/** Fetches live sessions; polls when tab visible. */
const POLL_MS = 1500

export function useLiveSessions() {
  const { data: _sessions, refresh } = useAsyncData(
    'live-sessions',
    async () => {
      try {
        return await $fetch('/api/live')
      }
      catch (err) {
        const msg = err?.message ?? String(err)
        const status = err?.statusCode ?? err?.status
        console.error('[useLiveSessions] Failed to fetch sessions:', status ? `${status}: ${msg}` : msg)
        return []
      }
    },
    { default: () => [] },
  )

  const sessions = computed(() => Object.freeze([...(_sessions.value ?? [])]))
  const pollInterval = ref(null)

  function startPolling() {
    if (pollInterval.value) return
    refresh()
    pollInterval.value = setInterval(refresh, POLL_MS)
  }

  function stopPolling() {
    if (pollInterval.value) {
      clearInterval(pollInterval.value)
      pollInterval.value = null
    }
  }

  onMounted(() => {
    if (typeof document === 'undefined') return
    document.addEventListener('visibilitychange', () => {
      document.visibilityState === 'visible' ? (startPolling(), refresh()) : stopPolling()
    })
    if (document.visibilityState === 'visible') startPolling()
  })
  onBeforeUnmount(stopPolling)

  return Object.freeze({ sessions, refresh, startPolling, stopPolling })
}