Automating Music With Google Home?

I had previously used an Amazon Echo with Echo Speaks to trigger music to play automatically when the light for the shower was turned on. For various reasons I no longer wish to use Echo devices or the Echo Speaks app. I've managed to add my Nest device and I can get it to work with TTS, and I can even get it to play an mp3, but I cannot figure out a way to get them to play "live" music. What's the easiest way, if possible, to accomplish this?