Turnpike/frontend/src/sync.js

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

let syncing = false
let sseSource = null

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

    await db.transaction('rw',
      [db.event, db.attendees, db.departments, db.volunteers, db.shifts, db.volunteer_shifts],
      async () => {
        if (data.event) {
          await db.event.put(data.event)
        }
        if (data.attendees?.length) {
          await db.attendees.bulkPut(data.attendees)
          // Purge hard-deleted records from Dexie
          const deleted = data.attendees.filter(a => a.deleted_at).map(a => a.id)
          if (deleted.length) await db.attendees.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)
        }
      }
    )

    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 = (e) => {
        try {
          const payload = JSON.parse(e.data)
          if (payload.event === 'checkin') {
            // Apply check-in to local Dexie immediately
            if (payload.data?.type === 'attendee' && payload.data?.attendee) {
              db.attendees.put(payload.data.attendee)
            }
            if (payload.data?.type === 'volunteer' && payload.data?.volunteer) {
              db.volunteers.put(payload.data.volunteer)
            }
            onEvent?.(payload)
          }
        } catch {}
      }

      sseSource.onerror = () => {
        sseSource?.close()
        sseSource = null
        // Reconnect after 5s
        setTimeout(connect, 5000)
      }
    })
  }

  connect()
}

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

// Poll for sync when online, with exponential backoff on failure
let syncInterval = null

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

export function stopSyncLoop() {
  clearInterval(syncInterval)
  syncInterval = null
}