/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

import { pathToFileURL } from 'node:url';
import l from 'lodash';

export default create;

// naive implementation of selection with replacement
function create<T extends { weight: number }>(list: T[]): () => [number, T] {
  const dist = l.reduce(
    list,
    (acc: number[], el, i) => {
      for (let j = 0; j < el.weight * 100; j++) {
        acc.push(i);
      }
      return acc;
    },
    []
  );

  return () => {
    const i = dist[l.random(0, dist.length - 1)];
    return [i, list[i]];
  };
}

function bench() {
  const items = [
    { weight: 0, value: 'zero' },
    { weight: 1, value: 'a' },
    { weight: 2, value: 'b' },
    { weight: 3, value: 'c' },
    { weight: 4, value: 'd' },
    { weight: 5, value: 'e' },
    { weight: 1, value: 'f' },
    { weight: 2, value: 'g' },
    { weight: 3, value: 'h' },
    { weight: 4, value: 'i' },
    { weight: 5, value: 'j' },
    { weight: 10, value: 'k' }
  ];

  const picker = create(items);

  const ITERS = 10 ** 6;
  const startedAt = Date.now();

  const picks = l.map(l.range(ITERS), () => {
    const x = picker()[1];
    return x;
  });

  const delta = Date.now() - startedAt;
  console.log(
    'ITERS = %s\ndelta = %s\nITERS/delta = %s',
    ITERS,
    delta,
    Math.round(ITERS / delta)
  );

  const sumWeights = l.reduce(items, (acc, item) => acc + item.weight, 0);

  console.log('sumWeights = %s', sumWeights);

  l.each(items, (p) => {
    const count = l.filter(picks, { value: p.value }).length;
    console.log(
      'Count of %s = %s (should be: %s%, is: %s%)',
      p.value,
      count,
      Math.round((p.weight / sumWeights) * 1000) / 1000,
      Math.round((count / ITERS) * 1000) / 1000
    );
  });
}

if (
  process.argv[1] &&
  import.meta.url === pathToFileURL(process.argv[1]).href
) {
  bench();
}