import { concat, identical, identity, pipe, reduce, when } from 'ramda';

import stubUndefined from './stubUndefined';

const leftIdentitySemigroup = { concat: identity };

/**
 * Returns the result of concatenating the given lists or strings.
 * Note: RA.concatAll expects all elements to be of the same type. It will throw an error if you concat an Array with a non-Array value.
 * Dispatches to the concat method of the preceding element, if present. Can also concatenate multiple elements of a [fantasy-land compatible semigroup](https://github.com/fantasyland/fantasy-land#semigroup).
 * Returns undefined if empty array was passed.
 *
 * @func concatAll
 * @memberOf RA
 * @since {@link https://char0n.github.io/ramda-adjunct/2.6.0|v2.6.0}
 * @category List
 * @sig [[a]] -> [a] | Undefined
 * @sig [String] -> String | Undefined
 * @sig Semigroup s => Foldable s f => f -> s | Undefined
 * @param {Array.<Array|string>} list List containing elements that will be concatenated
 * @return {Array|string|undefined} Concatenated elements
 * @see {@link http://ramdajs.com/docs/#concat|R.concat}, {@link RA.concatRight|concatRight}, {@link http://ramdajs.com/docs/#unnest|R.unnest}, {@link http://ramdajs.com/docs/#join|R.join}
 * @example
 *
 * concatAll([[1], [2], [3]]); //=> [1, 2, 3]
 * concatAll(['1', '2', '3']); //=> '123'
 * concatAll([]); //=> undefined
 * concatAll(null); //=> undefined
 */
const concatAll = pipe(
  reduce(concat, leftIdentitySemigroup),
  when(identical(leftIdentitySemigroup), stubUndefined)
);

export default concatAll;