Plugin example for pop-up auto-completion

I would like to write a simple plugin that, upon entering a certain character, provides the user with a pop-up list of search results from our API. When the user clicks on one of the entries in the list, the text from the triggering character up to the end of the text should be replaced by a standard link tag linking to the clicked search result from the list. It should basically work similar to the auto-complete for usernames, except that I would like to replace the text by a link. Is there any plugin that I can have a look at which already does this? The only one that comes close is this BBCodes Plugin, but maybe there is a simpler one that I can get inspiration from? I checked the beginners guide, but could not find any info about how to write a plugin that listens for keystrokes and shows or hides an auto-complete pop-up. Any pointer to some documentation would be appreciated!
Kind regards