);
    QueuedPresence.length = JsonWriteRichPresenceObj(QueuedPresence.buffer, sizeof(QueuedPresence.buffer), Nonce++, Pid, presence);
    UpdatePresence.exchange(true);
  }

  SignalIOActivity();

}

extern "C" void Discord_ClearPresence(void) {
  Discord_UpdatePresence(nullptr);
}

extern "C" void Discord_Respond(const char *userId, /* DISCORD_REPLY_ */ int reply) {

  // if we are not connected, let's not batch up stale messages for later
  if (!Connection || !Connection->IsOpen()) {
    return;
  }
  auto qmessage = SendQueue.GetNextAddMessage();
  if (qmessage) {
    qmessage->length = JsonWriteJoinReply(qmessage->buffer, sizeof(qmessage->buffer), userId, reply, Nonce++);
    SendQueue.CommitAdd();
    SignalIOActivity();
  }

}

extern "C" void Discord_RunCallbacks() {

  // Note on some weirdness: internally we might connect, get other signals, disconnect any number
  // of times inbetween calls here. Externally, we want the sequence to seem sane, so any other
  // signals are book-ended by calls to ready and disconnect.

  if (!Connection) {
    return;
  }

  const bool wasDisconnected = WasJustDisconnected.exchange(false);
  const bool isConnected = Connection->IsOpen();

  if (isConnected) {
    // if we are connected, disconnect cb first
    std::lock_guard<std::mutex> guard(HandlerMutex);
    if (wasDisconnected && Handlers.disconnected) {
      Handlers.disconnected(LastDisconnectErrorCode, LastDisconnectErrorMessage);
    }
  }

  if (WasJustConnected.exchange(false)) {
    std::lock_guard<std::mutex> guard(HandlerMutex);
    if (Handlers.ready) {
      DiscordUser du { connectedUser.userId, connectedUser.username, connectedUser.discriminator, connectedUser.avatar };
      Handlers.ready(&du);
    }
  }

  if (GotErrorMessage.exchange(false)) {
    std::lock_guard<std::mutex> guard(HandlerMutex);
    if (Handlers.errored) {
      Handlers.errored(LastErrorCode, LastErrorMessage);
    }
  }

  if (WasJoinGame.exchange(false)) {
    std::lock_guard<std::mutex> guard(HandlerMutex);
    if (Handlers.joinGame) {
      Handlers.joinGame(JoinGameSecret);
    }
  }

  if (WasSpectateGame.exchange(false)) {
    std::lock_guard<std::mutex> guard(HandlerMutex);
    if (Handlers.spectateGame) {
      Handlers.spectateGame(SpectateGameSecret);
    }
  }

  // Right now this batches up any requests and sends them all in a burst; I could imagine a world
  // where the implementer would rather sequentially accept/reject each one before the next invite
  // is sent. I left it this way because I could also imagine wanting to process these all and
  // maybe show them in one common dialog and/or start fetching the avatars in parallel, and if
  // not it should be trivial for the implementer to make a queue themselves.
  while (JoinAskQueue.HavePendingSends()) {
    const auto req = JoinAskQueue.GetNextSendMessage();
    {
      std::lock_guard<std::mutex> guard(HandlerMutex);
      if (Handlers.joinRequest) {
        DiscordUser du { req->userId, req->username, req->discriminator, req->avatar };
        Handlers.joinRequest(&du);
      }
    }
    JoinAskQueue.CommitSend();
  }

  if (!isConnected) {
    // if we are not connected, disconnect message last
    std::lock_guard<std::mutex> guard(HandlerMutex);
    if (wasDisconnected && Handlers.disconnected) {
      Handlers.disconnected(LastDisconnectErrorCode, LastDisconnectErrorMessage);
    }
  }

}

extern "C" void Discord_UpdateHandlers(DiscordEventHandlers *newHandlers) {

  if (newHandlers) {
#define HANDLE_EVENT_REGISTRATION(handler_name, event)            \
  if (!Handlers.handler_name && newHandlers->handler_name) {      \
    RegisterForEvent(event);                                      \
  }                                                               \
  else if (Handlers.handler_name && !newHandlers->handler_name) { \
    DeregisterForEvent(event);                                    \
  }

    std::lock_guard<std::mutex> guard(HandlerMutex);
    HANDLE_EVENT_REGISTRATION(joinGame, "ACTIVITY_JOIN")
    HANDLE_EVENT_REGISTRATION(spectateGame, "ACTIVITY_SPECTATE")
    HANDLE_EVENT_REGISTRATION(joinRequest, "ACTIVITY_JOIN_REQUEST")

#undef HANDLE_EVENT_REGISTRATION

    Handlers = *newHandlers;
  }
  else {
    std::lock_guard<std::mutex> guard(HandlerMutex);
    Handlers = {};
  }

}