"use strict";

Object.defineProperty(exports, "__esModule", {
  value: true
});
exports.stringReducer = stringReducer;
/*
 * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
 * or more contributor license agreements. Licensed under the Elastic License
 * 2.0; you may not use this file except in compliance with the Elastic License
 * 2.0.
 */

/**
 * The `stringReducer` is provided to handle plain string based streams with `streamFactory()`.
 *
 * @param state   - The current state, being the string fetched so far.
 * @param payload — The state update can be a plain string, an array of strings or `undefined`.
 *                  * An array of strings will be joined without a delimiter and added to the current string.
 *                    In combination with `useFetchStream`'s buffering this allows to do bulk updates
 *                    within the reducer without triggering a React/DOM update on every stream chunk.
 *                  * `undefined` can be used to reset the state to an empty string, for example, when a
 *                    UI has the option to trigger a refetch of a stream.
 *
 * @returns The updated state, a string that combines the previous string and the payload.
 */
function stringReducer(state, payload) {
  if (payload === undefined) {
    return '';
  }
  return `${state}${Array.isArray(payload) ? payload.join('') : payload}`;
}