utilities.js

const {
  ethers: { utils: { keccak256, defaultAbiCoder, toUtf8Bytes, solidityPack } },
} = require("ethers")

const PERMIT_TYPEHASH = keccak256(toUtf8Bytes("Permit(address owner,address spender,uint256 value,uint256 nonce,uint256 deadline)"))

function getDomainSeparator(name, chainId, tokenAddress) {
  return keccak256(
    defaultAbiCoder.encode(
      ["bytes32", "bytes32", "bytes32", "uint256", "address"],
      [
        keccak256(toUtf8Bytes("EIP712Domain(string name,string version,uint256 chainId,address verifyingContract)")),
        keccak256(toUtf8Bytes(name)),
        keccak256(toUtf8Bytes("1")),
        chainId,
        tokenAddress,
      ]
    )
  )
}

async function getApprovalDigest(token, chainId, approve, nonce, deadline) {
  const name = await token.name()
  const DOMAIN_SEPARATOR = getDomainSeparator(name, chainId, token.address)
  return keccak256(
    solidityPack(
      ["bytes1", "bytes1", "bytes32", "bytes32"],
      [
        "0x19",
        "0x01",
        DOMAIN_SEPARATOR,
        keccak256(
          defaultAbiCoder.encode(
            ["bytes32", "address", "address", "uint256", "uint256", "uint256"],
            [PERMIT_TYPEHASH, approve.owner, approve.spender, approve.value, nonce, deadline]
          )
        ),
      ]
    )
  )
}

module.exports = {
  getApprovalDigest
}