simple-machines

Simple finite state machine with explicit allowed state transitions, initial state, and options around how long to wait for state transitions when using waitForChange as well as explicitly naming the machine for better debugging when using multiple machines simultaneously.

The state machine will throw if an invalid state transition is attempted.

Example

import { fsm, StateTransitions } from 'simple-machines'
import timers from 'timers/promises'

type State = 'starting' | 'started' | 'stopping' | 'stopped'

const stateTransitions: StateTransitions<State> = {
  stopped: ['starting'],
  starting: ['started'],
  started: ['stopping'],
  stopping: ['stopped'],
}

const state = fsm<State>(stateTransitions, 'stopped', {
  name: 'Process Records',
  onStateChange(change) {
    console.log(change)
  },
})

// Simulate connecting to db
const connectToDb = async () => {
  await timers.setTimeout(1000)
}

const stopDoingStuff = async () => {
  await timers.setTimeout(1000)
}

// Simulate work
const doStuff = async () => {
  while(true) {
    await timers.setTimeout(250)
  }
}

const start = async () => {
  // Nothing to do
  if (state.is('starting', 'started')) {
    return
  }
  if (state.is('stopping')) {
    // Wait until stopping -> stopped
    await state.waitForChange('stopped')
  }
  state.change('starting')
  await connectToDb()
  doStuff()
  state.change('started')
}

const stop = async () => {
  // Nothing to do
  if (state.is('stopping', 'stopped')) {
    return
  }
  if (state.is('starting')) {
    // Wait until starting -> started
    await state.waitForChange('started')
  }
  state.change('stopping')
  await stopDoingStuff()
  state.change('stopped')
}

start()
setTimeout(stop, 500)