Implement backup cache for popular tasks

Improve data availability bu having a backup cache if the latest is not
availabile

- Added a backup cache mechanism to ensure data is available even if the
latest cache is expired or unavailable.
- Popular tasks data is now stored in both a latest cache (24 hours
expiration) and a backup cache (7 days expiration).
- Fallback to backup cache when the latest cache is missing, ensuring
users always see data even if fresh data retrieval fails.
- Updated methods to handle cache fallback logic, improving robustness
and reducing the likelihood of empty data responses.

app/helpers/browse_helper.rb

@@ -10,15 +10,23 @@ def display_popular_tasks_for_slug?(slug)
   def popular_links_for_slug(slug)
     browse_page = slug(slug)
 
-    # Try to fetch the cache first
-    popular_task_data = Rails.cache.read("popular_tasks_#{browse_page}_#{Date.yesterday.strftime("%Y-%m-%d")}")
+    # Cache keys for the specific browse page
+    cache_key_latest = "popular_tasks_#{browse_page}_#{Date.yesterday.strftime("%Y-%m-%d")}"
+    cache_key_backup = "popular_tasks_backup_#{browse_page}"
 
-    # If cache is empty fetch fresh data and cache it
+    # Try to fetch the latest cache first
+    popular_task_data = Rails.cache.read(cache_key_latest)
+
+    # If the latest cache doesn't exist, fall back to the backup cache
     if popular_task_data.nil?
-      popular_task_data = PopularTasks.new.fetch_data("/browse/#{browse_page}")
+      # Falling back to backup cache
+      popular_task_data = Rails.cache.read(cache_key_backup)
     end
 
-    return [] unless popular_task_data
+    # If both caches are empty, fetch fresh data and cache it
+    if popular_task_data.nil?
+      popular_task_data = PopularTasks.new.fetch_data("/browse/#{browse_page}")
+    end
 
     popular_task_data
   end

app/services/popular_tasks.rb

@@ -1,5 +1,6 @@
 class PopularTasks
   CACHE_EXPIRATION = 24.hours # Set the cache expiration time
+  BACKUP_CACHE_EXPIRATION = 7.days # Backup cache can have a longer expiration
 
   def initialize; end
 
@@ -11,10 +12,10 @@ def fetch_data(browse_page, date: Date.yesterday)
     @fetch_data = client
     @date = date.strftime("%Y-%m-%d")
 
-    # Define cache keys for the specific browse page
-    cache_key = "popular_tasks_#{browse_page}_#{@date}"
+    cache_key_latest = "popular_tasks_#{browse_page}_#{@date}"
+    cache_key_backup = "popular_tasks_backup_#{browse_page}"
 
-    Rails.cache.fetch(cache_key, expires_in: CACHE_EXPIRATION) do
+    Rails.cache.fetch(cache_key_latest, expires_in: CACHE_EXPIRATION) do
       # If cache is empty, this block is executed
       query = <<~SQL
         WITH cte1 as (SELECT
@@ -60,6 +61,11 @@ def fetch_data(browse_page, date: Date.yesterday)
         }
       end
       @results.sort_by { |link| link[:rank] } # Order the links by their rank
+
+      # Cache the results in the backup cache as well
+      Rails.cache.write(cache_key_backup, @results, expires_in: BACKUP_CACHE_EXPIRATION)
+
+      @results
     end
   end
 end