/**
 * @file Egress labels, after [Flower](https://github.com/NuxiNL/flower)'s
 * switchboard: string key-value pairs that only accumulate. A missing key
 * matches anything; a key present on both sides must agree.
 *
 * Keys that constrain a URL: `scheme` (`http`, `https`), `host` (name or
 * address, no port), `port` (explicit or the scheme's default). The
 * switchboard sets `network` per socket; it constrains no URL.
 */

const DEFAULT_PORT = { http: "80", https: "443" };

/**
 * Union of two label sets; throws on a key they give different values,
 * naming the key but not the values (they may end up in logs).
 *
 * @param {Record<string, string>} held
 * @param {Record<string, string>} more
 */
export const mergeLabels = (held, more) => {
	const merged = { ...held };
	for (const [k, v] of Object.entries(more)) {
		if (typeof v !== "string") throw new TypeError(`label ${k} is not a string`);
		if (k in merged && merged[k] !== v) throw new Error(`label ${k} is already set to a different value`);
		merged[k] = v;
	}
	return Object.freeze(merged);
};

/**
 * The labels a URL carries.
 *
 * @param {string} url
 */
export const urlLabels = (url) => {
	const u = new URL(url);
	const scheme = u.protocol.replace(/:$/, "");
	return { scheme, host: u.hostname, port: u.port || DEFAULT_PORT[scheme] || "" };
};

/**
 * Throws unless `url` is within `labels`.
 *
 * @param {Record<string, string>} labels
 * @param {string} url
 */
export const checkUrl = (labels, url) => {
	const actual = urlLabels(url);
	for (const [k, v] of Object.entries(actual)) {
		if (k in labels && labels[k] !== v) throw new Error(`egress to ${actual.host} not granted`);
	}
};