MODx Revolution plugin bound to OnHandleRequest event

subdomain-context.php

<?php
/**
 * plugin to map subdomain requests to contexts
 * @setting event OnHandleRequest
 * @todo currently, subdomains and context names are bound together.. remove this constraint through some mapping/lookup
 * @todo currently, assumes first name in host (name before first dot) is what maps to the context
 */

$context = 'web';

$host = $_SERVER['HTTP_HOST'];
if(!empty($host)) {
  $names = explode('.', $host);
  if(is_array($names)) {
    $subdomain = $names[0];
    $modx->getContext($subdomain);
    if(is_object($modx->contexts[$subdomain])) {
      $context = $subdomain;
    }
  }
}

if($context !== 'web') {
  $modx->switchContext($context);
}
?>