import { uuidv7 } from '@sims/domain'
import type { BillTotals, Item } from '@sims/domain'
import type { LineInput, TaxClassRow } from '@sims/billing-engine'
import type { BillOverride, BootstrapStore, OfflineBillBody, PosUser } from './api'

/**
 * S4 counter resilience — the browser POS survives the store-server dying mid-shift.
 * Two responsibilities, one IndexedDB database (`sims-pos-offline`):
 *
 *  1. `bills`  — bills committed while the server was unreachable. Each is a client-
 *     UUIDv7 fact with a provisional token (OFF-1, OFF-2…); the reconnect drain
 *     POSTs them oldest-first and the server assigns the real GST doc no.
 *  2. `cache`  — the catalog snapshot (items + tax classes + store/users) persisted
 *     at login so a mid-shift refresh with the server down still reaches billing.
 *
 * Raw IndexedDB, no new dependency (R-parity with the zero-runtime-dep discipline).
 * The pure helpers below (token/record/body shaping) hold the serialization logic
 * and are unit-tested without a browser; everything that touches `indexedDB` stays
 * inside a function body so this module still imports in Node (vitest).
 *
 * M11 (offline PII): the queued bill persists only `customerId` — never the buyer's
 * name or GSTIN — and the server re-resolves buyer identity from that id at drain, so
 * no customer PII is written to a shared counter PC. The catalog `cache` (which also
 * holds the staff roster) is wiped on Lock/logout via `clearCatalogCache`. NOTE: this
 * removes the standing PII, not the queue itself — true at-rest ENCRYPTION of the
 * remaining offline queue is a follow-up (server-tier SQLCipher is finding H3).
 */

// ---------- queued bill record ----------

export interface QueuedBill {
  /** Client-generated bill id (uuidv7) — the server's idempotency key on drain. */
  id: string
  /** Monotonic provisional sequence (1, 2, 3…) — drives OFF-n and drain order. */
  seq: number
  /** Human token shown on the provisional receipt and in drain notices ("OFF-1"). */
  provisionalToken: string
  storeId: string
  counterId: string
  /** Local provenance only — who rang it up on this device. The server attributes the
   *  drained bill to the session that drains it, never to this field (SEC fix). */
  cashierId: string
  shiftId: string
  /** The ONLY buyer identity persisted offline (M11): the server re-resolves the name,
   *  GSTIN and place-of-supply from this id + tenant at drain, exactly as for an online
   *  bill — so no customer PII (name/GSTIN) is ever written to this device. A walk-in
   *  bill has no customerId and stores nothing extra. */
  customerId?: string
  businessDate: string
  lines: LineInput[]
  payments: { mode: string; amountPaise: number }[]
  /** Full totals snapshot (immutable fact); `payablePaise` becomes clientPayablePaise on drain. */
  totals: BillTotals
  overrides?: BillOverride[]
  createdAt: string
}

// ---------- pure helpers (unit-tested; no IndexedDB) ----------

/** The provisional token printed instead of a GST doc no while offline. */
export function nextProvisionalToken(seq: number): string {
  return `OFF-${seq}`
}

/** Build the immutable queued-bill record from the cart at commit time. */
export function buildQueuedBill(input: {
  seq: number
  storeId: string; counterId: string; cashierId: string; shiftId: string
  customerId?: string
  businessDate: string
  lines: LineInput[]
  payments: { mode: string; amountPaise: number }[]
  totals: BillTotals
  overrides?: BillOverride[]
  /** Injectable clock for deterministic tests; defaults to now. */
  now?: number
}): QueuedBill {
  const at = input.now ?? Date.now()
  return {
    id: uuidv7(at),
    seq: input.seq,
    provisionalToken: nextProvisionalToken(input.seq),
    storeId: input.storeId,
    counterId: input.counterId,
    cashierId: input.cashierId,
    shiftId: input.shiftId,
    ...(input.customerId !== undefined ? { customerId: input.customerId } : {}),
    businessDate: input.businessDate,
    lines: input.lines,
    payments: input.payments,
    totals: input.totals,
    ...(input.overrides !== undefined && input.overrides.length > 0 ? { overrides: input.overrides } : {}),
    createdAt: new Date(at).toISOString(),
  }
}

/**
 * Shape a queued bill into the /api/bills/offline drain payload. Drops display-only
 * fields AND the local cashierId — the server takes tenant + cashier from the live
 * session, never from the body (SEC fix).
 */
export function toOfflineBillBody(q: QueuedBill): OfflineBillBody {
  return {
    id: q.id,
    storeId: q.storeId,
    counterId: q.counterId,
    shiftId: q.shiftId,
    ...(q.customerId !== undefined ? { customerId: q.customerId } : {}),
    businessDate: q.businessDate,
    lines: q.lines,
    payments: q.payments,
    clientPayablePaise: q.totals.payablePaise,
    ...(q.overrides !== undefined ? { overrides: q.overrides } : {}),
  }
}

/**
 * The provisional-token sequence, persisted in localStorage so OFF-n stays
 * monotonic across refreshes and never reuses a number after a bill drains and
 * leaves the queue (deriving from the queue's max seq would recycle numbers).
 */
const SEQ_KEY = 'pos.offSeq'
export function nextOffSeq(): number {
  let n = 0
  try { n = Number(localStorage.getItem(SEQ_KEY) ?? '0') } catch { n = 0 }
  const next = (Number.isFinite(n) ? n : 0) + 1
  try { localStorage.setItem(SEQ_KEY, String(next)) } catch { /* non-browser: caller supplies seq */ }
  return next
}

// ---------- IndexedDB access (browser-only) ----------

const DB_NAME = 'sims-pos-offline'
const DB_VERSION = 1
const BILLS = 'bills'
const CACHE = 'cache'

function openIdb(): Promise<IDBDatabase> {
  return new Promise((resolve, reject) => {
    const req = indexedDB.open(DB_NAME, DB_VERSION)
    req.onupgradeneeded = () => {
      const db = req.result
      if (!db.objectStoreNames.contains(BILLS)) db.createObjectStore(BILLS, { keyPath: 'id' })
      if (!db.objectStoreNames.contains(CACHE)) db.createObjectStore(CACHE, { keyPath: 'key' })
    }
    req.onsuccess = () => resolve(req.result)
    req.onerror = () => reject(req.error ?? new Error('IndexedDB open failed'))
  })
}

/** Run one request in its own transaction; resolves on transaction commit (durable). */
function run<T>(store: string, mode: IDBTransactionMode, fn: (s: IDBObjectStore) => IDBRequest<T>): Promise<T> {
  return openIdb().then((db) => new Promise<T>((resolve, reject) => {
    const tx = db.transaction(store, mode)
    const req = fn(tx.objectStore(store))
    let result: T
    req.onsuccess = () => { result = req.result }
    tx.oncomplete = () => { db.close(); resolve(result) }
    tx.onerror = () => { db.close(); reject(tx.error ?? new Error('IndexedDB tx failed')) }
    tx.onabort = () => { db.close(); reject(tx.error ?? new Error('IndexedDB tx aborted')) }
  }))
}

export async function enqueueBill(bill: QueuedBill): Promise<void> {
  await run(BILLS, 'readwrite', (s) => s.put(bill))
}

/** All queued bills, oldest-first (the drain order). */
export async function listQueuedBills(): Promise<QueuedBill[]> {
  const all = await run<QueuedBill[]>(BILLS, 'readonly', (s) => s.getAll() as IDBRequest<QueuedBill[]>)
  return all.sort((a, b) => a.seq - b.seq)
}

export async function removeQueuedBill(id: string): Promise<void> {
  await run(BILLS, 'readwrite', (s) => s.delete(id) as unknown as IDBRequest<undefined>)
}

export async function countQueuedBills(): Promise<number> {
  return run<number>(BILLS, 'readonly', (s) => s.count())
}

// ---------- catalog cache (browser-only) ----------

export interface CatalogCache {
  key: 'catalog'
  store: BootstrapStore
  users: PosUser[]
  taxClasses: TaxClassRow[]
  items: Item[]
  savedAt: string
}

export async function saveCatalogCache(data: Omit<CatalogCache, 'key'>): Promise<void> {
  await run(CACHE, 'readwrite', (s) => s.put({ key: 'catalog', ...data }))
}

export async function loadCatalogCache(): Promise<CatalogCache | undefined> {
  return run<CatalogCache | undefined>(CACHE, 'readonly', (s) => s.get('catalog') as IDBRequest<CatalogCache | undefined>)
}

/**
 * Wipe the catalog/roster cache on Lock/logout (M11). Clears the whole `cache` store —
 * store details, staff roster and item master — so nothing about the shop or its staff
 * lingers on a shared counter PC once the cashier locks. Un-drained queued bills live in
 * a SEPARATE store (`bills`) and are intentionally left intact: a lock must never lose a
 * sale (R18); the catalog is re-fetched fresh on the next login. Post-lock the resume
 * context is cleared too (App.onLock), so this cache would never be read again anyway.
 */
export async function clearCatalogCache(): Promise<void> {
  await run(CACHE, 'readwrite', (s) => s.clear() as unknown as IDBRequest<undefined>)
}