Chromecast Next episode rule

I have a local computer running openhab3 on my network, I also have a chromecast, and finally the computer has a drive I’m using to store episodes of some guilty pleasure shows we like to always have on.

Item:

String ChromecastSeriesEp “Series Season and Episode”

Sitemap:

Selection item=ChromecastSeriesEp label=“Series Season and Episode:” icon=“video” mappings=[S1E1=“1.1 Episode title”, S1E2=“1.2 Episode title”, etc, etc, etc, S5E10=“5.10 Episode title”]

Rule:

rule “Series Rule”
when Item ChromecastSeriesEp changed
then
ChromecastURI.sendCommand(“http://192.168.0.x/Video/Series” + ChromecastSeriesEp.state.toString + “.mp4”)
ChromecastMusic.sendCommand(PLAY)
end

I’ve also got it setup in the semantic model but I don’t think that’s relevant to what I’m hoping can be done:
I would like to have a rule, using a simple button that will evaluate the string (ChromecastSeasonEp) and allow me to advance the episode one, because then the rule above will fire and start the next Episode. This (creating the items and the sitemap) all seems pretty strait forward on everything except how to read the string and advance the episode number. I’m also not doing very well on googling this idea. :frowning: