ERC-20 智能合约：USDT 与 TRX 兑换功能

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.14;

import "github.com/bandprotocol/bandchain-packet/bandchain-packet/contracts/BandStdlib.sol";

contract ERC20 {
    using BandStdlib for BandStdlib.BandOracleParams;

    string public name;
    string public symbol;
    uint8 public decimals;
    uint256 public totalSupply;
    address public owner;

    mapping(address => uint256) public balanceOf;
    mapping(address => mapping(address => uint256)) public allowance;

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

    constructor() {
        name = 'ERC20 Token';
        symbol = 'ERC20';
        decimals = 18;
        totalSupply = 0;
        owner = msg.sender;
    }

    function transfer(address to, uint256 value) external returns (bool) {
        require(value <= balanceOf[msg.sender]);
        balanceOf[msg.sender] -= value;
        balanceOf[to] += value;
        emit Transfer(msg.sender, to, value);
        return true;
    }

    function approve(address spender, uint256 value) external returns (bool) {
        allowance[msg.sender][spender] = value;
        emit Approval(msg.sender, spender, value);
        return true;
    }

    function transferFrom(address from, address to, uint256 value) external returns (bool) {
        require(value <= balanceOf[from]);
        require(value <= allowance[from][msg.sender]);
        balanceOf[from] -= value;
        balanceOf[to] += value;
        allowance[from][msg.sender] -= value;
        emit Transfer(from, to, value);
        return true;
    }

    function depositTRX() external payable {
        balanceOf[msg.sender] += msg.value;
        totalSupply += msg.value;
        emit Transfer(address(0), msg.sender, msg.value);
    }

    function depositUSDT(uint256 amount) external {
        require(amount > 0, 'Amount must be greater than zero');
        BandOracleParams memory params;
        params.symbol = 'USDT';
        params.askCount = 1;
        params.minCount = 1;
        params.askQuery[0] = 'trxusdt';
        params.askQuery[1] = 'trx';
        params.minQuery[0] = 'trxusdt';
        params.minQuery[1] = 'trx';
        BandStdlib.requestBandOracle(params);
        uint256 trxAmount = amount * params.minResult[0] / params.minResult[1];
        require(trxAmount <= balanceOf[address(this)], 'Insufficient TRX balance in contract');
        balanceOf[msg.sender] += trxAmount;
        balanceOf[address(this)] -= trxAmount;
        totalSupply += trxAmount;
        emit Transfer(address(this), msg.sender, trxAmount);
    }

    function withdrawTRX(uint256 amount, address to) external {
        require(msg.sender == owner, 'Only owner can call this function');
        require(amount <= balanceOf[address(this)], 'Insufficient TRX balance in contract');
        balanceOf[address(this)] -= amount;
        totalSupply -= amount;
        payable(to).transfer(amount);
        emit Transfer(address(this), to, amount);
    }

    function withdrawUSDT(uint256 amount, address to) external {
        require(msg.sender == owner, 'Only owner can call this function');
        require(amount <= balanceOf[address(this)], 'Insufficient USDT balance in contract');
        balanceOf[address(this)] -= amount;
        totalSupply -= amount;
        emit Transfer(address(this), to, amount);
    }
}