withReadyAtom.ts

import { AsyncAction } from '@reatom/async'
import { Atom, atom } from '@reatom/core'

export const withReadyAtom =
  <T extends AsyncAction & { dataAtom?: Atom }>(initState = false) =>
  (anAsync: T): T & { readyAtom: Atom<boolean> } => {
    // use `spy` to prevent any race conditions
    const readyAtom = atom((ctx, state?: boolean) => {
      // trigger connection to start the fetch if `onConnect` used
      if (anAsync.dataAtom) ctx.spy(anAsync.dataAtom)

      const pending = ctx.spy(anAsync.pendingAtom)

      return state === undefined ? initState : pending === 0
    }, `${anAsync.__reatom.name}.readyAtom`)

    // grand correct state even for unconnected atom
    anAsync.pendingAtom.onChange((ctx) => {
      ctx.get(readyAtom)
    })

    return Object.assign(anAsync, { readyAtom })
  }