/**
 * The MIT License (MIT)
 * Copyright (c) 2022 PaperNick
 *
 * Resouces used:
 * https://github.com/auth0/node-jwks-rsa
 * https://github.com/auth0/node-jsonwebtoken
 * https://auth0.com/blog/navigating-rs256-and-jwks/
 * https://gist.github.com/westmark/faee223e05bcbab433bfd4ed8e36fb5f
 * https://auth0.com/blog/critical-vulnerabilities-in-json-web-token-libraries/
 */

const AUTH0_AUTHORITY = 'https://auth0.tenant.com';
const AUTH0_AUDIENCE = 'https://api.yourapp.com/';

const jwksRsa = require('jwks-rsa');
const jwt = require('jsonwebtoken');

const jwksClient = jwksRsa({
  jwksUri: `${AUTH0_AUTHORITY.replace(/\/+$/, '')}/.well-known/jwks.json`,
});

/**
 * Attempt to parse the given JWT token. Throws an Error if token is invalid.
 *
 * @param {string} token JWT token without "Bearer " in the beginning
 * @throws {Error}
 * @returns {JwtPayload}
 */
async function parseJwtToken(token) {
  if (!token) {
    throw new Error('Missing authorization token');
  }

  // Decode without verifying if the signature is valid.
  // Warning: do not access decoded token payload before verifying with jwt.verify()
  const decodedToken = jwt.decode(token, { complete: true });
  if (!decodedToken || decodedToken.header.alg !== 'RS256') {
    // Only RS256 tokens are supported at the moment
    throw new Error('Invalid token or algorithm');
  }

  let signingKey;
  try {
    signingKey = await jwksClient.getSigningKey(decodedToken.header.kid);
  } catch (error) {
    throw new Error('Could not retrieve key to verify token');
  }

  try {
    const jwtPayload = jwt.verify(token, signingKey.getPublicKey(), { audience: AUTH0_AUDIENCE });
    return jwtPayload;
  } catch (error) {
    throw new Error('The token is invalid or has expired');
  }
}

/**
 * Attempt to parse the given JWT token. Returns undefined on error.
 *
 * @param {string} token 
 * @returns {JwtPayload|undefined}
 */
async function parseJwtTokenQuiet(token) {
  try {
    return await parseJwtToken(token);
  } catch (error) {
    return;
  }
}

module.exports = { parseJwtToken, parseJwtTokenQuiet };