import { onUnmounted, watch } from 'vue'
import { storeToRefs } from 'pinia'
import { useDevicesStore } from '@/stores/devices'
import type { Device } from '@/types'

const TOPIC_PREFIX = 'https://wevisto.com/devices/'

declare global {
  interface Window {
    __PF_MERCURE_URL__?: string
  }
}

/**
 * Open one EventSource per device topic and merge inbound updates into the
 * devices store. Reconnect on close (Mercure usually proxies through Traefik
 * which can drop idle connections). Cleans up on unmount.
 *
 * The subscription set is reactive — when the device list changes (a new
 * frame is provisioned, or one is removed), connections are added/dropped
 * to match. The server publishes the same JSON shape that GET /api/devices
 * returns, so updates are a straight splat into the existing store entry.
 */
export function useDeviceMercure() {
  const devicesStore = useDevicesStore()
  const { devices } = storeToRefs(devicesStore)

  // deviceId → EventSource. Tracked outside Vue's reactivity to avoid
  // accidentally proxying the native EventSource and breaking it.
  const sources = new Map<number, EventSource>()
  // deviceId → reconnect timer handle.
  const reconnectTimers = new Map<number, number>()

  const baseUrl = window.__PF_MERCURE_URL__
  if (!baseUrl) {
    // No URL configured (dev without a hub, or SSR-render fallback) — quietly
    // no-op rather than throwing. Polling-on-visibility-change is still wired
    // up in HomeView, so the UI keeps working.
    return { connectedCount: () => 0 }
  }

  function open(deviceId: number) {
    if (sources.has(deviceId)) return
    try {
      const url = new URL(baseUrl!)
      url.searchParams.append('topic', TOPIC_PREFIX + deviceId)
      const es = new EventSource(url.toString(), { withCredentials: true })

      es.onmessage = (event) => {
        try {
          const payload = JSON.parse(event.data) as Device | { id: number; deleted: true }
          // Deletion sentinel: server sends {id, deleted: true} when the
          // owner removed the frame. Splice out + close our subscription.
          if ('deleted' in payload && payload.deleted === true) {
            devices.value = devices.value.filter(d => d.id !== payload.id)
            close(payload.id)
            return
          }
          const updated = payload as Device
          const idx = devices.value.findIndex(d => d.id === updated.id)
          if (idx !== -1) {
            // Splice replacement so Vue's reactivity tracks the swap.
            devices.value[idx] = updated
          }
        } catch (e) {
          console.warn('[mercure] parse error', e)
        }
      }

      es.onerror = () => {
        // Mercure / Traefik will sometimes close idle connections; reopen
        // after a short delay rather than spinning. CLOSED is the only
        // terminal state that needs a manual reconnect.
        if (es.readyState === EventSource.CLOSED) {
          close(deviceId)
          const handle = window.setTimeout(() => {
            reconnectTimers.delete(deviceId)
            open(deviceId)
          }, 5000)
          reconnectTimers.set(deviceId, handle)
        }
      }

      sources.set(deviceId, es)
    } catch (e) {
      console.warn('[mercure] open failed for device ' + deviceId, e)
    }
  }

  function close(deviceId: number) {
    const es = sources.get(deviceId)
    if (es) {
      es.close()
      sources.delete(deviceId)
    }
    const timer = reconnectTimers.get(deviceId)
    if (timer !== undefined) {
      clearTimeout(timer)
      reconnectTimers.delete(deviceId)
    }
  }

  // Sync subscriptions to the current device list.
  watch(
    devices,
    (list) => {
      const wantIds = new Set(list.map(d => d.id))
      // Open new ones.
      for (const id of wantIds) if (!sources.has(id)) open(id)
      // Close stale ones.
      for (const id of [...sources.keys()]) if (!wantIds.has(id)) close(id)
    },
    { immediate: true, deep: false },
  )

  onUnmounted(() => {
    for (const id of [...sources.keys()]) close(id)
  })

  return { connectedCount: () => sources.size }
}