Add .define call for creating FiniteMachine templates

lib/finite_machine.rb

@@ -63,6 +63,20 @@ class << self
     def new(*args, **options, &block)
       StateMachine.new(*args, **options, &block)
     end
+
+    # A factory method for creating reusable FiniteMachine definitions
+    #
+    # @example
+    #   TrafficLights = FiniteMachine.define
+    #   lights_fm_a = TrafficLights.new
+    #   lights_fm_b = TrafficLights.new
+    #
+    # @return [Class]
+    #
+    # @api public
+    def define(&block)
+      Class.new(Definition, &block)
+    end
   end
 end # FiniteMachine
 

spec/unit/define_spec.rb

@@ -0,0 +1,55 @@
+# frozen_string_literal: true
+
+RSpec.describe FiniteMachine, '.define' do
+  context 'with block' do
+    it "creates system state machine" do
+      stub_const("TrafficLights", FiniteMachine.define do
+        initial :green
+
+        event :slow,  :green  => :yellow
+        event :stop,  :yellow => :red
+        event :ready, :red    => :yellow
+        event :go,    :yellow => :green
+      end)
+
+      lights_fsm_a = TrafficLights.new
+      lights_fsm_b = TrafficLights.new
+
+      expect(lights_fsm_a.current).to eql(:green)
+      expect(lights_fsm_b.current).to eql(:green)
+
+      lights_fsm_a.slow
+      expect(lights_fsm_a.current).to eql(:yellow)
+      expect(lights_fsm_b.current).to eql(:green)
+
+      lights_fsm_a.stop
+      expect(lights_fsm_a.current).to eql(:red)
+      expect(lights_fsm_b.current).to eql(:green)
+    end
+  end
+
+  context 'without block' do
+    it "creates state machine" do
+      called = []
+      stub_const("TrafficLights", FiniteMachine.define)
+      TrafficLights.initial(:green)
+      TrafficLights.event(:slow, :green => :yellow)
+      TrafficLights.event(:stop, :yellow => :red)
+      TrafficLights.event(:ready,:red    => :yellow)
+      TrafficLights.event(:go,   :yellow => :green)
+      TrafficLights.on_enter(:yellow) { |event| called << 'on_enter_yellow' }
+      TrafficLights.handle(FiniteMachine::InvalidStateError) { |exception|
+        called << 'error_handler'
+      }
+
+      fsm = TrafficLights.new
+
+      expect(fsm.current).to eql(:green)
+      fsm.slow
+      expect(fsm.current).to eql(:yellow)
+      fsm.ready
+      expect(fsm.current).to eql(:yellow)
+      expect(called).to match_array(['on_enter_yellow', 'error_handler'])
+    end
+  end
+end