Autoinject Keywords into Content

AT FIRST! I don't want spammy msg with url list of jobs you have done.... i don't like automated msg in my inbox... i don't like "sir i/we can/will..." my name is andreas.... use it, please. I need a script that: a) takes a text from an textarea b) takes a keyword / density per keyword list c) put both together and show it in a textarea e.g. i got a text: "The quick brown fox jumps over the lazy dog" i got a keyword/density list: black:2 cat:1 it should be randomly insert the keywords into the text in the given density/amount.... e.g.: "The quick black brown fox cat jumps over the brown lazy dog" should be a quick thing, it's for testing purposes... no need to make it nice... you can use jquery,ajax if you wish.