// Copyright 2014 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.

import 'dart:ui';
import 'package:meta/meta.dart';

/// The maximum amount of time considered safe to spend for a frame's build
/// phase. Anything past that is in the danger of missing the frame as 60FPS.
///
/// Changing this doesn't re-evaluate existing summary.
Duration kBuildBudget = const Duration(milliseconds: 16);
// TODO(CareF): Automatically calculate the refresh budget (#61958)

/// This class and summarizes a list of [FrameTiming] for the performance
/// metrics.
class FrameTimingSummarizer {
  /// Summarize `data` to frame build time and frame rasterizer time statistics.
  ///
  /// See [TimelineSummary.summaryJson] for detail.
  factory FrameTimingSummarizer(List<FrameTiming> data) {
    assert(data != null);
    assert(data.isNotEmpty);
    final List<Duration> frameBuildTime = List<Duration>.unmodifiable(
      data.map<Duration>((FrameTiming datum) => datum.buildDuration),
    );
    final List<Duration> frameBuildTimeSorted =
        List<Duration>.from(frameBuildTime)..sort();
    final List<Duration> frameRasterizerTime = List<Duration>.unmodifiable(
      data.map<Duration>((FrameTiming datum) => datum.rasterDuration),
    );
    final List<Duration> frameRasterizerTimeSorted =
        List<Duration>.from(frameRasterizerTime)..sort();
    final List<Duration> vsyncOverhead = List<Duration>.unmodifiable(
      data.map<Duration>((FrameTiming datum) => datum.vsyncOverhead),
    );
    final List<Duration> vsyncOverheadSorted =
        List<Duration>.from(vsyncOverhead)..sort();
    final Duration Function(Duration, Duration) add =
        (Duration a, Duration b) => a + b;
    return FrameTimingSummarizer._(
      frameBuildTime: frameBuildTime,
      frameRasterizerTime: frameRasterizerTime,
      vsyncOverhead: vsyncOverhead,
      // This average calculation is microsecond precision, which is fine
      // because typical values of these times are milliseconds.
      averageFrameBuildTime: frameBuildTime.reduce(add) ~/ data.length,
      p90FrameBuildTime: _findPercentile(frameBuildTimeSorted, 0.90),
      p99FrameBuildTime: _findPercentile(frameBuildTimeSorted, 0.99),
      worstFrameBuildTime: frameBuildTimeSorted.last,
      missedFrameBuildBudget: _countExceed(frameBuildTimeSorted, kBuildBudget),
      averageFrameRasterizerTime:
          frameRasterizerTime.reduce(add) ~/ data.length,
      p90FrameRasterizerTime: _findPercentile(frameRasterizerTimeSorted, 0.90),
      p99FrameRasterizerTime: _findPercentile(frameRasterizerTimeSorted, 0.99),
      worstFrameRasterizerTime: frameRasterizerTimeSorted.last,
      missedFrameRasterizerBudget:
          _countExceed(frameRasterizerTimeSorted, kBuildBudget),
      averageVsyncOverhead: vsyncOverhead.reduce(add) ~/ data.length,
      p90VsyncOverhead: _findPercentile(vsyncOverheadSorted, 0.90),
      p99VsyncOverhead: _findPercentile(vsyncOverheadSorted, 0.99),
      worstVsyncOverhead: vsyncOverheadSorted.last,
    );
  }

  const FrameTimingSummarizer._({
    @required this.frameBuildTime,
    @required this.frameRasterizerTime,
    @required this.averageFrameBuildTime,
    @required this.p90FrameBuildTime,
    @required this.p99FrameBuildTime,
    @required this.worstFrameBuildTime,
    @required this.missedFrameBuildBudget,
    @required this.averageFrameRasterizerTime,
    @required this.p90FrameRasterizerTime,
    @required this.p99FrameRasterizerTime,
    @required this.worstFrameRasterizerTime,
    @required this.missedFrameRasterizerBudget,
    @required this.vsyncOverhead,
    @required this.averageVsyncOverhead,
    @required this.p90VsyncOverhead,
    @required this.p99VsyncOverhead,
    @required this.worstVsyncOverhead,
  });

  /// List of frame build time in microseconds
  final List<Duration> frameBuildTime;

  /// List of frame rasterizer time in microseconds
  final List<Duration> frameRasterizerTime;

  /// List of the time difference between vsync signal and frame building start
  /// time
  final List<Duration> vsyncOverhead;

  /// The average value of [frameBuildTime] in milliseconds.
  final Duration averageFrameBuildTime;

  /// The 90-th percentile value of [frameBuildTime] in milliseconds
  final Duration p90FrameBuildTime;

  /// The 99-th percentile value of [frameBuildTime] in milliseconds
  final Duration p99FrameBuildTime;

  /// The largest value of [frameBuildTime] in milliseconds
  final Duration worstFrameBuildTime;

  /// Number of items in [frameBuildTime] that's greater than [kBuildBudget]
  final int missedFrameBuildBudget;

  /// The average value of [frameRasterizerTime] in milliseconds.
  final Duration averageFrameRasterizerTime;

  /// The 90-th percentile value of [frameRasterizerTime] in milliseconds.
  final Duration p90FrameRasterizerTime;

  /// The 99-th percentile value of [frameRasterizerTime] in milliseconds.
  final Duration p99FrameRasterizerTime;

  /// The largest value of [frameRasterizerTime] in milliseconds.
  final Duration worstFrameRasterizerTime;

  /// Number of items in [frameRasterizerTime] that's greater than [kBuildBudget]
  final int missedFrameRasterizerBudget;

  /// The average value of [vsyncOverhead];
  final Duration averageVsyncOverhead;

  /// The 90-th percentile value of [vsyncOverhead] in milliseconds
  final Duration p90VsyncOverhead;

  /// The 99-th percentile value of [vsyncOverhead] in milliseconds
  final Duration p99VsyncOverhead;

  /// The largest value of [vsyncOverhead] in milliseconds.
  final Duration worstVsyncOverhead;

  /// Convert the summary result to a json object.
  ///
  /// See [TimelineSummary.summaryJson] for detail.
  Map<String, dynamic> get summary => <String, dynamic>{
        'average_frame_build_time_millis':
            averageFrameBuildTime.inMicroseconds / 1E3,
        '90th_percentile_frame_build_time_millis':
            p90FrameBuildTime.inMicroseconds / 1E3,
        '99th_percentile_frame_build_time_millis':
            p99FrameBuildTime.inMicroseconds / 1E3,
        'worst_frame_build_time_millis':
            worstFrameBuildTime.inMicroseconds / 1E3,
        'missed_frame_build_budget_count': missedFrameBuildBudget,
        'average_frame_rasterizer_time_millis':
            averageFrameRasterizerTime.inMicroseconds / 1E3,
        '90th_percentile_frame_rasterizer_time_millis':
            p90FrameRasterizerTime.inMicroseconds / 1E3,
        '99th_percentile_frame_rasterizer_time_millis':
            p99FrameRasterizerTime.inMicroseconds / 1E3,
        'worst_frame_rasterizer_time_millis':
            worstFrameRasterizerTime.inMicroseconds / 1E3,
        'missed_frame_rasterizer_budget_count': missedFrameRasterizerBudget,
        'frame_count': frameBuildTime.length,
        'frame_build_times': frameBuildTime
            .map<int>((Duration datum) => datum.inMicroseconds)
            .toList(),
        'frame_rasterizer_times': frameRasterizerTime
            .map<int>((Duration datum) => datum.inMicroseconds)
            .toList(),
      };
}

// The following helper functions require data sorted

// return the 100*p-th percentile of the data
T _findPercentile<T>(List<T> data, double p) {
  assert(p >= 0 && p <= 1);
  return data[((data.length - 1) * p).round()];
}

// return the number of items in data that > threshold
int _countExceed<T extends Comparable<T>>(List<T> data, T threshold) {
  return data.length -
      data.indexWhere((T datum) => datum.compareTo(threshold) > 0);
}