import { invariant } from "./utils.js";
/**
* https://tc39.es/ecma402/#sec-unicodeextensionvalue
* @param extension
* @param key
*/
export function UnicodeExtensionValue(extension, key) {
	invariant(key.length === 2, "key must have 2 elements");
	const size = extension.length;
	let searchValue = `-${key}-`;
	let pos = extension.indexOf(searchValue);
	if (pos !== -1) {
		const start = pos + 4;
		let end = start;
		let k = start;
		let done = false;
		while (!done) {
			const e = extension.indexOf("-", k);
			let len;
			if (e === -1) {
				len = size - k;
			} else {
				len = e - k;
			}
			if (len === 2) {
				done = true;
			} else if (e === -1) {
				end = size;
				done = true;
			} else {
				end = e;
				k = e + 1;
			}
		}
		return extension.slice(start, end);
	}
	searchValue = `-${key}`;
	pos = extension.indexOf(searchValue);
	if (pos !== -1 && pos + 3 === size) {
		return "";
	}
	return undefined;
}