// Copyright (c) 2016 The Chromium Embedded Framework Authors. All rights
// reserved. Use of this source code is governed by a BSD-style license that
// can be found in the LICENSE file.

#include "cefclient/browser/main_message_loop_external_pump.h"

#include <errno.h>
#include <fcntl.h>
#include <math.h>

#include <glib.h>

#include "include/base/cef_logging.h"
#include "include/cef_app.h"

// From base/posix/eintr_wrapper.h.
// This provides a wrapper around system calls which may be interrupted by a
// signal and return EINTR. See man 7 signal.
// To prevent long-lasting loops (which would likely be a bug, such as a signal
// that should be masked) to go unnoticed, there is a limit after which the
// caller will nonetheless see an EINTR in Debug builds.
#if !defined(HANDLE_EINTR)
#if !DCHECK_IS_ON()

#define HANDLE_EINTR(x) ({ \
  decltype(x) eintr_wrapper_result; \
  do { \
    eintr_wrapper_result = (x); \
  } while (eintr_wrapper_result == -1 && errno == EINTR); \
  eintr_wrapper_result; \
})

#else

#define HANDLE_EINTR(x) ({ \
  int eintr_wrapper_counter = 0; \
  decltype(x) eintr_wrapper_result; \
  do { \
    eintr_wrapper_result = (x); \
  } while (eintr_wrapper_result == -1 && errno == EINTR && \
           eintr_wrapper_counter++ < 100); \
  eintr_wrapper_result; \
})

#endif  // !DCHECK_IS_ON()
#endif  // !defined(HANDLE_EINTR)

namespace client {

namespace {

class MainMessageLoopExternalPumpLinux : public MainMessageLoopExternalPump {
 public:
  MainMessageLoopExternalPumpLinux();
  ~MainMessageLoopExternalPumpLinux();

  // MainMessageLoopStd methods:
  void Quit() OVERRIDE;
  int Run() OVERRIDE;

  // MainMessageLoopExternalPump methods:
  void OnScheduleMessagePumpWork(int64 delay_ms) OVERRIDE;

  // Internal methods used for processing the pump callbacks. They are public
  // for simplicity but should not be used directly. HandlePrepare is called
  // during the prepare step of glib, and returns a timeout that will be passed
  // to the poll. HandleCheck is called after the poll has completed, and
  // returns whether or not HandleDispatch should be called. HandleDispatch is
  // called if HandleCheck returned true.
  int HandlePrepare();
  bool HandleCheck();
  void HandleDispatch();

 protected:
  // MainMessageLoopExternalPump methods:
  void SetTimer(int64 delay_ms) OVERRIDE;
  void KillTimer() OVERRIDE;
  bool IsTimerPending() OVERRIDE;

 private:
  // Used to flag that the Run() invocation should return ASAP.
  bool should_quit_;

  // A GLib structure that we can add event sources to. We use the default GLib
  // context, which is the one to which all GTK events are dispatched.
  GMainContext* context_;

  // The work source. It is destroyed when the message pump is destroyed.
  GSource* work_source_;

  // The time when we need to do delayed work.
  CefTime delayed_work_time_;

  // We use a wakeup pipe to make sure we'll get out of the glib polling phase
  // when another thread has scheduled us to do some work. There is a glib
  // mechanism g_main_context_wakeup, but this won't guarantee that our event's
  // Dispatch() will be called.
  int wakeup_pipe_read_;
  int wakeup_pipe_write_;

  // Use a scoped_ptr to avoid needing the definition of GPollFD in the header.
  SCOPED_PTR(GPollFD) wakeup_gpollfd_;
};

// Return a timeout suitable for the glib loop, -1 to block forever,
// 0 to return right away, or a timeout in milliseconds from now.
int GetTimeIntervalMilliseconds(const CefTime& from) {
  if (from.GetDoubleT() == 0.0)
    return -1;

  CefTime now;
  now.Now();

  // Be careful here. CefTime has a precision of microseconds, but we want a
  // value in milliseconds. If there are 5.5ms left, should the delay be 5 or
  // 6?  It should be 6 to avoid executing delayed work too early.
  int delay = static_cast<int>(
      ceil((from.GetDoubleT() - now.GetDoubleT()) * 1000.0));

  // If this value is negative, then we need to run delayed work soon.
  return delay < 0 ? 0 : delay;
}

struct WorkSource : public GSource {
  MainMessageLoopExternalPumpLinux* pump;
};

gboolean WorkSourcePrepare(GSource* source,
                           gint* timeout_ms) {
  *timeout_ms = static_cast<WorkSource*>(source)->pump->HandlePrepare();
  // We always return FALSE, so that our timeout is honored.  If we were
  // to return TRUE, the timeout would be considered to be 0 and the poll
  // would never block.  Once the poll is finished, Check will be called.
  return FALSE;
}

gboolean WorkSourceCheck(GSource* source) {
  // Only return TRUE if Dispatch should be called.
  return static_cast<WorkSource*>(source)->pump->HandleCheck();
}

gboolean WorkSourceDispatch(GSource* source,
                            GSourceFunc unused_func,
                            gpointer unused_data) {

  static_cast<WorkSource*>(source)->pump->HandleDispatch();
  // Always return TRUE so our source stays registered.
  return TRUE;
}

// I wish these could be const, but g_source_new wants non-const.
GSourceFuncs WorkSourceFuncs = {
  WorkSourcePrepare,
  WorkSourceCheck,
  WorkSourceDispatch,
  NULL
};

MainMessageLoopExternalPumpLinux::MainMessageLoopExternalPumpLinux()
  : should_quit_(false),
    context_(g_main_context_default()),
    wakeup_gpollfd_(new GPollFD) {
  // Create our wakeup pipe, which is used to flag when work was scheduled.
  int fds[2];
  int ret = pipe(fds);
  DCHECK_EQ(ret, 0);
  (void)ret;  // Prevent warning in release mode.

  wakeup_pipe_read_  = fds[0];
  wakeup_pipe_write_ = fds[1];
  wakeup_gpollfd_->fd = wakeup_pipe_read_;
  wakeup_gpollfd_->events = G_IO_IN;

  work_source_ = g_source_new(&WorkSourceFuncs, sizeof(WorkSource));
  static_cast<WorkSource*>(work_source_)->pump = this;
  g_source_add_poll(work_source_, wakeup_gpollfd_.get());
  // Use a low priority so that we let other events in the queue go first.
  g_source_set_priority(work_source_, G_PRIORITY_DEFAULT_IDLE);
  // This is needed to allow Run calls inside Dispatch.
  g_source_set_can_recurse(work_source_, TRUE);
  g_source_attach(work_source_, context_);
}

MainMessageLoopExternalPumpLinux::~MainMessageLoopExternalPumpLinux() {
  g_source_destroy(work_source_);
  g_source_unref(work_source_);
  close(wakeup_pipe_read_);
  close(wakeup_pipe_write_);
}

void MainMessageLoopExternalPumpLinux::Quit() {
  should_quit_ = true;
}

int MainMessageLoopExternalPumpLinux::Run() {
  // We really only do a single task for each iteration of the loop. If we
  // have done something, assume there is likely something more to do. This
  // will mean that we don't block on the message pump until there was nothing
  // more to do. We also set this to true to make sure not to block on the
  // first iteration of the loop.
  bool more_work_is_plausible = true;

  // We run our own loop instead of using g_main_loop_quit in one of the
  // callbacks. This is so we only quit our own loops, and we don't quit
  // nested loops run by others.
  for (;;) {
    // Don't block if we think we have more work to do.
    bool block = !more_work_is_plausible;

    more_work_is_plausible = g_main_context_iteration(context_, block);
    if (should_quit_)
      break;
  }

  // We need to run the message pump until it is idle. However we don't have
  // that information here so we run the message loop "for a while".
  for (int i = 0; i < 10; ++i) {
    // Do some work.
    CefDoMessageLoopWork();

    // Sleep to allow the CEF proc to do work.
    usleep(50000);
  }

  return 0;
}

void MainMessageLoopExternalPumpLinux::OnScheduleMessagePumpWork(
    int64 delay_ms) {
  // This can be called on any thread, so we don't want to touch any state
  // variables as we would then need locks all over. This ensures that if we
  // are sleeping in a poll that we will wake up.
  if (HANDLE_EINTR(write(wakeup_pipe_write_, &delay_ms, sizeof(int64))) !=
                   sizeof(int64)) {
    NOTREACHED() << "Could not write to the UI message loop wakeup pipe!";
  }
}

// Return the timeout we want passed to poll.
int MainMessageLoopExternalPumpLinux::HandlePrepare() {
  // We don't think we have work to do, but make sure not to block longer than
  // the next time we need to run delayed work.
  return GetTimeIntervalMilliseconds(delayed_work_time_);
}

bool MainMessageLoopExternalPumpLinux::HandleCheck() {
  // We usually have a single message on the wakeup pipe, since we are only
  // signaled when the queue went from empty to non-empty, but there can be
  // two messages if a task posted a task, hence we read at most two bytes.
  // The glib poll will tell us whether there was data, so this read shouldn't
  // block.
  if (wakeup_gpollfd_->revents & G_IO_IN) {
    int64 delay_ms[2];
    const size_t num_bytes =
        HANDLE_EINTR(read(wakeup_pipe_read_, delay_ms, sizeof(int64) * 2));
    if (num_bytes < sizeof(int64)) {
      NOTREACHED() << "Error reading from the wakeup pipe.";
    }
    if (num_bytes == sizeof(int64))
      OnScheduleWork(delay_ms[0]);
    if (num_bytes == sizeof(int64) * 2)
      OnScheduleWork(delay_ms[1]);
  }

  if (GetTimeIntervalMilliseconds(delayed_work_time_) == 0) {
    // The timer has expired. That condition will stay true until we process
    // that delayed work, so we don't need to record this differently.
    return true;
  }

  return false;
}

void MainMessageLoopExternalPumpLinux::HandleDispatch() {
  OnTimerTimeout();
}

void MainMessageLoopExternalPumpLinux::SetTimer(int64 delay_ms) {
  DCHECK_GT(delay_ms, 0);

  CefTime now;
  now.Now();

  delayed_work_time_ =
      CefTime(now.GetDoubleT() + static_cast<double>(delay_ms) / 1000.0);
}

void MainMessageLoopExternalPumpLinux::KillTimer() {
  delayed_work_time_ = CefTime();
}

bool MainMessageLoopExternalPumpLinux::IsTimerPending() {
  return GetTimeIntervalMilliseconds(delayed_work_time_) > 0;
}

} // namespace

// static
SCOPED_PTR(MainMessageLoopExternalPump)
MainMessageLoopExternalPump::Create() {
  return SCOPED_PTR(MainMessageLoopExternalPump)(
      new MainMessageLoopExternalPumpLinux());
}

}  // namespace client