function approve(
    address token,
    address spender,
    uint160 amount,
    uint48 expiration
) external;

const permit2 = new ethers.Contract(PERMIT2_ADDRESS, PERMIT2_ABI, signer);

await permit2.approve(
  tokenAddress,
  UNIVERSAL_ROUTER,
  ethers.MaxUint160,                           // Max amount
  Math.floor(Date.now() / 1000) + 365 * 86400  // 1 year expiration
);

function allowance(
    address owner,
    address token,
    address spender
) external view returns (
    uint160 amount,
    uint48 expiration,
    uint48 nonce
);

const [amount, expiration, nonce] = await permit2.allowance(
  userAddress,
  tokenAddress,
  UNIVERSAL_ROUTER
);

const needsApproval = amount < requiredAmount || expiration < Math.floor(Date.now() / 1000);

[
  "function approve(address token, address spender, uint160 amount, uint48 expiration)",
  "function allowance(address owner, address token, address spender) view returns (uint160 amount, uint48 expiration, uint48 nonce)"
]

async function ensurePermit2Approval(signer, tokenAddress, spender, requiredAmount) {
  const permit2 = new ethers.Contract(PERMIT2_ADDRESS, PERMIT2_ABI, signer);
  const owner = await signer.getAddress();

  // 1. Check existing Permit2 sub-approval
  const [amount, expiration] = await permit2.allowance(owner, tokenAddress, spender);
  const now = Math.floor(Date.now() / 1000);

  if (amount >= requiredAmount && expiration > now) {
    return; // Already approved
  }

  // 2. Check ERC-20 approval to Permit2
  const token = new ethers.Contract(tokenAddress, ERC20_ABI, signer);
  const tokenAllowance = await token.allowance(owner, PERMIT2_ADDRESS);

  if (tokenAllowance < requiredAmount) {
    const tx = await token.approve(PERMIT2_ADDRESS, ethers.MaxUint256);
    await tx.wait();
  }

  // 3. Grant Permit2 sub-approval
  const tx = await permit2.approve(
    tokenAddress,
    spender,
    ethers.MaxUint160,
    now + 365 * 86400
  );
  await tx.wait();
}