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| state machine

I am able.

  • From potis (“able, capable”) + sum (“I am”).

======== Fork me on GitHub

Build Status

License

MIT

Install

npm install --save possum

Size

  • unminified 3.05kb
  • minified 1.68kb

Building

make build => ./build/possum.js

minified builds are broken atm

Documentation

Found here

IMPORTANT BREAKING CHANGE FOR v1+... EventEmitter api is no longer mixed in by default...that is up to you!!!

Example

make example

Module Support

Works in nodejs and the browser.

Getting Started

This is in the app.js for the example.

//listening to Kiss' Love Gun on my record player

//first, define our state machine spec

let gun = possum
    .config({
        namespace: 'kiss'
        , initialState: 'uninitialized'
    })
    .methods({
        enable: function(actions) {
            Object.keys(controls).forEach(function(key){
                controls[key].setAttribute('disabled','disabled')
            })
            if(!actions || !actions.length) {
                return
            }
            actions.forEach(function(action){
                controls[action].removeAttribute('disabled')
            })
        }
        ,loadWeapon: function(bullets){
            return this.bullets = bullets || [
                'I Stole Your Love'
                ,'Shock Me'
                ,'Love Gun'
            ]
        }
        ,fire: function(){
            //asynchronous, returns a Promise
            return this.recordPlayer.play(this.song)
        }
    })
    .states({
        'uninitialized': {
            _enter: function(){
                this.enable(['initialize'])
                return this.recordPlayer.turnOn()
            }
            ,'initialize': function(args) {
                return this.recordPlayer.spinRecord()
                    .then(this.transition.bind(this,'initialized'))
            }
        }
        ,'initialized': {
            _enter: function(){
                this.enable(['pullTrigger','load'])
            }
            ,'pullTrigger': function() {
                this.deferUntilTransition('aimed')
            }
            ,'load': function(args) {
                this.deferUntilTransition('loading')
                return this.transition('loading')
            }
        }
        ,'loading': {
            _enter: function(){
                this.enable(['load'])
            }
            ,'load': function(args) {
                this.loadWeapon(args && args.bullets)
                return this.transition('loaded')
            }
            ,'reload': function() {
                return this.handle('load')
            }
        }
        ,'loaded': {
            _enter: function(){
                document.querySelector('.remaining').innerHTML = ''
                this.enable(['aim'])
            }
            ,'aim': function(args) {
                this.song = (args && args.target) || this.bullets.shift()
                this.recordPlayer.hoverNeedleOver(this.song)
                return this.transition('aimed')
            }
        }
        ,'aimed':{
            _enter: function(){
                this.enable(['pullTrigger'])
            }
            ,'pullTrigger': function() {
                return this.fire()
                    .then(this.transition.bind(this,'smoking'))
            }
        }
        ,'smoking': {
            _enter: function(){
                console.log('light cigarette, sit back and relax')
                this.enable(['liftNeedle'])
            }
            ,'aim': function(args){
                this.deferUntilNextHandler()
                return this.handle('liftNeedle')
            }
            ,'liftNeedle': function(){
                if(this.bullets.length) {
                    return this.transition('loaded')
                }
                return this.transition('emptied')
            }
        }
        ,'emptied': {
            _enter: function(){
                this.enable(['reload'])
                return this.handle('aim')
            }
            ,'aim': function(args){
                return this.recordPlayer.returnArm()
            }
            ,'reload': function(){
                this.deferUntilTransition('loading')
                return this.transition('loading')
            }
        }

    })
    .create()

gun.currentState == 'uninitialized' // true

What is a Possum?

A marsupial.

But for our purposes, possum uses stampit under-the-hood for model prototyping.

This means that when you do this:

var p = possum.states({ ... }).create()

A possum will compose any settings you put on the top level possum call and then exposes this to the api (see below for more details):

possum
.config( /* configure initialState, namespace, etc */) // alias to stampit `props`
.states( /* configure states */) 
.methods(/* special methods */) //stampit method
.init(function(){
    //initializing stuff
    var secretData = 'shhhh'
    this.prop == 'erty' // -> true
}) //stampit method
.compose(/* mixin other stamps into the machine */) //stampit method
.target(/* the state object to use (default is the machine itself) */)
.create() //this creates the possum instance; you may also just call it as a function

Isolation and prototypes

Every call to the builder functions on possum return a new stamp. This is important to know and also to take advantage of. Consider the following:

let loggable = possum.compose(logger)
let eventable = possum.compose(eventSourcer)
let kitchen = loggable.compose(eventable)

let model = loggable.config({initialState: 'a'}).create() //has loggable, not eventable, behavior
let model2 = eventable.config({initialState:'a'}).create() //has eventable, not loggable, behavior
let everything = kitchen.config({initialState:'a' }).create() // has both

See the tests here for seeing in action.

Asynchronous and synchronous transitions and handlers

Oftentimes handlers end up being async, breaking all the callers. Initially possum did Promises for all api calls.

As of v0.1.0 possum supports both synchronous and Promised handlers.

It is worth noting that the events which are emitted are ordered differently depending on the flow model you choose.

Behavioral State Machine support

Possum supports splitting the control state from the target model being acted upon using target(). The value of target by default is the machine instance itself but each handler, except for _enter and _exit, will receive the target instance as the second argument in every handler.

// one approach

let machine = possum.config({initialState:'ready'})
.states({ 
    ready: {
        // target is passed in as secon argument
        go(args, target) {
            //1. mutate the target model here. It can consume the target's API, or whatever
            //2. determine the next state to transition based on the target state
            //3. do it
            target.doThatThing(args)
            if(target.isGoing) {
                retun this.transition('going')
            }
            //nextAction (manually calced)
            if(target.isWaiting) {
                return this.handle('wait', args)
            }
        },
        wait(args, target) {

        }
    } 
    going: {
        // special handlers only receive the target as argument
        _enter: (target) {
            this.emit('going')
        },
        complete(args, target) { }
    }
})

let modelApi = {
    doThatThing(args) { 
        this.isGoing = args.isGoing; // like from a checkbox 
        this.isWaiting = !args.isGoing; 
    },
}

//create machine instance and set the target
// you may also set `target` on the machine prototype...

let state = machine().target(modelApi)

// from view
state.handle('go', { isGoing: true }); //target will always be passed as second arg in input handler!
state.currentState == 'going' // true

Possum Builder API (extensions atop stampit)

config {Object} required

These attributes can (should) be set here:

namespace {String} [optional]

The namespace for this instance

var p = possum.config({
    namespace: 'secure'
})
initialState {String} required

The state to transition to initially

var p = possum.config({
    initialState: 'uninitialized'
})

NOTE:

  • the _enter callback will NOT get called immediately upon construction if the state designated by initialState has one. This is to avoid the need for asynchronous instantiation support. If really need an initialization routing you can just use stampit's built in facility for this:
var p = possum
.config({
    initialState: 'a'
})
.states({
    'a': {
        '_enter': function(){
            //wont get called on creation!
        }
    }
})
.init(function(){
    //do init stuff here
    //...you can even return a Promise and stampit will return the promise
    //for you to control it
})
states {Object} required

The states handlers configuration in the shape of:

var states = {
    'myState': {
        _enter: function( target ){
            //optional
            //steps to perform right when entering a state
            //can return an Promise for async support
        }
        ,'doIt': function(args, target) {
            //optionally make changes to the state target
            //handle the command 'doIt'
            //receiving exactly ONE argument
            return this.doIt()
        }
        ... 
        ,_exit: function( target ) {
            //optional
            //steps to perform right before transitioning
            //out of this state
        }
    }
}

Note that each state's input handler, will receive one arguments parameter. That means you must invoke the handlers this way:

model.handle('doIt','myArgument')

Additional arguments will be ignored.

emit {Function} required

The implementation of event emitter is left up to you, the implementer. That means that possum doesn't come bundled with a eventing API out-of-the-box. To use possum with eventemitter2 you can do something like this:

var EventEmitter2 = require('eventemitter2').EventEmitter2;
var emittable = stampit.convertConstructor(EventEmitter2);
var machine = possum.compose(emittable).states(...)

Possum Instance API

currentState {String}

The current state of the possum instance. This is the same as initialState upon creation

priorState {String}

The priorState state of the possum instance, if any. This is undefined until a transition has occurred.

namespaced([str,namespace]) {Function}

Receives an optional str argument to produce an namespaced string using underlying delimiter rules.

If str is not provided, the instance's namespace is returned (from the spec).

If the instance has an undefined namespace the input namespace argument is used; if that is undefined the str is returned.

This utility is used for producing underlying events for subscription; eg :

possumInstance.on(possumInstance.namespaced('handled'),function(){...})

handle(inputType, args) {Function}

Queues the command inputType and processes it with the singular args payload. Note that only one argument will be used. Other arguments will be ignored.

Returns the result of the handler (Promise or not)

transition(toState) {Function}

Convenience method that queues the transition commands exit, _transition, and _onEnter and processes them. Returns a Promise if an _enter or _exit handler does so; otherwise, it returns the possum instance.

deferUntilTransition(toState) {Function}

Queues the current message (input) to be replayed after the possum has transitioned to toState. If toState is not provided, then it will replay after any transition has occurred.

Returns this possum instance.

Possum Events

{namespace}.handling

Emitted during an input handler.

Event properties:

  • topic: 'handling'
  • inputType: {String} the name of the handler you just called
  • payload: {Any} The arguments passed into the handle call
  • action: {String} the path of the handler you just called ; eg 'myState.myHandler'
  • namespace: {String} the namespace of the possum
{namespace}.invoked

Emitted just after an input handler has been invoked but possibly before the handler has completed (asynchronously).

Event properties:

  • topic: 'invoked'
  • inputType: {String} the name of the handler you just called
  • payload: {Any} The arguments passed into the handle call
  • action: {String} the path of the handler you just called ; eg 'myState.myHandler'
  • namespace: {String} the namespace of the possum
{namespace}.handled

Emitted after an input handler Promise has resolved (if async).

Event properties:

  • topic: 'handled'
  • inputType: {String} the name of the handler you just called
  • payload: {Any} The arguments passed into the handle call
  • action: {String} the path of the handler you just called ; eg 'myState.myHandler'
  • namespace: {String} the namespace of the possum
{namespace}.transitioned

Emitted after a possum has transitioned into a state, and after its entry callback has been invoked (_enter).

Event properties:

  • topic: 'transitioned'
  • inputType: {String} the name of the handler you just called
  • payload: {Object} having these properties
    • toState The state you just transitioned to
    • fromState The state you just transitioned from
  • action: {String} the path of the handler you just called ; eg 'myState.myHandler'
  • namespace: {String} the namespace of the possum
{namespace}.noHandler

Emitted when an input has been attempted on a state that does not declare it.

{namespace}.invalidTransition

Emitted when an transition is attempted to a state that does not exist.

Tests

  • make test will by default run tests on Node.
  • make browser will run tape tests on any browser you visit at http://localhost:2222

Roadmap

  • Hierarchical State Machine support
  • Behavior tree generation (ala machine.js).

Acknowledgements

API inspiration from machina.js.

Credits