A privacy first period tracker? Is it even possible?

Do I want to track my cycles? Yes. Do I want the tracker to push my data to a third party? Hell NO! Do I want the data lying around unencrypted in a database somewhere? Not really. Do I want backup and access from multiple devices? Kinda.. What would I need to learn and is it even possible? Come along on my journey, as a run of the mill web developer, to create a secure and private web-based period tracker.