refactor: clean up city model and adjust worker timing

- Implement caching methods for last weather fetch and image generation
- Adjust sleep duration in BatchGenerateWeatherArtsWorker from 10 seconds to 3 seconds
- Remove unused fields `last_weather_fetch` and `last_image_generation` from the cities table
- Add index on the weather_arts table for optimized querying

This refactor improves data retrieval performance for weather data
associated with cities. Caching reduces database load while the
worker modification allows for faster iterations in generating
weather arts without significantly impacting performance.

app/models/city.rb

@@ -48,6 +48,20 @@ class City < ApplicationRecord
     [ "active", "country", "created_at", "id", "id_value", "last_image_generation", "last_weather_fetch", "latitude", "longitude", "name", "priority", "region", "slug", "timezone", "updated_at" ]
   end
 
+  def last_weather_fetch
+    # latest_weather_art&.created_at
+    Rails.cache.fetch("city/#{id}/last_weather_fetch", expires_in: 1.hour) do
+      latest_weather_art&.created_at
+    end
+  end
+
+  def last_image_generation
+    # latest_weather_art&.image&.created_at
+    Rails.cache.fetch("city/#{id}/last_image_generation", expires_in: 1.hour) do
+      latest_weather_art&.image&.created_at
+    end
+  end
+
   def latest_weather_art
     weather_arts.order(weather_date: :desc).first
   end

app/workers/batch_generate_weather_arts_worker.rb

@@ -12,7 +12,7 @@ class BatchGenerateWeatherArtsWorker
 
       # GenerateWeatherArtJob.perform_now(city)
       GenerateWeatherArtWorker.perform_async(city.id)
-      sleep 10.seconds
+      sleep 3.seconds
     end
   end
 
@@ -25,10 +25,4 @@ class BatchGenerateWeatherArtsWorker
     # .select { |city| early_morning_in_timezone?(city.timezone) }
   end
 
-  # def early_morning_in_timezone?(timezone)
-  #   return false if timezone.blank?
-
-  #   time = Time.current.in_time_zone(timezone)
-  #   time.hour == 2
-  # end
 end

db/migrate/20250123155234_remove_last_fetch_fields_from_cities.rb

@@ -0,0 +1,8 @@
+class RemoveLastFetchFieldsFromCities < ActiveRecord::Migration[8.0]
+  def change
+    remove_column :cities, :last_weather_fetch
+    remove_column :cities, :last_image_generation
+
+    add_index :weather_arts, [:city_id, :weather_date]
+  end
+end

db/schema.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema[8.0].define(version: 2025_01_22_053220) do
+ActiveRecord::Schema[8.0].define(version: 2025_01_23_155234) do
   create_table "active_admin_comments", force: :cascade do |t|
     t.string "namespace"
     t.text "body"
@@ -72,8 +72,6 @@ ActiveRecord::Schema[8.0].define(version: 2025_01_22_053220) do
     t.boolean "active"
     t.integer "priority"
     t.string "timezone"
-    t.datetime "last_weather_fetch"
-    t.datetime "last_image_generation"
     t.datetime "created_at", null: false
     t.datetime "updated_at", null: false
     t.string "slug"
@@ -132,6 +130,7 @@ ActiveRecord::Schema[8.0].define(version: 2025_01_22_053220) do
     t.datetime "created_at", null: false
     t.datetime "updated_at", null: false
     t.string "slug"
+    t.index ["city_id", "weather_date"], name: "index_weather_arts_on_city_id_and_weather_date"
     t.index ["city_id"], name: "index_weather_arts_on_city_id"
     t.index ["slug"], name: "index_weather_arts_on_slug", unique: true
   end