From 70ddef2654a931827ce5e4323e3042365f6078f2 Mon Sep 17 00:00:00 2001
From: Eugen Rochko <eugen@zeonfederated.com>
Date: Mon, 2 Sep 2019 18:11:13 +0200
Subject: Change trending hashtags to not disappear instantly after midnight
 (#11712)

---
 app/models/trending_tags.rb | 102 +++++++++++++++++++++++++++++++-------------
 1 file changed, 72 insertions(+), 30 deletions(-)

(limited to 'app/models/trending_tags.rb')

diff --git a/app/models/trending_tags.rb b/app/models/trending_tags.rb
index e4ce988c1..e1b92b175 100644
--- a/app/models/trending_tags.rb
+++ b/app/models/trending_tags.rb
@@ -7,6 +7,8 @@ class TrendingTags
   THRESHOLD            = 5
   LIMIT                = 10
   REVIEW_THRESHOLD     = 3
+  MAX_SCORE_COOLDOWN   = 3.days.freeze
+  MAX_SCORE_HALFLIFE   = 6.hours.freeze
 
   class << self
     include Redisable
@@ -16,14 +18,75 @@ class TrendingTags
 
       increment_historical_use!(tag.id, at_time)
       increment_unique_use!(tag.id, account.id, at_time)
-      increment_vote!(tag, at_time)
+      increment_use!(tag.id, at_time)
 
       tag.update(last_status_at: Time.now.utc) if tag.last_status_at.nil? || tag.last_status_at < 12.hours.ago
-      tag.update(last_trend_at: Time.now.utc)  if trending?(tag) && (tag.last_trend_at.nil? || tag.last_trend_at < 12.hours.ago)
+    end
+
+    def update!(at_time = Time.now.utc)
+      tag_ids = redis.smembers("#{KEY}:used:#{at_time.beginning_of_day.to_i}") + redis.zrange(KEY, 0, -1)
+      tags    = Tag.where(id: tag_ids.uniq)
+
+      # First pass to calculate scores and update the set
+
+      tags.each do |tag|
+        expected  = redis.pfcount("activity:tags:#{tag.id}:#{(at_time - 1.day).beginning_of_day.to_i}:accounts").to_f
+        expected  = 1.0 if expected.zero?
+        observed  = redis.pfcount("activity:tags:#{tag.id}:#{at_time.beginning_of_day.to_i}:accounts").to_f
+        max_time  = tag.max_score_at
+        max_score = tag.max_score
+        max_score = 0 if max_time.nil? || max_time < (at_time - MAX_SCORE_COOLDOWN)
+
+        score = begin
+          if expected > observed || observed < THRESHOLD
+            0
+          else
+            ((observed - expected)**2) / expected
+          end
+        end
+
+        if score > max_score
+          max_score = score
+          max_time  = at_time
+
+          # Not interested in triggering any callbacks for this
+          tag.update_columns(max_score: max_score, max_score_at: max_time)
+        end
+
+        decaying_score = max_score * (0.5**((at_time.to_f - max_time.to_f) / MAX_SCORE_HALFLIFE.to_f))
+
+        if decaying_score.zero?
+          redis.zrem(KEY, tag.id)
+        else
+          redis.zadd(KEY, decaying_score, tag.id)
+        end
+      end
+
+      users_for_review = User.staff.includes(:account).to_a.select(&:allows_trending_tag_emails?)
+
+      # Second pass to notify about previously unreviewed trends
+
+      tags.each do |tag|
+        current_rank              = redis.zrevrank(KEY, tag.id)
+        needs_review_notification = tag.requires_review? && !tag.requested_review?
+        rank_passes_threshold     = current_rank.present? && current_rank <= REVIEW_THRESHOLD
+
+        next unless !tag.trendable? && rank_passes_threshold && needs_review_notification
+
+        tag.touch(:requested_review_at)
+
+        users_for_review.each do |user|
+          AdminMailer.new_trending_tag(user.account, tag).deliver_later!
+        end
+      end
+
+      # Trim older items
+
+      redis.zremrangebyrank(KEY, 0, -(LIMIT + 1))
     end
 
     def get(limit, filtered: true)
-      tag_ids = redis.zrevrange("#{KEY}:#{Time.now.utc.beginning_of_day.to_i}", 0, LIMIT - 1).map(&:to_i)
+      tag_ids = redis.zrevrange(KEY, 0, LIMIT - 1).map(&:to_i)
 
       tags = Tag.where(id: tag_ids)
       tags = tags.where(trendable: true) if filtered
@@ -33,8 +96,8 @@ class TrendingTags
     end
 
     def trending?(tag)
-      rank = redis.zrevrank("#{KEY}:#{Time.now.utc.beginning_of_day.to_i}", tag.id)
-      rank.present? && rank <= LIMIT
+      rank = redis.zrevrank(KEY, tag.id)
+      rank.present? && rank < LIMIT
     end
 
     private
@@ -51,31 +114,10 @@ class TrendingTags
       redis.expire(key, EXPIRE_HISTORY_AFTER)
     end
 
-    def increment_vote!(tag, at_time)
-      key      = "#{KEY}:#{at_time.beginning_of_day.to_i}"
-      expected = redis.pfcount("activity:tags:#{tag.id}:#{(at_time - 1.day).beginning_of_day.to_i}:accounts").to_f
-      expected = 1.0 if expected.zero?
-      observed = redis.pfcount("activity:tags:#{tag.id}:#{at_time.beginning_of_day.to_i}:accounts").to_f
-
-      if expected > observed || observed < THRESHOLD
-        redis.zrem(key, tag.id)
-      else
-        score    = ((observed - expected)**2) / expected
-        old_rank = redis.zrevrank(key, tag.id)
-
-        redis.zadd(key, score, tag.id)
-        request_review!(tag) if (old_rank.nil? || old_rank > REVIEW_THRESHOLD) && redis.zrevrank(key, tag.id) <= REVIEW_THRESHOLD && !tag.trendable? && tag.requires_review? && !tag.requested_review?
-      end
-
-      redis.expire(key, EXPIRE_TRENDS_AFTER)
-    end
-
-    def request_review!(tag)
-      return unless Setting.trends
-
-      tag.touch(:requested_review_at)
-
-      User.staff.includes(:account).find_each { |u| AdminMailer.new_trending_tag(u.account, tag).deliver_later! if u.allows_trending_tag_emails? }
+    def increment_use!(tag_id, at_time)
+      key = "#{KEY}:used:#{at_time.beginning_of_day.to_i}"
+      redis.sadd(key, tag_id)
+      redis.expire(key, EXPIRE_HISTORY_AFTER)
     end
   end
 end
-- 
cgit