// SPDX-License-Identifier: MIT

pragma solidity ^0.6.12;
pragma experimental ABIEncoderV2;

contract Permit {
    function getPermitMessage(
        string memory tokenName,
        address tokenAddress,
        string memory version,
        address owner,
        address spender,
        uint256 chainId,
        uint256 nonce,
        uint256 amount,
        uint256 deadline
    ) public pure returns (bytes32) {
        bytes32 permitTypehash = keccak256(
            "Permit(address owner,address spender,uint256 value,uint256 nonce,uint256 deadline)"
        );
        uint16 permitFuncSelector = uint16(0x1901);
        bytes32 domain = keccak256(
            abi.encode(
                keccak256("EIP712Domain(string name,string version,uint256 chainId,address verifyingContract)"),
                keccak256(bytes(tokenName)),
                keccak256(bytes(version)),
                chainId,
                tokenAddress
            )
        );

        return
            keccak256(
                abi.encodePacked(
                    permitFuncSelector,
                    domain,
                    keccak256(abi.encode(permitTypehash, owner, spender, amount, nonce, deadline))
                )
            );
    }
}