class UrlHelper

class UrlHelper {
    
    /**
     * The list of allowed protocols.
     *
     * @var array
     */
    protected static $allowedProtocols = [
        'http',
        'https',
    ];
    
    /**
     * Parses an array into a valid, rawurlencoded query string.
     *
     * Function rawurlencode() is RFC3986 compliant, and as a consequence RFC3987
     * compliant. The latter defines the required format of "URLs" in HTML5.
     * urlencode() is almost the same as rawurlencode(), except that it encodes
     * spaces as "+" instead of "%20". This makes its result non compliant to
     * RFC3986 and as a consequence non compliant to RFC3987 and as a consequence
     * not valid as a "URL" in HTML5.
     *
     * @param array $query
     *   The query parameter array to be processed; for instance,
     *   \Drupal::request()->query->all().
     * @param string $parent
     *   (optional) Internal use only. Used to build the $query array key for
     *   nested items. Defaults to an empty string.
     *
     * @return string
     *   A rawurlencoded string which can be used as or appended to the URL query
     *   string.
     *
     * @ingroup php_wrappers
     */
    public static function buildQuery(array $query, $parent = '') {
        $params = [];
        foreach ($query as $key => $value) {
            $key = $parent ? $parent . rawurlencode('[' . $key . ']') : rawurlencode($key);
            // Recurse into children.
            if (is_array($value)) {
                $params[] = static::buildQuery($value, $key);
            }
            elseif (!isset($value)) {
                $params[] = $key;
            }
            else {
                // For better readability of paths in query strings, we decode slashes.
                $params[] = $key . '=' . str_replace('%2F', '/', rawurlencode($value));
            }
        }
        return implode('&', $params);
    }
    
    /**
     * Filters a URL query parameter array to remove unwanted elements.
     *
     * @param array $query
     *   An array to be processed.
     * @param array $exclude
     *   (optional) A list of $query array keys to remove. Use "parent[child]" to
     *   exclude nested items.
     * @param string $parent
     *   Internal use only. Used to build the $query array key for nested items.
     *
     * @return
     *   An array containing query parameters.
     */
    public static function filterQueryParameters(array $query, array $exclude = [], $parent = '') {
        // If $exclude is empty, there is nothing to filter.
        if (empty($exclude)) {
            return $query;
        }
        elseif (!$parent) {
            $exclude = array_flip($exclude);
        }
        $params = [];
        foreach ($query as $key => $value) {
            $string_key = $parent ? $parent . '[' . $key . ']' : $key;
            if (isset($exclude[$string_key])) {
                continue;
            }
            if (is_array($value)) {
                $params[$key] = static::filterQueryParameters($value, $exclude, $string_key);
            }
            else {
                $params[$key] = $value;
            }
        }
        return $params;
    }
    
    /**
     * Parses a URL string into its path, query, and fragment components.
     *
     * This function splits both internal paths like @code node?b=c#d @endcode and
     * external URLs like @code https://example.com/a?b=c#d @endcode into their
     * component parts. See
     * @link http://tools.ietf.org/html/rfc3986#section-3 RFC 3986 @endlink for an
     * explanation of what the component parts are.
     *
     * Note that, unlike the RFC, when passed an external URL, this function
     * groups the scheme, authority, and path together into the path component.
     *
     * @param string $url
     *   The internal path or external URL string to parse.
     *
     * @return array
     *   An associative array containing:
     *   - path: The path component of $url. If $url is an external URL, this
     *     includes the scheme, authority, and path.
     *   - query: An array of query parameters from $url, if they exist.
     *   - fragment: The fragment component from $url, if it exists.
     *
     * @see \Drupal\Core\Utility\LinkGenerator
     * @see http://tools.ietf.org/html/rfc3986
     *
     * @ingroup php_wrappers
     */
    public static function parse($url) {
        $options = [
            'path' => NULL,
            'query' => [],
            'fragment' => '',
        ];
        // External URLs: not using parse_url() here, so we do not have to rebuild
        // the scheme, host, and path without having any use for it.
        // The URL is considered external if it contains the '://' delimiter. Since
        // a URL can also be passed as a query argument, we check if this delimiter
        // appears in front of the '?' query argument delimiter.
        $scheme_delimiter_position = strpos($url, '://');
        $query_delimiter_position = strpos($url, '?');
        if ($scheme_delimiter_position !== FALSE && ($query_delimiter_position === FALSE || $scheme_delimiter_position < $query_delimiter_position)) {
            // Split off the fragment, if any.
            if (strpos($url, '#') !== FALSE) {
                list($url, $options['fragment']) = explode('#', $url, 2);
            }
            // Split off everything before the query string into 'path'.
            $parts = explode('?', $url, 2);
            // Don't support URLs without a path, like 'http://'.
            list(, $path) = explode('://', $parts[0], 2);
            if ($path != '') {
                $options['path'] = $parts[0];
            }
            // If there is a query string, transform it into keyed query parameters.
            if (isset($parts[1])) {
                parse_str($parts[1], $options['query']);
            }
        }
        else {
            // parse_url() does not support relative URLs, so make it absolute. For
            // instance, the relative URL "foo/bar:1" isn't properly parsed.
            $parts = parse_url('http://example.com/' . $url);
            // Strip the leading slash that was just added.
            $options['path'] = substr($parts['path'], 1);
            if (isset($parts['query'])) {
                parse_str($parts['query'], $options['query']);
            }
            if (isset($parts['fragment'])) {
                $options['fragment'] = $parts['fragment'];
            }
        }
        return $options;
    }
    
    /**
     * Encodes a Drupal path for use in a URL.
     *
     * For aesthetic reasons slashes are not escaped.
     *
     * @param string $path
     *   The Drupal path to encode.
     *
     * @return string
     *   The encoded path.
     */
    public static function encodePath($path) {
        return str_replace('%2F', '/', rawurlencode($path));
    }
    
    /**
     * Determines whether a path is external to Drupal.
     *
     * An example of an external path is http://example.com. If a path cannot be
     * assessed by Drupal's menu handler, then we must treat it as potentially
     * insecure.
     *
     * @param string $path
     *   The internal path or external URL being linked to, such as "node/34" or
     *   "http://example.com/foo".
     *
     * @return bool
     *   TRUE or FALSE, where TRUE indicates an external path.
     */
    public static function isExternal($path) {
        $colonpos = strpos($path, ':');
        // Some browsers treat \ as / so normalize to forward slashes.
        $path = str_replace('\\', '/', $path);
        // If the path starts with 2 slashes then it is always considered an
        // external URL without an explicit protocol part.
        return strpos($path, '//') === 0 || preg_match('/^\\p{C}/u', $path) !== 0 || $colonpos !== FALSE && !preg_match('![/?#]!', substr($path, 0, $colonpos)) && static::stripDangerousProtocols($path) == $path;
    }
    
    /**
     * Determines if an external URL points to this installation.
     *
     * @param string $url
     *   A string containing an external URL, such as "http://example.com/foo".
     * @param string $base_url
     *   The base URL string to check against, such as "http://example.com/"
     *
     * @return bool
     *   TRUE if the URL has the same domain and base path.
     *
     * @throws \InvalidArgumentException
     *   Exception thrown when a either $url or $bath_url are not fully qualified.
     */
    public static function externalIsLocal($url, $base_url) {
        // Some browsers treat \ as / so normalize to forward slashes.
        $url = str_replace('\\', '/', $url);
        // Leading control characters may be ignored or mishandled by browsers, so
        // assume such a path may lead to an non-local location. The \p{C} character
        // class matches all UTF-8 control, unassigned, and private characters.
        if (preg_match('/^\\p{C}/u', $url) !== 0) {
            return FALSE;
        }
        $url_parts = parse_url($url);
        $base_parts = parse_url($base_url);
        if (empty($base_parts['host']) || empty($url_parts['host'])) {
            throw new \InvalidArgumentException('A path was passed when a fully qualified domain was expected.');
        }
        if (!isset($url_parts['path']) || !isset($base_parts['path'])) {
            return (!isset($base_parts['path']) || $base_parts['path'] == '/') && $url_parts['host'] == $base_parts['host'];
        }
        else {
            // When comparing base paths, we need a trailing slash to make sure a
            // partial URL match isn't occurring. Since base_path() always returns
            // with a trailing slash, we don't need to add the trailing slash here.
            return $url_parts['host'] == $base_parts['host'] && stripos($url_parts['path'], $base_parts['path']) === 0;
        }
    }
    
    /**
     * Processes an HTML attribute value and strips dangerous protocols from URLs.
     *
     * @param string $string
     *   The string with the attribute value.
     *
     * @return string
     *   Cleaned up and HTML-escaped version of $string.
     */
    public static function filterBadProtocol($string) {
        // Get the plain text representation of the attribute value (i.e. its
        // meaning).
        $string = Html::decodeEntities($string);
        return Html::escape(static::stripDangerousProtocols($string));
    }
    
    /**
     * Gets the allowed protocols.
     *
     * @return array
     *   An array of protocols, for example http, https and irc.
     */
    public static function getAllowedProtocols() {
        return static::$allowedProtocols;
    }
    
    /**
     * Sets the allowed protocols.
     *
     * @param array $protocols
     *   An array of protocols, for example http, https and irc.
     */
    public static function setAllowedProtocols(array $protocols = []) {
        static::$allowedProtocols = $protocols;
    }
    
    /**
     * Strips dangerous protocols (for example, 'javascript:') from a URI.
     *
     * This function must be called for all URIs within user-entered input prior
     * to being output to an HTML attribute value. It is often called as part of
     * \Drupal\Component\Utility\UrlHelper::filterBadProtocol() or
     * \Drupal\Component\Utility\Xss::filter(), but those functions return an
     * HTML-encoded string, so this function can be called independently when the
     * output needs to be a plain-text string for passing to functions that will
     * call Html::escape() separately. The exact behavior depends on the value:
     * - If the value is a well-formed (per RFC 3986) relative URL or
     *   absolute URL that does not use a dangerous protocol (like
     *   "javascript:"), then the URL remains unchanged. This includes all
     *   URLs generated via Url::toString() and UrlGeneratorTrait::url().
     * - If the value is a well-formed absolute URL with a dangerous protocol,
     *   the protocol is stripped. This process is repeated on the remaining URL
     *   until it is stripped down to a safe protocol.
     * - If the value is not a well-formed URL, the same sanitization behavior as
     *   for well-formed URLs will be invoked, which strips most substrings that
     *   precede a ":". The result can be used in URL attributes such as "href"
     *   or "src" (only after calling Html::escape() separately), but this may not
     *   produce valid HTML (for example, malformed URLs within "href" attributes
     *   fail HTML validation). This can be avoided by using
     *   Url::fromUri($possibly_not_a_url)->toString(), which either throws an
     *   exception or returns a well-formed URL.
     *
     * @param string $uri
     *   A plain-text URI that might contain dangerous protocols.
     *
     * @return string
     *   A plain-text URI stripped of dangerous protocols. As with all plain-text
     *   strings, this return value must not be output to an HTML page without
     *   being sanitized first. However, it can be passed to functions
     *   expecting plain-text strings.
     *
     * @see \Drupal\Component\Utility\Html::escape()
     * @see \Drupal\Core\Url::toString()
     * @see \Drupal\Core\Routing\UrlGeneratorTrait::url()
     * @see \Drupal\Core\Url::fromUri()
     */
    public static function stripDangerousProtocols($uri) {
        $allowed_protocols = array_flip(static::$allowedProtocols);
        // Iteratively remove any invalid protocol found.
        do {
            $before = $uri;
            $colonpos = strpos($uri, ':');
            if ($colonpos > 0) {
                // We found a colon, possibly a protocol. Verify.
                $protocol = substr($uri, 0, $colonpos);
                // If a colon is preceded by a slash, question mark or hash, it cannot
                // possibly be part of the URL scheme. This must be a relative URL, which
                // inherits the (safe) protocol of the base document.
                if (preg_match('![/?#]!', $protocol)) {
                    break;
                }
                // Check if this is a disallowed protocol. Per RFC2616, section 3.2.3
                // (URI Comparison) scheme comparison must be case-insensitive.
                if (!isset($allowed_protocols[strtolower($protocol)])) {
                    $uri = substr($uri, $colonpos + 1);
                }
            }
        } while ($before != $uri);
        return $uri;
    }
    
    /**
     * Verifies the syntax of the given URL.
     *
     * This function should only be used on actual URLs. It should not be used for
     * Drupal menu paths, which can contain arbitrary characters.
     * Valid values per RFC 3986.
     *
     * @param string $url
     *   The URL to verify.
     * @param bool $absolute
     *   Whether the URL is absolute (beginning with a scheme such as "http:").
     *
     * @return bool
     *   TRUE if the URL is in a valid format, FALSE otherwise.
     */
    public static function isValid($url, $absolute = FALSE) {
        if ($absolute) {
            return (bool) preg_match("\n        /^                                                      # Start at the beginning of the text\n        (?:ftp|https?|feed):\\/\\/                                # Look for ftp, http, https or feed schemes\n        (?:                                                     # Userinfo (optional) which is typically\n          (?:(?:[\\w\\.\\-\\+!\$&'\\(\\)*\\+,;=]|%[0-9a-f]{2})+:)*      # a username or a username and password\n          (?:[\\w\\.\\-\\+%!\$&'\\(\\)*\\+,;=]|%[0-9a-f]{2})+@          # combination\n        )?\n        (?:\n          (?:[a-z0-9\\-\\.]|%[0-9a-f]{2})+                        # A domain name or a IPv4 address\n          |(?:\\[(?:[0-9a-f]{0,4}:)*(?:[0-9a-f]{0,4})\\])         # or a well formed IPv6 address\n        )\n        (?::[0-9]+)?                                            # Server port number (optional)\n        (?:[\\/|\\?]\n          (?:[\\w#!:\\.\\?\\+=&@\$'~*,;\\/\\(\\)\\[\\]\\-]|%[0-9a-f]{2})   # The path and query (optional)\n        *)?\n      \$/xi", $url);
        }
        else {
            return (bool) preg_match("/^(?:[\\w#!:\\.\\?\\+=&@\$'~*,;\\/\\(\\)\\[\\]\\-]|%[0-9a-f]{2})+\$/i", $url);
        }
    }

}