public function env($key) {
		if (array_key_exists($key, $this->_computed)) {
			return $this->_computed[$key];
		}
		$val = null;

		if (!empty($this->_env[$key])) {
			$val = $this->_env[$key];
			if ($key !== 'REMOTE_ADDR' && $key !== 'HTTPS' && $key !== 'REQUEST_METHOD') {
				return $this->_computed[$key] = $val;
			}
		}
		switch ($key) {
			case 'BASE':
			case 'base':
				$val = $this->_base($this->_config['base']);
			break;
			case 'HTTP_HOST':
				$val = 'localhost';
			break;
			case 'SERVER_PROTOCOL':
				$val = 'HTTP/1.1';
			break;
			case 'REQUEST_METHOD':
				if ($this->env('HTTP_X_HTTP_METHOD_OVERRIDE')) {
					$val = $this->env('HTTP_X_HTTP_METHOD_OVERRIDE');
				} elseif (isset($this->_env['REQUEST_METHOD'])) {
					$val = $this->_env['REQUEST_METHOD'];
				} else {
					$val = 'GET';
				}
			break;
			case 'CONTENT_TYPE':
				$val = 'text/html';
			break;
			case 'PLATFORM':
				$envs = array('isapi' => 'IIS', 'cgi' => 'CGI', 'cgi-fcgi' => 'CGI');
				$val = isset($envs[PHP_SAPI]) ? $envs[PHP_SAPI] : null;
			break;
			case 'REMOTE_ADDR':
				$https = array(
					'HTTP_X_FORWARDED_FOR',
					'HTTP_PC_REMOTE_ADDR',
					'HTTP_X_REAL_IP'
				);
				foreach ($https as $altKey) {
					if ($addr = $this->env($altKey)) {
						list($val) = explode(', ', $addr);
						break;
					}
				}
			break;
			case 'SCRIPT_NAME':
				if ($this->env('PLATFORM') === 'CGI') {
					return $this->env('SCRIPT_URL');
				}
				$val = null;
			break;
			case 'HTTPS':
				if (isset($this->_env['SCRIPT_URI'])) {
					$val = strpos($this->_env['SCRIPT_URI'], 'https://') === 0;
				} elseif (isset($this->_env['HTTPS'])) {
					$val = (!empty($this->_env['HTTPS']) && $this->_env['HTTPS'] !== 'off');
				} else {
					$val = false;
				}
			break;
			case 'SERVER_ADDR':
				if (empty($this->_env['SERVER_ADDR']) && !empty($this->_env['LOCAL_ADDR'])) {
					$val = $this->_env['LOCAL_ADDR'];
				} elseif (isset($this->_env['SERVER_ADDR'])) {
					$val = $this->_env['SERVER_ADDR'];
				}
			break;
			case 'SCRIPT_FILENAME':
				if ($this->env('PLATFORM') === 'IIS') {
					$val = str_replace('\\\\', '\\', $this->env('PATH_TRANSLATED'));
				} elseif (isset($this->_env['DOCUMENT_ROOT']) && isset($this->_env['PHP_SELF'])) {
					$val = $this->_env['DOCUMENT_ROOT'] . $this->_env['PHP_SELF'];
				}
			break;
			case 'DOCUMENT_ROOT':
				$fileName = $this->env('SCRIPT_FILENAME');
				$offset = (!strpos($this->env('SCRIPT_NAME'), '.php')) ? 4 : 0;
				$offset = strlen($fileName) - (strlen($this->env('SCRIPT_NAME')) + $offset);
				$val = substr($fileName, 0, $offset);
			break;
			case 'PHP_SELF':
				$val = '/';
			break;
			case 'CGI':
			case 'CGI_MODE':
				$val = $this->env('PLATFORM') === 'CGI';
			break;
			case 'HTTP_BASE':
				$val = preg_replace('/^([^.])*/i', null, $this->env('HTTP_HOST'));
			break;
			case 'PHP_AUTH_USER':
			case 'PHP_AUTH_PW':
			case 'PHP_AUTH_DIGEST':
				if (!$header = $this->env('HTTP_AUTHORIZATION')) {
					if (!$header = $this->env('REDIRECT_HTTP_AUTHORIZATION')) {
						return $this->_computed[$key] = $val;
					}
				}
				if (stripos($header, 'basic') === 0) {
					$decoded = base64_decode(substr($header, strlen('basic ')));

					if (strpos($decoded, ':') !== false) {
						list($user, $password) = explode(':', $decoded, 2);

						$this->_computed['PHP_AUTH_USER'] = $user;
						$this->_computed['PHP_AUTH_PW'] = $password;
						return $this->_computed[$key];
					}
				} elseif (stripos($header, 'digest') === 0) {
					return $this->_computed[$key] = substr($header, strlen('digest '));
				}
			default:
				$val = array_key_exists($key, $this->_env) ? $this->_env[$key] : $val;
			break;
		}
		return $this->_computed[$key] = $val;
	}