approver pruner: change inactivity threshold to 30 approvals in 45 days.

* Change minimum activity threshold to 30 approvals in 45 days.
* Exclude mods from losing privileges, not just admins.
* Fix undeletions of old posts not counting towards the activity threshold.

app/logical/approver_pruner.rb

@@ -1,25 +1,25 @@
 module ApproverPruner
   module_function
 
+  APPROVAL_PERIOD = 45.days
+  MINIMUM_APPROVALS = 30
+
   def inactive_approvers
-    User.where("bit_prefs & ? > 0", User.flag_value_for("can_approve_posts")).select do |user|
-      approval_count = Post.where("created_at >= ? and approver_id = ?", 3.months.ago, user.id).count
-      approval_count < 10
-    end
+    approvals = PostApproval.where("created_at >= ?", APPROVAL_PERIOD.ago)
+    approvers = User.where("bit_prefs & ? > 0", User.flag_value_for("can_approve_posts")).where("level < ?", User::Levels::MODERATOR)
+    approvers.where(id: approvals.group(:user_id).having("count(*) < ?", MINIMUM_APPROVALS).select(:user_id))
   end
 
   def prune!
     inactive_approvers.each do |user|
       CurrentUser.scoped(User.system, "127.0.0.1") do
-        next if user.is_admin?
-
         user.update!(can_approve_posts: false)
         user.feedback.create(category: "neutral", body: "Lost approval privileges")
 
         Dmail.create_automated(
-          :to_id => user.id,
-          :title => "Approver inactivity",
-          :body => "You've approved fewer than 10 posts in the past three months. In order to make sure the list of active approvers is up-to-date, you have lost your approval privileges. If you wish to dispute this, you can message an admin to have your permission reinstated."
+          to_id: user.id,
+          title: "Approver inactivity",
+          body: "You've approved fewer than #{MINIMUM_APPROVALS} posts in the past #{APPROVAL_PERIOD.inspect}. In order to make sure the list of active approvers is up-to-date, you have lost your approval privileges. If you wish to dispute this, you can message an admin to have your permission reinstated."
         )
       end
     end