#include "source/common/event/file_event_impl.h"

#include <cstdint>

#include "source/common/common/assert.h"

#include "source/common/event/dispatcher_impl.h"

#include "event2/event.h"

namespace Envoy {

namespace Event {

FileEventImpl::FileEventImpl(DispatcherImpl& dispatcher, os_fd_t fd, FileReadyCb cb,

                             FileTriggerType trigger, uint32_t events)

  // Treat the lack of a valid fd (which in practice should only happen if we run out of FDs) as

  // an OOM condition and just crash.

#ifdef WIN32

  ASSERT(trigger_ != FileTriggerType::Edge, "libevent does not support edge triggers on Windows");

#endif

  // events is not empty.

  // Only supported event types are set.

  // Schedule the activation callback so it runs as part of the next loop iteration if it is not

  // already scheduled.

  // Merge new events with pending injected events.

  // The update can be skipped in cases where the old and new event mask are the same if the fd is

  // using Level or EmulatedEdge trigger modes, but not Edge trigger mode. When the fd is registered

  // in edge trigger mode, re-registering the fd will force re-computation of the readable/writable

  // state even in cases where the event mask is not changing. See

  // https://github.com/envoyproxy/envoy/pull/16389 for more details.

  // TODO(antoniovicente) Consider ways to optimize away event registration updates in edge trigger

  // mode once setEnabled stops clearing injected_activation_events_ before calling updateEvents

  // and/or implement optimizations at the Network::ConnectionImpl level to reduce the number of

  // calls to setEnabled.

    // Clear pending events on updates to the fd event mask to avoid delivering events that are no

    // longer relevant. Updating the event mask will reset the fd edge trigger state so the proxy

    // will be able to determine the fd read/write state without need for the injected activation

    // events.

  // This constexpr if allows the compiler to optimize away the function on POSIX

  if constexpr (PlatformDefaultTriggerType == FileTriggerType::EmulatedEdge) {

    if (trigger_ == FileTriggerType::EmulatedEdge) {

      auto new_event_mask = enabled_events_ & ~event;

      updateEvents(new_event_mask);

    }

  }

  // This constexpr if allows the compiler to optimize away the function on POSIX

  if constexpr (PlatformDefaultTriggerType == FileTriggerType::EmulatedEdge) {

    ASSERT((event & (FileReadyType::Read | FileReadyType::Write)) == event);

    if (trigger_ == FileTriggerType::EmulatedEdge) {

      auto new_event_mask = enabled_events_ | event;

      updateEvents(new_event_mask);

    }

  }

  // TODO(davinci26): This can be optimized further in (w)epoll backends using the `EPOLLONESHOT`

  // flag. With this flag `EPOLLIN`/`EPOLLOUT` are automatically disabled when the event is

  // activated.

  if constexpr (PlatformDefaultTriggerType == FileTriggerType::EmulatedEdge) {

    if (trigger_ == FileTriggerType::EmulatedEdge) {

      unregisterEventIfEmulatedEdge(events &

                                    (Event::FileReadyType::Write | Event::FileReadyType::Read));

    }

  }

} // namespace Event

} // namespace Envoy