ETRXFixedPriceSale

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

interface IERC20 {
  function transfer(address to, uint256 amount) external returns (bool);
  function balanceOf(address account) external view returns (uint256);
  function decimals() external view returns (uint8);
}

contract ETRXFixedPriceSale {
  address public owner;
  IERC20  public token;
  // tokens per 1 ETH (whole tokens, not 1e18 scaled)
  uint256 public rate;
  uint256 public weiRaised;
  bool    public live;

  event Contributed(address indexed buyer, uint256 weiAmount, uint256 tokensOut);
  event WithdrawETH(address to, uint256 amount);
  event WithdrawUnsold(address to, uint256 amount);

  modifier onlyOwner(){ require(msg.sender == owner, "not owner"); _; }

  constructor(address _token, uint256 _rate) {
    owner = msg.sender;
    token = IERC20(_token);
    rate  = _rate; // e.g., 40000 means 1 ETH -> 40,000 ETRX
  }

  function setLive(bool _live) external onlyOwner { live = _live; }
  function setRate(uint256 _rate) external onlyOwner { rate = _rate; }

  receive() external payable { contribute(); }

  function contribute() public payable {
    require(live, "presale not live");
    require(msg.value > 0, "no ETH");

    uint8 d = token.decimals(); // expected 18; still safe if not
    // tokensOut = ETH_in_wei * rate / 1 ether * 10^decimals
    uint256 tokensOut = (msg.value * rate * (10 ** d)) / 1 ether;

    require(token.balanceOf(address(this)) >= tokensOut, "insufficient ETRX in sale");
    weiRaised += msg.value;

    require(token.transfer(msg.sender, tokensOut), "token transfer failed");
    emit Contributed(msg.sender, msg.value, tokensOut);
  }

  function withdrawETH(address payable to) external onlyOwner {
    uint256 bal = address(this).balance;
    (bool ok,) = to.call{value: bal}("");
    require(ok, "withdraw failed");
    emit WithdrawETH(to, bal);
  }

  function withdrawUnsold(address to, uint256 amount) external onlyOwner {
    require(token.transfer(to, amount), "withdraw unsold failed");
    emit WithdrawUnsold(to, amount);
  }
}