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contracts...martketContract.sol

// SPDX-License-Identifier: MIT
pragma solidity >= 0.8.0 < 0.9.0;

import "@openzeppelin/contracts/token/ERC20/ERC20.sol";

contract regimenToken is ERC20 {
    constructor(uint256 initialSupply) ERC20("Gold", "GLD") {
        _mint(msg.sender, initialSupply);
    }
}

contract Payment {

    event Bought(uint256 amount);
    event Sold(uint256 amount);


    ERC20 public token;
    
    // Total tokens(regiment) of the account
    constructor(uint256 initialSupply) {
        token = new regimenToken(initialSupply);
    }

    function buy() payable public {
        uint256 amountTobuy = msg.value;
        uint256 dexBalance = token.balanceOf(address(this));
        require(amountTobuy > 0, "You need to send some ether");
        require(amountTobuy <= dexBalance, "Not enough tokens in the reserve");
        token.transfer(msg.sender, amountTobuy);
        emit Bought(amountTobuy);
    }

    function sell(uint256 amount) public {
        require(amount > 0, "You need to sell at least some tokens");
        uint256 allowance = token.allowance(msg.sender, address(this));
        require(allowance >= amount, "Check the token allowance");
        token.transferFrom(msg.sender, address(this), amount);
        payable(msg.sender).transfer(amount);
        emit Sold(amount);
    }

}