Feature: Add permitted_transitions to group permitted event with state (#664)

* Feature: Add permitted_transitions to group permitted event with state

resolves #656

README.md

@@ -1141,6 +1141,10 @@ job = Job.new
 job.aasm.states(permitted: true).map(&:name)
 #=> [:running]
 
+# List all the permitted transitions(event and state pairs) from initial state
+job.aasm.permitted_transitions
+#=> [{ :event => :run, :state => :running }]
+
 job.run
 job.aasm.states(permitted: true).map(&:name)
 #=> [:sleeping]

lib/aasm/instance_base.rb

@@ -78,6 +78,17 @@ module AASM
       events
     end
 
+    def permitted_transitions
+      events(permitted: true).flat_map do |event|
+        available_transitions = event.transitions_from_state(current_state)
+        allowed_transitions = available_transitions.select { |t| t.allowed?(@instance) }
+
+        allowed_transitions.map do |transition|
+          { event: event.name, state: transition.to }
+        end
+      end
+    end
+
     def state_object_for_name(name)
       obj = @instance.class.aasm(@name).states.find {|s| s.name == name}
       raise AASM::UndefinedState, "State :#{name} doesn't exist" if obj.nil?

spec/models/simple_example.rb

@@ -3,11 +3,17 @@ class SimpleExample
   aasm do
     state :initialised, :initial => true
     state :filled_out
+    state :denied
     state :authorised
 
     event :fill_out do
       transitions :from => :initialised, :to => :filled_out
     end
+
+    event :deny do
+      transitions from: :initialised, to: :denied
+    end
+
     event :authorise do
       transitions :from => :filled_out, :to => :authorised
     end

spec/unit/simple_example_spec.rb

@@ -23,6 +23,21 @@ describe 'state machine' do
     expect(simple).to be_authorised
   end
 
+  it 'shows the permitted transitions' do
+    expect(simple.aasm.permitted_transitions).to eq(
+      [
+        { event: :fill_out, state: :filled_out },
+        { event: :deny, state: :denied }
+      ]
+    )
+
+    simple.fill_out!
+    expect(simple.aasm.permitted_transitions).to eq([{ event: :authorise, state: :authorised }])
+
+    simple.authorise
+    expect(simple.aasm.permitted_transitions).to eq([])
+  end
+
   it 'denies transitions to other states' do
     expect {simple.authorise}.to raise_error(AASM::InvalidTransition)
     expect {simple.authorise!}.to raise_error(AASM::InvalidTransition)