ExpressionEngine file upload paths swapping method

addon.php

<?php
/*
    Usage

    $mystring = $this->swap_file_tokens('{filedir_3}path/to/image.jpg');
    echo $mystring;

        returns: 'http://mysite.com/images/path/to/image.jpg';

    $mystring = $this->swap_file_tokens('{filedir_3}path/to/image.jpg', 'server_path');
    echo $mystring;

        returns: '/var/www/mysite.com/images/path/to/image.jpg';

    $mystring = $this->swap_file_tokens('http://mysite.com/images/path/to/image.jpg');
    echo $mystring;

        returns: '{filedir_3}path/to/image.jpg';

    $mystring = $this->swap_file_tokens('/var/www/mysite.com/images/path/to/image.jpg');
    echo $mystring;

        returns: '{filedir_3}path/to/image.jpg';
*/


private function get_upload_prefs($group_id = NULL, $id = NULL)
{
    if ( ! isset($this->EE->session->cache[__CLASS__]['upload_prefs']))
    {
        if (version_compare(APP_VER, '2.4', '>='))
        {
            $this->EE->load->model('file_upload_preferences_model');
            return $this->EE->file_upload_preferences_model->get_file_upload_preferences($group_id, $id);
        }
        
        if (version_compare(APP_VER, '2.1.5', '>='))
        {
            $this->EE->load->model('file_upload_preferences_model');
            $result = $this->EE->file_upload_preferences_model->get_upload_preferences($group_id, $id);
        }
        else
        {
            $this->EE->load->model('tools_model');
            $result = $this->EE->tools_model->get_upload_preferences($group_id, $id);
        }

        $this->EE->session->cache[__CLASS__]['upload_prefs'] = $result->result_array();
    }
    
    return $this->EE->session->cache[__CLASS__]['upload_prefs'];
}

private function swap_file_tokens($str, $which = 'url')
{
    $prefs = $this->get_upload_prefs();
    $upload_paths = array();

    if ( ! isset($this->EE->session->cache[__CLASS__]['upload_paths']))
    {
        foreach ($prefs as $dir => $data)
        {
            $upload_paths[$dir] = array(
                'server_path'   => $data['server_path'],
                'url'           => $data['url']
            );
        }

        $this->EE->session->cache[__CLASS__]['upload_paths'] = $upload_paths;
    }

    $paths = $this->EE->session->cache[__CLASS__]['upload_paths'];

    //  Simple search for {filedir_N} tokens and replace with full url (default) or server_path
    if (preg_match('/\{filedir_(\d+)\}/', $str, $matches))
    {
        if ($matches && is_numeric($matches[1]))
        {
            return preg_replace('/\{filedir_(\d+)\}/', $paths[$matches[1]][$which], $str);
        }
    }

    // No tokens found? Then search for full url or server_path and swap back to a token
    
    // See if its a server_path
    if (substr($str, 1) == '/')
    {
        foreach ($paths as $dir => $path)
        {
            // If the string contains a server path
            if (strstr($str, $path['server_path']))
            {
                // Replace the path with the token.
                return str_replace($path['server_path'], '{filedir_'. $dir .'}', $str);
            }
        }
    }

    // We have a possible url
    if (substr($str, 4) == 'http')
    {
        foreach ($paths as $dir => $path)
        {
            // If the string contains a server path
            if (strstr($str, $path['url']))
            {
                // Replace the path with the token.
                return str_replace($path['url'], '{filedir_'. $dir .'}', $str);
            }
        }
    }

    return $str;
}