//at init:
add_filter('wp_handle_upload_prefilter', 'cud_pre_upload');	

// Called once for each uploaded file.
function cud_pre_upload($file){	
    [...]
	add_filter('upload_dir', 'cud_custom_upload_dir');
	return $file;
}

function cud_custom_upload_dir($path){		
	if(!empty($path['error'])) { return $path; } //error; do nothing.	
	$customdir = cud_generate_path();
	$path['path'] 	 = str_replace($path['subdir'], '', $path['path']); //remove default subdir (year/month)
	$path['url']	 = str_replace($path['subdir'], '', $path['url']);		
	$path['subdir']  = $customdir;
	$path['path'] 	.= $customdir; 
	$path['url'] 	.= $customdir;	
	return $path;
}

function cud_generate_path(){	
	global $post, $post_id, $current_user, $cud_file_ext, $cud_file_type, $cud_rpc_id;	
	$post_id = (!empty($post_id) ? $post_id : (!empty($_REQUEST['post_id']) ? $_REQUEST['post_id'] : (!empty($cud_rpc_id) ? $cud_rpc_id : '')));
	$my_post;
	if(empty($post) || (!empty($post) && is_numeric($post_id) && $post_id != $post->ID)){ 
		$my_post = get_post($post_id);
	}	
	$customdir = = get_option('custom_upload_dir_template');
	
	//defaults
	$user_id = $post_type = $post_name = $author = '';
	$time = (!empty($_SERVER['REQUEST_TIME'])) ? $_SERVER['REQUEST_TIME'] : (time() + (get_option('gmt_offset')*3600));	
	$user_id = (is_user_logged_in() && !empty($current_user)) ? $current_user->ID : '';		
	if(empty($user_id)){	
		$current_user = wp_get_current_user();
		if($current_user instanceof WP_User){
			$user_id = $current_user->ID;
		}
	}
	if(!empty($my_post)){ 		
		$post_id = $my_post->ID;
		$time = ($my_post->post_date == '0000-00-00 00:00:00') ? $time : strtotime($my_post->post_date);	
		$post_type = $my_post->post_type;
		$author = $my_post->post_author; 
		$post_name = (!empty($my_post->post_name)) ? $my_post->post_name : (!empty($my_post->post_title) ? sanitize_title($my_post->post_title) : $post_id);	
	}else{		
		$post_id = '';
	}	
	
	$date = explode(" ", date('Y m d H i s', $time));			
	$tags = array('%post_id%','%postname%','%post_type%','%year%','%monthnum%','%month%', '%day%','%hour%','%minute%','%second%', '%file_ext%', '%file_type%');
	$replace = array($post_id, $post_name, $post_type, $date[0], $date[1], $date[1], $date[2], $date[3], $date[4], $date[5], $cud_file_ext, $cud_file_type);
	
	$customdir = str_replace($tags,	$replace, $customdir); //do all cheap replacements in one go.
	$customdir = str_replace('%permalink%', 	cud_get_permalink($post_id),$customdir);
	$customdir = str_replace('%author%', 		cud_get_user_name($author), $customdir);
	$customdir = str_replace('%author_role%', 	cud_get_user_role($author), $customdir);
	$customdir = str_replace('%current_user%', 	cud_get_user_name($user_id),$customdir);
	$customdir = str_replace('%parent_name%', 	cud_get_parent_slug($my_post),	$customdir);	
	$customdir = str_replace('%post_category%', cud_get_category_name($post_id), 	$customdir);/*DEPRECATED SINCE 3.0.3*/
	$customdir = str_replace('%post_categories%',cud_get_categories_name($post_id), $customdir);/*DEPRECATED SINCE 3.0.3*/
				
	//Now, let's deal with taxonomies (category, tags, custom)	
	$matches = array();
	if(preg_match_all('/%(.*?)%/s', $customdir, $matches) == true){
		for($i = 0; $i < count($matches[0]); $i++){			
			if(taxonomy_exists($matches[1][$i])){
				$customdir = str_replace($matches[0][$i], cud_get_taxonomies($post_id, $matches[1][$i]), $customdir);
			}else{
				$customdir = str_replace($matches[0][$i], '', $customdir);
			}
		}
	}	
	$customdir = cud_leadingslashit($customdir); //for good measure.
	$customdir = untrailingslashit($customdir);	
	while(strpos($customdir, '//') !== false){
		$customdir = str_replace('//', '/', $customdir); //avoid duplicate slashes.
	}	
	return apply_filters('cud_generate_path', $customdir, $post_id);
}