/**
 * Signs and verifies the server's three kinds of token (session, media and
 * password reset), all HS256 with the one key, and hashes passwords. Only a
 * token's signature and expiry are checked here: `lib/auth.ts` checks a session
 * or media token against its user.
 *
 * Importing this module throws when `GERBEUR_JWT_SECRET` is unset.
 *
 * @module
 */

import { randomBytes, scrypt, timingSafeEqual } from "node:crypto";
import { Buffer } from "node:buffer";
import { jwtVerify, SignJWT } from "@panva/jose";

import {
  type AuthPayload,
  isAuthPayload,
  isPasswordResetPayload,
  type PasswordResetPayload,
} from "../model/auth.ts";
import { JWT_SECRET } from "../config.ts";

if (!JWT_SECRET) {
  throw new Error(
    "GERBEUR_JWT_SECRET environment variable is required. Generate one with: openssl rand -hex 32",
  );
}
const JWT_KEY = new TextEncoder().encode(JWT_SECRET);

/**
 * Signs a password reset token for `userId`, valid for an hour. The token
 * isn't single-use by itself: `requestPasswordReset` stores it, and
 * `resetPassword` marks it used.
 */
export async function createPasswordResetToken(
  userId: string,
): Promise<string> {
  return await new SignJWT({ purpose: "password-reset", userId })
    .setProtectedHeader({ alg: "HS256" })
    // Two requests in the same second would otherwise sign the same token,
    // which is the primary key of `password_reset_tokens`.
    .setJti(crypto.randomUUID())
    .setExpirationTime("1h")
    .sign(JWT_KEY);
}

/**
 * Returns the payload of a password reset token, or null when it is invalid,
 * expired or another kind of token. Whether it was used is the caller's check.
 */
export async function verifyPasswordResetToken(
  token: string,
): Promise<PasswordResetPayload | null> {
  try {
    const { payload } = await jwtVerify(token, JWT_KEY);
    if (!isPasswordResetPayload(payload)) return null;
    return payload as PasswordResetPayload;
  } catch {
    return null;
  }
}

/**
 * Signs a session token carrying `payload`, valid for 7 days. The users routes
 * issue it on sign-up, sign-in and password change, and the client sends it as
 * a bearer token.
 */
export async function createJWT(
  payload: Omit<AuthPayload, "exp">,
): Promise<string> {
  return await new SignJWT(payload)
    .setProtectedHeader({ alg: "HS256" })
    // A password change revokes tokens by comparing `iat` with
    // `users.tokens_valid_after`.
    .setIssuedAt()
    .setExpirationTime("7d")
    .sign(JWT_KEY);
}

/**
 * Signs a media token for `userId`, valid for 7 days. Media elements can't send
 * an `Authorization` header, so the URLs of private files, thumbnails and
 * playlist covers carry this token as `?token=`, where it lands in logs and
 * browser history. It only reads media, so a leaked URL doesn't expose the
 * account.
 */
export async function createMediaToken(userId: string): Promise<string> {
  return await new SignJWT({ purpose: "media", userId })
    .setProtectedHeader({ alg: "HS256" })
    .setIssuedAt()
    .setExpirationTime("7d")
    .sign(JWT_KEY);
}

/**
 * Returns the user id and issue time of a media token, or null when it is
 * invalid, expired or another kind of token.
 */
export async function verifyMediaToken(
  token: string,
): Promise<{ userId: string; iat?: number } | null> {
  try {
    const { payload } = await jwtVerify(token, JWT_KEY);
    if (payload.purpose !== "media" || typeof payload.userId !== "string") {
      return null;
    }
    return { userId: payload.userId, iat: payload.iat };
  } catch {
    return null;
  }
}

/**
 * Returns the payload of a session token whose signature and expiry are valid,
 * or null. Call `authenticate` (`lib/auth.ts`) instead, which also checks the
 * token against its user.
 */
export async function verifyJWT(token: string): Promise<AuthPayload | null> {
  try {
    const { payload } = await jwtVerify(token, JWT_KEY);

    if (!isAuthPayload(payload)) {
      return null;
    }

    return payload;
  } catch (err) {
    console.error("JWT verification failed:", err);
    return null;
  }
}

/**
 * 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),
        );
      }
    });
  });
}