/**
 * Signs and verifies the server's four kinds of token (session, media,
 * password reset and unsubscribe), all HS256 with the one key. 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 { jwtVerify, SignJWT } from "@panva/jose";

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

/**
 * Signs the token of a digest's unsubscribe link, which turns off `cadence`
 * for `userId` without signing in. It never expires, so the link in an old
 * email still works; turning the digest back on doesn't revoke it, which is
 * harmless since all it can do is turn it off again.
 */
export async function createUnsubscribeToken(
  userId: string,
  cadence: DigestCadence,
): Promise<string> {
  return await new SignJWT({ purpose: "unsubscribe", userId, cadence })
    .setProtectedHeader({ alg: "HS256" })
    .sign(JWT_KEY);
}

/**
 * Returns the user and cadence of an unsubscribe token, or null when it is
 * invalid or another kind of token.
 */
export async function verifyUnsubscribeToken(
  token: string,
): Promise<{ userId: string; cadence: DigestCadence } | null> {
  try {
    const { payload } = await jwtVerify(token, JWT_KEY);
    if (
      payload.purpose !== "unsubscribe" || typeof payload.userId !== "string" ||
      !isDigestCadence(payload.cadence)
    ) {
      return null;
    }
    return { userId: payload.userId, cadence: payload.cadence };
  } catch {
    return null;
  }
}