Keep references to all reblogs of a status on home feed (#5419)

* Keep references to all reblogs of a status on home feed

When inserting reblog: Add to set of reblogs of this status on
the feed, if original status was present in the feed, add it to
that set as well.

When removing a reblog: Remove it from that set. Take random
remaining item from the set. If one exists, re-insert it into feed,
otherwise do not re-insert anything.

Fix #4210

* When original is removed, toss out reblog references

3 files changed, 72 insertions, 27 deletions

diff --git a/app/lib/feed_manager.rb b/app/lib/feed_manager.rb
index cc19c1d1a..7f95d7784 100644
--- a/app/lib/feed_manager.rb
+++ b/app/lib/feed_manager.rb
@@ -174,13 +174,19 @@ class FeedManager
   # either action is appropriate.
   def add_to_feed(timeline_type, account, status)
     timeline_key = key(timeline_type, account.id)
-    reblog_key = key(timeline_type, account.id, 'reblogs')
+    reblog_key   = key(timeline_type, account.id, 'reblogs')
 
     if status.reblog?
+      reblog_set_key = key(timeline_type, account.id, "reblogs:#{status.reblog_of_id}")
+
       # If the original status or a reblog of it is within
       # REBLOG_FALLOFF statuses from the top, do not re-insert it into
       # the feed
       rank = redis.zrevrank(timeline_key, status.reblog_of_id)
+
+      redis.sadd(reblog_set_key, status.reblog_of_id) unless rank.nil?
+      redis.sadd(reblog_set_key, status.id)
+
       return false if !rank.nil? && rank < FeedManager::REBLOG_FALLOFF
 
       reblog_rank = redis.zrevrank(reblog_key, status.reblog_of_id)
@@ -201,7 +207,7 @@ class FeedManager
   # do so if appropriate.
   def remove_from_feed(timeline_type, account, status)
     timeline_key = key(timeline_type, account.id)
-    reblog_key = key(timeline_type, account.id, 'reblogs')
+    reblog_key   = key(timeline_type, account.id, 'reblogs')
 
     if status.reblog?
       # 1. If the reblogging status is not in the feed, stop.
@@ -211,13 +217,21 @@ class FeedManager
       # 2. Remove the reblogged status from the `:reblogs` zset.
       redis.zrem(reblog_key, status.reblog_of_id)
 
-      # 3. Add the reblogged status to the feed.
-      # Note that we can't use old score in here
-      # and it must be an ID of corresponding status
-      # because we need to filter timeline by status ID.
-      redis.zadd(timeline_key, status.reblog_of_id, status.reblog_of_id)
+      # 3. Remove reblog from set of this status's reblogs, and
+      # re-insert another reblog or original into the feed if
+      # one remains in the set
+      reblog_set_key = key(timeline_type, account.id, "reblogs:#{status.reblog_of_id}")
+
+      redis.srem(reblog_set_key, status.id)
+      other_reblog = redis.srandmember(reblog_set_key)
+
+      redis.zadd(timeline_key, other_reblog, other_reblog) if other_reblog
 
       # 4. Remove the reblogging status from the feed (as normal)
+      # (outside conditional)
+    else
+      # If the original is getting deleted, no use for reblog references
+      redis.del(key(timeline_type, account.id, "reblogs:#{status.id}"))
     end
 
     redis.zrem(timeline_key, status.id)
diff --git a/app/workers/scheduler/feed_cleanup_scheduler.rb b/app/workers/scheduler/feed_cleanup_scheduler.rb
index dbebaa2c3..222f5ed84 100644
--- a/app/workers/scheduler/feed_cleanup_scheduler.rb
+++ b/app/workers/scheduler/feed_cleanup_scheduler.rb
@@ -6,8 +6,9 @@ class Scheduler::FeedCleanupScheduler
 
   def perform
     redis.pipelined do
-      inactive_users.pluck(:account_id).each do |account_id|
+      inactive_users.each do |account_id|
         redis.del(FeedManager.instance.key(:home, account_id))
+        redis.del(FeedManager.instance.key(:home, account_id, 'reblogs'))
       end
     end
   end
@@ -15,7 +16,7 @@ class Scheduler::FeedCleanupScheduler
   private
 
   def inactive_users
-    User.confirmed.inactive
+    @inactive_users ||= User.confirmed.inactive.pluck(:account_id)
   end
 
   def redis
diff --git a/spec/lib/feed_manager_spec.rb b/spec/lib/feed_manager_spec.rb
index 643f1f003..454c3afec 100644
--- a/spec/lib/feed_manager_spec.rb
+++ b/spec/lib/feed_manager_spec.rb
@@ -231,36 +231,66 @@ RSpec.describe FeedManager do
   end
 
   describe '#unpush' do
-    it 'leaves a reblogged status when deleting the reblog' do
-      account = Fabricate(:account)
-      reblogged = Fabricate(:status, id: Mastodon::Snowflake.id_at(2.day.ago.utc))
-      other_status = Fabricate(:status, id: Mastodon::Snowflake.id_at(1.day.ago.utc))
-      status = Fabricate(:status, reblog: reblogged)
+    let(:receiver) { Fabricate(:account) }
 
-      FeedManager.instance.push('type', account, other_status)
-      FeedManager.instance.push('type', account, status)
+    it 'leaves a reblogged status if original was on feed' do
+      reblogged = Fabricate(:status)
+      status    = Fabricate(:status, reblog: reblogged)
+
+      FeedManager.instance.push('type', receiver, reblogged)
+      FeedManager::REBLOG_FALLOFF.times { FeedManager.instance.push('type', receiver, Fabricate(:status)) }
+      FeedManager.instance.push('type', receiver, status)
 
       # The reblogging status should show up under normal conditions.
-      expect(Redis.current.zrange("feed:type:#{account.id}", 0, -1)).to eq [other_status.id.to_s, status.id.to_s]
+      expect(Redis.current.zrange("feed:type:#{receiver.id}", 0, -1)).to include(status.id.to_s)
 
-      FeedManager.instance.unpush('type', account, status)
+      FeedManager.instance.unpush('type', receiver, status)
 
-      # Because we couldn't tell if the status showed up any other way,
-      # we had to stick the reblogged status in by itself.
-      # And it must be ordered by status ids.
-      expect(Redis.current.zrange("feed:type:#{account.id}", 0, -1)).to eq [reblogged.id.to_s, other_status.id.to_s]
+      # Restore original status
+      expect(Redis.current.zrange("feed:type:#{receiver.id}", 0, -1)).to_not include(status.id.to_s)
+      expect(Redis.current.zrange("feed:type:#{receiver.id}", 0, -1)).to include(reblogged.id.to_s)
+    end
+
+    it 'removes a reblogged status if it was only reblogged once' do
+      reblogged = Fabricate(:status)
+      status    = Fabricate(:status, reblog: reblogged)
+
+      FeedManager.instance.push('type', receiver, status)
+
+      # The reblogging status should show up under normal conditions.
+      expect(Redis.current.zrange("feed:type:#{receiver.id}", 0, -1)).to eq [status.id.to_s]
+
+      FeedManager.instance.unpush('type', receiver, status)
+
+      expect(Redis.current.zrange("feed:type:#{receiver.id}", 0, -1)).to be_empty
+    end
+
+    it 'leaves a reblogged status if another reblog was in feed' do
+      reblogged      = Fabricate(:status)
+      status         = Fabricate(:status, reblog: reblogged)
+      another_status = Fabricate(:status, reblog: reblogged)
+
+      FeedManager.instance.push('type', receiver, status)
+      FeedManager.instance.push('type', receiver, another_status)
+
+      # The reblogging status should show up under normal conditions.
+      expect(Redis.current.zrange("feed:type:#{receiver.id}", 0, -1)).to eq [status.id.to_s]
+
+      FeedManager.instance.unpush('type', receiver, status)
+
+      expect(Redis.current.zrange("feed:type:#{receiver.id}", 0, -1)).to eq [another_status.id.to_s]
     end
 
     it 'sends push updates' do
-      account = Fabricate(:account)
-      status = Fabricate(:status)
-      FeedManager.instance.push('type', account, status)
+      status  = Fabricate(:status)
+
+      FeedManager.instance.push('type', receiver, status)
 
       allow(Redis.current).to receive_messages(publish: nil)
-      FeedManager.instance.unpush('type', account, status)
+      FeedManager.instance.unpush('type', receiver, status)
 
       deletion = Oj.dump(event: :delete, payload: status.id.to_s)
-      expect(Redis.current).to have_received(:publish).with("timeline:#{account.id}", deletion)
+      expect(Redis.current).to have_received(:publish).with("timeline:#{receiver.id}", deletion)
     end
   end
 end