import { db, getLastSync, setLastSync } from './db.js'
import { api } from './api.js'

let syncing = false
let sseSource = null

async function checkBuildChanged() {
  try {
    const res = await fetch('/api/version')
    const { build } = await res.json()
    if (!build) return
    const stored = await db.meta.get('build')
    if (!stored || stored.value !== build) {
      await db.transaction('rw',
        [db.meta, db.event, db.participants, db.tickets, db.departments, db.volunteers, db.shifts, db.volunteer_shifts],
        async () => {
          await db.meta.clear()
          await db.event.clear()
          await db.participants.clear()
          await db.tickets.clear()
          await db.departments.clear()
          await db.volunteers.clear()
          await db.shifts.clear()
          await db.volunteer_shifts.clear()
          await db.meta.put({ key: 'build', value: build })
        }
      )
    }
  } catch {}
}

export async function syncPull() {
  if (syncing) return
  syncing = true
  try {
    await checkBuildChanged()
    const since = await getLastSync()
    const data = await api.sync.pull(since)

    await db.transaction('rw',
      [db.event, db.participants, db.tickets, db.departments, db.volunteers, db.shifts, db.volunteer_shifts],
      async () => {
        if (data.event) {
          await db.event.put(data.event)
        }
        if (data.participants?.length) {
          await db.participants.bulkPut(data.participants)
          const deleted = data.participants.filter(p => p.deleted_at).map(p => p.id)
          if (deleted.length) await db.participants.bulkDelete(deleted)
        }
        if (data.tickets?.length) {
          await db.tickets.bulkPut(data.tickets)
          const deleted = data.tickets.filter(t => t.deleted_at).map(t => t.id)
          if (deleted.length) await db.tickets.bulkDelete(deleted)
        }
        if (data.departments?.length) {
          await db.departments.bulkPut(data.departments)
          const deleted = data.departments.filter(d => d.deleted_at).map(d => d.id)
          if (deleted.length) await db.departments.bulkDelete(deleted)
        }
        if (data.volunteers?.length) {
          await db.volunteers.bulkPut(data.volunteers)
          const deleted = data.volunteers.filter(v => v.deleted_at).map(v => v.id)
          if (deleted.length) await db.volunteers.bulkDelete(deleted)
        }
        if (data.shifts?.length) {
          await db.shifts.bulkPut(data.shifts)
          const deleted = data.shifts.filter(s => s.deleted_at).map(s => s.id)
          if (deleted.length) await db.shifts.bulkDelete(deleted)
        }
        if (data.volunteer_shifts?.length) {
          await db.volunteer_shifts.bulkPut(data.volunteer_shifts)
          const deleted = data.volunteer_shifts.filter(vs => vs.deleted_at)
            .map(vs => [vs.volunteer_id, vs.shift_id])
          if (deleted.length) await db.volunteer_shifts.bulkDelete(deleted)
        }
      }
    )

    if (data.server_time) await setLastSync(data.server_time)
    return true
  } catch (err) {
    console.warn('Sync pull failed:', err.message)
    return false
  } finally {
    syncing = false
  }
}

export function startSSE(onEvent) {
  if (sseSource) return

  const connect = () => {
    // Get token synchronously from Dexie — SSE doesn't support headers natively,
    // so we pass the token as a query param (acceptable since it's same-origin HTTPS).
    db.session.get(1).then(session => {
      if (!session?.token) return

      sseSource = new EventSource(`/api/sync/stream?token=${encodeURIComponent(session.token)}`)

      sseSource.onmessage = async (e) => {
        try {
          const payload = JSON.parse(e.data)
          if (payload.event === 'checkin') {
            if (payload.data?.type === 'ticket' && payload.data?.ticket) {
              await db.tickets.put(payload.data.ticket)
            }
            if (payload.data?.type === 'volunteer' && payload.data?.volunteer) {
              await db.volunteers.put(payload.data.volunteer)
            }
            onEvent?.(payload)
          }
        } catch (err) {
          console.warn('SSE message error:', err.message)
        }
      }

      sseSource.onerror = () => {
        sseSource?.close()
        sseSource = null
        setTimeout(() => {
          connect()
          syncPull()
        }, 5000)
      }
    }).catch(() => {})
  }

  connect()
}

export function stopSSE() {
  sseSource?.close()
  sseSource = null
}

let syncInterval = null
let onlineHandler = null

export function startSyncLoop(intervalMs = 30000) {
  if (syncInterval) return
  syncInterval = setInterval(() => {
    if (navigator.onLine) syncPull()
  }, intervalMs)
  onlineHandler = () => syncPull()
  window.addEventListener('online', onlineHandler)
}

export function stopSyncLoop() {
  clearInterval(syncInterval)
  syncInterval = null
  if (onlineHandler) {
    window.removeEventListener('online', onlineHandler)
    onlineHandler = null
  }
}