feat: add least popular active cities panel

- Introduce new panel in the admin dashboard for displaying
  the least popular active cities.
- Implement a database scope `least_popular_active` to
  retrieve cities based on their view counts.
- Ensure compatibility with both SQLite and PostgreSQL
  for fetching city view data.

This addition enhances the admin dashboard by allowing
administrators to easily identify and manage cities that
are receiving less user interaction, thus aiding in strategic
planning for engagement and promotion.

app/admin/dashboard.rb

@@ -37,6 +37,16 @@ ActiveAdmin.register_page "Dashboard" do
           end
         end
       end
+
+      column do
+        panel "冷门活跃城市" do
+          table_for City.least_popular_active.limit(10) do
+            column("城市") { |city| link_to(city.name, admin_city_path(city)) }
+            column("访问量") { |city| city.view_count }
+            # column("状态") { |city| status_tag(city.active? ? "活跃" : "停用") }
+          end
+        end
+      end
     end
 
     # 添加一个事件列表面板

app/models/city.rb

@@ -37,6 +37,24 @@ class City < ApplicationRecord
     end
   }
 
+  scope :least_popular_active, -> {
+    if ActiveRecord::Base.connection.adapter_name.downcase == 'sqlite'
+      active
+        .joins("LEFT JOIN ahoy_events ON json_extract(ahoy_events.properties, '$.city_id') = cities.id
+               AND json_extract(ahoy_events.properties, '$.event_type') = 'city_view'")
+        .group("cities.id")
+        .select("cities.*, COUNT(ahoy_events.id) as visit_count")
+        .order("visit_count ASC, cities.name ASC")
+    else
+      active
+        .joins("LEFT JOIN ahoy_events ON (ahoy_events.properties->>'city_id')::integer = cities.id
+               AND ahoy_events.properties->>'event_type' = 'city_view'")
+        .group("cities.id")
+        .select("cities.*, COUNT(ahoy_events.id) as visit_count")
+        .order("visit_count ASC, cities.name ASC")
+    end
+  }
+
   def to_s
     name
   end