// Copyright (C) 2018 The Android Open Source Project
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

import m from 'mithril';

const hooks = {
  isDebug: () => false,
  toggleDebug: () => {},
};

export function setPerfHooks(isDebug: () => boolean, toggleDebug: () => void) {
  hooks.isDebug = isDebug;
  hooks.toggleDebug = toggleDebug;
}

// Shorthand for if globals perf debug mode is on.
export const perfDebug = () => hooks.isDebug();

// Returns performance.now() if perfDebug is enabled, otherwise 0.
// This is needed because calling performance.now is generally expensive
// and should not be done for every frame.
export const debugNow = () => (perfDebug() ? performance.now() : 0);

// Returns execution time of |fn| if perf debug mode is on. Returns 0 otherwise.
export function measure(fn: () => void): number {
  const start = debugNow();
  fn();
  return debugNow() - start;
}

// Stores statistics about samples, and keeps a fixed size buffer of most recent
// samples.
export class RunningStatistics {
  private _count = 0;
  private _mean = 0;
  private _lastValue = 0;
  private _ptr = 0;

  private buffer: number[] = [];

  constructor(private _maxBufferSize = 10) {}

  addValue(value: number) {
    this._lastValue = value;
    if (this.buffer.length >= this._maxBufferSize) {
      this.buffer[this._ptr++] = value;
      if (this._ptr >= this.buffer.length) {
        this._ptr -= this.buffer.length;
      }
    } else {
      this.buffer.push(value);
    }

    this._mean = (this._mean * this._count + value) / (this._count + 1);
    this._count++;
  }

  get mean() {
    return this._mean;
  }
  get count() {
    return this._count;
  }
  get bufferMean() {
    return this.buffer.reduce((sum, v) => sum + v, 0) / this.buffer.length;
  }
  get bufferSize() {
    return this.buffer.length;
  }
  get maxBufferSize() {
    return this._maxBufferSize;
  }
  get last() {
    return this._lastValue;
  }
}

// Returns a summary string representation of a RunningStatistics object.
export function runningStatStr(stat: RunningStatistics) {
  return (
    `Last: ${stat.last.toFixed(2)}ms | ` +
    `Avg: ${stat.mean.toFixed(2)}ms | ` +
    `Avg${stat.maxBufferSize}: ${stat.bufferMean.toFixed(2)}ms`
  );
}

export interface PerfStatsSource {
  renderPerfStats(): m.Children;
}

// Globals singleton class that renders performance stats for the whole app.
class PerfDisplay {
  private containers: PerfStatsSource[] = [];

  addContainer(container: PerfStatsSource) {
    this.containers.push(container);
  }

  removeContainer(container: PerfStatsSource) {
    const i = this.containers.indexOf(container);
    this.containers.splice(i, 1);
  }

  renderPerfStats(src: PerfStatsSource) {
    if (!perfDebug()) return;
    const perfDisplayEl = document.querySelector('.perf-stats');
    if (!perfDisplayEl) return;
    m.render(perfDisplayEl, [
      m('section', src.renderPerfStats()),
      m(
        'button.close-button',
        {
          onclick: hooks.toggleDebug,
        },
        m('i.material-icons', 'close'),
      ),
      this.containers.map((c, i) =>
        m('section', m('div', `Panel Container ${i + 1}`), c.renderPerfStats()),
      ),
    ]);
  }
}

export const perfDisplay = new PerfDisplay();