// lib/amazon/auth.ts — LWA OAuth token with caching
let tokenCache: { accessToken: string; expiresAt: number } | null = null;

export async function getAccessToken(): Promise<string> {
  if (tokenCache && tokenCache.expiresAt > Date.now() + 60000) return tokenCache.accessToken;

  const res = await fetch('https://api.amazon.com/auth/o2/token', {
    method: 'POST',
    headers: { 'Content-Type': 'application/x-www-form-urlencoded' },
    body: new URLSearchParams({
      grant_type: 'refresh_token',
      refresh_token: process.env.AMAZON_REFRESH_TOKEN!,
      client_id: process.env.AMAZON_CLIENT_ID!,
      client_secret: process.env.AMAZON_CLIENT_SECRET!,
    }),
  });

  const data = await res.json();
  tokenCache = { accessToken: data.access_token, expiresAt: Date.now() + data.expires_in * 1000 };
  return tokenCache.accessToken;
}

export async function updateAmazonInventory(sellerId: string, sku: string, quantity: number) {
  const accessToken = await getAccessToken();
  // SP-API also requires AWS Signature V4 — use @smithy/signature-v4
  return fetch(`https://sellingpartnerapi-na.amazon.com/listings/2021-08-01/items/${sellerId}/${encodeURIComponent(sku)}`, {
    method: 'PATCH',
    headers: { 'x-amz-access-token': accessToken, 'Content-Type': 'application/json' },
    body: JSON.stringify({
      productType: 'PRODUCT',
      patches: [{ op: 'replace', path: '/attributes/fulfillment_availability', value: [{
        fulfillment_channel_code: 'DEFAULT',
        quantity,
        marketplace_id: 'ATVPDKIKX0DER', // US marketplace
      }] }],
    }),
  });
}

export async function pollAmazonOrders() {
  const lastPolledAt = await db.syncState.getLastPolled('amazon') ?? new Date(Date.now() - 3_600_000);
  const accessToken = await getAccessToken();

  const params = new URLSearchParams({
    MarketplaceIds: 'ATVPDKIKX0DER',
    CreatedAfter: lastPolledAt.toISOString(),
    OrderStatuses: 'Unshipped,PartiallyShipped',
  });

  const res = await fetch(`https://sellingpartnerapi-na.amazon.com/orders/v0/orders?${params}`, {
    headers: { 'x-amz-access-token': accessToken },
  });
  const { payload } = await res.json();

  for (const amazonOrder of payload.Orders ?? []) {
    // Idempotent: skip if already imported
    if (await db.orders.findByExternalId(amazonOrder.AmazonOrderId)) continue;

    await orderQueue.add('import-order', {
      externalId: amazonOrder.AmazonOrderId,
      channel: 'amazon',
      // ...map order fields
    }, { jobId: `amazon-${amazonOrder.AmazonOrderId}` });
  }

  await db.syncState.updateLastPolled('amazon', new Date());
}

export async function syncInventoryAcrossChannels(sku: string, quantity: number, source: string) {
  const tasks = [];

  if (source !== 'amazon') {
    tasks.push(updateAmazonInventory(process.env.AMAZON_SELLER_ID!, sku, quantity)
      .catch(err => console.error(`Amazon sync failed for ${sku}:`, err)));
  }

  if (source !== 'ebay') {
    tasks.push(ebayClient.updateInventoryItem(sku, quantity)
      .catch(err => console.error(`eBay sync failed for ${sku}:`, err)));
  }

  // Run all syncs in parallel; individual failures logged but don't block others
  await Promise.allSettled(tasks);
}