import { useEffect, useRef, useState } from 'react'
import { api } from '../api/client'

// How often to ask the server whether a newer frontend has shipped. Gentle —
// a deploy is rare, and the check is a tiny no-store GET.
const POLL_MS = 90_000

// useVersionWatch records the build id the app loaded with, then quietly polls
// /api/version. When the server reports a different id, a new version has been
// deployed and `updateAvailable` flips true (and stays true) so the UI can
// offer a refresh. Network blips are ignored — it only ever reacts to a real,
// confirmed change. Returns false until the baseline is established.
export function useVersionWatch(): boolean {
  const [updateAvailable, setUpdateAvailable] = useState(false)
  // The version we're currently running. Null until the first successful fetch.
  const baseline = useRef<string | null>(null)

  useEffect(() => {
    let active = true

    const check = async () => {
      try {
        const { version } = await api.version()
        if (!active || !version) return
        if (baseline.current === null) {
          baseline.current = version // first read: this is "us"
        } else if (version !== baseline.current) {
          setUpdateAvailable(true)
        }
      } catch {
        /* offline / server bounce — try again next tick, never alarm the user */
      }
    }

    check()
    const id = setInterval(check, POLL_MS)
    // Re-check the moment she returns to the tab, so a deploy that happened while
    // she was away surfaces right away instead of up to POLL_MS later.
    const onVisible = () => {
      if (document.visibilityState === 'visible') check()
    }
    document.addEventListener('visibilitychange', onVisible)

    return () => {
      active = false
      clearInterval(id)
      document.removeEventListener('visibilitychange', onVisible)
    }
  }, [])

  return updateAvailable
}