Watch for Payments

export async function watchPayments(
  startBlock: bigint,
  store: PaymentEventStore,
) {
  async function backfillConfirmed() {
    const head = await client.getBlockNumber();
    if (head <= confirmations) return;
    const toBlock = head - confirmations;
    const cursor = await store.lastScannedBlock();
    const fromBlock = cursor && cursor > startBlock + confirmations
      ? cursor - confirmations
      : startBlock;
    const logs = await client.getContractEvents({
      address: AUTH_CAPTURE_ESCROW,
      abi: authCaptureEscrowAbi,
      fromBlock,
      toBlock,
      strict: true,
    });

    // Replace the overlap and advance the cursor in one database transaction.
    await store.replaceRange(fromBlock, toBlock, logs);
  }

  await backfillConfirmed();
  return client.watchContractEvent({
    address: AUTH_CAPTURE_ESCROW,
    abi: authCaptureEscrowAbi,
    onLogs: backfillConfirmed,
    onError: (error) => console.error("Payment watcher failed", error),
  });
}