<?php

  class Url implements ArrayAccess
  {

    const DEFAULT_PORT = 80;

    private $_protocol;
    private $_user;
    private $_password;
    private $_host;
    private $_port;
    private $_path;
    private $_query;
    private $_fragement;

    public function __construct ($arg_url)
    {
      $parts = parse_url($arg_url);

      if (array_key_exists('scheme', $parts))
      {
        $this->_protocol = $parts['scheme'];
      }

      if (array_key_exists('user', $parts))
      {
        $this->_user = $parts['user'];
      }

      if (array_key_exists('pass', $parts))
      {
        $this->_password = $parts['pass'];
      }

      if (array_key_exists('host', $parts))
      {
        $this->_host = $parts['host'];
      }

      if (array_key_exists('port', $parts))
      {
        $this->_port = $parts['port'];
      }

      if (array_key_exists('path', $parts))
      {
        $this->_path = $parts['path'];
      }

      if (array_key_exists('query', $parts))
      {
        parse_str($parts['query'], $this->_query);
      }

      if (array_key_exists('fragment', $parts))
      {
        $this->_fragment = $parts['fragment'];
      }
    }

    public function setProtocol ($arg_protocol)
    {
      $this->_protocol = $arg_protocol;

      return $this;
    }

    public function setUser ($arg_user)
    {
      $this->_user = $arg_user;

      return $this;
    }

    public function setPassword ($arg_password)
    {
      $this->_password = $arg_password;

      return $this;
    }

    public function setHost ($arg_host)
    {
      $this->_host = $arg_host;

      return $this;
    }

    public function setPort ($arg_port)
    {
      $this->_port = $arg_port;

      return $this;
    }

    public function setPath ($arg_path)
    {
      $this->_path = $arg_path;

      return $this;
    }

    public function setQuery ($arg_query)
    {
      $this->_query = $arg_query;

      return $this;
    }

    public function setFragment ($arg_fragment)
    {
      $this->_fragment = $arg_fragment;

      return $this;
    }

    public function setQueryParameter ($arg_key, $arg_value)
    {
      $this->_query[$arg_key] = $arg_value;

      return $this;
    }

    public function getQueryParameter ($arg_key)
    {
      return $this->_query[$arg_key];
    }

    public function hasQueryParameter ($arg_key)
    {
      return array_key_exists($arg_key, $this->_query);
    }

    public function removeQueryParameter ($arg_key)
    {
      return unset($this->_query[$arg_key])
    }

    public function offsetSet ($arg_key, $value)
    {
      $this->setQueryParameter($arg_key, $value);
    }

    public function offsetGet ($arg_key)
    {
      if ( ! $this->hasQueryParameter($arg_key))
      {
        throw new InvalidArgumentException(sprintf('Query parameter "%s" is not defined.', $arg_key));
      }

      return $this->getQueryParameter($arg_key, $value);;
    }

    public function offsetExists ($arg_key)
    {
      return $this->hasQueryParameter($arg_key);
    }

    public function offsetUnset ($arg_key)
    {
      $this->removeQueryParameter($arg_key);
    }

    public function __toString ()
    {
      $format = NULL !== $this->_protocol ? '%1$s://' : '';

      if (NULL !== $this->_user)
      {
        $format .= '%2$s';

        if (NULL !== $this->_password)
        {
          $format .= ':%3$s';
        }

        $format .= '@';
      }

      if (NULL !== $this->_host)
      {
        $format .= '%4$s';
      }

      if (NULL !== $this->_port && self::DEFAULT_PORT !== $this->_port)
      {
        $format .= ':%5$d';
      }

      if (NULL !== $this->_path)
      {
        $format .= '/%6$s';
      }

      if (NULL !== $this->_query)
      {
        $format .= '?%7$s';
      }

      if (NULL !== $this->_fragment)
      {
        $format .= '#%8$s';
      }

      return sprintf($format, $this->_protocol, $this->_user, $this->_password, $this->_host, $this->_port, $this->_path, http_build_query($this->_query, NULL, $this->_seperator), $this->_fragment);
    }

  }