<?php
/* Copyright © 2022 Jamie Zawinski <jwz@jwz.org>

   Permission to use, copy, modify, distribute, and sell this software and its
   documentation for any purpose is hereby granted without fee, provided that
   the above copyright notice appear in all copies and that both that
   copyright notice and this permission notice appear in supporting
   documentation.  No representations are made about the suitability of this
   software for any purpose.  It is provided "as is" without express or 
   implied warranty.

   Allows you to be discoverable on Mastodon with your own domain name,
   without needing to run your own server.  Makes "you@your-domain" be
   an alias for "also-you@the-actual-mastodon-server".

   This is not as useful as it sounds.  While it makes it possible for
   someone to search for "you@your-domain" and find you, it does not
   make your posts on Mastodon *present* themselves that way: they will
   still appear as "also-you@the-actual-mastodon-server".  The only way
   to change that presentation is to run your whole own Mastodon instance,
   which takes a colossal amount of effort and resources.

   Created: 8-Nov-2022.

   Installation:

    - Edit $ACCOUNTS, below.
    - Install this script in "/.well-known/webfinger"
    - Make it be runnable, e.g. by putting this in "/.well-known/.htaccess" --
      <Files "webfinger">
        ForceType application/x-httpd-php
      </Files>
 */

$ACCOUNTS = [
  //
  // Alias account name		Real underlying account name
  //
  'jwz@jwz.org'			=> 'jwz@mastodon.social',
  'jwz@dnalounge.com'		=> 'jwz@mastodon.social',
  'dnalounge@dnalounge.com'	=> 'dnalounge@sfba.social',
  'dnapizza@dnapizza.com'	=> 'dnapizza@sfba.social',
  'dnapizza@dnalounge.com'	=> 'dnapizza@sfba.social',
  ];

function webfinger() {
  global $ACCOUNTS;

  $acct = $_GET['resource'] ?? null;
  if (! $acct) error ("unparsable: no resource");

  if (! preg_match ('/^(?:acct:)?@?(.*)$/s', $acct, $m))
    error ("unparsable acct: \"$acct\"");
  $acct = $m[1];

  $redir = $ACCOUNTS[strtolower($acct)] ?? null;
  if (!$redir) error ("no match: \"$acct\"");

  if (! preg_match ('/@(.*)$/s', $redir, $m))
    error ("internal error: no domain");
  $domain = $m[1];

  $url = "https://$domain/.well-known/webfinger?resource=acct:$redir";

  header ("HTTP/1.1 301 Moved Permanently");
  header ("Location: $url");
  header ("Content-Type: text/plain");
}

function error($err) {
  $err = preg_replace ('/\s+/', ' ', $err);
  error_log ("webfinger: $err");
  header ("HTTP/1.1 400 $err");
  header ("Content-Type: text/plain");
  print "$err\n";
  exit (1);
}

webfinger();
exit (0);