Arrow of time

Experiment with minimum possible composable implementation of a history (such as a Redux store, Act history, etc).

To try it out, clone the repo and npm install. Then npm start and head to http://localhost:3000/demo/timeline.html and http://localhost:3000/demo/snapshot.html.

Install

npm install --save-dev arrow-of-time

Snapshot

import getSnapshot, { subscribe } from 'arrow-of-time/snapshot'

const snapshot = getSnapshot((state, action) => {
  switch (action.type) {
    case 'item':
      return {
        ...state,
        items: [...state.items, action.payload]
      }

    case 'article':
      return {
        ...state,
        articles: [...state.articles, action.payload]
      }
    default:
      state
  }
}, { items: [], articles: [] })

const subscribedSnapshot = subscribe(({ getAction, getState }) => {
  console.log('ACTION', getAction())
  console.log('STATE', getState())
})(snapshot)

const snapshots = []

snapshots.push(subscribedSnapshot.getNext({ type: 'item', payload: 'home' }))
snapshots.push(snapshots[0].getNext({ type: 'item', payload: 'sea' }))
snapshots.push(snapshots[1].getNext({ type: 'item', payload: 'mountains' }))

Timeline

import getTimeline, { subscribe } from 'arrow-of-time/timeline'

const timeline = getTimeline((state, action) => {
  switch (action.type) {
    case 'item':
      return {
        ...state,
        items: [...state.items, action.payload]
      }

    case 'article':
      return {
        ...state,
        articles: [...state.articles, action.payload]
      }
    default:
      state
  }
}, { items: [], articles: [] })

const subscribedTimeline = subscribe(({ getAction, getState }) => {
  console.log('ACTION', getAction())
  console.log('STATE', getState())
})(timeline)

const timelines = []

timelines.push(subscribedTimeline.getNext({ type: 'item', payload: 'home' }))
timelines.push(timelines[0].getNext({ type: 'item', payload: 'sea' }))
timelines.push(timelines[1].getNext({ type: 'item', payload: 'mountains' }))

timelines.push(timelines[2].rewind())
timelines.push(timelines[3].rewind())
timelines.push(timelines[4].redo())

Store

import getStore from 'arrow-of-time/store'

const store = getStore((state, action) => {
  switch (action.type) {
    case 'item':
      return {
        ...state,
        items: [...state.items, action.payload]
      }

    case 'article':
      return {
        ...state,
        articles: [...state.articles, action.payload]
      }
    default:
      state
  }
}, { items: [], articles: [] })

store.subscribe(({ getAction, getState }) => {
  console.log('ACTION', getAction())
  console.log('STATE', getState())
})(timeline)

store.dispatch({ type: 'item', payload: 'home' }))
store.dispatch(timelines[0].getNext({ type: 'item', payload: 'sea' }))
store.dispatch(timelines[1].getNext({ type: 'item', payload: 'mountains' }))

store.update((timeline) => timeline.rewind())
store.update((timeline) => timeline.rewind())
store.update((timeline) => timeline.redo())

Known issues

• redoable and rewindable need to be the outermost higher order snapshots to be applied, because the way they work they will not play well in spreading the properties set by other higher order snapshots.