Enhanced Foolproof Multi-Environment Config

index.php

<?php

define('CRAFT_ENVIRONMENT', call_user_func_array(function ($environments, $fallback) {
    if (array_key_exists('APP_ENV', $_SERVER) && in_array($environment = $_SERVER['APP_ENV'], array_keys($environments))) {
        return $environment;
    }

    foreach ($environments as $environment => $value) {
        $serverName = $_SERVER['SERVER_NAME'];

        if ((is_array($value) && in_array($serverName, $value)) || $e == $value) {
            return $environment;
        }
    }

    return $fallback;
}, array(

    // Environment Definitions
    array(
        'local'   => array('local.project.com'),
        'dev'     => array('dev.project.com'),
        'staging' => array('staging.project.com'),
    ),

    // Default Environment
    'production',

)));

// ...