Added export every x days

[Apflkuacha]

I have added the possibility to export every x days, that fixes #219

[tmo1]

Thanks! I'll take a look.

[tmo1]

Sorry for forgetting about this.

IIUC, your code schedules exports on the next dayOfYear evenly divisible by exportIntervalDays. Wouldn't it be simpler from a code perspective as well as more intuitive from a user perspective to just schedule exports for now + exportIntervalDays?

[Apflkuacha]

I've updated the code how you suggested - is that what you ment?

[tmo1]

Thanks! That is more or less what I meant, but the logic is still not quite correct. Say exportTime is 2:00 AM, and exportIntervalDays is 2. An export runs on Jan. 1 2:00 AM and finishes at 2:05. When scheduling the next export, the app will first note that export_time < now and will accordingly add 1 to the DAY_OF_MONTH. Then, since exportIntervalDays > 1, it will further add exportIntervalDays to the DAY_OF_MONTH, which will result in the next export being scheduled for Jan. 4, rather than Jan. 3.

Edit: I think the correct behavior would be achieved with exportTime.add(Calendar.DAY_OF_MONTH, exportIntervalDays - 1) rather than exportTime.add(Calendar.DAY_OF_MONTH, exportIntervalDays).

[Apflkuacha]

Once more I updated the code as you suggested. The first version I have successfully tested on my device, but now I haven't find enough time to test the changes. So feel free to further adapt if necessary.