FEATURE: adjust autobump system

- We spread out bumping through the day, if you are bumping
 4 topics then a topic will be bumped every 6 hours

- We add a small, bumping action at the bottom of the post to
 denote a topic got bumped

app/models/category.rb

@@ -378,16 +378,20 @@ class Category < ActiveRecord::Base
   end
 
   def auto_bump_limiter
-    RateLimiter.new(nil, "auto_bump_limit_#{self.id}", num_auto_bump_daily.to_i, 86400)
+    return nil if num_auto_bump_daily.to_i == 0
+    RateLimiter.new(nil, "auto_bump_limit_#{self.id}", 1, 86400 / num_auto_bump_daily.to_i)
   end
 
   def clear_auto_bump_cache!
-    auto_bump_limiter.clear!
+    auto_bump_limiter&.clear!
   end
 
   def self.auto_bump_topic!
     bumped = false
-    auto_bumps = CategoryCustomField.where(name: Category::NUM_AUTO_BUMP_DAILY).pluck(:category_id)
+    auto_bumps = CategoryCustomField
+      .where(name: Category::NUM_AUTO_BUMP_DAILY)
+      .where('value::int > 0')
+      .pluck(:category_id)
 
     if (auto_bumps.length > 0)
       auto_bumps.shuffle.each do |category_id|
@@ -406,7 +410,7 @@ class Category < ActiveRecord::Base
     limiter = auto_bump_limiter
     return false if !limiter.can_perform?
 
-    id = Topic
+    topic = Topic
       .visible
       .listable_topics
       .where(category_id: self.id)
@@ -415,10 +419,10 @@ class Category < ActiveRecord::Base
       .where('pinned_at IS NULL AND NOT closed AND NOT archived')
       .order('bumped_at ASC')
       .limit(1)
-      .pluck(:id).first
+      .first
 
-    if id
-      Topic.where(id: id).update_all(bumped_at: Time.zone.now)
+    if topic
+      topic.add_small_action(Discourse.system_user, "autobumped", nil, bump: true)
       limiter.performed!
       true
     else

app/models/topic.rb

@@ -698,10 +698,16 @@ class Topic < ActiveRecord::Base
     true
   end
 
-  def add_small_action(user, action_code, who = nil)
+  def add_small_action(user, action_code, who = nil, opts = {})
     custom_fields = {}
     custom_fields["action_code_who"] = who if who.present?
-    add_moderator_post(user, nil, post_type: Post.types[:small_action], action_code: action_code, custom_fields: custom_fields)
+    opts = opts.merge(
+      post_type: Post.types[:small_action],
+      action_code: action_code,
+      custom_fields: custom_fields
+    )
+
+    add_moderator_post(user, nil, opts)
   end
 
   def add_moderator_post(user, text, opts = nil)

config/locales/client.en.yml

@@ -152,6 +152,7 @@ en:
       user_left: "%{who} removed themselves from this message %{when}"
       removed_user: "removed %{who} %{when}"
       removed_group: "removed %{who} %{when}"
+      autobumped: "automatically bumped topic"
       autoclosed:
         enabled: 'closed %{when}'
         disabled: 'opened %{when}'

spec/models/category_spec.rb

@@ -695,8 +695,11 @@ describe Category do
       category = Fabricate(:category)
       category.clear_auto_bump_cache!
 
-      _post1 = create_post(category: category)
+      freeze_time 1.second.from_now
+      post1 = create_post(category: category)
+      freeze_time 1.second.from_now
       _post2 = create_post(category: category)
+      freeze_time 1.second.from_now
       _post3 = create_post(category: category)
 
       # no limits on post creation or category creation please
@@ -713,12 +716,17 @@ describe Category do
 
       expect(category.auto_bump_topic!).to eq(true)
       expect(Topic.where(bumped_at: time).count).to eq(1)
+      # our extra bump message
+      expect(post1.topic.reload.posts_count).to eq(2)
+
+      time = time + 13.hours
+      freeze_time time
 
       expect(category.auto_bump_topic!).to eq(true)
-      expect(Topic.where(bumped_at: time).count).to eq(2)
+      expect(Topic.where(bumped_at: time).count).to eq(1)
 
       expect(category.auto_bump_topic!).to eq(false)
-      expect(Topic.where(bumped_at: time).count).to eq(2)
+      expect(Topic.where(bumped_at: time).count).to eq(1)
 
       time = 1.month.from_now
       freeze_time time