import * as marky from 'marky';

const fmt = time => `${Math.round(time * 100) / 100}ms`;

const measure = (name, fn) => {
  marky.mark(name);
  fn();
  const performanceMeasure = marky.stop(name);
  return performanceMeasure.duration;
};

const mean = values => {
  const sum = values.reduce((sum, value) => sum + value, 0);
  return sum / values.length;
};

const median = values => {
  if (!Array.isArray(values)) {
    return 0;
  }
  if (values.length === 1) {
    return values[0];
  }

  const numbers = [...values].sort((a, b) => a - b);
  return (numbers[(numbers.length - 1) >> 1] + numbers[numbers.length >> 1]) / 2;
};

const standardDeviation = values => {
  const avg = mean(values);

  const squareDiffs = values.map(value => {
    const diff = value - avg;
    return diff * diff;
  });

  const meanSquareDiff = mean(squareDiffs);
  return Math.sqrt(meanSquareDiff);
};

const benchmark = ({ name, description, setup, teardown, task, runs }) => {
  return new Promise(resolve => {
    const durations = [];
    let i = 0;

    setup();
    const first = measure('first', task);
    teardown();

    const done = () => {
      const stdDev = standardDeviation(durations);
      const formattedFirst = fmt(first);
      const formattedMean = fmt(mean(durations));
      const formattedMedian = fmt(median(durations));
      const formattedStdDev = fmt(stdDev);

      console.groupCollapsed(`${name}\n${formattedMean} ±${fmt(2 * stdDev)}`);
      description && console.log(description);
      console.log(`First: ${formattedFirst}`);
      console.log(`Median: ${formattedMedian}`);
      console.log(`Mean: ${formattedMean}`);
      console.log(`Standard deviation: ${formattedStdDev}`);
      console.log(durations);
      console.groupEnd();
      resolve();
    };

    const a = () => {
      setup();
      window.requestAnimationFrame(b);
    };

    const b = () => {
      const duration = measure('mean', task);
      durations.push(duration);
      window.requestAnimationFrame(c);
    };

    const c = () => {
      teardown();
      window.requestAnimationFrame(d);
    };

    const d = () => {
      i += 1;
      if (i < runs) {
        window.requestAnimationFrame(a);
      } else {
        window.requestAnimationFrame(done);
      }
    };

    window.requestAnimationFrame(a);
  });
};

export default benchmark;