CodeIgniter helper: http_build_url() PHP implementation

http_build_url.php

<?php

/**
 * Takes an associative array in the layout of parse_url, and constructs a URL from it
 *
 * see http://www.php.net/manual/en/function.http-build-url.php#96335
 *
 * @param   mixed   (Part(s) of) an URL in form of a string or associative array like parse_url() returns
 * @param   mixed   Same as the first argument
 * @param   int     A bitmask of binary or'ed HTTP_URL constants (Optional)HTTP_URL_REPLACE is the default
 * @param   array   If set, it will be filled with the parts of the composed url like parse_url() would return
 *
 * @return  string  constructed URL
 */
// Based on https://github.com/fuel/core/blob/974281dde67345ca8d7cfa27bcf4aa55c984d48e/base.php#L248
// Bug http://stackoverflow.com/questions/7751679/php-http-build-url-and-pecl-install/7753154#comment11239561_7753154
if (!function_exists('http_build_url'))
{
  define('HTTP_URL_REPLACE', 1);				// Replace every part of the first URL when there's one of the second URL
	define('HTTP_URL_JOIN_PATH', 2);			// Join relative paths
	define('HTTP_URL_JOIN_QUERY', 4);			// Join query strings
	define('HTTP_URL_STRIP_USER', 8);			// Strip any user authentication information
	define('HTTP_URL_STRIP_PASS', 16);			// Strip any password authentication information
	define('HTTP_URL_STRIP_AUTH', 32);			// Strip any authentication information
	define('HTTP_URL_STRIP_PORT', 64);			// Strip explicit port numbers
	define('HTTP_URL_STRIP_PATH', 128);			// Strip complete path
	define('HTTP_URL_STRIP_QUERY', 256);		// Strip query string
	define('HTTP_URL_STRIP_FRAGMENT', 512);		// Strip any fragments (#identifier)
	define('HTTP_URL_STRIP_ALL', 1024);			// Strip anything but scheme and host

	function http_build_url($url, $parts = array(), $flags = HTTP_URL_REPLACE, &$new_url = false)
	{
		$keys = array('user','pass','port','path','query','fragment');

		// HTTP_URL_STRIP_ALL becomes all the HTTP_URL_STRIP_Xs
		if ($flags & HTTP_URL_STRIP_ALL)
		{
			$flags |= HTTP_URL_STRIP_USER;
			$flags |= HTTP_URL_STRIP_PASS;
			$flags |= HTTP_URL_STRIP_PORT;
			$flags |= HTTP_URL_STRIP_PATH;
			$flags |= HTTP_URL_STRIP_QUERY;
			$flags |= HTTP_URL_STRIP_FRAGMENT;
		}
		// HTTP_URL_STRIP_AUTH becomes HTTP_URL_STRIP_USER and HTTP_URL_STRIP_PASS
		else if ($flags & HTTP_URL_STRIP_AUTH)
		{
			$flags |= HTTP_URL_STRIP_USER;
			$flags |= HTTP_URL_STRIP_PASS;
		}

    		// parse the current URL
		$current_url = parse_url(current_url());
    
		// parse the original URL
		$parse_url = is_array($url) ? $url : parse_url($url);

		// make sure we always have a scheme, host and path
		empty($parse_url['scheme']) and $parse_url['scheme'] = $current_url['scheme'];
		empty($parse_url['host']) and $parse_url['host'] = $current_url['host'];
		isset($parse_url['path']) or $parse_url['path'] = '';

		// make the path absolute if needed
		if ( ! empty($parse_url['path']) and substr($parse_url['path'], 0, 1) != '/')
		{
			$parse_url['path'] = '/'.$parse_url['path'];
		}

		// scheme and host are always replaced
		isset($parts['scheme']) and $parse_url['scheme'] = $parts['scheme'];
		isset($parts['host']) and $parse_url['host'] = $parts['host'];

		// replace the original URL with it's new parts (if applicable)
		if ($flags & HTTP_URL_REPLACE)
		{
			foreach ($keys as $key)
			{
				if (isset($parts[$key]))
					$parse_url[$key] = $parts[$key];
			}
		}
		else
		{
			// join the original URL path with the new path
			if (isset($parts['path']) && ($flags & HTTP_URL_JOIN_PATH))
			{
				if (isset($parse_url['path']))
					$parse_url['path'] = rtrim(str_replace(basename($parse_url['path']), '', $parse_url['path']), '/') . '/' . ltrim($parts['path'], '/');
				else
					$parse_url['path'] = $parts['path'];
			}

			// join the original query string with the new query string
			if (isset($parts['query']) && ($flags & HTTP_URL_JOIN_QUERY))
			{
				if (isset($parse_url['query']))
					$parse_url['query'] .= '&' . $parts['query'];
				else
					$parse_url['query'] = $parts['query'];
			}
		}

		// strips all the applicable sections of the URL
		// note: scheme and host are never stripped
		foreach ($keys as $key)
		{
			if ($flags & (int)constant('HTTP_URL_STRIP_' . strtoupper($key)))
				unset($parse_url[$key]);
		}


		$new_url = $parse_url;

		return
			 ((isset($parse_url['scheme'])) ? $parse_url['scheme'] . '://' : '')
			.((isset($parse_url['user'])) ? $parse_url['user'] . ((isset($parse_url['pass'])) ? ':' . $parse_url['pass'] : '') .'@' : '')
			.((isset($parse_url['host'])) ? $parse_url['host'] : '')
			.((isset($parse_url['port'])) ? ':' . $parse_url['port'] : '')
			.((isset($parse_url['path'])) ? $parse_url['path'] : '')
			.((isset($parse_url['query'])) ? '?' . $parse_url['query'] : '')
			.((isset($parse_url['fragment'])) ? '#' . $parse_url['fragment'] : '')
		;
	}
}