pragma solidity 0.5.10;

/**
 * @dev Wrappers over Solidity's arithmetic operations with added overflow
 * checks.
 *
 * Arithmetic operations in Solidity wrap on overflow. This can easily result
 * in bugs, because programmers usually assume that an overflow raises an
 * error, which is the standard behavior in high level programming languages.
 * `SafeMath` restores this intuition by reverting the transaction when an
 * operation overflows.
 *
 * Using this library instead of the unchecked operations eliminates an entire
 * class of bugs, so it's recommended to use it always.
 */
library SafeMath {
    /**
     * @dev Returns the addition of two unsigned integers, reverting on
     * overflow.
     *
     * Counterpart to Solidity's `+` operator.
     *
     * Requirements:
     * - Addition cannot overflow.
     */
    function add(uint256 a, uint256 b) internal pure returns (uint256) {
        uint256 c = a + b;
        require(c >= a, "SafeMath: addition overflow");

        return c;
    }

    /**
     * @dev Returns the subtraction of two unsigned integers, reverting on
     * overflow (when the result is negative).
     *
     * Counterpart to Solidity's `-` operator.
     *
     * Requirements:
     * - Subtraction cannot overflow.
     */
    function sub(uint256 a, uint256 b) internal pure returns (uint256) {
        return sub(a, b, "SafeMath: subtraction overflow");
    }

    /**
     * @dev Returns the subtraction of two unsigned integers, reverting with custom message on
     * overflow (when the result is negative).
     *
     * Counterpart to Solidity's `-` operator.
     *
     * Requirements:
     * - Subtraction cannot overflow.
     *
     * _Available since v2.4.0._
     */
    function sub(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b <= a, errorMessage);
        uint256 c = a - b;

        return c;
    }

    /**
     * @dev Returns the multiplication of two unsigned integers, reverting on
     * overflow.
     *
     * Counterpart to Solidity's `*` operator.
     *
     * Requirements:
     * - Multiplication cannot overflow.
     */
    function mul(uint256 a, uint256 b) internal pure returns (uint256) {
        // Gas optimization: this is cheaper than requiring 'a' not being zero, but the
        // benefit is lost if 'b' is also tested.
        // See: https://github.com/OpenZeppelin/openzeppelin-contracts/pull/522
        if (a == 0) {
            return 0;
        }

        uint256 c = a * b;
        require(c / a == b, "SafeMath: multiplication overflow");

        return c;
    }

    /**
     * @dev Returns the integer division of two unsigned integers. Reverts on
     * division by zero. The result is rounded towards zero.
     *
     * Counterpart to Solidity's `/` operator. Note: this function uses a
     * `revert` opcode (which leaves remaining gas untouched) while Solidity
     * uses an invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     * - The divisor cannot be zero.
     */
    function div(uint256 a, uint256 b) internal pure returns (uint256) {
        return div(a, b, "SafeMath: division by zero");
    }

    /**
     * @dev Returns the integer division of two unsigned integers. Reverts with custom message on
     * division by zero. The result is rounded towards zero.
     *
     * Counterpart to Solidity's `/` operator. Note: this function uses a
     * `revert` opcode (which leaves remaining gas untouched) while Solidity
     * uses an invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     * - The divisor cannot be zero.
     *
     * _Available since v2.4.0._
     */
    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;
        // assert(a == b * c + a % b); // There is no case in which this doesn't hold

        return c;
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * Reverts when dividing by zero.
     *
     * Counterpart to Solidity's `%` operator. This function uses a `revert`
     * opcode (which leaves remaining gas untouched) while Solidity uses an
     * invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     * - The divisor cannot be zero.
     */
    function mod(uint256 a, uint256 b) internal pure returns (uint256) {
        return mod(a, b, "SafeMath: modulo by zero");
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * Reverts with custom message when dividing by zero.
     *
     * Counterpart to Solidity's `%` operator. This function uses a `revert`
     * opcode (which leaves remaining gas untouched) while Solidity uses an
     * invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     * - The divisor cannot be zero.
     *
     * _Available since v2.4.0._
     */
    function mod(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b != 0, errorMessage);
        return a % b;
    }
}


/**
 * @dev Interface of the ERC20 standard as defined in the EIP. Does not include
 * the optional functions; to access them see {ERC20Detailed}.
 */
interface IERC20 {
    /**
     * @dev Returns the amount of tokens in existence.
     */
    function totalSupply() external view returns (uint256);

    /**
     * @dev Returns the amount of tokens owned by `account`.
     */
    function balanceOf(address account) external view returns (uint256);

    /**
     * @dev Moves `amount` tokens from the caller's account to `recipient`.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * Emits a {Transfer} event.
     */
    function transfer(address recipient, uint256 amount) external returns (bool);

    /**
     * @dev Returns the remaining number of tokens that `spender` will be
     * allowed to spend on behalf of `owner` through {transferFrom}. This is
     * zero by default.
     *
     * This value changes when {approve} or {transferFrom} are called.
     */
    function allowance(address owner, address spender) external view returns (uint256);

    /**
     * @dev Sets `amount` as the allowance of `spender` over the caller's tokens.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * IMPORTANT: Beware that changing an allowance with this method brings the risk
     * that someone may use both the old and the new allowance by unfortunate
     * transaction ordering. One possible solution to mitigate this race
     * condition is to first reduce the spender's allowance to 0 and set the
     * desired value afterwards:
     * https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729
     *
     * Emits an {Approval} event.
     */
    function approve(address spender, uint256 amount) external returns (bool);

    /**
     * @dev Moves `amount` tokens from `sender` to `recipient` using the
     * allowance mechanism. `amount` is then deducted from the caller's
     * allowance.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * Emits a {Transfer} event.
     */
    function transferFrom(address sender, address recipient, uint256 amount) external returns (bool);

    /**
     * @dev Emitted when `value` tokens are moved from one account (`from`) to
     * another (`to`).
     *
     * Note that `value` may be zero.
     */
    event Transfer(address indexed from, address indexed to, uint256 value);

    /**
     * @dev Emitted when the allowance of a `spender` for an `owner` is set by
     * a call to {approve}. `value` is the new allowance.
     */
    event Approval(address indexed owner, address indexed spender, uint256 value);
}

/**
 * @dev Collection of functions related to the address type
 */
library Address {
    /**
     * @dev Returns true if `account` is a contract.
     *
     * This test is non-exhaustive, and there may be false-negatives: during the
     * execution of a contract's constructor, its address will be reported as
     * not containing a contract.
     *
     * IMPORTANT: It is unsafe to assume that an address for which this
     * function returns false is an externally-owned account (EOA) and not a
     * contract.
     */
    function isContract(address account) internal view returns (bool) {
        // This method relies in extcodesize, which returns 0 for contracts in
        // construction, since the code is only stored at the end of the
        // constructor execution.

        // According to EIP-1052, 0x0 is the value returned for not-yet created accounts
        // and 0xc5d2460186f7233c927e7db2dcc703c0e500b653ca82273b7bfad8045d85a470 is returned
        // for accounts without code, i.e. `keccak256('')`
        bytes32 codehash;
        bytes32 accountHash = 0xc5d2460186f7233c927e7db2dcc703c0e500b653ca82273b7bfad8045d85a470;
        // solhint-disable-next-line no-inline-assembly
        assembly { codehash := extcodehash(account) }
        return (codehash != 0x0 && codehash != accountHash);
    }

    /**
     * @dev Converts an `address` into `address payable`. Note that this is
     * simply a type cast: the actual underlying value is not changed.
     *
     * _Available since v2.4.0._
     */
    function toPayable(address account) internal pure returns (address payable) {
        return address(uint160(account));
    }

    /**
     * @dev Replacement for Solidity's `transfer`: sends `amount` wei to
     * `recipient`, forwarding all available gas and reverting on errors.
     *
     * https://eips.ethereum.org/EIPS/eip-1884[EIP1884] increases the gas cost
     * of certain opcodes, possibly making contracts go over the 2300 gas limit
     * imposed by `transfer`, making them unable to receive funds via
     * `transfer`. {sendValue} removes this limitation.
     *
     * https://diligence.consensys.net/posts/2019/09/stop-using-soliditys-transfer-now/[Learn more].
     *
     * IMPORTANT: because control is transferred to `recipient`, care must be
     * taken to not create reentrancy vulnerabilities. Consider using
     * {ReentrancyGuard} or the
     * https://solidity.readthedocs.io/en/v0.5.11/security-considerations.html#use-the-checks-effects-interactions-pattern[checks-effects-interactions pattern].
     *
     * _Available since v2.4.0._
     */
    function sendValue(address payable recipient, uint256 amount) internal {
        require(address(this).balance >= amount, "Address: insufficient balance");

        // solhint-disable-next-line avoid-call-value
        (bool success, ) = recipient.call.value(amount)("");
        require(success, "Address: unable to send value, recipient may have reverted");
    }
}

library SafeERC20 {
    using SafeMath for uint256;
    using Address for address;

    function safeTransfer(IERC20 token, address to, uint256 value) internal {
        callOptionalReturn(token, abi.encodeWithSelector(token.transfer.selector, to, value));
    }

    function safeTransferFrom(IERC20 token, address from, address to, uint256 value) internal {
        callOptionalReturn(token, abi.encodeWithSelector(token.transferFrom.selector, from, to, value));
    }

    function safeApprove(IERC20 token, address spender, uint256 value) internal {
        // safeApprove should only be called when setting an initial allowance,
        // or when resetting it to zero. To increase and decrease it, use
        // 'safeIncreaseAllowance' and 'safeDecreaseAllowance'
        // solhint-disable-next-line max-line-length
        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 safeIncreaseAllowance(IERC20 token, address spender, uint256 value) internal {
        uint256 newAllowance = token.allowance(address(this), spender).add(value);
        callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, newAllowance));
    }

    function safeDecreaseAllowance(IERC20 token, address spender, uint256 value) internal {
        uint256 newAllowance = token.allowance(address(this), spender).sub(value, "SafeERC20: decreased allowance below zero");
        callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, newAllowance));
    }

    /**
     * @dev Imitates a Solidity high-level call (i.e. a regular function call to a contract), relaxing the requirement
     * on the return value: the return value is optional (but if data is returned, it must not be false).
     * @param token The token targeted by the call.
     * @param data The call data (encoded using abi.encode or one of its variants).
     */
    function callOptionalReturn(IERC20 token, bytes memory data) private {
        // We need to perform a low level call here, to bypass Solidity's return data size checking mechanism, since
        // we're implementing it ourselves.

        // A Solidity high level call has three parts:
        //  1. The target address is checked to verify it contains contract code
        //  2. The call itself is made, and success asserted
        //  3. The return value is decoded, which in turn checks the size of the returned data.
        // solhint-disable-next-line max-line-length
        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 FlashLoanReceiverBase {

    using SafeERC20 for IERC20;
    using SafeMath for uint256;

    ILendingPoolAddressesProvider public addressesProvider;

    constructor(ILendingPoolAddressesProvider _provider) public {
        addressesProvider = _provider;
    }

    function () external payable {
    }

    function ethAddress() internal pure returns(address) {
        return 0xEeeeeEeeeEeEeeEeEeEeeEEEeeeeEeeeeeeeEEeE;
    }

    function transferFundsBackToPoolInternal(address _reserve, uint256 _amount) internal {

        address payable core = addressesProvider.getLendingPoolCore();

        transferInternal(core,_reserve, _amount);
    }

    function transferInternal(address payable _destination, address _reserve, uint256  _amount) internal {
        if(_reserve == ethAddress()) {
            //solium-disable-next-line
            _destination.call.value(_amount)("");
            return;
        }

        IERC20(_reserve).safeTransfer(_destination, _amount);


    }

    function getBalanceInternal(address _target, address _reserve) internal view returns(uint256) {
        if(_reserve == ethAddress()) {

            return _target.balance;
        }

        return IERC20(_reserve).balanceOf(_target);

    }
}

contract OptionsContract {
    function liquidate(address payable vaultOwner, uint256 oTokensToLiquidate)
        public;

    function optionsExchange() public returns (address);

    function maxOTokensLiquidatable(address payable vaultOwner)
        public
        view
        returns (uint256);

    function isUnsafe(address payable vaultOwner) public view returns (bool);

    function hasVault(address valtowner) public view returns (bool);

    function openVault() public returns (bool);

    function addETHCollateral(address payable vaultOwner)
        public
        payable
        returns (uint256);

    function maxOTokensIssuable(uint256 collateralAmt)
        public
        view
        returns (uint256);

    function getVault(address payable vaultOwner)
        public
        view
        returns (uint256, uint256, uint256, bool);

    function issueOTokens(uint256 oTokensToIssue, address receiver) public;

    function approve(address spender, uint256 amount) public returns (bool);
}


contract OptionsExchange {
        function buyOTokens(
        address payable receiver,
        address oTokenAddress,
        address paymentTokenAddress,
        uint256 oTokensToBuy
    ) public payable;

    function premiumToPay(
        address oTokenAddress,
        address paymentTokenAddress,
        uint256 oTokensToBuy
    ) public view returns (uint256);
}

contract ILendingPoolAddressesProvider {

    function getLendingPool() public view returns (address);
    function setLendingPoolImpl(address _pool) public;

    function getLendingPoolCore() public view returns (address payable);
    function setLendingPoolCoreImpl(address _lendingPoolCore) public;

    function getLendingPoolConfigurator() public view returns (address);
    function setLendingPoolConfiguratorImpl(address _configurator) public;

    function getLendingPoolDataProvider() public view returns (address);
    function setLendingPoolDataProviderImpl(address _provider) public;

    function getLendingPoolParametersProvider() public view returns (address);
    function setLendingPoolParametersProviderImpl(address _parametersProvider) public;

    function getTokenDistributor() public view returns (address);
    function setTokenDistributor(address _tokenDistributor) public;


    function getFeeProvider() public view returns (address);
    function setFeeProviderImpl(address _feeProvider) public;

    function getLendingPoolLiquidationManager() public view returns (address);
    function setLendingPoolLiquidationManager(address _manager) public;

    function getLendingPoolManager() public view returns (address);
    function setLendingPoolManager(address _lendingPoolManager) public;

    function getPriceOracle() public view returns (address);
    function setPriceOracle(address _priceOracle) public;

    function getLendingRateOracle() public view returns (address);
    function setLendingRateOracle(address _lendingRateOracle) public;

}

contract IUniswapFactory {
    // Public Variables
    address public exchangeTemplate;
    uint256 public tokenCount;

    
    // Get Exchange and Token Info
    function getExchange(address token)
        external
        view
        returns (address exchange);
}


contract IUniswapExchange {
    // Address of ERC20 token sold on this exchange
    function tokenAddress() external view returns (address token);

    // Address of Uniswap Factory
    function factoryAddress() external view returns (address factory);

    // Get Prices
    function getEthToTokenInputPrice(uint256 eth_sold)
        external
        view
        returns (uint256 tokens_bought);

    function getEthToTokenOutputPrice(uint256 tokens_bought)
        external
        view
        returns (uint256 eth_sold);

    function getTokenToEthInputPrice(uint256 tokens_sold)
        external
        view
        returns (uint256 eth_bought);

    function getTokenToEthOutputPrice(uint256 eth_bought)
        external
        view
        returns (uint256 tokens_sold);

    // Trade ETH to ERC20
    function ethToTokenSwapInput(uint256 min_tokens, uint256 deadline)
        external
        payable
        returns (uint256 tokens_bought);

    function ethToTokenTransferInput(
        uint256 min_tokens,
        uint256 deadline,
        address recipient
    ) external payable returns (uint256 tokens_bought);

    function ethToTokenSwapOutput(uint256 tokens_bought, uint256 deadline)
        external
        payable
        returns (uint256 eth_sold);

    function ethToTokenTransferOutput(
        uint256 tokens_bought,
        uint256 deadline,
        address recipient
    ) external payable returns (uint256 eth_sold);

}


contract Liquidator is FlashLoanReceiverBase {
    using SafeMath for uint256;
    IUniswapFactory public factory;

    constructor(
        ILendingPoolAddressesProvider _provider,
        IUniswapFactory _factory
    ) public FlashLoanReceiverBase(_provider) {
        factory = _factory;
    }

    function executeOperation(
        address _reserve,
        uint256 _amount,
        uint256 _fee,
        bytes calldata _params
    ) external {
        // 1. Parse params
        (address oTokenAddr, address vaultAddr) = getParams(_params);
        address payable vaultOwner = address(uint160(vaultAddr));
        OptionsContract oToken = OptionsContract(oTokenAddr);

        // 2. Buy oTokens on uniswap
        uint256 oTokensToBuy = oToken.maxOTokensLiquidatable(vaultOwner);
        require(oTokensToBuy > 0, "cannot liquidate a safe vault");

        OptionsExchange exchange = OptionsExchange(oToken.optionsExchange());

        IERC20(_reserve).approve(address(exchange), _amount);
        exchange.buyOTokens(
            address(uint160(address(this))),
            oTokenAddr,
            _reserve,
            oTokensToBuy
        );
        // 3. Liquidate
        oToken.liquidate(vaultOwner, oTokensToBuy);

        // 4. Use eth to buy back _reserve
        IUniswapExchange uniswap = IUniswapExchange(
            factory.getExchange(_reserve)
        );
        uint256 buyAmount = uniswap.getEthToTokenInputPrice(
            address(this).balance
        );
        uniswap.ethToTokenSwapInput.value(address(this).balance)(
            buyAmount,
            now + 10 minutes
        );

        // // 5. pay back the $
        transferFundsBackToPoolInternal(_reserve, _amount.add(_fee));

        // // 6. pay the user who liquidated
        uint256 balance = IERC20(_reserve).balanceOf(address(this));
        IERC20(_reserve).transfer(tx.origin, balance);
    }

    function bytesToAddress(bytes memory bys)
        private
        pure
        returns (address addr)
    {
        //solium-disable-next-line
        assembly {
            addr := mload(add(bys, 20))
        }
    }

    function getParams(bytes memory source)
        public
        pure
        returns (address, address)
    {
        bytes memory half1 = new bytes(20);
        bytes memory half2 = new bytes(20);
        for (uint256 j = 0; j < 20; j++) {
            half1[j] = source[j];
            half2[j] = source[j + 20];
        }
        return (bytesToAddress(half1), bytesToAddress(half2));
    }
}