require 'state_machine/machine' # A state machine is a model of behavior composed of states, events, and # transitions. This helper adds support for defining this type of # functionality on any Ruby class. module StateMachine module MacroMethods # Creates a new state machine with the given name. The default name, if not # specified, is :state. # # Configuration options: # * :attribute - The name of the attribute to store the state value # in. By default, this is the same as the name of the machine. # * :initial - The initial state of the attribute. This can be a # static state or a lambda block which will be evaluated at runtime # (e.g. lambda {|vehicle| vehicle.speed == 0 ? :parked : :idling}). # Default is nil. # * :action - The instance method to invoke when an object # transitions. Default is nil unless otherwise specified by the # configured integration. # * :namespace - The name to use for namespacing all generated # state / event instance methods (e.g. "heater" would generate # :turn_on_heater and :turn_off_heater for the :turn_on/:turn_off events). # Default is nil. # * :integration - The name of the integration to use for adding # library-specific behavior to the machine. Built-in integrations # include :data_mapper, :active_record, and :sequel. By default, this # is determined automatically. # # Configuration options relevant to ORM integrations: # * :plural - The pluralized name of the attribute. By default, # this will attempt to call +pluralize+ on the attribute. If this # method is not available, an "s" is appended. This is used for # generating scopes. # * :messages - The error messages to use when invalidating # objects due to failed transitions. Messages include: # * :invalid # * :invalid_event # * :invalid_transition # * :use_transactions - Whether transactions should be used when # firing events. Default is true unless otherwise specified by the # configured integration. # # This also expects a block which will be used to actually configure the # states, events and transitions for the state machine. *Note* that this # block will be executed within the context of the state machine. As a # result, you will not be able to access any class methods unless you refer # to them directly (i.e. specifying the class name). # # For examples on the types of configured state machines and blocks, see # the section below. # # == Examples # # With the default name/attribute and no configuration: # # class Vehicle # state_machine do # event :park do # ... # end # end # end # # The above example will define a state machine named "state" that will # store the value in the +state+ attribute. Every vehicle will start # without an initial state. # # With a custom name / attribute: # # class Vehicle # state_machine :status, :attribute => :status_value do # ... # end # end # # With a static initial state: # # class Vehicle # state_machine :status, :initial => :parked do # ... # end # end # # With a dynamic initial state: # # class Vehicle # state_machine :status, :initial => lambda {|vehicle| vehicle.speed == 0 ? :parked : :idling} do # ... # end # end # # == Instance Methods # # The following instance methods will be automatically generated by the # state machine based on the *name* of the machine. Any existing methods # will not be overwritten. # * state - Gets the current value for the attribute # * state=(value) - Sets the current value for the attribute # * state?(name) - Checks the given state name against the current # state. If the name is not a known state, then an ArgumentError is raised. # * state_name - Gets the name of the state for the current value # * state_events - Gets the list of events that can be fired on # the current object's state (uses the *unqualified* event names) # * state_transitions - Gets the list of possible transitions # that can be made on the current object's state # # For example, # # class Vehicle # state_machine :state, :initial => :parked do # event :ignite do # transition :parked => :idling # end # # event :park do # transition :idling => :parked # end # end # end # # vehicle = Vehicle.new # vehicle.state # => "parked" # vehicle.state_name # => :parked # vehicle.state?(:parked) # => true # # # Changing state # vehicle.state = 'idling' # vehicle.state # => "idling" # vehicle.state_name # => :idling # vehicle.state?(:parked) # => false # # # Getting current event / transition availability # vehicle.state_events # => [:park] # vehicle.park # => true # vehicle.state_events # => [:ignite] # # vehicle.state_transitions # => [#] # vehicle.ignite # vehicle.state_transitions # => [#] # # == Attribute initialization # # For most classes, the initial values for state machine attributes are # automatically assigned when a new object is created. However, this # behavior will *not* work if the class defines an +initialize+ method # without properly calling +super+. # # For example, # # class Vehicle # state_machine :state, :initial => :parked do # ... # end # end # # vehicle = Vehicle.new # => # # vehicle.state # => "parked" # # In the above example, no +initialize+ method is defined. As a result, # the default behavior of initializing the state machine attributes is used. # # In the following example, a custom +initialize+ method is defined: # # class Vehicle # state_machine :state, :initial => :parked do # ... # end # # def initialize # end # end # # vehicle = Vehicle.new # => # # vehicle.state # => nil # # Since the +initialize+ method is defined, the state machine attributes # never get initialized. In order to ensure that all initialization hooks # are called, the custom method *must* call +super+ without any arguments # like so: # # class Vehicle # state_machine :state, :initial => :parked do # ... # end # # def initialize(attributes = {}) # ... # super() # end # end # # vehicle = Vehicle.new # => # # vehicle.state # => "parked" # # Because of the way the inclusion of modules works in Ruby, calling # super() will not only call the superclass's +initialize+, but # also +initialize+ on all included modules. This allows the original state # machine hook to get called properly. # # If you want to avoid calling the superclass's constructor, but still want # to initialize the state machine attributes: # # class Vehicle # state_machine :state, :initial => :parked do # ... # end # # def initialize(attributes = {}) # ... # initialize_state_machines # end # end # # vehicle = Vehicle.new # => # # vehicle.state # => "parked" # # == States # # All of the valid states for the machine are automatically tracked based # on the events, transitions, and callbacks defined for the machine. If # there are additional states that are never referenced, these should be # explicitly added using the StateMachine::Machine#state or # StateMachine::Machine#other_states helpers. # # When a new state is defined, a predicate method for that state is # generated on the class. For example, # # class Vehicle # state_machine :initial => :parked do # event :ignite do # transition all => :idling # end # end # end # # ...will generate the following instance methods (assuming they're not # already defined in the class): # * parked? # * idling? # # Each predicate method will return true if it matches the object's # current state. Otherwise, it will return false. # # == Events and Transitions # # Events defined on the machine are the interface to transitioning states # for an object. Events can be fired either directly (through the method # generated for the event) or indirectly (through attributes defined on # the machine). # # For example, # # class Vehicle # include DataMapper::Resource # property :id, Integer, :serial => true # # state_machine :initial => :parked do # event :ignite do # transition :parked => :idling # end # end # # state_machine :alarm_state, :initial => :active do # event :disable do # transition all => :off # end # end # end # # # Fire +ignite+ event directly # vehicle = Vehicle.create # => # # vehicle.ignite # => true # vehicle.state # => "idling" # vehicle.alarm_state # => "active" # # # Fire +disable+ event automatically # vehicle.alarm_state_event = 'disable' # vehicle.save # => true # vehicle.alarm_state # => "off" # # In the above example, the +state+ attribute is transitioned using the # +ignite+ action that's generated from the state machine. On the other # hand, the +alarm_state+ attribute is transitioned using the +alarm_state_event+ # attribute that automatically gets fired when the machine's action (+save+) # is invoked. # # For more information about how to configure an event and its associated # transitions, see StateMachine::Machine#event. # # == Defining callbacks # # Within the +state_machine+ block, you can also define callbacks for # transitions. For more information about defining these callbacks, # see StateMachine::Machine#before_transition and # StateMachine::Machine#after_transition. # # == Namespaces # # When a namespace is configured for a state machine, the name provided # will be used in generating the instance methods for interacting with # states/events in the machine. This is particularly useful when a class # has multiple state machines and it would be difficult to differentiate # between the various states / events. # # For example, # # class Vehicle # state_machine :heater_state, :initial => :off, :namespace => 'heater' do # event :turn_on do # transition all => :on # end # # event :turn_off do # transition all => :off # end # end # # state_machine :alarm_state, :initial => :active, :namespace => 'alarm' do # event :turn_on do # transition all => :active # end # # event :turn_off do # transition all => :off # end # end # end # # The above class defines two state machines: +heater_state+ and +alarm_state+. # For the +heater_state+ machine, the following methods are generated since # it's namespaced by "heater": # * can_turn_on_heater? # * turn_on_heater # * ... # * can_turn_off_heater? # * turn_off_heater # * .. # * heater_off? # * heater_on? # # As shown, each method is unique to the state machine so that the states # and events don't conflict. The same goes for the +alarm_state+ machine: # * can_turn_on_alarm? # * turn_on_alarm # * ... # * can_turn_off_alarm? # * turn_off_alarm # * .. # * alarm_active? # * alarm_off? # # == Scopes # # For integrations that support it, a group of default scope filters will # be automatically created for assisting in finding objects that have the # attribute set to the value for a given set of states. # # For example, # # Vehicle.with_state(:parked) # => All vehicles where the state is parked # Vehicle.with_states(:parked, :idling) # => All vehicles where the state is either parked or idling # # Vehicle.without_state(:parked) # => All vehicles where the state is *not* parked # Vehicle.without_states(:parked, :idling) # => All vehicles where the state is *not* parked or idling # # *Note* that if class methods already exist with those names (i.e. # :with_state, :with_states, :without_state, or :without_states), then a # scope will not be defined for that name. # # See StateMachine::Machine for more information about using # integrations and the individual integration docs for information about # the actual scopes that are generated. def state_machine(*args, &block) StateMachine::Machine.find_or_create(self, *args, &block) end end end Class.class_eval do include StateMachine::MacroMethods end # Register rake tasks for supported libraries Merb::Plugins.add_rakefiles("#{File.dirname(__FILE__)}/../tasks/state_machine") if defined?(Merb::Plugins)