Add comments subscriptions to core

[jdalsem]

There are currently 2 plugins around that provide a very basic feature, and are both very well maintained.

https://github.com/AU-Landing-Project/comment_tracker

• Subscribes commenters to an entity so they receive notifications of new comments.

https://github.com/ColdTrick/content_subscriptions

• Automaticly follow a discussion or content on your first comment
• Subscribe to a discussion/content to get notifications about new comments

Both projects almost provide identical features related to getting notifications of new comments on a certain piece of content (and automatically subscribing to those notifications if you comment).

I think this is such a valuable feature that we should add it to core.

Questions:

• as a separate plugin, as a part of notifications or as part of core (build into comments or subscriptions lib)
• Elgg 2.0 or 1.11?

cc @Elgg/owners @Elgg/contributors

[juho-jaakkola]

I've been deliberately holding this back until we overhaul the subscriptions system. I created a new issue for that: #7859

[mrclay]

I'm not intimately familiar with either in their current state, though I've hacked on one. My biggest concern was that the "auto-subscribe" feature subscribed users to all their active notification methods. I also auto-subscribe on likes (walking up if it's a comment). Are either/both of these handling these?

[mrclay]

See also #7863

[mrclay]

I see content_subscriptions does handle all notification handlers as well as the weird way discussions are stored.

An important part of these would be providing a UI to see what you're subscribe to. I think comment_tracker has that.

Let's say we add this as a plugin. What happens if a site already has one of these enabled? I could see adding this in 1.x as long as we don't enable by default. I think the individual plugins should be responsible for migrating to the chosen format.

[mrclay]

I wouldn't mind creating an Elgg/content_subscribe repo, adding you all as contributors and we start merging these two (including scripts to migrate from either plugin). /cc @beck24

[beck24]

That sounds good to me, to be honest the comment tracker upgrade has been entirely the work of @juho-jaakkola - all credit for that goes to him. I would certainly like to help see the functionality become part of core though.

[mrclay]

Upon closer inspection I see content_subscriptions directly uses elgg_add_subscription() to subscribe the user to all available handlers, whereas comment_tracker instead queries its own relationship to provide Elgg with the subscribed users. What are the pros/cons of each method?

[juho-jaakkola]

In comment_tracker the idea is that new notification methods are enabled by default. Only the ones explicitly blocked are not being used.

[mrclay]

And notification methods change, new user-item relationships don't need to be added/removed.

[jdalsem]

in both situations you will receive notifications on all services, but comment_tracker has the benefit (or the downside) of future services, that are introduced after you subscribed, automatically being included as a notification service.

Downside is you need to provide your own mechanisme of providing the subscribers as where content_subscriptions can rely on default Elgg to handle those...

[jdalsem]

Assigning this to 2.0 as it is a killer feature

[ewinslow]

Killer feature perhaps but not a blocker for 2.0 since it shouldn't be breaking, amirite?

[jdalsem]

urrite

[jdalsem]

Added in #13408