Issue: XF user alerts: possible pollution from multiple same page revisions by one person in a short timeframe

"Another might be to issue a user alert once per page until the subscriber next views that page (which is basically how XenForo handles a thread's new post alerts)."


This.

X updated to the page Y. There may be more edits after this.
45 minutes ago

Note: in 4.0.16 we already limited that only 1 subscription can send an instant-email/alert for each new-content that triggers it (so being subscribed to multiple parents would not create duplicate alerts).

In addition, the following should be implemented in the next release:

A user should only receive 1 instant-email/alert for each action-type for each wiki subscription, until they visit the subscribed content again.
This means that if a page is edited, and the user is watching the page, they will only be alerted 1 time, even if the page is edited again.
However, if that page is edited again, and the user is watching a parent of the page, they may be alerted of the second edit through the page's parent (but also only 1 time for that parent).
If a page gets commented, and the user is watching the page, they only will be alerted 1 time, even if the page is commented again.
However, if a user already received their 1 alert for an edit, it does not apply towards their 1 alert for a comment, and vice verse.

edit: alert 1 time per subscription
comment: alert 1 time per subscription
new content: alert 1 time per subscription
etc

As with the previous limit, the log expires after 30 days, so after 30 days the user may receive another 1 alert even if they haven't viewed the subscribed content again.