<?php

/**
 * ArangoDB PHP client: autoloader
 * 
 * @package ArangoDbPhpClient
 * @author Jan Steemann
 * @copyright Copyright 2012, triagens GmbH, Cologne, Germany
 */

namespace triagens\ArangoDb;

/**
 * Handles automatic loading of missing class files
 * The autoloader can be nested with other autoloaders. It will only
 * process classes from its own namespace and ignore all others.
 *
 * @package ArangoDbPhpClient
 */
class Autoloader {
  /**
   * Directory with library files
   * @var string
   */
  private static $libDir = NULL;
  
  /**
   * Class file extension
   */
  const EXTENSION = '.php';

  /**
   * Initialise the autoloader
   *
   * @throws Exception
   * @return void
   */
  public static function init() {
    self::checkEnvironment();

    self::$libDir    = dirname(__FILE__) . DIRECTORY_SEPARATOR;
  }

  /**
   * Handle loading of an unknown class
   *
   * This will only handle class from its own namespace and ignore all others.
   * This allows multiple autoloaders to be used in a nested fashion.
   *
   * @param string $className - name of class to be loaded 
   * @return void
   */
  public static function load($className) {
    $namespace = __NAMESPACE__ . '\\';
    $length = strlen($namespace);

    if (substr($className, 0, $length) !== $namespace) {
      return;
    }

    // init() must have been called before
    assert(self::$libDir !== NULL);

    require self::$libDir . substr($className, $length) . self::EXTENSION;
  }
  
  /**
   * Check the runtime environment
   *
   * This will check whether the runtime environment is compatible with the
   * Arango PHP client.
   *
   * @throws ClientException
   * @return void
   */
  private static function checkEnvironment() {
    list($major, $minor) = explode('.', phpversion());

    if ((int) $major < 5 or ((int) $major === 5 && (int) $minor < 3)) {
      throw new ClientException('Incompatible PHP environment. Expecting PHP 5.3 or higher');
    }
  }
}