/* eslint no-bitwise: 0 */

/**
 * taken from punycode@2.1.0
 *
 * Creates an array containing the numeric code points of each Unicode
 * character in the string. While JavaScript uses UCS-2 internally,
 * this function will convert a pair of surrogate halves (each of which
 * UCS-2 exposes as separate characters) into a single code point,
 * matching UTF-16.
 * @see `punycode.ucs2.encode`
 * @see <https://mathiasbynens.be/notes/javascript-encoding>
 * @memberOf punycode.ucs2
 * @name decode
 * @param string The Unicode input string (UCS-2).
 * @returns The new array of code points.
 */
export default function ucs2decode(string: string): string[] {
    const output = [];
    let counter = 0;
    const length = string.length;
    while (counter < length) {
        const value = string.charCodeAt(counter++);
        if (value >= 0xd800 && value <= 0xdbff && counter < length) {
            // It's a high surrogate, and there is a next character.
            const extra = string.charCodeAt(counter++);
            // eslint-disable-next-line eqeqeq
            if ((extra & 0xfc00) == 0xdc00) {
                // Low surrogate.
                output.push(((value & 0x3ff) << 10) + (extra & 0x3ff) + 0x10000);
            } else {
                // It's an unmatched surrogate; only append this code unit, in case the
                // next code unit is the high surrogate of a surrogate pair.
                output.push(value);
                counter--;
            }
        } else {
            output.push(value);
        }
    }
    return output as unknown as string[];
}