FraxswapERC20.sol

// SPDX-License-Identifier: BUSL-1.1
pragma solidity ^0.8.0;

// ====================================================================
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// |   / /_  / ___/ __ `| |/_/  / /_  / / __ \/ __ `/ __ \/ ___/ _ \  |
// |  / __/ / /  / /_/ _>  <   / __/ / / / / / /_/ / / / / /__/  __/  |
// | /_/   /_/   \__,_/_/|_|  /_/   /_/_/ /_/\__,_/_/ /_/\___/\___/   |
// |                                                                  |
// ====================================================================
// ========================== FraxswapERC20 ===========================
// ====================================================================
// Fraxswap ERC-20
// Inspired by https://www.paradigm.xyz/2021/07/twamm
// https://github.com/para-dave/twamm

// Frax Finance: https://github.com/FraxFinance

// Primary Author(s)
// Rich Gee: https://github.com/zer0blockchain
// Dennis: https://github.com/denett

// Logic / Algorithm Ideas
// FrankieIsLost: https://github.com/FrankieIsLost

// Reviewer(s) / Contributor(s)
// Travis Moore: https://github.com/FortisFortuna
// Sam Kazemian: https://github.com/samkazemian
// Drake Evans: https://github.com/DrakeEvans
// Jack Corddry: https://github.com/corddry
// Justin Moore: https://github.com/0xJM

import './interfaces/IUniswapV2ERC20V5.sol';

contract FraxswapERC20 is IUniswapV2ERC20V5 {

    string public constant override name = 'Fraxswap V2';
    string public constant override symbol = 'FS-V2';
    uint8 public constant override decimals = 18;
    uint  public override totalSupply;
    mapping(address => uint) public override balanceOf;
    mapping(address => mapping(address => uint)) public override allowance;

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

    constructor() public {
        uint chainId = block.chainid;
        DOMAIN_SEPARATOR = keccak256(
            abi.encode(
                keccak256('EIP712Domain(string name,string version,uint256 chainId,address verifyingContract)'),
                keccak256(bytes(name)),
                keccak256(bytes('1')),
                chainId,
                address(this)
            )
        );
    }

    function _mint(address to, uint value) internal {
        totalSupply = totalSupply + value;
        balanceOf[to] = balanceOf[to] + value;
        emit Transfer(address(0), to, value);
    }

    function _burn(address from, uint value) internal {
        balanceOf[from] = balanceOf[from] - value;
        totalSupply = totalSupply - value;
        emit Transfer(from, address(0), value);
    }

    function _approve(address owner, address spender, uint value) private {
        allowance[owner][spender] = value;
        emit Approval(owner, spender, value);
    }

    function _transfer(address from, address to, uint value) private {
        balanceOf[from] = balanceOf[from] - value;
        balanceOf[to] = balanceOf[to] + value;
        emit Transfer(from, to, value);
    }

    function approve(address spender, uint value) external override returns (bool) {
        _approve(msg.sender, spender, value);
        return true;
    }

    function transfer(address to, uint value) external override returns (bool) {
        _transfer(msg.sender, to, value);
        return true;
    }

    function transferFrom(address from, address to, uint value) external override returns (bool) {
        if (allowance[from][msg.sender] != type(uint).max) {
            allowance[from][msg.sender] = allowance[from][msg.sender] - value;
        }
        _transfer(from, to, value);
        return true;
    }

    function permit(address owner, address spender, uint value, uint deadline, uint8 v, bytes32 r, bytes32 s) external override {
        require(deadline >= block.timestamp); // 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); // INVALID_SIGNATURE
        _approve(owner, spender, value);
    }
}