// Copyright 2018-2021 the Deno authors. All rights reserved. MIT license.
// This module is browser compatible.

/**
 * Splits the given array into chunks of the given size and returns them
 *
 * Example:
 *
 * ```ts
 * import { chunk } from "https://deno.land/std@$STD_VERSION/collections/mod.ts";
 * import { assertEquals } from "https://deno.land/std@$STD_VERSION/testing/asserts.ts";
 *
 * const words = [ 'lorem', 'ipsum', 'dolor', 'sit', 'amet', 'consetetur', 'sadipscing' ]
 * const chunks = chunk(words, 3)
 *
 * assertEquals(chunks, [
 *     [ 'lorem', 'ipsum', 'dolor' ],
 *     [ 'sit', 'amet', 'consetetur' ],
 *     [ 'sadipscing' ],
 * ])
 * ```
 */
export function chunk<T>(array: readonly T[], size: number): T[][] {
  if (size <= 0 || !Number.isInteger(size)) {
    throw new Error(
      `Expected size to be an integer greater than 0 but found ${size}`,
    );
  }

  if (array.length === 0) {
    return [];
  }

  const ret = Array.from<T[]>({ length: Math.ceil(array.length / size) });
  let readIndex = 0;
  let writeIndex = 0;

  while (readIndex < array.length) {
    ret[writeIndex] = array.slice(readIndex, readIndex + size);

    writeIndex += 1;
    readIndex += size;
  }

  return ret;
}
