ТЗ: Offline-First PWA с синхронизацией фоновых мутаций и IndexedDB

// lib/offline/queue.ts
import { openDB, DBSchema } from 'idb'

interface OfflineMutation {
  id: string
  url: string
  method: 'POST' | 'PUT' | 'PATCH'
  payload: unknown
  createdAt: number
}

interface AppDB extends DBSchema {
  outbox: {
    key: string
    value: OfflineMutation
  }
}

const dbPromise = openDB<AppDB>('fullstacklab-offline', 1, {
  upgrade(db) {
    db.createObjectStore('outbox', { keyPath: 'id' })
  }
})

export async function enqueueMutation(url: string, method: 'POST' | 'PUT' | 'PATCH', payload: unknown) {
  const db = await dbPromise
  const mutation: OfflineMutation = {
    id: crypto.randomUUID(),
    url,
    method,
    payload,
    createdAt: Date.now()
  }
  await db.put('outbox', mutation)
}

export async function flushMutationQueue(): Promise<number> {
  const db = await dbPromise
  const mutations = await db.getAll('outbox')
  let synced = 0

  for (const m of mutations) {
    try {
      const res = await fetch(m.url, {
        method: m.method,
        headers: { 'Content-Type': 'application/json' },
        body: JSON.stringify(m.payload)
      })

      if (res.ok) {
        await db.delete('outbox', m.id)
        synced++
      }
    } catch {
      // При сетевой ошибке прерываем цикл до следующего подключения
      break
    }
  }

  return synced
}