Push notification by email when number is shown

[fzesch]

User story

1. A user $usr enters a number $num and his email adress $mail.
2. He receives an email with a confirmation link (double opt-in)
3. He confirms by link. (if not, abort)
4. When the number $num is entered sufficiently often by different users (e.g. 3 times), the program sends instantly a localized email to $mail with informations about the event.

Implementation proposals

• rely on existing libraries for sending email and double opt-in
• keep requirements for local mail server as low as possible
• store $num as hash
• verify $mail address with reg exp
• verify $num with reg exp

Optional features

Above, only the minimum viable product is described. But enhancements are possible:

• Daily notification that number has not been drawn today (to confirm that the system is working)
• Daily digest of shown numbers
• Option to unsubscribe (via double opt-out)