As noted in #80 we currently maintain a local cache of the feed-items which have been seen, but we do that globally:

• Assume we are monitoring three feeds
  • https://example.com/index.rss
  • https://example.org/index.xml
  • https://example.net/index.atom
• We have a single state-directory which is used to keep track of items which have been seen:
  • ~/.rss2email/seen
• This makes it impossible to expire state-files on a per-feed basis.

Having our record of seen-items be prefixed with the source-feed from which it came would be very useful. It would allow removing all state-files when an URL was removed, for example.

To resolve this issue we need to do two things:

• Continue writing our state to ~/.rss2email/state/$file.
• But also write to ~/.rss2email/seen/$feed/$file
  • Where $feed is some kind of normalized feed-URL representation.

We then expire things in both locations. After this has been released in the wild for "a while" we can drop the /state directory and avoid losing track of seen vs. unseen items.