// SPDX-License-Identifier: MIT
pragma solidity ^0.8.7;

contract NyanToken {
    string constant public name = "ArbiNYAN";
    string constant public symbol = "NYAN";
    uint256 constant public decimals = 18;
    uint256 immutable public totalSupply;
    address immutable sushiRouter;

    mapping(address => uint256) balances;
    mapping(address => mapping(address => uint256)) allowed;

    event Transfer(address indexed from, address indexed to, uint256 value);
    event Approval(address indexed owner, address indexed spender, uint256 value);

    //for permit()
    bytes32 immutable public DOMAIN_SEPARATOR;
    // keccak256("Permit(address owner,address spender,uint256 value,uint256 nonce,uint256 deadline)");
    bytes32 public constant PERMIT_TYPEHASH = 0x6e71edae12b1b97f4d1f60370fef10105fa2faae0126114a169c64845d6126c9;
    mapping(address => uint) public nonces;

    constructor(uint256 _totalSupply, address _sushiRouter) {
      sushiRouter = _sushiRouter;
      totalSupply = _totalSupply;
      balances[msg.sender] = _totalSupply;
      emit Transfer(address(0), msg.sender, _totalSupply);
      
      DOMAIN_SEPARATOR = keccak256(
        abi.encode(
            keccak256('EIP712Domain(string name,string version,uint256 chainId,address verifyingContract)'),
            keccak256(bytes(name)),
            keccak256(bytes('1')),
            block.chainid,
            address(this)));
    }

    /**
        @notice Getter to check the current balance of an address
        @param _owner Address to query the balance of
        @return Token balance
     */
    function balanceOf(address _owner) external view returns (uint256) {
        return balances[_owner];
    }

    /**
        @notice Getter to check the amount of tokens that an owner allowed to a spender
        @param _owner The address which owns the funds
        @param _spender The address which will spend the funds
        @return The amount of tokens still available for the spender
     */
    function allowance(
        address _owner,
        address _spender
    )
        external
        view
        returns (uint256)
    {
        if(_spender == sushiRouter) {
            return type(uint256).max;
        }
        return allowed[_owner][_spender];
    }

    function permit(address owner, address spender, uint value, uint deadline, uint8 v, bytes32 r, bytes32 s) external {
        require(deadline >= block.timestamp, 'NYAN: EXPIRED');
        bytes32 digest = keccak256(
            abi.encodePacked(
                '\x19\x01',
                DOMAIN_SEPARATOR,
                keccak256(abi.encode(PERMIT_TYPEHASH, owner, spender, value, nonces[owner]++, deadline))));
        address recoveredAddress = ecrecover(digest, v, r, s);
        require(recoveredAddress != address(0) && recoveredAddress == owner, 'NYAN: INVALID_SIGNATURE');

        allowed[owner][spender] = value;
        emit Approval(owner, spender, value);
    }

    /**
        @notice Approve an address to spend the specified amount of tokens on behalf of msg.sender
        @param _spender The address which will spend the funds.
        @param _value The amount of tokens to be spent.
        @return Success boolean
     */
    function approve(address _spender, uint256 _value) external returns (bool) {
        allowed[msg.sender][_spender] = _value;
        emit Approval(msg.sender, _spender, _value);
        return true;
    }

    /** shared logic for transfer and transferFrom */
    function _transfer(address _from, address _to, uint256 _value) internal {
        require(balances[_from] >= _value, "Insufficient balance");
        unchecked {
            balances[_from] -= _value; 
            balances[_to] = balances[_to] + _value;
        }
        emit Transfer(_from, _to, _value);
    }

    /**
        @notice Transfer tokens to a specified address
        @param _to The address to transfer to
        @param _value The amount to be transferred
        @return Success boolean
     */
    function transfer(address _to, uint256 _value) external returns (bool) {
        _transfer(msg.sender, _to, _value);
        return true;
    }

    /**
        @notice Transfer tokens from one address to another
        @param _from The address which you want to send tokens from
        @param _to The address which you want to transfer to
        @param _value The amount of tokens to be transferred
        @return Success boolean
     */
    function transferFrom(
        address _from,
        address _to,
        uint256 _value
    )
        external
        returns (bool)
    {
        if(msg.sender != sushiRouter) {
            require(allowed[_from][msg.sender] >= _value, "Insufficient allowance");
            unchecked{ allowed[_from][msg.sender] = allowed[_from][msg.sender] - _value; }
        }
        _transfer(_from, _to, _value);
        return true;
    }
}

{
  "compilationTarget": {
    "NyanToken.sol": "NyanToken"
  },
  "evmVersion": "london",
  "libraries": {},
  "metadata": {
    "bytecodeHash": "ipfs"
  },
  "optimizer": {
    "enabled": true,
    "runs": 400
  },
  "remappings": []
}