pragma solidity 0.5.17;
pragma experimental ABIEncoderV2;

interface IERC20 {
    function totalSupply() external view returns (uint256);
    function balanceOf(address account) external view returns (uint256);
    function transfer(address recipient, uint256 amount) external returns (bool);
    function allowance(address owner, address spender) external view returns (uint256);
    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 Context {
    constructor () internal { }
    // solhint-disable-previous-line no-empty-blocks

    function _msgSender() internal view returns (address payable) {
        return msg.sender;
    }

    function _msgData() internal view returns (bytes memory) {
        this; // silence state mutability warning without generating bytecode - see https://github.com/ethereum/solidity/issues/2691
        return msg.data;
    }
}

contract Ownable is Context {
    address payable private _owner;

    event OwnershipTransferred(address indexed previousOwner, address indexed newOwner);
    constructor () internal {
        _owner = _msgSender();
        emit OwnershipTransferred(address(0), _owner);
    }
    function owner() public view returns (address payable) {
        return _owner;
    }
    modifier onlyOwner() {
        require(isOwner(), "Ownable: caller is not the owner");
        _;
    }
    function isOwner() public view returns (bool) {
        return _msgSender() == _owner;
    }
    function renounceOwnership() public onlyOwner {
        emit OwnershipTransferred(_owner, address(0));
        _owner = address(0);
    }
    function transferOwnership(address payable newOwner) public onlyOwner {
        _transferOwnership(newOwner);
    }
    function _transferOwnership(address payable newOwner) internal {
        require(newOwner != address(0), "Ownable: new owner is the zero address");
        emit OwnershipTransferred(_owner, newOwner);
        _owner = newOwner;
    }
}

contract ERC20 is Context, IERC20 {
    using SafeMath for uint256;

    mapping (address => uint256) _balances;

    mapping (address => mapping (address => uint256)) private _allowances;

    uint256 _totalSupply;
    function totalSupply() public view returns (uint256) {
        return _totalSupply;
    }
    function balanceOf(address account) public view returns (uint256) {
        return _balances[account];
    }
    function transfer(address recipient, uint256 amount) public returns (bool) {
        _transfer(_msgSender(), recipient, amount);
        return true;
    }
    function allowance(address owner, address spender) public view returns (uint256) {
        return _allowances[owner][spender];
    }
    function approve(address spender, uint256 amount) public returns (bool) {
        _approve(_msgSender(), spender, amount);
        return true;
    }
    function transferFrom(address sender, address recipient, uint256 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, uint256 addedValue) public returns (bool) {
        _approve(_msgSender(), spender, _allowances[_msgSender()][spender].add(addedValue));
        return true;
    }
    function decreaseAllowance(address spender, uint256 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, uint256 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, uint256 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, uint256 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, uint256 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);
    }
    function _burnFrom(address account, uint256 amount) internal {
        _burn(account, amount);
        _approve(account, _msgSender(), _allowances[account][_msgSender()].sub(amount, "ERC20: burn amount exceeds allowance"));
    }
}

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;
    }
}

library SafeMath {
    function add(uint256 a, uint256 b) internal pure returns (uint256) {
        uint256 c = a + b;
        require(c >= a, "SafeMath: addition overflow");

        return c;
    }
    function sub(uint256 a, uint256 b) internal pure returns (uint256) {
        return sub(a, b, "SafeMath: subtraction overflow");
    }
    function sub(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b <= a, errorMessage);
        uint256 c = a - b;

        return c;
    }
    function mul(uint256 a, uint256 b) internal pure returns (uint256) {
        if (a == 0) {
            return 0;
        }

        uint256 c = a * b;
        require(c / a == b, "SafeMath: multiplication overflow");

        return c;
    }
    function div(uint256 a, uint256 b) internal pure returns (uint256) {
        return div(a, b, "SafeMath: division by zero");
    }
    function div(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        // Solidity only automatically asserts when dividing by 0
        require(b > 0, errorMessage);
        uint256 c = a / b;

        return c;
    }
    function mod(uint256 a, uint256 b) internal pure returns (uint256) {
        return mod(a, b, "SafeMath: modulo by zero");
    }
    function mod(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b != 0, errorMessage);
        return a % b;
    }
}

contract yeldUSDT is ERC20, ERC20Detailed, Ownable {
  using SafeMath for uint256;

  address public yUSDTAddress;
  uint256 public initialPrice = 10000;
  uint256 public fromYeldUSDTToYeld = initialPrice * (10 ** 18); // Must be divided by 1e18 to get the real value
  uint256 public fromUSDTToYeldUSDTPrice = fromYeldUSDTToYeld / initialPrice; // Must be divided by 1e18 to get the real value
  uint256 public yeldReward = 1;
  uint256 public yeldUSDTDecimals = 18; // The price has 18 decimals meaning you'll have to divide by 1e18 to get the real value
  uint256 public lastPriceUpdate = now;
	uint256 public priceUpdatePeriod = 1 days;
  
  modifier onlyYUSDT {
    require(msg.sender == yUSDTAddress);
    _;
  }

  constructor() public payable ERC20Detailed("yeld USDT", "yeldUSDT", 18) {}

  function setYUSDT(address _yUSDTAddress) public onlyOwner {
    yUSDTAddress = _yUSDTAddress;
  }
  
  function mint(address _to, uint256 _amount) public onlyYUSDT {
    _mint(_to, _amount);
  }

  function burn(address _to, uint256 _amount) public onlyYUSDT {
    _burn(_to, _amount);
  }

	/// To change how many tokens the users get. 
	/// Right now it's at 10k which means 1 million USDT staked = 100 yeld a day
	function changePriceRatio(uint256 _price) public onlyOwner {
		initialPrice = _price;
	}

	function checkIfPriceNeedsUpdating() public view returns(bool) {
		return now >= lastPriceUpdate + priceUpdatePeriod;
	}

	/// Updates the current price everyday
	/// Everyday this function will be called to calculate how many YELD each staker gets,
	/// to get half the generated yield by everybody, use it to buy YELD on uniswap and burn it,
	/// and to increase the 1% retirement yield treasury that can be redeemed by holders
	function updatePrice() public {
		require(checkIfPriceNeedsUpdating(), "The price can't be updated yet");
		// Update the price
        uint256 daysPassed = (now - lastPriceUpdate) / 1 days;
		yeldReward = daysPassed;
		lastPriceUpdate = now;
		fromYeldUSDTToYeld = initialPrice.mul(10 ** yeldUSDTDecimals).div(yeldReward);
		fromUSDTToYeldUSDTPrice = fromYeldUSDTToYeld.div(initialPrice);
	}
  
  function extractTokensIfStuck(address _token, uint256 _amount) public onlyOwner {
    IERC20(_token).transfer(msg.sender, _amount);
  }

  function extractETHIfStuck() public onlyOwner {
    owner().transfer(address(this).balance);
  }
}