// File: /contracts/TreasurySwap.sol



// SPDX-License-Identifier: MIT
pragma solidity 0.6.12;

import "./interfaces/IRewardStaking.sol";
import "./interfaces/ICvxCrvStaking.sol";
import "./interfaces/IConvexDeposits.sol";
import '@openzeppelin/contracts/token/ERC20/IERC20.sol';
import '@openzeppelin/contracts/token/ERC20/SafeERC20.sol';
import '@openzeppelin/contracts/math/SafeMath.sol';



interface ICvxCrvExchange {

    function exchange(
        int128,
        int128,
        uint256,
        uint256,
        address
    ) external returns (uint256);

    function calc_token_amount(uint256[2] calldata _amounts, bool _isDeposit) external view returns(uint256);
    function calc_withdraw_one_coin(uint256 _amount, int128 _index) external view returns(uint256);
    function add_liquidity(uint256[2] calldata _amounts, uint256 _min_mint_amount, address _receiver) external returns(uint256);
    function remove_liquidity(uint256 _amount, uint256[2] calldata _min_amounts, address _receiver) external returns(uint256[2] calldata);
    function remove_liquidity_one_coin(uint256 _amount, int128 _index, uint256 _min_amount, address _receiver) external returns(uint256);
}


contract TreasurySwap{
    using SafeERC20 for IERC20;
    using SafeMath for uint256;

    address public constant crv = address(0xD533a949740bb3306d119CC777fa900bA034cd52);
    address public constant cvx = address(0x4e3FBD56CD56c3e72c1403e103b45Db9da5B9D2B);
    address public constant cvxCrv = address(0x62B9c7356A2Dc64a1969e19C23e4f579F9810Aa7);
    address public constant cvxCrvRewards = address(0x3Fe65692bfCD0e6CF84cB1E7d24108E434A7587e);
    address public constant treasury = address(0x1389388d01708118b497f59521f6943Be2541bb7);
    address public constant exchange = address(0x971add32Ea87f10bD192671630be3BE8A11b8623);
    address public constant booster = address(0xF403C135812408BFbE8713b5A23a04b3D48AAE31);
    address public constant lprewards = address(0x39D78f11b246ea4A1f68573c3A5B64E83Cff2cAe);
    uint256 public constant pid = 157;

    address public immutable owner;


    mapping(address => bool) public operators;
    address public stakedCvxcrv;
    uint256 public slippage;

    event OperatorSet(address indexed _op, bool _active);
    event Swap(uint256 _amountIn, uint256 _amountOut);
    event Convert(uint256 _amount);
    event Burn(uint256 _amount);
    event Stake(uint256 _amount);
    event Unstake(uint256 _amount);
    event AddedToLP(uint256 _lpamount);
    event RemovedFromLp(uint256 _lpamount);
    event ClaimedReward(address indexed _token, uint256 _amount);

    constructor() public {
        owner = address(0xa3C5A1e09150B75ff251c1a7815A07182c3de2FB);
        operators[msg.sender] = true;

        slippage = 999 * 1e15;
        IERC20(cvxCrv).safeApprove(cvxCrvRewards, uint256(-1));
        IERC20(crv).safeApprove(exchange, uint256(-1));
        IERC20(cvxCrv).safeApprove(exchange, uint256(-1));
        IERC20(exchange).safeApprove(booster, uint256(-1));
    }


    modifier onlyOwner() {
        require(owner == msg.sender, "!owner");
        _;
    }

    modifier onlyOperator() {
        require(operators[msg.sender] || owner == msg.sender, "!operator");
        _;
    }

    function treasuryBalanceOfCrv() external view returns(uint256){
        return IERC20(crv).balanceOf(treasury);
    }

    function treasuryBalanceOfCvxCrv() external view returns(uint256){
        return IERC20(cvxCrv).balanceOf(treasury);
    }

    function setStakeAddress(address _stake) external onlyOwner{
        stakedCvxcrv = _stake;
        IERC20(cvxCrv).safeApprove(_stake, 0);
        IERC20(cvxCrv).safeApprove(_stake, uint256(-1));
    }

    function setOperator(address _op, bool _active) external onlyOwner{
        operators[_op] = _active;
        emit OperatorSet(_op, _active);
    }

    function setSlippageAllowance(uint256 _slip) external onlyOwner{
        require(_slip > 0, "!valid slip");
        slippage = _slip;
    }

    function withdrawTo(IERC20 _asset, uint256 _amount, address _to) external onlyOwner{
        _asset.safeTransfer(_to, _amount);
    }

    function execute(
        address _to,
        uint256 _value,
        bytes calldata _data
    ) external onlyOwner returns (bool, bytes memory) {

        (bool success, bytes memory result) = _to.call{value:_value}(_data);

        return (success, result);
    }

    function calc_minOut_swap(uint256 _amount) external view returns(uint256){
        uint256[2] memory amounts = [_amount,0];
        uint256 tokenOut = ICvxCrvExchange(exchange).calc_token_amount(amounts, false);
        tokenOut = tokenOut * slippage / 1e18;
        return tokenOut;
    }

    function calc_minOut_deposit(uint256 _crvamount, uint256 _cvxcrvamount) external view returns(uint256){
        uint256[2] memory amounts = [_crvamount,_cvxcrvamount];
        uint256 tokenOut = ICvxCrvExchange(exchange).calc_token_amount(amounts, true);
        tokenOut = tokenOut * slippage / 1e18;
        return tokenOut;
    }

    function calc_withdraw_one_coin(uint256 _amount) external view returns(uint256){
        uint256 tokenOut = ICvxCrvExchange(exchange).calc_withdraw_one_coin(_amount, 1);
        tokenOut = tokenOut * slippage / 1e18;
        return tokenOut;
    }

    function swap(uint256 _amount, uint256 _minAmountOut) external onlyOperator{
        require(_minAmountOut > 0, "!min_out");

        uint256 before = IERC20(cvxCrv).balanceOf(treasury);

        //pull
        IERC20(crv).safeTransferFrom(treasury,address(this),_amount);
        
        //swap and return to treasury
        ICvxCrvExchange(exchange).exchange(0,1,_amount,_minAmountOut, treasury);

        emit Swap(_amount, IERC20(cvxCrv).balanceOf(treasury) - before );
    }

    function stake(uint256 _amount) external onlyOperator{
        require(stakedCvxcrv != address(0),"!stkAddress");

        //pull
        IERC20(cvxCrv).safeTransferFrom(treasury,address(this),_amount);

        //stake for treasury
        uint256 bal = IERC20(cvxCrv).balanceOf(address(this));
        IRewardStaking(stakedCvxcrv).stakeFor(treasury, bal);

        emit Stake(bal);
    }

    function burn(uint256 _amount) external onlyOperator{
        //pull
        IERC20(cvxCrv).safeTransferFrom(treasury,address(this),_amount);

        //burn
        uint256 bal = IERC20(cvxCrv).balanceOf(address(this));
        IRewardStaking(cvxCrvRewards).stakeFor(stakedCvxcrv, bal);

        emit Burn(bal);
    }

    function swapAndStake(uint256 _amount, uint256 _minAmountOut) external onlyOperator{
        require(_minAmountOut > 0, "!min_out");
        require(stakedCvxcrv != address(0),"!stkAddress");

        //pull
        IERC20(crv).safeTransferFrom(treasury,address(this),_amount);

        //swap
        ICvxCrvExchange(exchange).exchange(0,1,_amount,_minAmountOut, address(this));
        uint256 bal = IERC20(cvxCrv).balanceOf(address(this));
        emit Swap(_amount, bal );

        //stake for treasury
        IRewardStaking(stakedCvxcrv).stakeFor(treasury, bal);
        emit Stake(bal);
    }

    function swapAndBurn(uint256 _amount, uint256 _minAmountOut) external onlyOperator{
        require(_minAmountOut > 0, "!min_out");
        require(stakedCvxcrv != address(0),"!stkAddress");

        //pull
        IERC20(crv).safeTransferFrom(treasury,address(this),_amount);

        //swap
        ICvxCrvExchange(exchange).exchange(0,1,_amount,_minAmountOut, address(this));
        uint256 bal = IERC20(cvxCrv).balanceOf(address(this));
        emit Swap(_amount, bal );

        //burn
        IRewardStaking(cvxCrvRewards).stakeFor(stakedCvxcrv, IERC20(cvxCrv).balanceOf(address(this)));
        emit Burn(bal);
    }


    function unstake(uint256 _amount) external onlyOperator{
        require(stakedCvxcrv != address(0),"!stkAddress");

        //pull staked tokens
        IERC20(stakedCvxcrv).safeTransferFrom(treasury,address(this),_amount);
        //unstake
        ICvxCrvStaking(stakedCvxcrv).withdraw(_amount);
        //transfer to treasury
        IERC20(cvxCrv).safeTransfer(treasury, IERC20(cvxCrv).balanceOf(address(this)));
        //get rewards for treasury
        ICvxCrvStaking(stakedCvxcrv).getReward(treasury);

        emit Unstake(_amount);
    }

    function unstakeAndBurn(uint256 _amount) external onlyOperator{
        require(stakedCvxcrv != address(0),"!stkAddress");

        //pull staked tokens
        IERC20(stakedCvxcrv).safeTransferFrom(treasury,address(this),_amount);
        //unstake
        ICvxCrvStaking(stakedCvxcrv).withdraw(_amount);
        uint256 bal = IERC20(cvxCrv).balanceOf(address(this));
        //burn
        IRewardStaking(cvxCrvRewards).stakeFor(stakedCvxcrv, bal);
        //get rewards for treasury
        ICvxCrvStaking(stakedCvxcrv).getReward(treasury);

        emit Unstake(_amount);
        emit Burn(bal);
    }

    function addToPool(uint256 _crvamount, uint256 _cvxcrvamount, uint256 _minAmountOut) external onlyOperator{
        require(_minAmountOut > 0, "!min_out");

        //pull
        IERC20(crv).safeTransferFrom(treasury,address(this),_crvamount);
        IERC20(cvxCrv).safeTransferFrom(treasury,address(this),_cvxcrvamount);

        //add lp
        uint256[2] memory amounts = [_crvamount,_cvxcrvamount];
        ICvxCrvExchange(exchange).add_liquidity(amounts, _minAmountOut, address(this));

        //add to convex
        uint256 lpBalance = IERC20(exchange).balanceOf(address(this));
        IConvexDeposits(booster).deposit(pid, lpBalance, true);

        emit AddedToLP(lpBalance);
    }

    function removeFromPool(uint256 _amount, uint256 _minAmountOut) external onlyOperator{
        require(_minAmountOut > 0, "!min_out");

        //remove from convex
        IRewardStaking(lprewards).withdrawAndUnwrap(_amount, true);

        //remove from LP with treasury as receiver
        ICvxCrvExchange(exchange).remove_liquidity_one_coin(IERC20(exchange).balanceOf(address(this)), 1, _minAmountOut, treasury);

        uint256 bal = IERC20(crv).balanceOf(address(this));
        if(bal > 0){
            //transfer to treasury
            IERC20(crv).safeTransfer(treasury, bal);
            emit ClaimedReward(crv,bal);
        }

        bal = IERC20(cvx).balanceOf(address(this));
        if(bal > 0){
            //transfer to treasury
            IERC20(cvx).safeTransfer(treasury, bal);
            emit ClaimedReward(cvx,bal);
        }

        emit RemovedFromLp(_amount);
    }

    function removeAsLP(uint256 _amount) external onlyOperator{
        //remove from convex
        IRewardStaking(lprewards).withdrawAndUnwrap(_amount, true);

        //remove from LP with treasury as receiver
        IERC20(exchange).safeTransfer(treasury,IERC20(exchange).balanceOf(address(this)));

        uint256 bal = IERC20(crv).balanceOf(address(this));
        if(bal > 0){
            //transfer to treasury
            IERC20(crv).safeTransfer(treasury, bal);
            emit ClaimedReward(crv,bal);
        }

        bal = IERC20(cvx).balanceOf(address(this));
        if(bal > 0){
            //transfer to treasury
            IERC20(cvx).safeTransfer(treasury, bal);
            emit ClaimedReward(cvx,bal);
        }

        emit RemovedFromLp(_amount);
    }

    function claimLPRewards() external onlyOperator{
        //claim from convex
        IRewardStaking(lprewards).getReward();

        uint256 bal = IERC20(crv).balanceOf(address(this));
        if(bal > 0){
            //transfer to treasury
            IERC20(crv).safeTransfer(treasury, bal);
            emit ClaimedReward(crv,bal);
        }

        bal = IERC20(cvx).balanceOf(address(this));
        if(bal > 0){
            //transfer to treasury
            IERC20(cvx).safeTransfer(treasury, bal);
            emit ClaimedReward(cvx,bal);
        }
    }

}
// File: /contracts/interfaces/IRewardStaking.sol



// SPDX-License-Identifier: MIT
pragma solidity 0.6.12;

interface IRewardStaking {
    function stakeFor(address, uint256) external;
    function stake( uint256) external;
    function withdraw(uint256 amount, bool claim) external;
    function withdrawAndUnwrap(uint256 amount, bool claim) external;
    function earned(address account) external view returns (uint256);
    function getReward() external;
    function getReward(address _account, bool _claimExtras) external;
    function extraRewardsLength() external view returns (uint256);
    function extraRewards(uint256 _pid) external view returns (address);
    function rewardToken() external view returns (address);
    function balanceOf(address _account) external view returns (uint256);
    function rewardRate() external view returns(uint256);
    function totalSupply() external view returns(uint256);
}
// File: /contracts/interfaces/ICvxCrvStaking.sol



// SPDX-License-Identifier: MIT

pragma solidity 0.6.12;

interface ICvxCrvStaking {
    function userRewardBalance(address _address, uint256 _rewardGroup) external view returns(uint256);
    function rewardSupply(uint256 _rewardGroup) external view returns(uint256);
    function userRewardWeight(address _address) external view returns(uint256);
    function registeredRewards(address _address) external view returns(uint256);
    function rewards(uint256 _index) external view returns(address _token, uint8 _group, uint128 _reward_integral, uint128 _reward_remaining);
    function withdraw(uint256 _amount) external;
    function getReward(address _account) external;
    function balanceOf(address _account) external view returns (uint256);
}
// File: /contracts/interfaces/IConvexDeposits.sol



// SPDX-License-Identifier: MIT
pragma solidity 0.6.12;

interface IConvexDeposits {
    function deposit(uint256 _pid, uint256 _amount, bool _stake) external returns(bool);
    function deposit(uint256 _amount, bool _lock, address _stakeAddress) external;
}
// File: @openzeppelin/contracts/utils/Address.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.2 <0.8.0;

/**
 * @dev Collection of functions related to the address type
 */
library Address {
    /**
     * @dev Returns true if `account` is 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.
     *
     * Among others, `isContract` will return false for the following
     * types of addresses:
     *
     *  - an externally-owned account
     *  - a contract in construction
     *  - an address where a contract will be created
     *  - an address where a contract lived, but was destroyed
     * ====
     */
    function isContract(address account) internal view returns (bool) {
        // This method relies on extcodesize, which returns 0 for contracts in
        // construction, since the code is only stored at the end of the
        // constructor execution.

        uint256 size;
        // solhint-disable-next-line no-inline-assembly
        assembly { size := extcodesize(account) }
        return size > 0;
    }

    /**
     * @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].
     */
    function sendValue(address payable recipient, uint256 amount) internal {
        require(address(this).balance >= amount, "Address: insufficient balance");

        // solhint-disable-next-line avoid-low-level-calls, avoid-call-value
        (bool success, ) = recipient.call{ value: amount }("");
        require(success, "Address: unable to send value, recipient may have reverted");
    }

    /**
     * @dev Performs a Solidity function call using a low level `call`. A
     * plain`call` is an unsafe replacement for a function call: use this
     * function instead.
     *
     * If `target` reverts with a revert reason, it is bubbled up by this
     * function (like regular Solidity function calls).
     *
     * Returns the raw returned data. To convert to the expected return value,
     * use https://solidity.readthedocs.io/en/latest/units-and-global-variables.html?highlight=abi.decode#abi-encoding-and-decoding-functions[`abi.decode`].
     *
     * Requirements:
     *
     * - `target` must be a contract.
     * - calling `target` with `data` must not revert.
     *
     * _Available since v3.1._
     */
    function functionCall(address target, bytes memory data) internal returns (bytes memory) {
      return functionCall(target, data, "Address: low-level call failed");
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`], but with
     * `errorMessage` as a fallback revert reason when `target` reverts.
     *
     * _Available since v3.1._
     */
    function functionCall(address target, bytes memory data, string memory errorMessage) internal returns (bytes memory) {
        return functionCallWithValue(target, data, 0, errorMessage);
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`],
     * but also transferring `value` wei to `target`.
     *
     * Requirements:
     *
     * - the calling contract must have an ETH balance of at least `value`.
     * - the called Solidity function must be `payable`.
     *
     * _Available since v3.1._
     */
    function functionCallWithValue(address target, bytes memory data, uint256 value) internal returns (bytes memory) {
        return functionCallWithValue(target, data, value, "Address: low-level call with value failed");
    }

    /**
     * @dev Same as {xref-Address-functionCallWithValue-address-bytes-uint256-}[`functionCallWithValue`], but
     * with `errorMessage` as a fallback revert reason when `target` reverts.
     *
     * _Available since v3.1._
     */
    function functionCallWithValue(address target, bytes memory data, uint256 value, string memory errorMessage) internal returns (bytes memory) {
        require(address(this).balance >= value, "Address: insufficient balance for call");
        require(isContract(target), "Address: call to non-contract");

        // solhint-disable-next-line avoid-low-level-calls
        (bool success, bytes memory returndata) = target.call{ value: value }(data);
        return _verifyCallResult(success, returndata, errorMessage);
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`],
     * but performing a static call.
     *
     * _Available since v3.3._
     */
    function functionStaticCall(address target, bytes memory data) internal view returns (bytes memory) {
        return functionStaticCall(target, data, "Address: low-level static call failed");
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-string-}[`functionCall`],
     * but performing a static call.
     *
     * _Available since v3.3._
     */
    function functionStaticCall(address target, bytes memory data, string memory errorMessage) internal view returns (bytes memory) {
        require(isContract(target), "Address: static call to non-contract");

        // solhint-disable-next-line avoid-low-level-calls
        (bool success, bytes memory returndata) = target.staticcall(data);
        return _verifyCallResult(success, returndata, errorMessage);
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`],
     * but performing a delegate call.
     *
     * _Available since v3.4._
     */
    function functionDelegateCall(address target, bytes memory data) internal returns (bytes memory) {
        return functionDelegateCall(target, data, "Address: low-level delegate call failed");
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-string-}[`functionCall`],
     * but performing a delegate call.
     *
     * _Available since v3.4._
     */
    function functionDelegateCall(address target, bytes memory data, string memory errorMessage) internal returns (bytes memory) {
        require(isContract(target), "Address: delegate call to non-contract");

        // solhint-disable-next-line avoid-low-level-calls
        (bool success, bytes memory returndata) = target.delegatecall(data);
        return _verifyCallResult(success, returndata, errorMessage);
    }

    function _verifyCallResult(bool success, bytes memory returndata, string memory errorMessage) private pure returns(bytes memory) {
        if (success) {
            return returndata;
        } else {
            // Look for revert reason and bubble it up if present
            if (returndata.length > 0) {
                // The easiest way to bubble the revert reason is using memory via assembly

                // solhint-disable-next-line no-inline-assembly
                assembly {
                    let returndata_size := mload(returndata)
                    revert(add(32, returndata), returndata_size)
                }
            } else {
                revert(errorMessage);
            }
        }
    }
}

// File: @openzeppelin/contracts/token/ERC20/SafeERC20.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

import "./IERC20.sol";
import "../../math/SafeMath.sol";
import "../../utils/Address.sol";

/**
 * @title SafeERC20
 * @dev Wrappers around ERC20 operations that throw on failure (when the token
 * contract returns false). Tokens that return no value (and instead revert or
 * throw on failure) are also supported, non-reverting calls are assumed to be
 * successful.
 * To use this library you can add a `using SafeERC20 for IERC20;` statement to your contract,
 * which allows you to call the safe operations as `token.safeTransfer(...)`, etc.
 */
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));
    }

    /**
     * @dev Deprecated. This function has issues similar to the ones found in
     * {IERC20-approve}, and its usage is discouraged.
     *
     * Whenever possible, use {safeIncreaseAllowance} and
     * {safeDecreaseAllowance} instead.
     */
    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. We use {Address.functionCall} to perform this call, which verifies that
        // the target address contains contract code and also asserts for success in the low-level call.

        bytes memory returndata = address(token).functionCall(data, "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");
        }
    }
}

// File: @openzeppelin/contracts/token/ERC20/IERC20.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

/**
 * @dev Interface of the ERC20 standard as defined in the EIP.
 */
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);
}

// File: @openzeppelin/contracts/math/SafeMath.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

/**
 * @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, with an overflow flag.
     *
     * _Available since v3.4._
     */
    function tryAdd(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        uint256 c = a + b;
        if (c < a) return (false, 0);
        return (true, c);
    }

    /**
     * @dev Returns the substraction of two unsigned integers, with an overflow flag.
     *
     * _Available since v3.4._
     */
    function trySub(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        if (b > a) return (false, 0);
        return (true, a - b);
    }

    /**
     * @dev Returns the multiplication of two unsigned integers, with an overflow flag.
     *
     * _Available since v3.4._
     */
    function tryMul(uint256 a, uint256 b) internal pure returns (bool, 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 (true, 0);
        uint256 c = a * b;
        if (c / a != b) return (false, 0);
        return (true, c);
    }

    /**
     * @dev Returns the division of two unsigned integers, with a division by zero flag.
     *
     * _Available since v3.4._
     */
    function tryDiv(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        if (b == 0) return (false, 0);
        return (true, a / b);
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers, with a division by zero flag.
     *
     * _Available since v3.4._
     */
    function tryMod(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        if (b == 0) return (false, 0);
        return (true, a % b);
    }

    /**
     * @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) {
        require(b <= a, "SafeMath: subtraction overflow");
        return a - b;
    }

    /**
     * @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) {
        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, reverting 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) {
        require(b > 0, "SafeMath: division by zero");
        return a / b;
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * reverting 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) {
        require(b > 0, "SafeMath: modulo by zero");
        return a % b;
    }

    /**
     * @dev Returns the subtraction of two unsigned integers, reverting with custom message on
     * overflow (when the result is negative).
     *
     * CAUTION: This function is deprecated because it requires allocating memory for the error
     * message unnecessarily. For custom revert reasons use {trySub}.
     *
     * Counterpart to Solidity's `-` operator.
     *
     * Requirements:
     *
     * - Subtraction cannot overflow.
     */
    function sub(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b <= a, errorMessage);
        return a - b;
    }

    /**
     * @dev Returns the integer division of two unsigned integers, reverting with custom message on
     * division by zero. The result is rounded towards zero.
     *
     * CAUTION: This function is deprecated because it requires allocating memory for the error
     * message unnecessarily. For custom revert reasons use {tryDiv}.
     *
     * 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, string memory errorMessage) internal pure returns (uint256) {
        require(b > 0, errorMessage);
        return a / b;
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * reverting with custom message when dividing by zero.
     *
     * CAUTION: This function is deprecated because it requires allocating memory for the error
     * message unnecessarily. For custom revert reasons use {tryMod}.
     *
     * 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, string memory errorMessage) internal pure returns (uint256) {
        require(b > 0, errorMessage);
        return a % b;
    }
}