/**
 * Hashes and checks passwords, for sign-up, sign-in, password changes and the
 * admin that `db/startup.ts` seeds. It reads no config, so the startup tasks
 * can use it before the server's settings are checked.
 *
 * @module
 */

import { randomBytes, scrypt, timingSafeEqual } from "node:crypto";
import { Buffer } from "node:buffer";

/**
 * Hashes `password` with scrypt and a random salt, as `hash.salt` in hex, for
 * `users.password_hash`.
 */
export function hashPassword(password: string): Promise<string> {
  const salt = randomBytes(16).toString("hex");

  return new Promise((resolve, reject) => {
    scrypt(password, salt, 64, (err, derivedKey) => {
      if (err) reject(err);
      else resolve(`${derivedKey.toString("hex")}.${salt}`);
    });
  });
}

/** Checks `password` against a hash made by {@link hashPassword}. */
export function verifyPassword(
  password: string,
  storedHash: string,
): Promise<boolean> {
  const [hash, salt] = storedHash.split(".");
  // scrypt would throw on a missing salt, and a malformed hash matches nothing.
  if (!hash || !salt) return Promise.resolve(false);

  return new Promise((resolve, reject) => {
    scrypt(password, salt, 64, (err, derivedKey) => {
      if (err) reject(err);
      else {
        const expected = Buffer.from(hash ?? "", "hex");
        resolve(
          expected.length === derivedKey.length &&
            timingSafeEqual(expected, derivedKey),
        );
      }
    });
  });
}