Add ActorLimit adapter

lib/flipper/adapters/actor_limit.rb

@@ -0,0 +1,26 @@
+module Flipper
+  module Adapters
+    class ActorLimit < Wrapper
+      LimitExceeded = Class.new(Flipper::Error)
+
+      def initialize(adapter, limit = 100)
+        super(adapter)
+        @limit = limit
+      end
+
+      def enable(feature, gate, resource)
+        if gate.is_a?(Flipper::Gates::Actor) && over_limit?(feature)
+          raise LimitExceeded, "Actor limit of #{@limit} exceeded for feature #{feature.key}"
+        else
+          super
+        end
+      end
+
+      private
+
+      def over_limit?(feature)
+        feature.actors_value.size >= @limit
+      end
+    end
+  end
+end

spec/flipper/adapters/actor_limit_spec.rb

@@ -0,0 +1,20 @@
+require "flipper/adapters/actor_limit"
+
+RSpec.describe Flipper::Adapters::ActorLimit do
+  it_should_behave_like 'a flipper adapter' do
+    let(:limit) { 5 }
+    let(:adapter) { Flipper::Adapters::ActorLimit.new(Flipper::Adapters::Memory.new, limit) }
+
+    subject { adapter }
+
+    describe '#enable' do
+      it "fails when limit exceeded" do
+        5.times { |i| feature.enable Flipper::Actor.new("User;#{i}") }
+
+        expect {
+          feature.enable Flipper::Actor.new("User;6")
+        }.to raise_error(Flipper::Adapters::ActorLimit::LimitExceeded)
+      end
+    end
+  end
+end

test/adapters/actor_limit_test.rb

@@ -0,0 +1,20 @@
+require "test_helper"
+require "flipper/test/shared_adapter_test"
+require "flipper/adapters/actor_limit"
+
+class Flipper::Adapters::ActorLimitTest < MiniTest::Test
+  prepend Flipper::Test::SharedAdapterTests
+
+  def setup
+    @memory = Flipper::Adapters::Memory.new
+    @adapter = Flipper::Adapters::ActorLimit.new(@memory, 5)
+  end
+
+  def test_enable_fails_when_limit_exceeded
+    5.times { |i| @feature.enable Flipper::Actor.new("User;#{i}") }
+
+    assert_raises Flipper::Adapters::ActorLimit::LimitExceeded do
+      @feature.enable Flipper::Actor.new("User;6")
+    end
+  end
+end