Nst.sol

// SPDX-License-Identifier: AGPL-3.0-or-later

/// Nst.sol -- Nst token

// Copyright (C) 2017, 2018, 2019 dbrock, rain, mrchico
// Copyright (C) 2023 Dai Foundation
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU Affero General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU Affero General Public License for more details.
//
// You should have received a copy of the GNU Affero General Public License
// along with this program.  If not, see <https://www.gnu.org/licenses/>.

pragma solidity ^0.8.21;

import "@openzeppelin/contracts-upgradeable/proxy/utils/UUPSUpgradeable.sol";

interface IERC1271 {
    function isValidSignature(
        bytes32,
        bytes memory
    ) external view returns (bytes4);
}

contract Nst is UUPSUpgradeable {
    mapping (address => uint256) public wards;

    // --- ERC20 Data ---
    string  public constant name     = "Nst Stablecoin";
    string  public constant symbol   = "NST";
    string  public constant version  = "1";
    uint8   public constant decimals = 18;
    uint256 public totalSupply;

    mapping (address => uint256)                      public balanceOf;
    mapping (address => mapping (address => uint256)) public allowance;
    mapping (address => uint256)                      public nonces;

    // --- Events ---
    event Rely(address indexed usr);
    event Deny(address indexed usr);
    event Approval(address indexed owner, address indexed spender, uint256 value);
    event Transfer(address indexed from, address indexed to, uint256 value);

    // --- EIP712 niceties ---
    bytes32 public constant PERMIT_TYPEHASH = keccak256("Permit(address owner,address spender,uint256 value,uint256 nonce,uint256 deadline)");

    modifier auth {
        require(wards[msg.sender] == 1, "Nst/not-authorized");
        _;
    }

    constructor() {
        _disableInitializers(); // Avoid initializing in the context of the implementation
    }

    // --- Upgradability ---

    function initialize() initializer external {
        __UUPSUpgradeable_init();

        wards[msg.sender] = 1;
        emit Rely(msg.sender);
    }

    function _authorizeUpgrade(address newImplementation) internal override auth {}

    function getImplementation() external view returns (address) {
        return ERC1967Utils.getImplementation();
    }

    function _calculateDomainSeparator(uint256 chainId) private view returns (bytes32) {
        return keccak256(
            abi.encode(
                keccak256("EIP712Domain(string name,string version,uint256 chainId,address verifyingContract)"),
                keccak256(bytes(name)),
                keccak256(bytes(version)),
                chainId,
                address(this)
            )
        );
    }

    function DOMAIN_SEPARATOR() external view returns (bytes32) {
        return _calculateDomainSeparator(block.chainid);
    }

    // --- Administration ---
    function rely(address usr) external auth {
        wards[usr] = 1;
        emit Rely(usr);
    }

    function deny(address usr) external auth {
        wards[usr] = 0;
        emit Deny(usr);
    }

    // --- ERC20 Mutations ---
    function transfer(address to, uint256 value) external returns (bool) {
        require(to != address(0) && to != address(this), "Nst/invalid-address");
        uint256 balance = balanceOf[msg.sender];
        require(balance >= value, "Nst/insufficient-balance");

        unchecked {
            balanceOf[msg.sender] = balance - value;
            balanceOf[to] += value; // note: we don't need an overflow check here b/c sum of all balances == totalSupply
        }

        emit Transfer(msg.sender, to, value);

        return true;
    }

    function transferFrom(address from, address to, uint256 value) external returns (bool) {
        require(to != address(0) && to != address(this), "Nst/invalid-address");
        uint256 balance = balanceOf[from];
        require(balance >= value, "Nst/insufficient-balance");

        if (from != msg.sender) {
            uint256 allowed = allowance[from][msg.sender];
            if (allowed != type(uint256).max) {
                require(allowed >= value, "Nst/insufficient-allowance");

                unchecked {
                    allowance[from][msg.sender] = allowed - value;
                }
            }
        }

        unchecked {
            balanceOf[from] = balance - value;
            balanceOf[to] += value; // note: we don't need an overflow check here b/c sum of all balances == totalSupply
        }

        emit Transfer(from, to, value);

        return true;
    }

    function approve(address spender, uint256 value) external returns (bool) {
        allowance[msg.sender][spender] = value;

        emit Approval(msg.sender, spender, value);

        return true;
    }

    // --- Mint/Burn ---
    function mint(address to, uint256 value) external auth {
        require(to != address(0) && to != address(this), "Nst/invalid-address");
        unchecked {
            balanceOf[to] = balanceOf[to] + value; // note: we don't need an overflow check here b/c balanceOf[to] <= totalSupply and there is an overflow check below
        }
        totalSupply = totalSupply + value;

        emit Transfer(address(0), to, value);
    }

    function burn(address from, uint256 value) external {
        uint256 balance = balanceOf[from];
        require(balance >= value, "Nst/insufficient-balance");

        if (from != msg.sender) {
            uint256 allowed = allowance[from][msg.sender];
            if (allowed != type(uint256).max) {
                require(allowed >= value, "Nst/insufficient-allowance");

                unchecked {
                    allowance[from][msg.sender] = allowed - value;
                }
            }
        }

        unchecked {
            balanceOf[from] = balance - value; // note: we don't need overflow checks b/c require(balance >= value) and balance <= totalSupply
            totalSupply     = totalSupply - value;
        }

        emit Transfer(from, address(0), value);
    }

    // --- Approve by signature ---
    function _isValidSignature(
        address signer,
        bytes32 digest,
        bytes memory signature
    ) internal view returns (bool valid) {
        if (signature.length == 65) {
            bytes32 r;
            bytes32 s;
            uint8 v;
            assembly {
                r := mload(add(signature, 0x20))
                s := mload(add(signature, 0x40))
                v := byte(0, mload(add(signature, 0x60)))
            }
            if (signer == ecrecover(digest, v, r, s)) {
                return true;
            }
        }

        if (signer.code.length > 0) {
            (bool success, bytes memory result) = signer.staticcall(
                abi.encodeCall(IERC1271.isValidSignature, (digest, signature))
            );
            valid = (success &&
                result.length == 32 &&
                abi.decode(result, (bytes4)) == IERC1271.isValidSignature.selector);
        }
    }

    function permit(
        address owner,
        address spender,
        uint256 value,
        uint256 deadline,
        bytes memory signature
    ) public {
        require(block.timestamp <= deadline, "Nst/permit-expired");
        require(owner != address(0), "Nst/invalid-owner");

        uint256 nonce;
        unchecked { nonce = nonces[owner]++; }

        bytes32 digest =
            keccak256(abi.encodePacked(
                "\x19\x01",
                _calculateDomainSeparator(block.chainid),
                keccak256(abi.encode(
                    PERMIT_TYPEHASH,
                    owner,
                    spender,
                    value,
                    nonce,
                    deadline
                ))
            ));

        require(_isValidSignature(owner, digest, signature), "Nst/invalid-permit");

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

    function permit(
        address owner,
        address spender,
        uint256 value,
        uint256 deadline,
        uint8 v,
        bytes32 r,
        bytes32 s
    ) external {
        permit(owner, spender, value, deadline, abi.encodePacked(r, s, v));
    }
}