class MicroFSM

# File lib/microfsm.rb, line 10
def initialize(initial_state)
  @state = initial_state
  @transitions_for = {}
  @callbacks_for = {}
end

# File lib/microfsm.rb, line 46
def events
  @transitions_for.keys.sort
end

# File lib/microfsm.rb, line 54
def states
  @transitions_for.values.map(&:to_a).flatten.uniq.sort
end

# File lib/microfsm.rb, line 31
def trigger(event)
  trigger?(event) and transit(event)
end

# File lib/microfsm.rb, line 35
def trigger!(event)
  trigger(event) or
    raise InvalidState.new(msg(event))
end

# File lib/microfsm.rb, line 40
def trigger?(event)
  raise InvalidEvent.new(msg(event)) unless @transitions_for.has_key?(event)

  @transitions_for[event].has_key?(state)
end

# File lib/microfsm.rb, line 50
def triggerable_events
  events.select { |event| trigger?(event) }.sort
end

# File lib/microfsm.rb, line 16
def when(event, transitions, &block)
  @transitions_for[event] ||= {}
  @callbacks_for[event] ||= {}

  transitions.each do |from, to|
    nto = @transitions_for[event][from]
    raise InvalidTransition if nto && nto != to

    @transitions_for[event][from] = to
    @callbacks_for[event][from] ||= []
    @callbacks_for[event][from] << block if block
  end
  self
end

# File lib/microfsm.rb, line 66
def msg(event)
  "State: #{@state}; Event: #{event}"
end

# File lib/microfsm.rb, line 59
def transit(event)
  callbacks = @callbacks_for[event][@state]
  @state = @transitions_for[event][@state]
  callbacks.each { |callback| callback.call(event) }
  true
end