// Copyright 2013 The Flutter 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 "session_connection.h"

#include "flutter/fml/make_copyable.h"
#include "flutter/fml/trace_event.h"

#include "vsync_recorder.h"
#include "vsync_waiter.h"

namespace flutter_runner {

SessionConnection::SessionConnection(
    std::string debug_label,
    fidl::InterfaceHandle<fuchsia::ui::scenic::Session> session,
    fml::closure session_error_callback,
    on_frame_presented_event on_frame_presented_callback,
    zx_handle_t vsync_event_handle)
    : session_wrapper_(session.Bind(), nullptr),
      on_frame_presented_callback_(std::move(on_frame_presented_callback)),
      vsync_event_handle_(vsync_event_handle) {
  session_wrapper_.set_error_handler(
      [callback = session_error_callback](zx_status_t status) { callback(); });

  // Set the |fuchsia::ui::scenic::OnFramePresented()| event handler that will
  // fire every time a set of one or more frames is presented.
  session_wrapper_.set_on_frame_presented_handler(
      [this, handle = vsync_event_handle_](
          fuchsia::scenic::scheduling::FramePresentedInfo info) {
        // Update Scenic's limit for our remaining frames in flight allowed.
        size_t num_presents_handled = info.presentation_infos.size();
        frames_in_flight_allowed_ = info.num_presents_allowed;

        // A frame was presented: Update our |frames_in_flight| to match the
        // updated unfinalized present requests.
        frames_in_flight_ -= num_presents_handled;
        FML_DCHECK(frames_in_flight_ >= 0);

        VsyncRecorder::GetInstance().UpdateFramePresentedInfo(
            zx::time(info.actual_presentation_time));

        // Call the client-provided callback once we are done using |info|.
        on_frame_presented_callback_(std::move(info));

        if (present_session_pending_) {
          PresentSession();
        }
        ToggleSignal(handle, true);
      }  // callback
  );

  session_wrapper_.SetDebugName(debug_label);

  // Get information to finish initialization and only then allow Present()s.
  session_wrapper_.RequestPresentationTimes(
      /*requested_prediction_span=*/0,
      [this](fuchsia::scenic::scheduling::FuturePresentationTimes info) {
        frames_in_flight_allowed_ = info.remaining_presents_in_flight_allowed;

        // If Scenic alloted us 0 frames to begin with, we should fail here.
        FML_CHECK(frames_in_flight_allowed_ > 0);

        VsyncRecorder::GetInstance().UpdateNextPresentationInfo(
            std::move(info));

        // Signal is initially high indicating availability of the session.
        ToggleSignal(vsync_event_handle_, true);
        initialized_ = true;

        PresentSession();
      });
}

SessionConnection::~SessionConnection() = default;

void SessionConnection::Present() {
  TRACE_EVENT0("gfx", "SessionConnection::Present");

  TRACE_FLOW_BEGIN("gfx", "SessionConnection::PresentSession",
                   next_present_session_trace_id_);
  next_present_session_trace_id_++;

  present_requested_time_ = fml::TimePoint::Now();

  // Throttle frame submission to Scenic if we already have the maximum amount
  // of frames in flight. This allows the paint tasks for this frame to execute
  // in parallel with the presentation of previous frame but still provides
  // back-pressure to prevent us from enqueuing even more work.
  if (initialized_ && frames_in_flight_ < kMaxFramesInFlight) {
    PresentSession();
  } else {
    // We should never exceed the max frames in flight.
    FML_CHECK(frames_in_flight_ <= kMaxFramesInFlight);

    present_session_pending_ = true;
    ToggleSignal(vsync_event_handle_, false);
  }
}

fml::TimePoint SessionConnection::CalculateNextLatchPoint(
    fml::TimePoint present_requested_time,
    fml::TimePoint now,
    fml::TimePoint last_latch_point_targeted,
    fml::TimeDelta flutter_frame_build_time,
    fml::TimeDelta vsync_interval,
    std::deque<std::pair<fml::TimePoint, fml::TimePoint>>&
        future_presentation_infos) {
  // The minimum latch point is the largest of:
  // Now
  // When we expect the Flutter work for the frame to be completed
  // The last latch point targeted
  fml::TimePoint minimum_latch_point_to_target =
      std::max(std::max(now, present_requested_time + flutter_frame_build_time),
               last_latch_point_targeted);

  for (auto& info : future_presentation_infos) {
    fml::TimePoint latch_point = info.first;

    if (latch_point >= minimum_latch_point_to_target) {
      return latch_point;
    }
  }

  // We could not find a suitable latch point in the list given to us from
  // Scenic, so aim for the smallest safe value.
  return minimum_latch_point_to_target;
}

void SessionConnection::PresentSession() {
  TRACE_EVENT0("gfx", "SessionConnection::PresentSession");

  // If we cannot call Present2() because we have no more Scenic frame budget,
  // then we must wait until the OnFramePresented() event fires so we can
  // continue our work.
  if (frames_in_flight_allowed_ == 0) {
    FML_CHECK(!initialized_ || present_session_pending_);
    return;
  }

  present_session_pending_ = false;

  while (processed_present_session_trace_id_ < next_present_session_trace_id_) {
    TRACE_FLOW_END("gfx", "SessionConnection::PresentSession",
                   processed_present_session_trace_id_);
    processed_present_session_trace_id_++;
  }
  TRACE_FLOW_BEGIN("gfx", "Session::Present", next_present_trace_id_);
  next_present_trace_id_++;

  ++frames_in_flight_;

  // Flush all session ops. Paint tasks may not yet have executed but those are
  // fenced. The compositor can start processing ops while we finalize paint
  // tasks.

  fml::TimeDelta presentation_interval =
      VsyncRecorder::GetInstance().GetCurrentVsyncInfo().presentation_interval;

  fml::TimePoint next_latch_point = CalculateNextLatchPoint(
      fml::TimePoint::Now(), present_requested_time_,
      last_latch_point_targeted_,
      fml::TimeDelta::FromMicroseconds(0),  // flutter_frame_build_time
      presentation_interval, future_presentation_infos_);

  last_latch_point_targeted_ = next_latch_point;

  session_wrapper_.Present2(
      /*requested_presentation_time=*/next_latch_point.ToEpochDelta()
          .ToNanoseconds(),
      /*requested_prediction_span=*/presentation_interval.ToNanoseconds() * 10,
      [this](fuchsia::scenic::scheduling::FuturePresentationTimes info) {
        // Clear |future_presentation_infos_| and replace it with the updated
        // information.
        std::deque<std::pair<fml::TimePoint, fml::TimePoint>>().swap(
            future_presentation_infos_);

        for (fuchsia::scenic::scheduling::PresentationInfo& presentation_info :
             info.future_presentations) {
          future_presentation_infos_.push_back(
              {fml::TimePoint::FromEpochDelta(fml::TimeDelta::FromNanoseconds(
                   presentation_info.latch_point())),
               fml::TimePoint::FromEpochDelta(fml::TimeDelta::FromNanoseconds(
                   presentation_info.presentation_time()))});
        }

        frames_in_flight_allowed_ = info.remaining_presents_in_flight_allowed;
        VsyncRecorder::GetInstance().UpdateNextPresentationInfo(
            std::move(info));
      });
}

void SessionConnection::ToggleSignal(zx_handle_t handle, bool set) {
  const auto signal = VsyncWaiter::SessionPresentSignal;
  auto status = zx_object_signal(handle,            // handle
                                 set ? 0 : signal,  // clear mask
                                 set ? signal : 0   // set mask
  );
  if (status != ZX_OK) {
    FML_LOG(ERROR) << "Could not toggle vsync signal: " << set;
  }
}

}  // namespace flutter_runner