FEATURE: Track how many user flags are agreed/disagreed/ignored

Display the percentage when reviewing flags.

db/migrate/20181031165343_add_flag_stats_to_user.rb

@@ -0,0 +1,34 @@
+class AddFlagStatsToUser < ActiveRecord::Migration[5.2]
+  def up
+    add_column :user_stats, :flags_agreed, :integer, default: 0, null: false
+    add_column :user_stats, :flags_disagreed, :integer, default: 0, null: false
+    add_column :user_stats, :flags_ignored, :integer, default: 0, null: false
+
+    sql = <<~SQL
+      UPDATE user_stats
+      SET flags_agreed = x.flags_agreed,
+        flags_disagreed = x.flags_disagreed,
+        flags_ignored = x.flags_ignored
+      FROM (
+        SELECT u.id AS user_id,
+          SUM(CASE WHEN pa.disagreed_at IS NOT NULL THEN 1 ELSE 0 END) as flags_disagreed,
+          SUM(CASE WHEN pa.agreed_at IS NOT NULL THEN 1 ELSE 0 END) as flags_agreed,
+          SUM(CASE WHEN pa.deferred_at IS NOT NULL THEN 1 ELSE 0 END) as flags_ignored
+        FROM post_actions AS pa
+        INNER JOIN users AS u ON u.id = pa.user_id
+        WHERE pa.post_action_type_id IN (#{PostActionType.notify_flag_types.values.join(', ')})
+        AND pa.user_id > 0
+        GROUP BY u.id
+      ) AS x
+      WHERE x.user_id = user_stats.user_id
+    SQL
+
+    execute sql
+  end
+
+  def down
+    remove_column :user_stats, :flags_agreed
+    remove_column :user_stats, :flags_disagreed
+    remove_column :user_stats, :flags_ignored
+  end
+end