Daily time budget for playing audio

[ozonorg]

I would like to limit the daily time the box can actually play audio, i.e. x minutes on week(school)days and y minutes on weekend days. I am aware of the timer feature, but this is a different thing.

What I want to achieve is the following:
MVP:

• there is a budget (xx minutes) per day (24 hours)
• when the daily budget is reached, the box stops playing.
• at midnight/after 24hrs the budget is reset
• only the actual playing time counts towards the budget (not i.e. the uptime of the device)
• the actual remaining budget survives reboots and sudden loss of power. (This may not be possible without RTC/Network time.)

Extended features:

• there is a separate budget for every day of the week (RTC or network time required)
• when the daily budget is reached a status message is displayed or played over audio.
• you can get information on the remaining budget (display, webapp)
• you can trigger information output (audio) on the remaining budget with gpio-button/RFID-card
• you can extend the daily budget using an RFID-card (i.e. 30 minutes for a special ID once every 24 hours)
• when there is no RTC or network time, the budget can only be set as a one-off using RFID-cards

My first question would be if this is already done somehow. I couldn't find this feature here or using google.

If not I would be happy to share my ideas about this. So far I would work with one script running when the device is booted and a maintenance script that is called every minute. My current problem is to readout the actual playing time as MPD does not deliver this information. So the time would have to be counted pulling the status from MPD.