import { createWalletClient, http } from "viem";
import { privateKeyToAccount } from "viem/accounts";
import { sepolia } from "viem/chains";

const account = privateKeyToAccount("0x...");
const client = createWalletClient({ account, chain: sepolia, transport: http() });

const domain = {
  name: "MyDApp",
  version: "1",
  chainId: 11155111,
  verifyingContract: "0x...contract",
};

const types = {
  Permit: [
    { name: "owner", type: "address" },
    { name: "spender", type: "address" },
    { name: "value", type: "uint256" },
    { name: "nonce", type: "uint256" },
    { name: "deadline", type: "uint256" },
  ],
} as const;

const message = {
  owner: account.address,
  spender: "0x...spender",
  value: 1_000_000_000_000_000_000n,
  nonce: 0n,
  deadline: BigInt(Math.floor(Date.now() / 1000) + 3600),
};

const signature = await client.signTypedData({
  account,
  domain,
  types,
  primaryType: "Permit",
  message,
});
console.log("Signature:", signature);