// Copyright 2015 The Chromium 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 "components/scheduler/renderer/user_model.h"

#include "base/metrics/histogram_macros.h"

namespace scheduler {

namespace {
// This enum is used to back a histogram, and should therefore be treated as
// append-only.
enum GesturePredictionResult {
  GESTURE_OCCURED_WAS_PREDICTED = 0,
  GESTURE_OCCURED_BUT_NOT_PREDICTED = 1,
  GESTURE_PREDICTED_BUT_DID_NOT_OCCUR = 2,
  GESTURE_PREDICTION_RESULT_COUNT = 3
};

void RecordGesturePrediction(GesturePredictionResult result) {
  UMA_HISTOGRAM_ENUMERATION(
      "RendererScheduler.UserModel.GesturePredictedCorrectly", result,
      GESTURE_PREDICTION_RESULT_COUNT);
}

}  // namespace

UserModel::UserModel()
    : pending_input_event_count_(0),
      is_gesture_active_(false),
      is_gesture_expected_(false) {}
UserModel::~UserModel() {}

void UserModel::DidStartProcessingInputEvent(blink::WebInputEvent::Type type,
                                             const base::TimeTicks now) {
  last_input_signal_time_ = now;
  if (type == blink::WebInputEvent::TouchStart ||
      type == blink::WebInputEvent::GestureScrollBegin ||
      type == blink::WebInputEvent::GesturePinchBegin) {
    // Only update stats once per gesture.
    if (!is_gesture_active_) {
      last_gesture_start_time_ = now;

      RecordGesturePrediction(is_gesture_expected_
                                  ? GESTURE_OCCURED_WAS_PREDICTED
                                  : GESTURE_OCCURED_BUT_NOT_PREDICTED);

      if (!last_reset_time_.is_null()) {
        base::TimeDelta time_since_reset = now - last_reset_time_;
        UMA_HISTOGRAM_MEDIUM_TIMES(
            "RendererScheduler.UserModel.GestureStartTimeSinceModelReset",
            time_since_reset);
      }

      // If there has been a previous gesture, record a UMA metric for the time
      // interval between then and now.
      if (!last_continuous_gesture_time_.is_null()) {
        base::TimeDelta time_since_last_gesture =
            now - last_continuous_gesture_time_;
        UMA_HISTOGRAM_MEDIUM_TIMES(
            "RendererScheduler.UserModel.TimeBetweenGestures",
            time_since_last_gesture);
      }
    }

    is_gesture_active_ = true;
  }

  // We need to track continuous gestures seperatly for scroll detection
  // because taps should not be confused with scrolls.
  if (type == blink::WebInputEvent::GestureScrollBegin ||
      type == blink::WebInputEvent::GestureScrollEnd ||
      type == blink::WebInputEvent::GestureScrollUpdate ||
      type == blink::WebInputEvent::GestureFlingStart ||
      type == blink::WebInputEvent::GestureFlingCancel ||
      type == blink::WebInputEvent::GesturePinchBegin ||
      type == blink::WebInputEvent::GesturePinchEnd ||
      type == blink::WebInputEvent::GesturePinchUpdate) {
    last_continuous_gesture_time_ = now;
  }

  // If the gesture has ended, clear |is_gesture_active_| and record a UMA
  // metric that tracks its duration.
  if (type == blink::WebInputEvent::GestureScrollEnd ||
      type == blink::WebInputEvent::GesturePinchEnd ||
      type == blink::WebInputEvent::GestureFlingStart ||
      type == blink::WebInputEvent::TouchEnd) {
    // Only update stats once per gesture.
    if (is_gesture_active_) {
      base::TimeDelta duration = now - last_gesture_start_time_;
      UMA_HISTOGRAM_TIMES("RendererScheduler.UserModel.GestureDuration",
                          duration);
    }
    is_gesture_active_ = false;
  }

  TRACE_COUNTER1(TRACE_DISABLED_BY_DEFAULT("renderer.scheduler"),
                 "is_gesture_active", is_gesture_active_);

  pending_input_event_count_++;
}

void UserModel::DidFinishProcessingInputEvent(const base::TimeTicks now) {
  last_input_signal_time_ = now;
  if (pending_input_event_count_ > 0)
    pending_input_event_count_--;
}

base::TimeDelta UserModel::TimeLeftInUserGesture(base::TimeTicks now) const {
  base::TimeDelta escalated_priority_duration =
      base::TimeDelta::FromMilliseconds(kGestureEstimationLimitMillis);

  // If the input event is still pending, go into input prioritized policy and
  // check again later.
  if (pending_input_event_count_ > 0)
    return escalated_priority_duration;
  if (last_input_signal_time_.is_null() ||
      last_input_signal_time_ + escalated_priority_duration < now) {
    return base::TimeDelta();
  }
  return last_input_signal_time_ + escalated_priority_duration - now;
}

bool UserModel::IsGestureExpectedSoon(
    const base::TimeTicks now,
    base::TimeDelta* prediction_valid_duration) {
  bool was_gesture_expected = is_gesture_expected_;
  is_gesture_expected_ =
      IsGestureExpectedSoonImpl(now, prediction_valid_duration);

  // Track when we start expecting a gesture so we can work out later if a
  // gesture actually happened.
  if (!was_gesture_expected && is_gesture_expected_)
    last_gesture_expected_start_time_ = now;

  if (was_gesture_expected && !is_gesture_expected_ &&
      last_gesture_expected_start_time_ > last_gesture_start_time_) {
    RecordGesturePrediction(GESTURE_PREDICTED_BUT_DID_NOT_OCCUR);
  }
  return is_gesture_expected_;
}

bool UserModel::IsGestureExpectedSoonImpl(
    const base::TimeTicks now,
    base::TimeDelta* prediction_valid_duration) const {
  if (is_gesture_active_) {
    if (IsGestureExpectedToContinue(now, prediction_valid_duration)) {
      return false;
    } else {
      // If a gesture is not expected to continue then we expect a subsequent
      // gesture soon.
      *prediction_valid_duration =
          base::TimeDelta::FromMilliseconds(kExpectSubsequentGestureMillis);
      return true;
    }
  } else {
    // If we've have a finished a gesture then a subsequent gesture is deemed
    // likely.
    base::TimeDelta expect_subsequent_gesture_for =
        base::TimeDelta::FromMilliseconds(kExpectSubsequentGestureMillis);
    if (last_continuous_gesture_time_.is_null() ||
        last_continuous_gesture_time_ + expect_subsequent_gesture_for <= now) {
      return false;
    }
    *prediction_valid_duration =
        last_continuous_gesture_time_ + expect_subsequent_gesture_for - now;
    return true;
  }
}

bool UserModel::IsGestureExpectedToContinue(
    const base::TimeTicks now,
    base::TimeDelta* prediction_valid_duration) const {
  if (!is_gesture_active_)
    return false;

  base::TimeDelta median_gesture_duration =
      base::TimeDelta::FromMilliseconds(kMedianGestureDurationMillis);
  base::TimeTicks expected_gesture_end_time =
      last_gesture_start_time_ + median_gesture_duration;

  if (expected_gesture_end_time > now) {
    *prediction_valid_duration = expected_gesture_end_time - now;
    return true;
  }
  return false;
}

void UserModel::Reset(base::TimeTicks now) {
  last_input_signal_time_ = base::TimeTicks();
  last_gesture_start_time_ = base::TimeTicks();
  last_continuous_gesture_time_ = base::TimeTicks();
  last_gesture_expected_start_time_ = base::TimeTicks();
  last_reset_time_ = now;
  is_gesture_active_ = false;
  is_gesture_expected_ = false;
}

void UserModel::AsValueInto(base::trace_event::TracedValue* state) const {
  state->BeginDictionary("user_model");
  state->SetInteger("pending_input_event_count", pending_input_event_count_);
  state->SetDouble(
      "last_input_signal_time",
      (last_input_signal_time_ - base::TimeTicks()).InMillisecondsF());
  state->SetDouble(
      "last_gesture_start_time",
      (last_gesture_start_time_ - base::TimeTicks()).InMillisecondsF());
  state->SetDouble(
      "last_continuous_gesture_time",
      (last_continuous_gesture_time_ - base::TimeTicks()).InMillisecondsF());
  state->SetDouble("last_gesture_expected_start_time",
                   (last_gesture_expected_start_time_ - base::TimeTicks())
                       .InMillisecondsF());
  state->SetDouble("last_reset_time",
                   (last_reset_time_ - base::TimeTicks()).InMillisecondsF());
  state->SetBoolean("is_gesture_expected", is_gesture_expected_);
  state->SetBoolean("is_gesture_active", is_gesture_active_);
  state->EndDictionary();
}

}  // namespace scheduler