Create a Simple Dividend ERC20 token

---

//SPDX-License-Identifier: Unlicense

pragma solidity 0.8.4;

import { ERC20 } from "@openzeppelin/contracts/token/ERC20/ERC20.sol";

import { Ownable } from "@openzeppelin/contracts/access/Ownable.sol";

import { ReentrancyGuard } from "@openzeppelin/contracts/security/ReentrancyGuard.sol";

contract DToken is Ownable, ReentrancyGuard, ERC20 {

uint256 constant public MAX_SUPPLY = 100 ether;

uint32 constant private MULTIPLIER = 1e9; // in gwei

/// @notice Eth share of each token in gwei

uint256 dividendPerToken;

mapping(address => uint256) xDividendPerToken;

/// @notice Amount that should have been withdrawn

mapping (address => uint256) credit;

/// @notice State variable representing amount withdrawn by account in ETH

mapping (address => uint256) debt;

/// @notice If locked is true, users are not allowed to withdraw funds

bool public locked;

event FundsReceived(uint256 amount, uint256 dividendPerToken);

modifier mintable(uint256 amount) {

require(amount + totalSupply() <= MAX_SUPPLY, "amount surpasses max supply");

_;

}

modifier isUnlocked() {

require(!locked, "contract is currently locked");

_;

}

receive() external payable {

require(totalSupply() != 0, "No tokens minted");

dividendPerToken += msg.value * MULTIPLIER / totalSupply();

// gwei Multiplier decreases impact of remainder though

emit FundsReceived(msg.value, dividendPerToken);

}

constructor(string memory name_, string memory symbol_) ERC20(name_, symbol_) {

locked = true;

}

function mint(address to_, uint256 amount_) public onlyOwner mintable(amount_) {

_withdrawToCredit(to_);

_mint(to_, amount_);

}

function toggleLock() external onlyOwner {

locked = !locked;

}

/// @notice Withdraw Eth from contract onto the caller w.r.t balance of token held by caller

/// @dev Reentrancy Guard modifier in order to protect the transaction from reentrancy attack

function withdraw() external nonReentrant isUnlocked {

uint256 holderBalance = balanceOf(_msgSender());

require(holderBalance != 0, "DToken: caller possess no shares");

uint256 amount = ( (dividendPerToken - xDividendPerToken[_msgSender()]) * holderBalance / MULTIPLIER);

amount += credit[_msgSender()];

credit[_msgSender()] = 0;

xDividendPerToken[_msgSender()] = dividendPerToken;

(bool success, ) = payable(_msgSender()).call{value: amount}("");

require(success, "DToken: Could not withdraw eth");

}

/// @notice In extreme cases (i.e. lost tokens) leading to unaccessed funds, owner can resort to this function

/// @dev Putting this function there requires trust from the community, hence, this needs to be discussed

function emergencyWithdraw() external onlyOwner {

(bool success, ) = payable(owner()).call{value: address(this).balance}("");

require(success, "DToken: Could not withdraw eth");

}

//=================================== INTERNAL ==============================================

function _beforeTokenTransfer(

address from,

address to,

uint256 amount

) internal override {

if(from == address (0) || to == address(0)) return;

// receiver first withdraw funds to credit

_withdrawToCredit(to);

_withdrawToCredit(from);

}

//=================================== PRIVATE ==============================================

function _withdrawToCredit(

address to_

) private

{

uint256 recipientBalance = balanceOf(to_);

if(recipientBalance != 0) {

uint256 amount = ( (dividendPerToken - xDividendPerToken[to_]) * recipientBalance / MULTIPLIER);

credit[to_] += amount;

}

xDividendPerToken[to_] = dividendPerToken;

}

}