'use strict';

/**
 * Like `Array#splice`, but smarter for giant arrays.
 *
 * `Array#splice` takes all items to be inserted as individual argument which
 * causes a stack overflow in V8 when trying to insert 100k items for instance.
 *
 * Otherwise, this does not return the removed items, and takes `items` as an
 * array instead of rest parameters.
 *
 * @template {unknown} T
 *   Item type.
 * @param {Array<T>} list
 *   List to operate on.
 * @param {number} start
 *   Index to remove/insert at (can be negative).
 * @param {number} remove
 *   Number of items to remove.
 * @param {Array<T>} items
 *   Items to inject into `list`.
 * @returns {void}
 *   Nothing.
 */
function splice(list, start, remove, items) {
  const end = list.length;
  let chunkStart = 0;
  /** @type {Array<unknown>} */
  let parameters;

  // Make start between zero and `end` (included).
  if (start < 0) {
    start = -start > end ? 0 : end + start;
  } else {
    start = start > end ? end : start;
  }
  remove = remove > 0 ? remove : 0;

  // No need to chunk the items if there’s only a couple (10k) items.
  if (items.length < 10000) {
    parameters = Array.from(items);
    parameters.unshift(start, remove);
    // @ts-expect-error Hush, it’s fine.
    list.splice(...parameters);
  } else {
    // Delete `remove` items starting from `start`
    if (remove) list.splice(start, remove);

    // Insert the items in chunks to not cause stack overflows.
    while (chunkStart < items.length) {
      parameters = items.slice(chunkStart, chunkStart + 10000);
      parameters.unshift(start, 0);
      // @ts-expect-error Hush, it’s fine.
      list.splice(...parameters);
      chunkStart += 10000;
      start += 10000;
    }
  }
}

/**
 * Append `items` (an array) at the end of `list` (another array).
 * When `list` was empty, returns `items` instead.
 *
 * This prevents a potentially expensive operation when `list` is empty,
 * and adds items in batches to prevent V8 from hanging.
 *
 * @template {unknown} T
 *   Item type.
 * @param {Array<T>} list
 *   List to operate on.
 * @param {Array<T>} items
 *   Items to add to `list`.
 * @returns {Array<T>}
 *   Either `list` or `items`.
 */
function push(list, items) {
  if (list.length > 0) {
    splice(list, list.length, 0, items);
    return list
  }
  return items
}

exports.push = push;
exports.splice = splice;
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