import { useCallback, useEffect, useRef, useState } from 'react'

// usePolled runs `fn` now and every `everyMs`, and is careful about the two
// things every screen would otherwise get wrong on its own: overlapping
// requests when the server is slower than the interval, and setting state
// after the component has gone.
export function usePolled(fn, everyMs, deps = []) {
  const [data, setData] = useState(null)
  const [error, setError] = useState(null)
  const [loading, setLoading] = useState(true)
  const inFlight = useRef(false)
  const alive = useRef(true)

  const run = useCallback(async () => {
    if (inFlight.current) return
    inFlight.current = true
    try {
      const out = await fn()
      if (!alive.current) return
      setData(out)
      setError(null)
    } catch (err) {
      if (!alive.current) return
      setError(err)
    } finally {
      inFlight.current = false
      if (alive.current) setLoading(false)
    }
    // eslint-disable-next-line react-hooks/exhaustive-deps
  }, deps)

  useEffect(() => {
    alive.current = true
    run()
    if (!everyMs) return () => { alive.current = false }
    const t = setInterval(run, everyMs)
    return () => { alive.current = false; clearInterval(t) }
    // eslint-disable-next-line react-hooks/exhaustive-deps
  }, [run, everyMs])

  return { data, error, loading, reload: run }
}