nano-history.ts

import { type WritableStore, action, onNotify } from 'nanostores'

export function createHistory<Value>(store: WritableStore<Value>): {
  clearHistory: () => void
  redo: () => void
  undo: () => void
} {
  let historyIndex = -1
  let history: Value[] = [store.get()]
  let isInternalChange = false
  onNotify(store, () => {
    // The store value can be undefined if there are no subscribers
    // Do not update the history if there are no subscribers
    if (isInternalChange || store.lc <= 0) return
    const newHistory = history.slice(0, historyIndex + 1)
    newHistory.push(store.value!)
    history = newHistory
    historyIndex = history.length - 1
  })

  const undo = action(store, 'undo', (store) => {
    if (historyIndex <= 0) return
    historyIndex--
    isInternalChange = true
    store.set(history[historyIndex])
    isInternalChange = false
  })

  const redo = action(store, 'redo', (store) => {
    if (historyIndex === history.length - 1) return
    historyIndex++
    isInternalChange = true
    store.set(history[historyIndex])
    isInternalChange = false
  })

  const clearHistory = () => {
    history = [store.get()]
    historyIndex = 0
  }

  return { clearHistory, redo, undo }
}