Implemented chained_flags_with, which allows optimizing the bit search

When you chain multiple named scope generated by FlagShihTzu,
generated ActiveRecord query would look like this.

  Spaceship.warpdrive.shields.not_electrolytes
  # => (spaceships.flags in (1,3,5,7)) AND (spaceships.flags in (2,3,6,7)) AND (spaceships.flags not in (4,5,6,7))

With the chained_flags_with introduced with this patch, you can write
the same query in an optimized search.

  Spaceship.chained_flags_with("flags", :warpdrive, :shields, :not_electrolytes)
  # => (spaceships.flags in (3))

You can also name it with the named scope:

  scope :listed, chained_flags_with("flags", :warpdrive, :shields, :not_electrolytes)

lib/flag_shih_tzu.rb

@@ -93,8 +93,35 @@ def check_flag(flag, colmn)
       raise ArgumentError, "Invalid flag '#{flag}'" if flag_mapping[colmn].nil? || !flag_mapping[colmn].include?(flag)
     end
 
+    def chained_flags_with(*args)
+      where(chained_flags_condition(*args))
+    end
+
+    def chained_flags_condition(colmn, *args)
+      "(#{self.table_name}.#{colmn} in (#{chained_flags_values(colmn, *args).join(',')}))"
+    end
+
     private
 
+      def chained_flags_values(colmn, *args)
+        val = (1..(2 ** flag_mapping[flag_options[colmn][:column]].length)).to_a
+        args.each do |flag|
+          neg = false
+          if flag.match /^not_/
+            neg = true
+            flag = flag.to_s.sub(/^not_/, '').to_sym
+          end
+          check_flag(flag, colmn)
+          flag_values = sql_in_for_flag(flag, colmn)
+          if neg
+            val = val - flag_values
+          else
+            val = val & flag_values
+          end
+        end
+        val
+      end
+
       def parse_options(*args)
         options = args.shift
         if args.size >= 1

test/flag_shih_tzu_test.rb

@@ -241,6 +241,33 @@ def test_should_return_the_correct_number_of_items_from_a_named_scope
     assert_equal 0, Spaceship.not_warpdrive.not_shields.count
   end
 
+  def test_should_return_the_correct_condition_with_chained_flags
+    assert_equal "(spaceships.flags in (3,7))", Spaceship.chained_flags_condition("flags", :warpdrive, :shields)
+    assert_equal "(spaceships.flags in (7))", Spaceship.chained_flags_condition("flags", :warpdrive, :shields, :electrolytes)
+    assert_equal "(spaceships.flags in (2,6))", Spaceship.chained_flags_condition("flags", :not_warpdrive, :shields)
+  end
+
+  def test_should_return_the_correct_number_of_items_with_chained_flags_with
+    spaceship = Spaceship.new
+    spaceship.enable_flag(:warpdrive)
+    spaceship.enable_flag(:shields)
+    spaceship.save!
+    spaceship.reload
+    spaceship_2 = Spaceship.new
+    spaceship_2.enable_flag(:warpdrive)
+    spaceship_2.save!
+    spaceship_2.reload
+    spaceship_3 = Spaceship.new
+    spaceship_3.enable_flag(:shields)
+    spaceship_3.save!
+    spaceship_3.reload
+    assert_equal 2, Spaceship.chained_flags_with("flags", :warpdrive).count
+    assert_equal 1, Spaceship.chained_flags_with("flags", :warpdrive, :shields).count
+    assert_equal 1, Spaceship.chained_flags_with("flags", :warpdrive, :not_shields).count
+    assert_equal 0, Spaceship.chained_flags_with("flags", :not_warpdrive, :shields, :electrolytes).count
+    assert_equal 1, Spaceship.chained_flags_with("flags", :not_warpdrive, :shields, :not_electrolytes).count
+  end
+
   def test_should_not_define_named_scopes_if_not_wanted
     assert !SpaceshipWithoutNamedScopes.respond_to?(:warpdrive)
     assert !SpaceshipWithoutNamedScopesOldStyle.respond_to?(:warpdrive)