/*
 * Deskflow -- mouse and keyboard sharing utility
 * SPDX-FileCopyrightText: (C) 2012 - 2016 Symless Ltd.
 * SPDX-FileCopyrightText: (C) 2002 Chris Schoeneman
 * SPDX-License-Identifier: GPL-2.0-only WITH LicenseRef-OpenSSL-Exception
 */

#include "arch/unix/ArchMultithreadPosix.h"

#include "arch/Arch.h"
#include "arch/ArchException.h"

#include <cerrno>
#include <signal.h>
#include <sys/time.h>
#include <time.h>

#define SIGWAKEUP SIGUSR1

static void setSignalSet(sigset_t *sigset)
{
  sigemptyset(sigset);
  sigaddset(sigset, SIGHUP);
  sigaddset(sigset, SIGINT);
  sigaddset(sigset, SIGTERM);
  sigaddset(sigset, SIGUSR2);
}

//
// ArchThreadImpl
//

class ArchThreadImpl
{
public:
  ArchThreadImpl() = default;

public:
  int m_refCount = 1;
  IArchMultithread::ThreadID m_id = 0;
  pthread_t m_thread;
  IArchMultithread::ThreadFunc m_func = nullptr;
  void *m_userData = nullptr;
  bool m_cancel = false;
  bool m_cancelling = false;
  bool m_exited = false;
  void *m_result = nullptr;
  void *m_networkData = nullptr;
};

//
// ArchMultithreadPosix
//

ArchMultithreadPosix *ArchMultithreadPosix::s_instance = nullptr;

ArchMultithreadPosix::ArchMultithreadPosix()
{
  assert(s_instance == nullptr);

  s_instance = this;

  // no signal handlers
  for (size_t i = 0; i < static_cast<size_t>(ThreadSignal::MaxSignals); ++i) {
    m_signalFunc[i] = nullptr;
    m_signalUserData[i] = nullptr;
  }

  // create thread for calling (main) thread and add it to our
  // list.  no need to lock the mutex since we're the only thread.
  m_mainThread = new ArchThreadImpl;
  m_mainThread->m_thread = pthread_self();
  insert(m_mainThread);

  // install SIGWAKEUP handler.  this causes SIGWAKEUP to interrupt
  // system calls.  we use that when cancelling a thread to force it
  // to wake up immediately if it's blocked in a system call.  we
  // won't need this until another thread is created but it's fine
  // to install it now.
  struct sigaction act;
  sigemptyset(&act.sa_mask);
#if defined(SA_INTERRUPT)
  act.sa_flags = SA_INTERRUPT;
#else
  act.sa_flags = 0;
#endif
  act.sa_handler = &threadCancel;
  sigaction(SIGWAKEUP, &act, nullptr);

  // set desired signal dispositions.  let SIGWAKEUP through but
  // ignore SIGPIPE (we'll handle EPIPE).
  sigset_t sigset;
  sigemptyset(&sigset);
  sigaddset(&sigset, SIGWAKEUP);
  pthread_sigmask(SIG_UNBLOCK, &sigset, nullptr);
  sigemptyset(&sigset);
  sigaddset(&sigset, SIGPIPE);
  pthread_sigmask(SIG_BLOCK, &sigset, nullptr);
}

ArchMultithreadPosix::~ArchMultithreadPosix()
{
  assert(s_instance != nullptr);
  s_instance = nullptr;
}

void ArchMultithreadPosix::setNetworkDataForCurrentThread(void *data)
{
  std::scoped_lock lock{m_threadMutex};
  ArchThreadImpl *thread = find(pthread_self());
  thread->m_networkData = data;
}

void *ArchMultithreadPosix::getNetworkDataForThread(ArchThread thread)
{
  std::scoped_lock lock{m_threadMutex};
  return thread->m_networkData;
}

ArchMultithreadPosix *ArchMultithreadPosix::getInstance()
{
  return s_instance;
}

ArchCond ArchMultithreadPosix::newCondVar()
{
  auto *cond = new ArchCondImpl;
  int status = pthread_cond_init(&cond->m_cond, nullptr);
  (void)status;
  assert(status == 0);
  return cond;
}

void ArchMultithreadPosix::closeCondVar(ArchCond cond)
{
  int status = pthread_cond_destroy(&cond->m_cond);
  (void)status;
  assert(status == 0);
  delete cond;
}

void ArchMultithreadPosix::signalCondVar(ArchCond cond)
{
  int status = pthread_cond_signal(&cond->m_cond);
  (void)status;
  assert(status == 0);
}

void ArchMultithreadPosix::broadcastCondVar(ArchCond cond)
{
  int status = pthread_cond_broadcast(&cond->m_cond);
  (void)status;
  assert(status == 0);
}

bool ArchMultithreadPosix::waitCondVar(ArchCond cond, ArchMutex mutex, double timeout)
{
  // we can't wait on a condition variable and also wake it up for
  // cancellation since we don't use posix cancellation.  so we
  // must wake up periodically to check for cancellation.  we
  // can't simply go back to waiting after the check since the
  // condition may have changed and we'll have lost the signal.
  // so we have to return to the caller.  since the caller will
  // always check for spurious wakeups the only drawback here is
  // performance:  we're waking up a lot more than desired.
  if (static const double maxCancellationLatency = 0.1; timeout < 0.0 || timeout > maxCancellationLatency) {
    timeout = maxCancellationLatency;
  }

  // see if we should cancel this thread
  testCancelThread();

  // get final time
  struct timeval now;
  gettimeofday(&now, nullptr);
  struct timespec finalTime;
  finalTime.tv_sec = now.tv_sec;
  finalTime.tv_nsec = now.tv_usec * 1000;
  auto timeout_sec = (long)timeout;
  auto timeout_nsec = (long)(1.0e+9 * (timeout - timeout_sec));
  finalTime.tv_sec += timeout_sec;
  finalTime.tv_nsec += timeout_nsec;
  if (finalTime.tv_nsec >= 1000000000) {
    finalTime.tv_nsec -= 1000000000;
    finalTime.tv_sec += 1;
  }

  // wait
  int status = pthread_cond_timedwait(&cond->m_cond, &mutex->m_mutex, &finalTime);

  // check for cancel again
  testCancelThread();

  switch (status) {
  case 0:
    // success
    return true;

  case ETIMEDOUT:
    return false;

  default:
    assert(0 && "condition variable wait error");
    return false;
  }
}

ArchMutex ArchMultithreadPosix::newMutex()
{
  pthread_mutexattr_t attr;
  int status = pthread_mutexattr_init(&attr);
  assert(status == 0);
  auto *mutex = new ArchMutexImpl;
  status = pthread_mutex_init(&mutex->m_mutex, &attr);
  assert(status == 0);
  return mutex;
}

void ArchMultithreadPosix::closeMutex(ArchMutex mutex)
{
  int status = pthread_mutex_destroy(&mutex->m_mutex);
  (void)status;
  assert(status == 0);
  delete mutex;
}

void ArchMultithreadPosix::lockMutex(ArchMutex mutex)
{
  int status = pthread_mutex_lock(&mutex->m_mutex);

  switch (status) {
  case 0:
    // success
    return;

  case EDEADLK:
    assert(0 && "lock already owned");
    break;

  case EAGAIN:
    assert(0 && "too many recursive locks");
    break;

  default:
    assert(0 && "unexpected error");
    break;
  }
}

void ArchMultithreadPosix::unlockMutex(ArchMutex mutex)
{
  // TODO: S1-1767, we should use raii c++17 mutex instead of archaeic pthread
  // to solve possible lock order reversal.
  int status = pthread_mutex_unlock(&mutex->m_mutex);

  switch (status) {
  case 0:
    // success
    return;

  case EPERM:
    assert(0 && "thread doesn't own a lock");
    break;

  default:
    assert(0 && "unexpected error");
    break;
  }
}

ArchThread ArchMultithreadPosix::newThread(ThreadFunc func, void *data)
{
  assert(func != nullptr);

  // initialize signal handler.  we do this here instead of the
  // constructor so we can avoid daemonizing (using fork())
  // when there are multiple threads.  clients can safely
  // use condition variables and mutexes before creating a
  // new thread and they can safely use the only thread
  // they have access to, the main thread, so they really
  // can't tell the difference.
  if (!m_newThreadCalled) {
    m_newThreadCalled = true;
    startSignalHandler();
  }

  // note that the child thread will wait until we release this mutex
  std::scoped_lock lock{m_threadMutex};

  // create thread impl for new thread
  auto *thread = new ArchThreadImpl;
  thread->m_func = func;
  thread->m_userData = data;

  // create the thread.  pthread_create() on RedHat 7.2 smp fails
  // if passed a nullptr attr so use a default attr.
  pthread_attr_t attr;
  int status = pthread_attr_init(&attr);
  if (status == 0) {
    status = pthread_create(&thread->m_thread, &attr, &ArchMultithreadPosix::threadFunc, thread);
    pthread_attr_destroy(&attr);
  }

  // check if thread was started
  if (status != 0) {
    // failed to start thread so clean up
    delete thread;
    thread = nullptr;
  } else {
    // add thread to list
    insert(thread);

    // increment ref count to account for the thread itself
    refThread(thread);
  }

  return thread;
}

ArchThread ArchMultithreadPosix::newCurrentThread()
{
  std::scoped_lock lock{m_threadMutex};
  ArchThreadImpl *thread = find(pthread_self());
  assert(thread != nullptr);
  return thread;
}

void ArchMultithreadPosix::closeThread(ArchThread thread)
{
  assert(thread != nullptr);

  // decrement ref count and clean up thread if no more references
  if (--thread->m_refCount == 0) {
    // detach from thread (unless it's the main thread)
    if (thread->m_func != nullptr) {
      pthread_detach(thread->m_thread);
    }

    // remove thread from list
    {
      std::scoped_lock lock{m_threadMutex};
      assert(findNoRef(thread->m_thread) == thread);
      erase(thread);
    }

    // done with thread
    delete thread;
  }
}

ArchThread ArchMultithreadPosix::copyThread(ArchThread thread)
{
  refThread(thread);
  return thread;
}

void ArchMultithreadPosix::cancelThread(ArchThread thread)
{
  assert(thread != nullptr);

  // set cancel and wakeup flags if thread can be cancelled
  bool wakeup = false;

  {
    std::scoped_lock lock{m_threadMutex};
    if (!thread->m_exited && !thread->m_cancelling) {
      thread->m_cancel = true;
      wakeup = true;
    }
  }

  // force thread to exit system calls if wakeup is true
  if (wakeup) {
    pthread_kill(thread->m_thread, SIGWAKEUP);
  }
}

void ArchMultithreadPosix::setPriorityOfThread(ArchThread thread, int /*n*/)
{
  assert(thread != nullptr);

  // FIXME
}

void ArchMultithreadPosix::testCancelThread()
{
  // find current thread
  ArchThreadImpl *thread = nullptr;
  {
    std::scoped_lock lock{m_threadMutex};
    thread = findNoRef(pthread_self());
  }
  // test cancel on thread
  testCancelThreadImpl(thread);
}

bool ArchMultithreadPosix::wait(ArchThread target, double timeout)
{
  assert(target != nullptr);

  ArchThreadImpl *self = nullptr;
  {
    std::scoped_lock lock{m_threadMutex};
    // find current thread
    self = findNoRef(pthread_self());
    // ignore wait if trying to wait on ourself
    if (target == self) {
      return false;
    }
    // ref the target so it can't go away while we're watching it
    refThread(target);
  }

  try {
    // do first test regardless of timeout
    testCancelThreadImpl(self);
    if (isExitedThread(target)) {
      closeThread(target);
      return true;
    }

    // wait and repeat test if there's a timeout
    if (timeout != 0.0) {
      const double start = Arch::time();
      do {
        // wait a little
        Arch::sleep(0.05);

        // repeat test
        testCancelThreadImpl(self);
        if (isExitedThread(target)) {
          closeThread(target);
          return true;
        }

        // repeat wait and test until timed out
      } while (timeout < 0.0 || (Arch::time() - start) <= timeout);
    }

    closeThread(target);
    return false;
  } catch (...) {
    closeThread(target);
    throw;
  }
}

bool ArchMultithreadPosix::isSameThread(ArchThread thread1, ArchThread thread2)
{
  return (thread1 == thread2);
}

bool ArchMultithreadPosix::isExitedThread(ArchThread thread)
{
  std::scoped_lock lock{m_threadMutex};
  return thread->m_exited;
}

void *ArchMultithreadPosix::getResultOfThread(ArchThread thread)
{
  std::scoped_lock lock{m_threadMutex};
  return thread->m_result;
}

IArchMultithread::ThreadID ArchMultithreadPosix::getIDOfThread(ArchThread thread)
{
  return thread->m_id;
}

void ArchMultithreadPosix::setSignalHandler(ThreadSignal signal, SignalFunc func, void *userData)
{
  std::scoped_lock lock{m_threadMutex};
  const auto index = static_cast<int>(signal);
  m_signalFunc[index] = func;
  m_signalUserData[index] = userData;
}

void ArchMultithreadPosix::raiseSignal(ThreadSignal signal)
{
  using enum ThreadSignal;

  std::scoped_lock lock{m_threadMutex};
  const auto index = static_cast<int>(signal);
  if (m_signalFunc[index] != nullptr) {
    m_signalFunc[index](signal, m_signalUserData[index]);
    pthread_kill(m_mainThread->m_thread, SIGWAKEUP);
  } else if (signal == Interrupt || signal == Terminate) {
    ARCH->cancelThread(m_mainThread);
  }
}

void ArchMultithreadPosix::startSignalHandler()
{
  // set signal mask.  the main thread blocks these signals and
  // the signal handler thread will listen for them.
  sigset_t sigset;
  sigset_t oldsigset;
  setSignalSet(&sigset);
  pthread_sigmask(SIG_BLOCK, &sigset, &oldsigset);

  // fire up the INT and TERM signal handler thread.  we could
  // instead arrange to catch and handle these signals but
  // we'd be unable to cancel the main thread since no pthread
  // calls are allowed in a signal handler.
  pthread_attr_t attr;
  int status = pthread_attr_init(&attr);
  if (status == 0) {
    status = pthread_create(&m_signalThread, &attr, &ArchMultithreadPosix::threadSignalHandler, nullptr);
    pthread_attr_destroy(&attr);
  }
  if (status != 0) {
    // can't create thread to wait for signal so don't block
    // the signals.
    pthread_sigmask(SIG_UNBLOCK, &oldsigset, nullptr);
  }
}

ArchThreadImpl *ArchMultithreadPosix::find(pthread_t thread)
{
  ArchThreadImpl *impl = findNoRef(thread);
  if (impl != nullptr) {
    refThread(impl);
  }
  return impl;
}

ArchThreadImpl *ArchMultithreadPosix::findNoRef(pthread_t thread)
{
  // linear search
  for (ThreadList::const_iterator index = m_threadList.begin(); index != m_threadList.end(); ++index) {
    if ((*index)->m_thread == thread) {
      return *index;
    }
  }
  return nullptr;
}

void ArchMultithreadPosix::insert(ArchThreadImpl *thread)
{
  assert(thread != nullptr);

  // thread shouldn't already be on the list
  assert(findNoRef(thread->m_thread) == nullptr);

  // set thread id.  note that we don't worry about m_nextID
  // wrapping back to 0 and duplicating thread ID's since the
  // likelihood of deskflow running that long is vanishingly
  // small.
  thread->m_id = ++m_nextID;

  // append to list
  m_threadList.push_back(thread);
}

void ArchMultithreadPosix::erase(const ArchThreadImpl *thread)
{
  for (auto index = m_threadList.begin(); index != m_threadList.end(); ++index) {
    if (*index == thread) {
      m_threadList.erase(index);
      break;
    }
  }
}

void ArchMultithreadPosix::refThread(ArchThreadImpl *thread)
{
  assert(thread != nullptr);
  assert(findNoRef(thread->m_thread) != nullptr);
  ++thread->m_refCount;
}

void ArchMultithreadPosix::testCancelThreadImpl(ArchThreadImpl *thread)
{
  assert(thread != nullptr);

  // update cancel state
  std::scoped_lock lock{m_threadMutex};
  bool cancel = false;
  if (thread->m_cancel && !thread->m_cancelling) {
    thread->m_cancelling = true;
    thread->m_cancel = false;
    cancel = true;
  }

  // unwind thread's stack if cancelling
  if (cancel) {
    throw ThreadCancelException();
  }
}

void *ArchMultithreadPosix::threadFunc(void *vrep)
{
  // get the thread
  auto *thread = static_cast<ArchThreadImpl *>(vrep);

  // setup pthreads
  pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, nullptr);
  pthread_setcanceltype(PTHREAD_CANCEL_DEFERRED, nullptr);

  // run thread
  s_instance->doThreadFunc(thread);

  // terminate the thread
  return nullptr;
}

void ArchMultithreadPosix::doThreadFunc(ArchThread thread)
{
  // default priority is slightly below normal
  setPriorityOfThread(thread, 1);

  // wait for parent to initialize this object
  {
    std::scoped_lock lock{m_threadMutex};
  }

  void *result = nullptr;
  try {
    // go
    result = (*thread->m_func)(thread->m_userData);
  }

  catch (ThreadCancelException &) {
    // client called cancel()
    // set base value
    result = nullptr;
  } catch (...) {
    // note -- don't catch (...) to avoid masking bugs
    {
      std::scoped_lock lock{m_threadMutex};
      thread->m_exited = true;
    }
    closeThread(thread);
    throw;
  }

  // thread has exited
  {
    std::scoped_lock lock{m_threadMutex};
    thread->m_result = result;
    thread->m_exited = true;
  }

  // done with thread
  closeThread(thread);
}

void ArchMultithreadPosix::threadCancel(int)
{
  // do nothing
}

void *ArchMultithreadPosix::threadSignalHandler(void *)
{
  // detach
  pthread_detach(pthread_self());

  // add signal to mask
  sigset_t sigset;
  setSignalSet(&sigset);

  // also wait on SIGABRT.  on linux (others?) this thread (process)
  // will persist after all the other threads evaporate due to an
  // assert unless we wait on SIGABRT.  that means our resources (like
  // the socket we're listening on) are not released and never will be
  // until the lingering thread is killed.  i don't know why sigwait()
  // should protect the thread from being killed.  note that sigwait()
  // doesn't actually return if we receive SIGABRT and, for some
  // reason, we don't have to block SIGABRT.
  sigaddset(&sigset, SIGABRT);

  // we exit the loop via thread cancellation in sigwait()
  for (;;) {
    // wait
#if HAVE_POSIX_SIGWAIT
    int signal = 0;
    sigwait(&sigset, &signal);
#else
    sigwait(&sigset);
#endif

    // if we get here then the signal was raised
    switch (signal) {
      using enum ThreadSignal;
    case SIGINT:
      ARCH->raiseSignal(Interrupt);
      break;

    case SIGTERM:
      ARCH->raiseSignal(Terminate);
      break;

    case SIGHUP:
      ARCH->raiseSignal(Hangup);
      break;

    case SIGUSR2:
      ARCH->raiseSignal(User);
      break;

    default:
      // ignore
      break;
    }
  }

  return nullptr;
}