== state_machine

+state_machine+ adds support for creating state machines for attributes on any
Ruby class.

== Resources

API

* http://api.pluginaweek.org/state_machine

Bugs

* http://pluginaweek.lighthouseapp.com/projects/13288-state_machine

Development

* http://github.com/pluginaweek/state_machine

Source

* git://github.com/pluginaweek/state_machine.git

== Description

State machines make it dead-simple to manage the behavior of a class.  Too often,
the state of an object is kept by creating multiple boolean attributes and
deciding how to behave based on the values.  This can become cumbersome and
difficult to maintain when the complexity of your class starts to increase.

+state_machine+ simplifies this design by introducing the various parts of a real
state machine, including states, events, transitions, and callbacks.  However,
the api is designed to be so simple you don't even need to know what a
state machine is :)

Some brief, high-level features include:
* Defining state machines on any Ruby class
* Multiple state machines on a single class
* Namespaced state machines
* before/after transition hooks with explicit transition requirements
* ActiveRecord integration
* DataMapper integration
* Sequel integration
* State predicates
* State-driven instance / class behavior
* State values of any data type
* Dynamically-generated state values
* Event parallelization
* Attribute-based event transitions
* Inheritance
* Internationalization
* GraphViz visualization creator

Examples of the usage patterns for some of the above features are shown below.
You can find much more detailed documentation in the actual API.

== Usage

=== Example

Below is an example of many of the features offered by this plugin, including:
* Initial states
* Namespaced states
* Transition callbacks
* Conditional transitions
* State-driven instance behavior
* Customized state values
* Parallel events

Class definition:

  class Vehicle
    attr_accessor :seatbelt_on
    
    state_machine :state, :initial => :parked do
      before_transition :parked => any - :parked, :do => :put_on_seatbelt
      
      after_transition :on => :crash, :do => :tow
      after_transition :on => :repair, :do => :fix
      after_transition any => :parked do |vehicle, transition|
        vehicle.seatbelt_on = false
      end
      
      event :park do
        transition [:idling, :first_gear] => :parked
      end
      
      event :ignite do
        transition :stalled => same, :parked => :idling
      end
      
      event :idle do
        transition :first_gear => :idling
      end
      
      event :shift_up do
        transition :idling => :first_gear, :first_gear => :second_gear, :second_gear => :third_gear
      end
      
      event :shift_down do
        transition :third_gear => :second_gear, :second_gear => :first_gear
      end
      
      event :crash do
        transition all - [:parked, :stalled] => :stalled, :unless => :auto_shop_busy?
      end
      
      event :repair do
        transition :stalled => :parked, :if => :auto_shop_busy?
      end
      
      state :parked do
        def speed
          0
        end
      end
      
      state :idling, :first_gear do
        def speed
          10
        end
      end
      
      state :second_gear do
        def speed
          20
        end
      end
    end
    
    state_machine :alarm_state, :initial => :active, :namespace => 'alarm' do
      event :enable do
        transition all => :active
      end
      
      event :disable do
        transition all => :off
      end
      
      state :active, :value => 1
      state :off, :value => 0
    end
    
    def initialize
      @seatbelt_on = false
      super() # NOTE: This *must* be called, otherwise states won't get initialized
    end
    
    def put_on_seatbelt
      @seatbelt_on = true
    end
    
    def auto_shop_busy?
      false
    end
    
    def tow
      # tow the vehicle
    end
    
    def fix
      # get the vehicle fixed by a mechanic
    end
  end

*Note* the comment made on the +initialize+ method in the class.  In order for
state machine attributes to be properly initialized, <tt>super()</tt> must be called.
See StateMachine::MacroMethods for more information about this.

Using the above class as an example, you can interact with the state machine
like so:

  vehicle = Vehicle.new           # => #<Vehicle:0xb7cf4eac @state="parked", @seatbelt_on=false>
  vehicle.state                   # => "parked"
  vehicle.state_name              # => :parked
  vehicle.parked?                 # => true
  vehicle.can_ignite?             # => true
  vehicle.ignite_transition       # => #<StateMachine::Transition attribute=:state event=:ignite from="parked" from_name=:parked to="idling" to_name=:idling>
  vehicle.state_events            # => [:ignite]
  vehicle.state_transitions       # => [#<StateMachine::Transition attribute=:state event=:ignite from="parked" from_name=:parked to="idling" to_name=:idling>]
  vehicle.speed                   # => 0
  
  vehicle.ignite                  # => true
  vehicle.parked?                 # => false
  vehicle.idling?                 # => true
  vehicle.speed                   # => 10
  vehicle                         # => #<Vehicle:0xb7cf4eac @state="idling", @seatbelt_on=true>
  
  vehicle.shift_up                # => true
  vehicle.speed                   # => 10
  vehicle                         # => #<Vehicle:0xb7cf4eac @state="first_gear", @seatbelt_on=true>
  
  vehicle.shift_up                # => true
  vehicle.speed                   # => 20
  vehicle                         # => #<Vehicle:0xb7cf4eac @state="second_gear", @seatbelt_on=true>
  
  # The bang (!) operator can raise exceptions if the event fails
  vehicle.park!                   # => StateMachine::InvalidTransition: Cannot transition state via :park from :second_gear
  
  # Generic state predicates can raise exceptions if the value does not exist
  vehicle.state?(:parked)         # => false
  vehicle.state?(:invalid)        # => IndexError: :invalid is an invalid name
  
  # Namespaced machines have uniquely-generated methods
  vehicle.alarm_state             # => 1
  vehicle.alarm_state_name        # => :active
  
  vehicle.can_disable_alarm?      # => true
  vehicle.disable_alarm           # => true
  vehicle.alarm_state             # => 0
  vehicle.alarm_state_name        # => :off
  vehicle.can_enable_alarm?       # => true
  
  vehicle.alarm_off?              # => true
  vehicle.alarm_active?           # => false
  
  # Events can be fired in parallel
  vehicle.fire_events(:shift_down, :enable_alarm) # => true
  vehicle.state_name                              # => :first_gear
  vehicle.alarm_state_name                        # => :active
  
  vehicle.fire_events!(:ignite, :enable_alarm)    # => StateMachine::InvalidTransition: Cannot run events in parallel: ignite, enable_alarm

== Integrations

In addition to being able to define state machines on all Ruby classes, a set of
out-of-the-box integrations are available for some of the more popular Ruby
libraries.  These integrations add library-specific behavior, allowing for state
machines to work more tightly with the conventions defined by those libraries.

The integrations currently available include:
* ActiveRecord models
* DataMapper resources
* Sequel models

A brief overview of these integrations is described below.

=== ActiveRecord

The ActiveRecord integration adds support for database transactions, automatically
saving the record, named scopes, validation errors, and observers.  For example,

  class Vehicle < ActiveRecord::Base
    state_machine :initial => :parked do
      before_transition :parked => any - :parked, :do => :put_on_seatbelt
      after_transition any => :parked do |vehicle, transition|
        vehicle.seatbelt = 'off'
      end
      
      event :ignite do
        transition :parked => :idling
      end
      
      state :first_gear, :second_gear do
        validates_presence_of :seatbelt_on
      end
    end
    
    def put_on_seatbelt
      ...
    end
  end
  
  class VehicleObserver < ActiveRecord::Observer
    # Callback for :ignite event *before* the transition is performed
    def before_ignite(vehicle, transition)
      # log message
    end
    
    # Generic transition callback *after* the transition is performed
    def after_transition(vehicle, transition)
      Audit.log(vehicle, transition)
    end
  end

For more information about the various behaviors added for ActiveRecord state
machines, see StateMachine::Integrations::ActiveRecord.

=== DataMapper

Like the ActiveRecord integration, the DataMapper integration adds support for
database transactions, automatically saving the record, named scopes, Extlib-like
callbacks, validation errors, and observers.  For example,

  class Vehicle
    include DataMapper::Resource
    
    property :id, Serial
    property :state, String
    
    state_machine :initial => :parked do
      before_transition :parked => any - :parked, :do => :put_on_seatbelt
      after_transition any => :parked do |transition|
        self.seatbelt = 'off' # self is the record
      end
      
      event :ignite do
        transition :parked => :idling
      end
      
      state :first_gear, :second_gear do
        validates_present :seatbelt_on
      end
    end
    
    def put_on_seatbelt
      ...
    end
  end
  
  class VehicleObserver
    include DataMapper::Observer
    
    observe Vehicle
    
    # Callback for :ignite event *before* the transition is performed
    before_transition :on => :ignite do |transition|
      # log message (self is the record)
    end
    
    # Generic transition callback *after* the transition is performed
    after_transition do |transition|
      Audit.log(self, transition) # self is the record
    end
  end

*Note* that the DataMapper::Observer integration is optional and only available
when the dm-observer library is installed.

For more information about the various behaviors added for DataMapper state
machines, see StateMachine::Integrations::DataMapper.

=== Sequel

Like the ActiveRecord integration, the Sequel integration adds support for
database transactions, automatically saving the record, named scopes, validation
errors and callbacks.  For example,

  class Vehicle < Sequel::Model
    state_machine :initial => :parked do
      before_transition :parked => any - :parked, :do => :put_on_seatbelt
      after_transition any => :parked do |transition|
        self.seatbelt = 'off' # self is the record
      end
      
      event :ignite do
        transition :parked => :idling
      end
      
      state :first_gear, :second_gear do
        validates_presence_of :seatbelt_on
      end
    end
    
    def put_on_seatbelt
      ...
    end
  end

For more information about the various behaviors added for Sequel state
machines, see StateMachine::Integrations::Sequel.

== Compatibility

Although state_machine introduces a simplified syntax, it still remains
backwards compatible with previous versions and other state-related libraries.
For example, transitions and callbacks can continue to be defined like so:

  class Vehicle
    state_machine :initial => :parked do
      before_transition :from => :parked, :except_to => :parked, :do => :put_on_seatbelt
      after_transition :to => :parked do |transition|
        self.seatbelt = 'off' # self is the record
      end
      
      event :ignite do
        transition :from => :parked, :to => :idling
      end
    end
  end

Although this verbose syntax will most likely always be supported, it is
recommended that any state machines eventually migrate to the syntax introduced
in version 0.6.0.

== Tools

=== Generating graphs

This library comes with built-in support for generating di-graphs based on the
events, states, and transitions defined for a state machine using GraphViz[http://www.graphviz.org].
This requires that both the <tt>ruby-graphviz</tt> gem and graphviz library be
installed on the system.

==== Examples

To generate a graph for a specific file / class:

  rake state_machine:draw FILE=vehicle.rb CLASS=Vehicle

To save files to a specific path:

  rake state_machine:draw FILE=vehicle.rb CLASS=Vehicle TARGET=files

To customize the image format / orientation:

  rake state_machine:draw FILE=vehicle.rb CLASS=Vehicle FORMAT=jpg ORIENTATION=landscape

To generate multiple state machine graphs:

  rake state_machine:draw FILE=vehicle.rb,car.rb CLASS=Vehicle,Car

*Note* that this will generate a different file for every state machine defined
in the class.  The generated files will use an output filename of the format
#{class_name}_#{machine_name}.#{format}.

For examples of actual images generated using this task, see those under the
examples folder.

==== Ruby on Rails Integration

There is a special integration Rake task for generating state machines for
classes used in a Ruby on Rails application.  This task will load the application
environment, meaning that it's unnecessary to specify the actual file to load.

For example,

  rake state_machine:draw:rails CLASS=Vehicle

If you are using this library as a gem, the following must be added to the end
of your application's Rakefile in order for the above task to work:

  require 'tasks/state_machine'

If you are using Rails 3.0+, you must also add the following to your
application's Gemfile:

  gem 'ruby-graphviz', :require => 'graphviz'

==== Merb Integration

Like Ruby on Rails, there is a special integration Rake task for generating
state machines for classes used in a Merb application.  This task will load the
application environment, meaning that it's unnecessary to specify the actual
files to load.

For example,

  rake state_machine:draw:merb CLASS=Vehicle

=== Interactive graphs

Jean Bovet - {Visual Automata Simulator}[http://www.cs.usfca.edu/~jbovet/vas.html].
This is a great tool for "simulating, visualizing and transforming finite state
automata and Turing Machines".  This tool can help in the creation of states and
events for your models.  It is cross-platform, written in Java.

== Testing

To run the entire test suite (will test ActiveRecord, DataMapper, and Sequel
integrations if the proper dependencies are available):

  rake test

Target specific versions of integrations like so:

  rake test AR_VERSION=2.0.0 DM_VERSION=0.9.4 SEQUEL_VERSION=2.8.0

== Caveats

The following caveats should be noted when using state_machine:

* DataMapper: dm-validations 0.9.4 - 0.9.6 causes +after+ callbacks for
attribute-based event transitions to fail
* Overridden event methods won't get invoked when using attribute-based event
transitions

== Dependencies

* Ruby 1.8.6 or later

If using specific integrations:

* ActiveRecord[http://rubyonrails.org] integration: 2.0.0 or later
* DataMapper[http://datamapper.org] integration: 0.9.4 or later
* Sequel[http://sequel.rubyforge.org] integration: 2.8.0 or later