feat: add MySQL chart compatibility (#30)

* feat: add Mysql chart compatibility

* fix: Rubocop issues

Author: phmunhoz

app/services/solid_queue_monitor/chart_data_service.rb

@@ -81,16 +81,19 @@ def fill_buckets(buckets, index_counts)
     # Cross-DB bucket index expression.
     # PostgreSQL: CAST((EXTRACT(EPOCH FROM col) - start) / interval AS INTEGER)
     # SQLite:     CAST((CAST(strftime('%s', col) AS INTEGER) - start) / interval AS INTEGER)
+    # MySQL:      CAST((UNIX_TIMESTAMP(col) - start) / interval AS SIGNED)
     def bucket_index_expr(column, start_epoch, interval_seconds)
-      if sqlite?
+      if adapter?('sqlite')
         "CAST((CAST(strftime('%s', #{column}) AS INTEGER) - #{start_epoch}) / #{interval_seconds} AS INTEGER)"
+      elsif adapter?('mysql')
+        "CAST((UNIX_TIMESTAMP(#{column}) - #{start_epoch}) / #{interval_seconds} AS SIGNED)"
       else
         "CAST((EXTRACT(EPOCH FROM #{column}) - #{start_epoch}) / #{interval_seconds} AS INTEGER)"
       end
     end
 
-    def sqlite?
-      ActiveRecord::Base.connection.adapter_name.downcase.include?('sqlite')
+    def adapter?(name)
+      ActiveRecord::Base.connection.adapter_name.downcase.include?(name)
     end
   end
 end