import { useCallback, useEffect, useState } from 'react'
import apiFetch from '@wordpress/api-fetch'

export interface AutoUpdates {
  /** Whether WordPress updates the plugin automatically */
  enabled: boolean
  /** False for users who cannot update plugins, and when the host decides */
  canChange: boolean
}

const PATH = '/posten-bring-checkout/auto-updates'

/**
 * Every component following the status on the page, so that turning
 * automatic updates on in one of them updates the others too, such as the
 * update notice next to the set-up step that turned them on.
 */
const followers = new Set<(autoUpdates: AutoUpdates) => void>()

const tellFollowers = (autoUpdates: AutoUpdates) =>
  followers.forEach(follow => follow(autoUpdates))

/**
 * Counts the start and the end of every change, so that a status asked for
 * before or while it was changed, and answered after, is known to be stale.
 */
let changes = 0

/**
 * Follows whether the plugin updates automatically and lets the merchant
 * turn it on or off. Pages that already know the status, like the order page
 * that has it prefetched, pass it in instead of asking for it again.
 */
const useAutoUpdates = (known?: AutoUpdates) => {
  const [autoUpdates, setAutoUpdates] = useState<AutoUpdates | undefined>(
    known
  )
  const [isSaving, setIsSaving] = useState<boolean>(false)
  const [failed, setFailed] = useState<boolean>(false)

  useEffect(() => {
    followers.add(setAutoUpdates)
    if (!known) {
      const changesWhenAsked = changes
      apiFetch<AutoUpdates>({ path: PATH })
        .then(status => {
          if (changes === changesWhenAsked) {
            tellFollowers(status)
          }
        })
        .catch(() => undefined)
    }
    return () => {
      followers.delete(setAutoUpdates)
    }
  }, [])

  const turn = useCallback(async (enabled: boolean) => {
    setIsSaving(true)
    setFailed(false)
    changes += 1
    try {
      tellFollowers(
        await apiFetch<AutoUpdates>({
          path: PATH,
          method: 'POST',
          data: { enabled },
        })
      )
    } catch (e) {
      setFailed(true)
    } finally {
      changes += 1
      setIsSaving(false)
    }
  }, [])

  return { autoUpdates, isSaving, failed, turn }
}

export default useAutoUpdates