// Copyright (c) 2013 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.

#ifndef MEDIA_CAPTURE_CONTENT_VIDEO_CAPTURE_ORACLE_H_
#define MEDIA_CAPTURE_CONTENT_VIDEO_CAPTURE_ORACLE_H_

#include "base/callback_forward.h"
#include "base/time/time.h"
#include "media/base/feedback_signal_accumulator.h"
#include "media/capture/capture_export.h"
#include "media/capture/content/animated_content_sampler.h"
#include "media/capture/content/capture_resolution_chooser.h"
#include "media/capture/content/smooth_event_sampler.h"
#include "ui/gfx/geometry/rect.h"

namespace media {

// VideoCaptureOracle manages the producer-side throttling of captured frames
// from a video capture device.  It is informed of every update by the device;
// this empowers it to look into the future and decide if a particular frame
// ought to be captured in order to achieve its target frame rate.
class CAPTURE_EXPORT VideoCaptureOracle {
 public:
  enum Event {
    kCompositorUpdate,
    kRefreshRequest,
    kNumEvents,
  };

  // Constructs a VideoCaptureOracle with a default min capture period and
  // capture size constraints. Clients should call SetMinCapturePeriod() and
  // SetCaptureSizeConstraints() to provide more-accurate hard limits. If
  // |enable_auto_throttling| is true, enable realtime analysis of system
  // performance and auto-adjust the capture resolution and sampling decisions
  // to provide the best user experience.
  explicit VideoCaptureOracle(bool enable_auto_throttling);

  virtual ~VideoCaptureOracle();

  // Get/Update the minimum capture period.
  base::TimeDelta min_capture_period() const {
    return smoothing_sampler_.min_capture_period();
  }
  void SetMinCapturePeriod(base::TimeDelta period);

  // Sets the range of acceptable capture sizes and whether a fixed aspect ratio
  // is required. If a fixed aspect ratio is required, the aspect ratio of
  // |max_size| is used.
  void SetCaptureSizeConstraints(const gfx::Size& min_size,
                                 const gfx::Size& max_size,
                                 bool use_fixed_aspect_ratio);

  // Specifies whether the oracle should automatically adjust the capture size
  // in response to end-to-end utilization.
  void SetAutoThrottlingEnabled(bool enabled);

  // Get/Update the source content size.  Changes may not have an immediate
  // effect on the proposed capture size, as the oracle will prevent too-
  // frequent changes from occurring.
  gfx::Size source_size() const { return resolution_chooser_.source_size(); }
  void SetSourceSize(const gfx::Size& source_size);

  // Record a event of type |event|, and decide whether the caller should do a
  // frame capture.  |damage_rect| is the region of a frame about to be drawn,
  // and may be an empty Rect, if this is not known.  If the caller accepts the
  // oracle's proposal, it should call RecordCapture() to indicate this.
  bool ObserveEventAndDecideCapture(Event event,
                                    const gfx::Rect& damage_rect,
                                    base::TimeTicks event_time);

  // Returns the |frame_number| to be used with CompleteCapture().
  int next_frame_number() const { return next_frame_number_; }

  // Record and update internal state based on whether the frame capture will be
  // started.  |pool_utilization| is a value in the range 0.0 to 1.0 to indicate
  // the current buffer pool utilization relative to a sustainable maximum (not
  // the absolute maximum).  This method should only be called if the last call
  // to ObserveEventAndDecideCapture() returned true.
  void RecordCapture(double pool_utilization);
  void RecordWillNotCapture(double pool_utilization);

  // Notify of the completion of a capture, and whether it was successful.
  // Returns true iff the captured frame should be delivered.  |frame_timestamp|
  // is set to the timestamp that should be provided to the consumer of the
  // frame.
  virtual bool CompleteCapture(int frame_number,
                               bool capture_was_successful,
                               base::TimeTicks* frame_timestamp);

  // Notify that all in-flight captures have been canceled.  This has the same
  // effect as calling CompleteCapture() with a non-success status for all
  // outstanding frames.
  void CancelAllCaptures();

  // Record the resource utilization feedback for a frame that was processed by
  // the consumer.  This allows the oracle to reduce/increase future data volume
  // if the consumer is overloaded/under-utilized.  |resource_utilization| is a
  // value in the range 0.0 to 1.0 to indicate the current consumer resource
  // utilization relative to a sustainable maximum (not the absolute maximum).
  // This method should only be called for frames where CompleteCapture()
  // returned true.
  void RecordConsumerFeedback(int frame_number, double resource_utilization);

  // Sets the minimum amount of time that must pass between changes to the
  // capture size. This throttles the rate of size changes, to avoid stressing
  // consumers and to allow the end-to-end system sufficient time to stabilize
  // before re-evaluating the capture size.
  void SetMinSizeChangePeriod(base::TimeDelta period);

  // Returns the oracle's estimate of the duration of the next frame.  This
  // should be called just after ObserveEventAndDecideCapture(), and will only
  // be non-zero if the call returned true.
  base::TimeDelta estimated_frame_duration() const {
    return duration_of_next_frame_;
  }

  // Returns the capture frame size the client should use.  This is updated by
  // calls to ObserveEventAndDecideCapture().  The oracle prevents too-frequent
  // changes to the capture size, to avoid stressing the end-to-end pipeline.
  virtual gfx::Size capture_size() const;

  // Returns the oracle's estimate of the last time animation was detected.
  base::TimeTicks last_time_animation_was_detected() const {
    return last_time_animation_was_detected_;
  }

  // Returns a NUL-terminated string containing a short, human-readable form of
  // |event|.
  static const char* EventAsString(Event event);

  // Default minimum capture period. This is a rather low framerate for safety.
  // Clients are expected to set a better minimum capture period after
  // VideoCaptureOracle is constructed.
  static constexpr base::TimeDelta kDefaultMinCapturePeriod =
      base::TimeDelta::FromMicroseconds(1000000 / 5);  // 5 FPS

  // Default minimum size change period if SetMinSizeChangePeriod is not called.
  static constexpr base::TimeDelta kDefaultMinSizeChangePeriod =
      base::TimeDelta::FromSeconds(3);

 private:
  // Retrieve/Assign a frame timestamp by capture |frame_number|.  Only valid
  // when IsFrameInRecentHistory(frame_number) returns true.
  base::TimeTicks GetFrameTimestamp(int frame_number) const;
  void SetFrameTimestamp(int frame_number, base::TimeTicks timestamp);

  // Returns true if the frame timestamp ring-buffer currently includes a
  // slot for the given |frame_number|.
  bool IsFrameInRecentHistory(int frame_number) const;

  // Queries the ResolutionChooser to update |capture_size_|, and resets all the
  // FeedbackSignalAccumulator members to stable-state starting values.  The
  // accumulators are reset such that they can only apply feedback updates for
  // future frames (those with a timestamp after |last_frame_time|).
  void CommitCaptureSizeAndReset(base::TimeTicks last_frame_time);

  // Called after a capture or no-capture decision was recorded.  This analyzes
  // current state and may result in a future change to the capture frame size.
  void AnalyzeAndAdjust(base::TimeTicks analyze_time);

  // Analyzes current feedback signal accumulators for an indication that the
  // capture size should be decreased.  Returns either a decreased area, or -1
  // if no decrease should be made.
  int AnalyzeForDecreasedArea(base::TimeTicks analyze_time);

  // Analyzes current feedback signal accumulators for an indication that the
  // the system has had excellent long-term performance and the capture size
  // should be increased to improve quality.  Returns either an increased area,
  // or -1 if no increase should be made.
  int AnalyzeForIncreasedArea(base::TimeTicks analyze_time);

  // Returns the amount of time, since the source size last changed, to allow
  // frequent increases in capture area.  This allows the system a period of
  // time to quickly explore up and down to find an ideal point before being
  // more careful about capture size increases.
  base::TimeDelta GetExplorationPeriodAfterSourceSizeChange();

  // Returns true if updates have been accumulated by |accumulator| for a
  // sufficient amount of time and the latest update was fairly recent, relative
  // to |now|.
  bool HasSufficientRecentFeedback(
      const FeedbackSignalAccumulator<base::TimeTicks>& accumulator,
      base::TimeTicks now);

  // Set to false to prevent the oracle from automatically adjusting the capture
  // size in response to end-to-end utilization.
  bool auto_throttling_enabled_;

  // The minimum amount of time that must pass between changes to the capture
  // size.
  base::TimeDelta min_size_change_period_;

  // Incremented every time RecordCapture() is called.
  int next_frame_number_;

  // Stores the last |event_time| from the last observation/decision.  Used to
  // sanity-check that event times are monotonically non-decreasing.
  base::TimeTicks last_event_time_[kNumEvents];

  // Updated by the last call to ObserveEventAndDecideCapture() with the
  // estimated duration of the next frame to sample.  This is zero if the method
  // returned false.
  base::TimeDelta duration_of_next_frame_;

  // Stores the frame number from the last successfully delivered frame.
  int last_successfully_delivered_frame_number_;

  // Stores the number of pending frame captures.
  int num_frames_pending_;

  // These track present/paint history and propose whether to sample each event
  // for capture.  |smoothing_sampler_| uses a "works for all" heuristic, while
  // |content_sampler_| specifically detects animated content (e.g., video
  // playback) and decides which events to sample to "lock into" that content.
  SmoothEventSampler smoothing_sampler_;
  AnimatedContentSampler content_sampler_;

  // Determines video capture frame sizes.
  CaptureResolutionChooser resolution_chooser_;

  // The timestamp of the frame just before the last call to SetSourceSize().
  base::TimeTicks source_size_change_time_;

  // The current capture size.  |resolution_chooser_| may hold an updated value
  // because the oracle prevents this size from changing too frequently.  This
  // avoids over-stressing consumers (e.g., when a window is being activly
  // drag-resized) and allowing the end-to-end system time to stabilize.
  gfx::Size capture_size_;

  // Recent history of frame timestamps proposed by VideoCaptureOracle.  This is
  // a ring-buffer, and should only be accessed by the Get/SetFrameTimestamp()
  // methods.
  enum { kMaxFrameTimestamps = 16 };
  base::TimeTicks frame_timestamps_[kMaxFrameTimestamps];

  // Recent average buffer pool utilization for capture.
  FeedbackSignalAccumulator<base::TimeTicks> buffer_pool_utilization_;

  // Estimated maximum frame area that currently can be handled by the consumer,
  // in number of pixels per frame.  This is used to adjust the capture size up
  // or down to a data volume the consumer can handle.  Note that some consumers
  // do not provide feedback, and the analysis logic should account for that.
  FeedbackSignalAccumulator<base::TimeTicks> estimated_capable_area_;

  // The time of the first analysis which concluded the end-to-end system was
  // under-utilized.  If null, the system is not currently under-utilized.  This
  // is used to determine when a proving period has elapsed that justifies an
  // increase in capture size.
  base::TimeTicks start_time_of_underutilization_;

  // The timestamp of the frame where |content_sampler_| last detected
  // animation.  This determines whether capture size increases will be
  // aggressive (because content is not animating).
  base::TimeTicks last_time_animation_was_detected_;
};

}  // namespace media

#endif  // MEDIA_CAPTURE_CONTENT_VIDEO_CAPTURE_ORACLE_H_