Move db check to the Fizzy module

lib/fizzy.rb

@@ -1,6 +1,27 @@
 module Fizzy
-  def self.saas?
-    return @saas if defined?(@saas)
-    @saas = !!(ENV["SAAS"] || File.exist?(File.expand_path("../../tmp/saas.txt", __dir__)))
+  class << self
+    def saas?
+      return @saas if defined?(@saas)
+      @saas = !!(ENV["SAAS"] || File.exist?(File.expand_path("../../tmp/saas.txt", __dir__)))
+    end
+
+    def db_adapter
+      @db_adapter ||= DbAdapter.new ENV.fetch("DATABASE_ADAPTER", saas? ? "mysql" : "sqlite")
+    end
+  end
+
+  class DbAdapter
+    def initialize(name)
+      @name = name.to_s
+    end
+
+    def to_s
+      @name
+    end
+
+    # Not using inquiry so that it works before Rails env loads.
+    def sqlite?
+      @name == "sqlite"
+    end
   end
 end