একটি সলিডিটি স্মার্ট কন্ট্রাক্ট থেকে ERC-20 টোকেনের ট্রান্সফার এবং অ্যাপ্রুভাল

pragma solidity ^0.8.0;

interface IERC20 {

    function totalSupply() external view returns (uint256);
    function balanceOf(address account) external view returns (uint256);
    function allowance(address owner, address spender) external view returns (uint256);

    function transfer(address recipient, uint256 amount) external returns (bool);
    function approve(address spender, uint256 amount) external returns (bool);
    function transferFrom(address sender, address recipient, uint256 amount) external returns (bool);


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


contract ERC20Basic is IERC20 {

    string public constant name = "ERC20Basic";
    string public constant symbol = "ERC";
    uint8 public constant decimals = 18;


    mapping(address => uint256) balances;

    mapping(address => mapping (address => uint256)) allowed;

    uint256 totalSupply_ = 10 ether;


   constructor() {
	balances[msg.sender] = totalSupply_;
    }

    function totalSupply() public override view returns (uint256) {
	return totalSupply_;
    }

    function balanceOf(address tokenOwner) public override view returns (uint256) {
        return balances[tokenOwner];
    }

    function transfer(address receiver, uint256 numTokens) public override returns (bool) {
        require(numTokens <= balances[msg.sender]);
        balances[msg.sender] = balances[msg.sender]-numTokens;
        balances[receiver] = balances[receiver]+numTokens;
        emit Transfer(msg.sender, receiver, numTokens);
        return true;
    }

    function approve(address delegate, uint256 numTokens) public override returns (bool) {
        allowed[msg.sender][delegate] = numTokens;
        emit Approval(msg.sender, delegate, numTokens);
        return true;
    }

    function allowance(address owner, address delegate) public override view returns (uint) {
        return allowed[owner][delegate];
    }

    function transferFrom(address owner, address buyer, uint256 numTokens) public override returns (bool) {
        require(numTokens <= balances[owner]);
        require(numTokens <= allowed[owner][msg.sender]);

        balances[owner] = balances[owner]-numTokens;
        allowed[owner][msg.sender] = allowed[owner][msg.sender]-numTokens;
        balances[buyer] = balances[buyer]+numTokens;
        emit Transfer(owner, buyer, numTokens);
        return true;
    }
}

contract DEX {

    IERC20 public token;

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

    constructor() {
        token = new ERC20Basic();
    }

    function buy() payable public {
        // TODO
    }

    function sell(uint256 amount) public {
        // TODO
    }

}

# ### ইন্টারেক্টিভ ব্রাউনি কনসোলে পাইথন...

# DEX ডিপ্লয় করুন
dex = DEX.deploy({'from':account1})

# টোকেনের জন্য ইথার সোয়াপ করতে buy ফাংশনটি কল করুন
# 1e18 হলো ওয়েই (wei) এককে ১ ইথার
dex.buy({'from': account2, 1e18})

# ERC20 টোকেনের ডিপ্লয়মেন্ট অ্যাড্রেসটি সংগ্রহ করুন
# যা DEX কন্ট্রাক্ট তৈরির সময় ডিপ্লয় করা হয়েছিল
# dex.token() টোকেনের ডিপ্লয় করা অ্যাড্রেসটি রিটার্ন করে
token = ERC20Basic.at(dex.token())

# টোকেনের approve ফাংশনটি কল করুন
# স্পেন্ডার হিসেবে dex অ্যাড্রেসটিকে অ্যাপ্রুভ করুন
# এবং এটি আপনার কতগুলো টোকেন খরচ করার অনুমতি পাবে
token.approve(dex.address, 3e18, {'from':account2})

pragma solidity ^0.8.0;

interface IERC20 {

    function totalSupply() external view returns (uint256);
    function balanceOf(address account) external view returns (uint256);
    function allowance(address owner, address spender) external view returns (uint256);

    function transfer(address recipient, uint256 amount) external returns (bool);
    function approve(address spender, uint256 amount) external returns (bool);
    function transferFrom(address sender, address recipient, uint256 amount) external returns (bool);


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


contract ERC20Basic is IERC20 {

    string public constant name = "ERC20Basic";
    string public constant symbol = "ERC";
    uint8 public constant decimals = 18;


    mapping(address => uint256) balances;

    mapping(address => mapping (address => uint256)) allowed;

    uint256 totalSupply_ = 10 ether;


   constructor() {
	balances[msg.sender] = totalSupply_;
    }

    function totalSupply() public override view returns (uint256) {
	return totalSupply_;
    }

    function balanceOf(address tokenOwner) public override view returns (uint256) {
        return balances[tokenOwner];
    }

    function transfer(address receiver, uint256 numTokens) public override returns (bool) {
        require(numTokens <= balances[msg.sender]);
        balances[msg.sender] = balances[msg.sender]-numTokens;
        balances[receiver] = balances[receiver]+numTokens;
        emit Transfer(msg.sender, receiver, numTokens);
        return true;
    }

    function approve(address delegate, uint256 numTokens) public override returns (bool) {
        allowed[msg.sender][delegate] = numTokens;
        emit Approval(msg.sender, delegate, numTokens);
        return true;
    }

    function allowance(address owner, address delegate) public override view returns (uint) {
        return allowed[owner][delegate];
    }

    function transferFrom(address owner, address buyer, uint256 numTokens) public override returns (bool) {
        require(numTokens <= balances[owner]);
        require(numTokens <= allowed[owner][msg.sender]);

        balances[owner] = balances[owner]-numTokens;
        allowed[owner][msg.sender] = allowed[owner][msg.sender]-numTokens;
        balances[buyer] = balances[buyer]+numTokens;
        emit Transfer(owner, buyer, numTokens);
        return true;
    }
}


contract DEX {

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


    IERC20 public token;

    constructor() {
        token = new ERC20Basic();
    }

    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);
    }

}