Phing AdhocTask to find the relative path between two paths

phing.find_relative_path.xml

    <!--
        Usage:
        <relative-path from="${from}" to="${to}"
            output="project_property" />
    -->
    <adhoc-task name="relative-path"><![CDATA[
        class RelativePath extends Task {
            private $from;
            private $to;
            private $output;

            function setFrom($from) {
                $this->from = $from;
            }

            function setTo($to) {
                $this->to = $to;
            }
        
            function setOutput($output=null) {
                $this->output = $output;
            }

            function main() {
                $relpath = $this->find_relative_path($this->from, $this->to);
                $this->log("relpath = " . $relpath);
                if ($this->output != null) {
                    $this->project->setProperty($this->output, $relpath);
                }
            }

            /**
             * credits: https://gist.github.com/ohaal/2936041
             * Find the relative file system path between two file system paths
             *
             * @param  string  $frompath  Path to start from
             * @param  string  $topath    Path we want to end up in
             *
             * @return string             Path leading from $frompath to $topath
             */
            function find_relative_path ( $frompath, $topath ) {
                $from = explode( DIRECTORY_SEPARATOR, $frompath ); // Folders/File
                $to = explode( DIRECTORY_SEPARATOR, $topath ); // Folders/File
                $relpath = '';

                $i = 0;
                // Find how far the path is the same
                while ( isset($from[$i]) && isset($to[$i]) ) {
                    if ( $from[$i] != $to[$i] ) break;
                    $i++;
                }
                $j = count( $from ) - 1;
                // Add '..' until the path is the same
                while ( $i <= $j ) {
                    if ( !empty($from[$j]) ) $relpath .= '..'.DIRECTORY_SEPARATOR;
                    $j--;
                }
                // Go to folder from where it starts differing
                while ( isset($to[$i]) ) {
                    if ( !empty($to[$i]) ) $relpath .= $to[$i].DIRECTORY_SEPARATOR;
                    $i++;
                }

                // Strip last separator
                return substr($relpath, 0, -1);
            }
        }
    ]]></adhoc-task>