#include "common/event/file_event_impl.h"

#include <cstdint>

#include "common/common/assert.h"
#include "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)
    : cb_(cb), fd_(fd), trigger_(trigger), enabled_events_(events),
      activation_cb_(dispatcher.createSchedulableCallback([this]() {
        ASSERT(injected_activation_events_ != 0);
        mergeInjectedEventsAndRunCb(0);
      })) {
  // 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.
  RELEASE_ASSERT(SOCKET_VALID(fd), "");
#ifdef WIN32
  ASSERT(trigger_ != FileTriggerType::Edge, "libevent does not support edge triggers on Windows");
#endif
  if constexpr (PlatformDefaultTriggerType != FileTriggerType::EmulatedEdge) {
    ASSERT(trigger_ != FileTriggerType::EmulatedEdge,
           "Cannot use EmulatedEdge events if they are not the default platform type");
  }

  assignEvents(events, &dispatcher.base());
  event_add(&raw_event_, nullptr);
}

void FileEventImpl::activate(uint32_t events) {
  // events is not empty.
  ASSERT(events != 0);
  // Only supported event types are set.
  ASSERT((events & (FileReadyType::Read | FileReadyType::Write | FileReadyType::Closed)) == events);

  // Schedule the activation callback so it runs as part of the next loop iteration if it is not
  // already scheduled.
  if (injected_activation_events_ == 0) {
    ASSERT(!activation_cb_->enabled());
    activation_cb_->scheduleCallbackNextIteration();
  }
  ASSERT(activation_cb_->enabled());

  // Merge new events with pending injected events.
  injected_activation_events_ |= events;
}

void FileEventImpl::assignEvents(uint32_t events, event_base* base) {
  ASSERT(base != nullptr);
  enabled_events_ = events;
  event_assign(
      &raw_event_, base, fd_,
      EV_PERSIST | (trigger_ == FileTriggerType::Edge ? EV_ET : 0) |
          (events & FileReadyType::Read ? EV_READ : 0) |
          (events & FileReadyType::Write ? EV_WRITE : 0) |
          (events & FileReadyType::Closed ? EV_CLOSED : 0),
      [](evutil_socket_t, short what, void* arg) -> void {
        auto* event = static_cast<FileEventImpl*>(arg);
        uint32_t events = 0;
        if (what & EV_READ) {
          events |= FileReadyType::Read;
        }

        if (what & EV_WRITE) {
          events |= FileReadyType::Write;
        }

        if (what & EV_CLOSED) {
          events |= FileReadyType::Closed;
        }

        ASSERT(events != 0);
        event->mergeInjectedEventsAndRunCb(events);
      },
      this);
}

void FileEventImpl::updateEvents(uint32_t events) {
  if (events == enabled_events_) {
    return;
  }
  auto* base = event_get_base(&raw_event_);
  event_del(&raw_event_);
  assignEvents(events, base);
  event_add(&raw_event_, nullptr);
}

void FileEventImpl::setEnabled(uint32_t events) {
  if (injected_activation_events_ != 0) {
    // 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.
    injected_activation_events_ = 0;
    activation_cb_->cancel();
  }
  updateEvents(events);
}

void FileEventImpl::unregisterEventIfEmulatedEdge(uint32_t event) {
  // 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);
    }
  }
}

void FileEventImpl::registerEventIfEmulatedEdge(uint32_t event) {
  // 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;
      if (event & FileReadyType::Read && (enabled_events_ & FileReadyType::Closed)) {
        // We never ask for both early close and read at the same time.
        new_event_mask = new_event_mask & ~FileReadyType::Read;
      }
      updateEvents(new_event_mask);
    }
  }
}

void FileEventImpl::mergeInjectedEventsAndRunCb(uint32_t events) {
  if (injected_activation_events_ != 0) {
    // TODO(antoniovicente) remove this adjustment to activation events once ConnectionImpl can
    // handle Read and Close events delivered together.
    if constexpr (PlatformDefaultTriggerType == FileTriggerType::EmulatedEdge) {
      if (events & FileReadyType::Closed && injected_activation_events_ & FileReadyType::Read) {
        // We never ask for both early close and read at the same time. If close is requested
        // keep that instead.
        injected_activation_events_ = injected_activation_events_ & ~FileReadyType::Read;
      }
    }

    events |= injected_activation_events_;
    injected_activation_events_ = 0;
    activation_cb_->cancel();
  }

  // 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));
    }
  }

  cb_(events);
}

} // namespace Event
} // namespace Envoy