string-plumbing/split

import {ValueError} from '@failure-abstraction/error';

/**
 * _split.
 *
 * @param {string} string
 * @param {string=} sep
 * @param {number=} maxsplit
 * @return {IterableIterator<string>}
 */
export default function* _split(string, sep = undefined, maxsplit = undefined) {
    if (sep === '') {
        throw new ValueError('empty separator');
    }

    if (maxsplit === undefined) {
        maxsplit = -1;
    }

    if (sep === undefined) {
        let i = 0;

        const re = /\s+/g;

        while (maxsplit--) {
            const match = re.exec(string);

            if (match === null) {
                break;
            }

            const j = match.index;

            if (i < j) {
                yield string.slice(i, j);
            }

            i = j + match[0].length;
        }

        if (i < string.length) {
            yield string.slice(i);
        }
    } else {
        let i = 0;

        const n = sep.length;

        while (maxsplit--) {
            const j = string.indexOf(sep, i);

            if (j === -1) {
                break;
            }

            yield string.slice(i, j);

            i = j + n;
        }

        yield string.slice(i);
    }
}