// src/utils/httpAuth.js
//
// Shared-secret auth for HTTP API endpoints (used by index.js).
//
// Why this exists
// ---------------
// The generic /:command HTTP router dispatches to the same handlers used by
// the Webex bot, including destructive ones (offboardUser, provision-*,
// vcMonitor, bulkAvSwitchCSV, …). Without auth, anyone with network access to
// the bot's port can trigger them.
//
// Behavior
// --------
// - The token is taken from process.env.HTTP_API_TOKEN (read at request time
//   so it stays in sync with hot-reloaded .env in dev).
// - Accepted on either header: `Authorization: Bearer <token>` or
//   `X-API-Token: <token>`. The query string is intentionally NOT supported
//   to avoid leaking the token into proxy/access logs.
// - If HTTP_API_TOKEN is not configured the middleware fails closed with 503
//   so destructive endpoints are *never* accidentally exposed when the
//   operator forgot to set the variable.
// - Comparison uses crypto.timingSafeEqual to avoid timing oracles.

import crypto from 'node:crypto';
import { logger } from './logger.js';

function extractToken(req) {
  const auth = req.headers['authorization'];
  if (typeof auth === 'string') {
    const match = auth.match(/^Bearer\s+(.+)$/i);
    if (match) return match[1].trim();
  }
  const headerToken = req.headers['x-api-token'];
  if (typeof headerToken === 'string' && headerToken.trim()) {
    return headerToken.trim();
  }
  return null;
}

function constantTimeEquals(a, b) {
  if (typeof a !== 'string' || typeof b !== 'string') return false;
  const aBuf = Buffer.from(a, 'utf8');
  const bBuf = Buffer.from(b, 'utf8');
  // Pad to equal length so timingSafeEqual doesn't throw on length mismatch
  // (and so the length difference itself isn't a side channel).
  if (aBuf.length !== bBuf.length) {
    const max = Math.max(aBuf.length, bBuf.length);
    const aPad = Buffer.alloc(max);
    const bPad = Buffer.alloc(max);
    aBuf.copy(aPad);
    bBuf.copy(bPad);
    crypto.timingSafeEqual(aPad, bPad); // burn cycles for shape consistency
    return false;
  }
  return crypto.timingSafeEqual(aBuf, bBuf);
}

/**
 * Returns an Express middleware that requires a valid API token on the request.
 *
 * @param {object} [opts]
 * @param {string} [opts.scope='http'] - Tag used in log lines for context.
 */
export function requireApiToken({ scope = 'http' } = {}) {
  return function (req, res, next) {
    const expected = process.env.HTTP_API_TOKEN;

    if (!expected) {
      logger(
        `auth:${scope}`,
        `Refusing ${req.method} ${req.originalUrl} — HTTP_API_TOKEN is not configured (fail-closed)`,
        'error'
      );
      return res.status(503).json({
        error: 'HTTP_API_TOKEN not configured on server',
        hint: 'Set HTTP_API_TOKEN in the environment to enable authenticated HTTP API access.',
      });
    }

    const provided = extractToken(req);
    if (!provided) {
      logger(
        `auth:${scope}`,
        `Unauthorized ${req.method} ${req.originalUrl} — missing token`,
        'warn'
      );
      return res
        .status(401)
        .set('WWW-Authenticate', 'Bearer realm="collabfinder"')
        .json({ error: 'Missing API token (Authorization: Bearer <token> or X-API-Token header)' });
    }

    if (!constantTimeEquals(provided, expected)) {
      logger(
        `auth:${scope}`,
        `Forbidden ${req.method} ${req.originalUrl} — invalid token`,
        'warn'
      );
      return res.status(403).json({ error: 'Invalid API token' });
    }

    return next();
  };
}

/**
 * Convenience: returns true when HTTP_API_REQUIRE_AUTH is set to a truthy value,
 * meaning every /:command (not just mutating ones) should require a token.
 */
export function requireAuthForAllCommands() {
  const v = (process.env.HTTP_API_REQUIRE_AUTH || '').toLowerCase().trim();
  return v === '1' || v === 'true' || v === 'yes';
}

export default requireApiToken;