StateMachine

A minimalistic state machine implementation, loosely based on github.com/soveran/micromachine.

Usage

State

To create a new state machine, a type that satisfies the State interface must be set. i.e.

type State struct {
	state string
}

func New(state string) *State {
	return &State{state: state}
}

func (s *State) GetState() string {
	return s.state
}

func (s *State) SetState(state string) {
	s.state = state
}

Transitions, Callbacks and Errors

Transitions are assigned using the When method

import "github.com/r3labs/statemachine"

...

s := New("initializing")
sm := statemachine.New(s)

// Assign all transitions for a given event
sm.When("accept", statemachine.Transitions{"initializing": "accepted"})
sm.When("reject", statemachine.Transitions{"initializing": "rejected"})
sm.When("reset", statemachine.Transitions{"accepted": "initializing", "rejected": "initializing"})

Callbacks can be added for execution before transitioning to a state. Multiple callbacks for an event are supported. In the event of a callback failure, the transition will be halted

// Additional data can be passed into the callback via an interface
sm.On("accepted", func(state string, t interface{}) error {
    // produces new state: accepted
    fmt.Println("new state: " + state)   
    return nil
})

State transitions can be triggered with the Trigger method

// Returns an error
err := sm.Trigger("unknown", nil)

// Returns nil and sets state to 'accepted'
err := sm.Trigger("accept", nil)

If you wish to pass additional data into the callbacks, you can do so as following

sm.On("accepted", func(state string, t interface{}) error {
    data := t.(*map[string]string)
    fmt.Printf("welcome back %s!" + data["user"])   

    return nil
})

// Will print 'welcome back john!'
sm.Trigger("accept", &map[string]string{"user": "john"})

Default errors can be specified for when a transition fails

sm.Error("accepted", errors.New("unable to transition as state is currently 'accepted'"))

err := sm.Trigger("reject", nil)

Contributing

Please read through our contributing guidelines. Included are directions for opening issues, coding standards, and notes on development.

Moreover, if your pull request contains patches or features, you must include relevant unit tests.

Copyright and License

Code and documentation copyright since 2015 r3labs.io authors.

Code released under the Mozilla Public License Version 2.0.