Add support for the NX (not exists) option to flags (#51)

* Add support for the NX (not exists) option to flags

* Revert the version change

* Rename the param

* Update readme

Author: valeksenko

README.md

@@ -144,7 +144,8 @@ true == flag.marked?            # => EXISTS myflag
 flag.remove                     # => DEL myflag  
 false == flag.marked?           # => EXISTS myflag
 
-flag.mark(expires_in: 1.second) #=> SET myflag 1 EX 1
+true == flag.mark(expires_in: 1.second, force: false)    #=> SET myflag 1 EX 1 NX
+false == flag.mark(expires_in: 10.seconds, force: false) #=> SET myflag 10 EX 1 NX
 true == flag.marked?            #=> EXISTS myflag
 sleep 0.5.seconds
 true == flag.marked?            #=> EXISTS myflag

lib/kredis/types/flag.rb

@@ -3,8 +3,8 @@ class Kredis::Types::Flag < Kredis::Types::Proxying
 
   attr_accessor :expires_in
 
-  def mark(expires_in: nil)
-    set 1, ex: expires_in || self.expires_in
+  def mark(expires_in: nil, force: true)
+    set 1, ex: expires_in || self.expires_in, nx: !force
   end
 
   def marked?

test/attributes_test.rb

@@ -244,4 +244,15 @@ def suddenly_implemented_person.id; 8; end
       sleep 1.1.seconds
     end
   end
+
+  test "expiring flag with force" do
+    assert @person.temporary_special.mark
+
+    sleep 0.5.seconds
+    assert_not @person.temporary_special.mark(force: false)
+
+    assert_changes "@person.temporary_special.marked?", from: true, to: false do
+      sleep 0.6.seconds
+    end
+  end
 end

test/types/flag_test.rb

@@ -23,4 +23,19 @@ class FlagTest < ActiveSupport::TestCase
     sleep 0.6.seconds
     assert_not @flag.marked?
   end
+
+  test "mark with force" do
+    assert @flag.mark(expires_in: 1.second, force: false)
+    assert @flag.mark(expires_in: 1.second)
+    assert @flag.mark(expires_in: 1.second, force: true)
+    assert_not @flag.mark(expires_in: 10.seconds, force: false)
+
+    assert @flag.marked?
+
+    sleep 0.5.seconds
+    assert @flag.marked?
+
+    sleep 0.6.seconds
+    assert_not @flag.marked?
+  end
 end