class AASM::InstanceBase

def current_state
  @instance.aasm_read_state(@name)
end

def current_state=: (Symbol state) -> String

def current_state=(state)
  @instance.aasm_write_state_without_persistence(state, @name)
end

def determine_state_name(state)
  case state
    when Symbol, String
      state
    when Proc
      state.call(@instance)
    else
      raise NotImplementedError, "Unrecognized state-type given. Expected Symbol, String, or Proc."
  end
end

def enter_initial_state
  state_name = determine_state_name(@instance.class.aasm(@name).initial_state)
  state_object = state_object_for_name(state_name)
  state_object.fire_callbacks(:before_enter, @instance)
  self.current_state = state_name
  state_object.fire_callbacks(:after_enter, @instance)
  state_name
end

def event_exists?(event_name, bang = false)
  event = @instance.class.aasm(@name).state_machine.events[event_name.to_sym]
  return true if event
  event_error = bang ? "#{event_name}!" : event_name
  raise AASM::UndefinedEvent, "Event :#{event_error} doesn't exist" if event.nil?
end

def events(options={}, *args)
  state = options[:state] || current_state
  events = @instance.class.aasm(@name).events.select {|e| e.transitions_from_state?(state) }
  options[:reject] = Array(options[:reject])
  events.reject! { |e| options[:reject].include?(e.name) }
  if options.has_key?(:permitted)
    # filters the results of events_for_current_state so that only those that
    # are really currently possible (given transition guards) are shown.
    if options[:permitted]
      events.select! { |e| @instance.send("may_#{e.name}?", *args) }
    else
      events.select! { |e| !@instance.send("may_#{e.name}?", *args) }
    end
  end
  events
end

def fire(event_name, *args, &block)
  event_exists?(event_name)
  @instance.send(event_name, *args, &block)
end

def fire!(event_name, *args, &block)
  event_exists?(event_name, true)
  bang_event_name = "#{event_name}!".to_sym
  @instance.send(bang_event_name, *args, &block)
end

def human_state
  state_object_for_name(current_state).display_name
end

def initialize(instance, name=:default) # instance of the class including AASM, name of the state machine
  @instance = instance
  @name = name
end

def may_fire_event?(name, *args)
  if event = @instance.class.aasm(@name).state_machine.events[name]
    !!event.may_fire?(@instance, *args)
  else
    false # unknown event
  end
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 set_current_state_with_persistence(state)
  save_success = @instance.aasm_write_state(state, @name)
  self.current_state = state if save_success
  save_success
end

def state_object_for_name: (Symbol name) -> AASM::Core::State

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?
  obj
end

def states(options={}, *args)
  if options.has_key?(:permitted)
    selected_events = events({:permitted => options[:permitted]}, *args)
    # An array of arrays. Each inner array represents the transitions that
    # transition from the current state for an event
    event_transitions = selected_events.map {|e| e.transitions_from_state(current_state) }
    # An array of :to transition states
    to_state_names = event_transitions.map do |transitions|
      return nil if transitions.empty?
      # Return the :to state of the first transition that is allowed (or not) or nil
      if options[:permitted]
        transition = transitions.find { |t| t.allowed?(@instance, *args) }
      else
        transition = transitions.find { |t| !t.allowed?(@instance, *args) }
      end
      transition ? transition.to : nil
    end.flatten.compact.uniq
    # Select states that are in to_state_names
    @instance.class.aasm(@name).states.select {|s| to_state_names.include?(s.name)}
  else
    @instance.class.aasm(@name).states
  end
end