/**

     * Returns a path to a folder relative from another folder. Both parameters

     * must be absolute.

     *

     * - check for valid parameters

     * - in case paths are equal return './'

     * - explode parameters using '/'

     * - remove similar base folders

     * - make final address

     *

     * @param String $strFileFrom Base from the path. This must be an absolute path.

     * @param String $strFileTo Destination of the path. This must be an absolute path.

     * @param Boolean $booValidPath Use false if you don't want to check for valid folders.

     * @throws InvalidArgumentException In case of invalid values

     *

     * @example $path = CorujaStringManipulation::getRelativePath( "/www/folder/", "/www/another/big/" ); // "../another/big/"

     *

     * @assert ( "/www/folder/", "/www/another/big/", false ) == "../another/big/"

     * @assert ( "", "" ) throws InvalidArgumentException

     * @assert ( "hello", "" ) throws InvalidArgumentException

     * @assert ( "", "hello" ) throws InvalidArgumentException

     * @assert ( "cool", "hello" ) throws InvalidArgumentException

     * @assert ( "/cool/", "hello" ) throws InvalidArgumentException

     * @assert ( "cool", "/hello/" ) throws InvalidArgumentException

     * @assert ( "/cool/", "/hello/", false ) == "../hello/"

     * @assert ( "/cool/", "/hello/", false ) == "../hello/"

     * @assert ( "/cool/", "/cool/", false ) == "./"

     * @assert ( "/cool/more/", "/other/", false ) == "../../other/"

     * @assert ( "/cool/", "/other/more/", false ) == "../other/more/"

     */

    public static function getRelativePath( $strFileFrom, $strFileTo, $booValidPath = true )

    {

        // check for valid parameters

        $strFileFrom = str_replace( "\\" , "/" , $strFileFrom );

        $strFileTo = str_replace( "\\" , "/" , $strFileTo );

        if( $booValidPath

            && ( ! is_dir( $strFileFrom ) || ! is_dir( $strFileTo ) )

        )

        {

            throw new InvalidArgumentException("Invalid parameter: strFileFrom: ".$strFileFrom." strFileTo: ".$strFileTo);

        }

        // special case: equal paths

        if( $strFileFrom == $strFileTo )

        {

             $strReturnPath = './';

        }

        else

        {

            // explode parameters using '/'

            $arrFileFrom = explode( '/', $strFileFrom );

            $arrFileTo   = explode( '/', $strFileTo );

            // remove similar base folders

            while(

                current( $arrFileFrom ) == current( $arrFileTo )

                && count( $arrFileFrom ) > 0

            )

            {

                array_shift( $arrFileFrom );

                array_shift( $arrFileTo );

            }

            $arrReturnPath = array();

            // make final address

            foreach( $arrFileFrom as $strFolder )

            {

                if( $strFolder != "" ) {

                    $arrReturnPath[] = "..";

                }

            }

            foreach( $arrFileTo as $strFolder )

            {

                $arrReturnPath[] = $strFolder;

            }

            $strReturnPath = implode( '/', $arrReturnPath );

        }

        return $strReturnPath;

    }