Wordpress Function: Related Tags 2

Function for Wordpress themes: Develop a function that shows tags related to a certain tag. What do I mean by 'related tags'? Related tags are tags that are used by the same posts. I wish to use the function on the tag-archive page. It should do the following: - get single_tag_id - check which posts use this specific tag - check which other tags are used by these posts - return the mostly related tags - 1. fallback (if there are equally related tags): chose the tags with the highest number of posts - 2. fallback (if equally related tags with equal number of posts): either alphabetical or random - return nothing, if there are no related tags - return as many related tags, as there are, maximum 7 - return the tags in alphabetic order, separated by commas