Contract Source Code:

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.20;

/*    
┌─────────────────────────────────────────────────────────────────────────┐
│                                                                         │
│       _______         ______                      _                     │
│      |__   __|       |  ____|                    (_)                    │
│         | | __ ___  _| |__ __ _ _ __ _ __ ___     _ _ __   __ _         │
│         | |/ _` \ \/ /  __/ _` | '__| '_ ` _ \   | | '_ \ / _` |        │
│         | | (_| |>  <| | | (_| | |  | | | | | |  | | | | | (_| |        │
│         |_|\__,_/_/\_\_|  \__,_|_|  |_| |_| |_|(_)_|_| |_|\__, |        │
│                                                            __/ |        │
│                                                           |___/         │
│                                                                         │
│                               taxfarm.ing                               │
│                                                                         │
└─────────────────────────────────────────────────────────────────────────┘
*/

// utils
import {ERC20Logic} from "./utils/ERC20Logic.sol";
import {IUniswapV2Router02} from "./utils/IUniswapV2Router02.sol";
import {IUniswapV2Factory} from "./utils/IUniswapV2Factory.sol";
import {IUniswapV2Pair} from "./utils/IUniswapV2Pair.sol";
import {IWETH} from "./utils/IWETH.sol";

interface ITokenLogic {
    function initialize(address _deployer, string memory _name, string memory _symbol) external payable;
    function launchTimestamp() external view returns(uint);
    function deployer() external view returns(address payable);
}

// token logic (code used by token proxies contracts)
contract TokenLogic is ERC20Logic, ITokenLogic {
    enum FeesTier {
        HIGH_FEES, // 20/20 fees the first 5 minutes
        MEDIUM_FEES, // 5/5 fees until contract has less than 1% of the supply to sell
        LOW_FEES // 1/1 then
    }

    // - token logic constants (not colliding proxies storages)

    uint private constant HIGH_FEES_DURATION = 300; // duration of the high fees stage (20% during 5 minutes)
    uint private constant LIMITS_DURATION = 300; // duration of max tx and max wallet limits in seconds
    uint private constant BASE_TOTAL_SUPPLY = 1_000_000_000 * 10**18;
    uint public constant MAX_TX_AMOUNT = (1 * BASE_TOTAL_SUPPLY) / 100; // max tx 10M (1%)
    uint public constant MAX_WALLET_AMOUNT = (3 * BASE_TOTAL_SUPPLY) / 100; // max wallet 30M (3%)
    uint private constant LIQUIDITY_AMOUNT = (80 * BASE_TOTAL_SUPPLY) / 100; // uniswap liquidity (80%)

    address public immutable tokenFactory;
    address public immutable WETH;

    IUniswapV2Factory public immutable uniswapFactory;
    IUniswapV2Router02 constant uniswapRouter = IUniswapV2Router02(0x7a250d5630B4cF539739dF2C5dAcb4c659F2488D);

    // - instance token storage (stored in each token proxies)

    bool _swapping;

    uint public launchTimestamp; // token launch timestamp

    address payable public deployer;
    address public uniswapPair;

    FeesTier public feesTier; // current token fees tier (could be outdated and updated during the transaction)

    constructor (address _tokenFactory) {
        tokenFactory = _tokenFactory;

        uniswapFactory = IUniswapV2Factory(uniswapRouter.factory());
        WETH = uniswapRouter.WETH();
    }

    modifier lockSwap {
        _swapping = true;
        _;
        _swapping = false;
    }

    // initialize new token datas (called from the factory to the token proxy delegating the call here)
    function initialize(address _deployer, string memory _name, string memory _symbol) external payable {
        require(msg.sender == tokenFactory, "Unauthorized"); // initialized only on the same deployment transaction from token factory
        require(msg.value == 1 ether, "Wrong initial liquidity");

        name = _name;
        symbol = _symbol;
        deployer = payable(_deployer);

        launchTimestamp = block.timestamp;

        _mint(address(this), BASE_TOTAL_SUPPLY - LIQUIDITY_AMOUNT); // mint clogged amount to the contract

        uniswapPair = uniswapFactory.createPair(address(this), WETH);
        _mint(uniswapPair, LIQUIDITY_AMOUNT); // mint liquidity amount to the pair

        IWETH(WETH).deposit{value: 1 ether}();
        assert(IWETH(WETH).transfer(uniswapPair, 1 ether)); // transfer weth to the pair
        IUniswapV2Pair(uniswapPair).mint(tokenFactory); // call low level mint function on pair
    }

    function _transfer(address sender, address recipient, uint256 amount) internal override {
        if (_swapping) return super._transfer(sender, recipient, amount);

        uint fees = _takeFees(sender, recipient, amount);
        if (fees != 0) {
            super._transfer(sender, address(this), fees);
            amount -= fees;
        }

        if (recipient == uniswapPair) _swapFees(amount);

        super._transfer(sender, recipient, amount);

        _forwardFees();
    }

    // return fees amount taken from the transfer (and check for tx and wallet limits)
    function _takeFees(address sender, address recipient, uint amount) private returns (uint) {
        if ((sender != uniswapPair && recipient != uniswapPair) || recipient == tokenFactory || sender == address(this) || recipient == address(uniswapRouter)) return 0;

        // ensure max tx and max wallet
        if (limitsActive() && sender == uniswapPair) {
            require(amount <= MAX_TX_AMOUNT, "Max tx amount reached");
            require(balanceOf(recipient) + amount <= MAX_WALLET_AMOUNT, "Max wallet amount reached");
        }

        // if token has low fees tier, fees are immutable at 1% 
        if (feesTier == FeesTier.LOW_FEES) return amount / 100; // 1% fees

        // else, if token has medium fees, check if we can change tier and return correct fees
        else if (feesTier == FeesTier.MEDIUM_FEES) {
            if (balanceOf(address(this)) <= totalSupply / 100) {
                feesTier = FeesTier.LOW_FEES;
                return amount / 100; // 1% fees
            }
            return amount / 20; // 5% fees
        }

        // else, token is at high fees tier and we check if we can change tier and return correct fees
        else {
            if (block.timestamp - launchTimestamp > HIGH_FEES_DURATION) {
                feesTier = FeesTier.MEDIUM_FEES;
                return amount / 20; // 5% fees
            }
            return amount / 5; // 20% fees
        }
    }

    // swap some fees tokens to eth
    function _swapFees(uint maxAmount) private lockSwap {
        uint tokenAmount = min(min(maxAmount, balanceOf(address(this))), totalSupply / 100);
        if (tokenAmount < 1e18) return; // prevent too small swaps

        address[] memory path = new address[](2);
        path[0] = address(this);
        path[1] = WETH;

        _approve(address(this), address(uniswapRouter), tokenAmount);
        uniswapRouter.swapExactTokensForETHSupportingFeeOnTransferTokens(
            tokenAmount,
            0,
            path,
            address(this),
            block.timestamp
        );
    }   

    // return true if max wallet and max tx limitations are still active
    function limitsActive() public view returns (bool) {
        return block.timestamp - launchTimestamp <= LIMITS_DURATION;
    }
    
    // forward contract fees to token factory (also try to burn liquidity)
    function _forwardFees() private {
        uint balance = address(this).balance;

        if (balance == 0) return;

        (bool result, ) = tokenFactory.call{value: balance}("");
        require(result, "Failed to forward fees");
    }

    function min(uint a, uint b) private pure returns (uint) {
        return a < b ? a : b;
    }

    receive() external payable {}
}

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.20;

abstract contract Context {
    function _msgSender() internal view virtual returns (address) {
        return msg.sender;
    }

    function _msgData() internal view virtual returns (bytes calldata) {
        return msg.data;
    }
}

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.20;

import {IERC20} from "./IERC20.sol";
import {Context} from "./Context.sol";

interface IERC20Metadata is IERC20 {
    function name() external view returns (string memory);
    function symbol() external view returns (string memory);
    function decimals() external view returns (uint8);
}

// contract implementing the logic of ERC20 standard (thus usable from proxies)
contract ERC20Logic is Context, IERC20, IERC20Metadata {
    mapping(address => uint256) private _balances;
    mapping(address => mapping(address => uint256)) private _allowances;

    uint256 public totalSupply;

    string public name;
    string public symbol;

    function decimals() public view virtual override returns (uint8) {
        return 18;
    }

    function balanceOf(address account) public view virtual override returns (uint256) {
        return _balances[account];
    }

    function transfer(address recipient, uint256 amount) public virtual override returns (bool) {
        _transfer(_msgSender(), recipient, amount);
        return true;
    }

    function allowance(address owner, address spender) public view virtual override returns (uint256) {
        return _allowances[owner][spender];
    }

    function approve(address spender, uint256 amount) public virtual override returns (bool) {
        _approve(_msgSender(), spender, amount);
        return true;
    }

    function transferFrom(
        address sender,
        address recipient,
        uint256 amount
    ) public virtual override returns (bool) {
        _transfer(sender, recipient, amount);

        uint256 currentAllowance = _allowances[sender][_msgSender()];
        require(currentAllowance >= amount, "ERC20: transfer amount exceeds allowance");
        unchecked {
            _approve(sender, _msgSender(), currentAllowance - amount);
        }

        return true;
    }

    function burn(uint256 value) public virtual {
        _burn(_msgSender(), value);
    }

    function increaseAllowance(address spender, uint256 addedValue) public virtual returns (bool) {
        _approve(_msgSender(), spender, _allowances[_msgSender()][spender] + addedValue);
        return true;
    }

    function decreaseAllowance(address spender, uint256 subtractedValue) public virtual returns (bool) {
        uint256 currentAllowance = _allowances[_msgSender()][spender];
        require(currentAllowance >= subtractedValue, "ERC20: decreased allowance below zero");
        unchecked {
            _approve(_msgSender(), spender, currentAllowance - subtractedValue);
        }

        return true;
    }

    function _transfer(
        address sender,
        address recipient,
        uint256 amount
    ) internal virtual {
        require(sender != address(0), "ERC20: transfer from the zero address");
        require(recipient != address(0), "ERC20: transfer to the zero address");

        uint256 senderBalance = _balances[sender];
        require(senderBalance >= amount, "ERC20: transfer amount exceeds balance");
        unchecked {
            _balances[sender] = senderBalance - amount;
        }
        _balances[recipient] += amount;

        emit Transfer(sender, recipient, amount);
    }

    function _mint(address account, uint256 amount) internal virtual {
        require(account != address(0), "ERC20: mint to the zero address");

        totalSupply += amount;
        _balances[account] += amount;
        emit Transfer(address(0), account, amount);
    }

    function _burn(address account, uint256 amount) internal virtual {
        require(account != address(0), "ERC20: burn from the zero address");

        uint256 accountBalance = _balances[account];
        require(accountBalance >= amount, "ERC20: burn amount exceeds balance");
        unchecked {
            _balances[account] = accountBalance - amount;
        }
        totalSupply -= amount;

        emit Transfer(account, address(0), amount);
    }

    function _approve(
        address owner,
        address spender,
        uint256 amount
    ) internal virtual {
        require(owner != address(0), "ERC20: approve from the zero address");
        require(spender != address(0), "ERC20: approve to the zero address");

        _allowances[owner][spender] = amount;
        emit Approval(owner, spender, amount);
    }
}

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.20;

interface IERC20 {
    function totalSupply() external view returns (uint256);
    function balanceOf(address account) external view returns (uint256);
    function transfer(address recipient, uint256 amount) external returns (bool);
    function allowance(address owner, address spender) external view returns (uint256);
    function approve(address spender, uint256 amount) external returns (bool);
    function transferFrom(
        address sender,
        address recipient,
        uint256 amount
    ) external returns (bool);
    function burn(uint256 value) external;

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

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.20;

interface IUniswapV2Factory {
    function getPair(address tokenA, address tokenB) external view returns (address pair);
    function createPair(address tokenA, address tokenB) external returns (address pair);
}

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.20;

interface IUniswapV2Pair {
    function mint(address to) external returns (uint liquidity);
}

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.20;

interface IUniswapV2Router02 {
    function swapExactTokensForETHSupportingFeeOnTransferTokens(
        uint amountIn,
        uint amountOutMin,
        address[] calldata path,
        address to,
        uint deadline
    ) external;

    function factory() external pure returns (address);

    function WETH() external pure returns (address);
    
    function addLiquidityETH(
        address token,
        uint amountTokenDesired,
        uint amountTokenMin,
        uint amountETHMin,
        address to,
        uint deadline
    ) external payable returns (uint amountToken, uint amountETH, uint liquidity);

    function removeLiquidityETH(
        address token,
        uint liquidity,
        uint amountTokenMin,
        uint amountETHMin,
        address to,
        uint deadline
    ) external returns (uint amountToken, uint amountETH);
}

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.20;

interface IWETH {
    function deposit() external payable;
    function transfer(address to, uint value) external returns (bool);
    function withdraw(uint) external;
}