// SPDX-License-Identifier: MIT
pragma solidity >=0.7.2;
pragma experimental ABIEncoderV2;

import '@openzeppelin/contracts/access/Ownable.sol';
import '@openzeppelin/contracts/token/ERC20/ERC20.sol';
import '@openzeppelin/contracts/utils/ReentrancyGuard.sol';
import { SafeMath } from '@openzeppelin/contracts/math/SafeMath.sol';
import { IERC20 } from '@openzeppelin/contracts/token/ERC20/IERC20.sol';
import { SafeERC20 } from '@openzeppelin/contracts/token/ERC20/SafeERC20.sol';

import { IAction } from '../interfaces/IAction.sol';
import { ICurve } from '../interfaces/ICurve.sol';
import { IStakeDao } from '../interfaces/IStakeDao.sol';

/**
 * Error Codes
 * O1: actions for the vault have not been initialized
 * O2: cannot execute transaction, vault is in emergency state
 * O3: cannot call setActions, actions have already been initialized
 * O4: action being set is using an invalid address
 * O5: action being set is a duplicated action
 * O6: deposited ETH (msg.value) must be greater than 0
 * O7: cannot accept ETH deposit, total sdecrv controlled by the vault would exceed vault cap
 * O8: unable to withdraw ETH, sdecrv to withdraw would exceed or be equal to the current vault sdecrv balance
 * O9: unable to withdraw ETH, ETH fee transfer to fee recipient (feeRecipient) failed
 * O10: unable to withdraw ETH, ETH withdrawal to user (msg.sender) failed
 * O11: cannot close vault positions, vault is not in locked state (VaultState.Locked)
 * O12: unable to rollover vault, length of allocation percentages (_allocationPercentages) passed is not equal to the initialized actions length
 * O13: unable to rollover vault, vault is not in unlocked state (VaultState.Unlocked)
 * O14: unable to rollover vault, the calculated percentage sum (sumPercentage) is greater than the base (BASE)
 * O15: unable to rollover vault, the calculated percentage sum (sumPercentage) is not equal to the base (BASE)
 * O16: withdraw reserve percentage must be less than 50% (5000)
 * O17: cannot call emergencyPause, vault is already in emergency state
 * O18: cannot call resumeFromPause, vault is not in emergency state
 * O19: cannot receive ETH from any address other than the curve pool address (curvePool)
 */

/** 
 * @title OpynPerpVault
 * @author Opyn Team
 * @dev implementation of the Opyn Perp Vault contract that works with stakedao's ETH strategy. 
 * Note that this implementation is meant to only specifically work for the stakedao ETH strategy and is not 
 * a generalized contract. Stakedao's ETH strategy currently accepts curvePool LP tokens called ecrv from the 
 * sETH-ETH curvePool pool. This strategy allows users to convert their ETH into yield earning sdecrv tokens
 * and use the sdecrv tokens as collateral to sell ETH call options on Opyn. 
 */

contract OpynPerpVault is ERC20, ReentrancyGuard, Ownable {
  using SafeERC20 for IERC20;
  using SafeMath for uint256;

  enum VaultState {
    Emergency,
    Locked,
    Unlocked
  }

  /// @dev actions that build up this strategy (vault)
  address[] public actions;

  /// @dev address to which all fees are sent
  address public feeRecipient;

  /// @dev stake dao sdecrvAddress
  address public sdecrvAddress;

  uint256 public constant BASE = 10000; // 100%

  /// @dev Cap for the vault. hardcoded at 1000 for initial release
  uint256 public cap = 1000 ether;

  /// @dev withdrawal fee percentage. 50 being 0.5%
  uint256 public withdrawalFeePercentage = 50;

  /// @dev how many percentage should be reserved in vault for withdraw. 1000 being 10%
  uint256 public withdrawReserve = 0;

  /// @dev curvePool ETH/sETH stableswap 
  ICurve public curvePool;

  VaultState public state;
  VaultState public stateBeforePause;

  /*=====================
   *       Events       *
   *====================*/

  event CapUpdated(uint256 newCap);

  event Deposit(address account, uint256 amountDeposited, uint256 shareMinted);

  event Rollover(uint256[] allocations);

  event StateUpdated(VaultState state);

  event Withdraw(address account, uint256 amountWithdrawn, uint256 fee, uint256 shareBurned);

  /*=====================
   *     Modifiers      *
   *====================*/

  /** 
   * @dev can only be called if actions are initialized 
   */
  function actionsInitialized() private view {
    require(actions.length > 0, "O1");
  }
  
  /**
   * @dev can only be executed if vault is not in emergency state
   */
  function notEmergency() private view {
    require(state != VaultState.Emergency, "O2");
  }

  /*=====================
   * external function *
   *====================*/

  constructor (
    address _sdecrvAddress,
    address _curvePool,
    address _feeRecipient,
    string memory _tokenName,
    string memory _tokenSymbol
    ) ERC20(_tokenName, _tokenSymbol) {
    sdecrvAddress = _sdecrvAddress;
    feeRecipient = _feeRecipient;
    curvePool = ICurve(_curvePool);
    state = VaultState.Unlocked;
  }

  function setActions(address[] memory _actions) external onlyOwner {
    require(actions.length == 0, "O3");

    // assign actions
    for(uint256 i = 0 ; i < _actions.length; i++ ) {
      // check all items before actions[i], does not equal to action[i]
      require(_actions[i] != address(0), "O4");

      for(uint256 j = 0; j < i; j++) {
        require(_actions[i] != _actions[j], "O5");
      }

      actions.push(_actions[i]);
    }
  }

  /** 
   * @notice allows owner to change the cap
   */
   function setCap(uint256 _newCap) external onlyOwner {
     cap = _newCap;

     emit CapUpdated(_newCap);
   }

  /**
   * @notice total sdecrv controlled by this vault
   */
  function totalStakedaoAsset() public view returns (uint256) {
    uint256 debt = 0;
    uint256 length = actions.length;

    for (uint256 i = 0; i < length; i++) {
      debt = debt.add(IAction(actions[i]).currentValue());
    }

    return _balance().add(debt);
  }

  /**
   * total eth value of the sdecrv controlled by this vault
   */
  function totalETHControlled() external view returns (uint256) { 
    IStakeDao sdecrv = IStakeDao(sdecrvAddress);
    // hard coded to 36 because ecrv and sdecrv are both 18 decimals. 
    return totalStakedaoAsset().mul(sdecrv.getPricePerFullShare()).mul(curvePool.get_virtual_price()).div(10**36);
  }

  /**
   * @dev return how many sdecrv you can get if you burn the number of shares, after charging the fee.
   */
  function getWithdrawAmountByShares(uint256 _shares) external view returns (uint256) {
    uint256 withdrawAmount = _getWithdrawAmountByShares(_shares);
    return withdrawAmount.sub(_getWithdrawFee(withdrawAmount));
  }

  /**
   * @notice Deposits ETH into the contract and mint vault shares. 
   * @dev deposit into the curvePool, then into stakedao, then mint the shares to depositor, and emit the deposit event
   * @param minEcrv minimum amount of ecrv to get out from adding liquidity. 
   */
  function depositETH(uint256 minEcrv) external payable nonReentrant {
    notEmergency();
    actionsInitialized();
    uint256 amount = msg.value;
    require(amount > 0, 'O6');

    // the sdecrv is already deposited into the contract at this point, need to substract it from total
    uint256[2] memory amounts;
    amounts[0] = amount;
    amounts[1] = 0; // not depositing any seth

    // deposit ETH to curvePool
    curvePool.add_liquidity{value:amount}(amounts, minEcrv);

    // keep track of balance before
    uint256 totalSdecrvBalanceBeforeDeposit = totalStakedaoAsset();

    // deposit ecrv to stakedao
    address cacheSdecrvAddress = sdecrvAddress;
    IStakeDao sdecrv = IStakeDao(cacheSdecrvAddress);
    IERC20 ecrv = sdecrv.token();
    uint256 ecrvToDeposit = ecrv.balanceOf(address(this));

    ecrv.safeIncreaseAllowance(cacheSdecrvAddress, ecrvToDeposit);
    sdecrv.deposit(ecrvToDeposit);

    // mint shares and emit event 
    uint256 totalWithDepositedAmount = totalStakedaoAsset();
    require(totalWithDepositedAmount < cap, 'O7');
    uint256 sdecrvDeposited = totalWithDepositedAmount.sub(totalSdecrvBalanceBeforeDeposit);
    uint256 share = _getSharesByDepositAmount(sdecrvDeposited, totalSdecrvBalanceBeforeDeposit);

    emit Deposit(msg.sender, amount, share);

    _mint(msg.sender, share);
  }

  /**
   * @notice Withdraws ETH from vault using vault shares
   * @dev burns shares, withdraws ecrv from stakdao, withdraws ETH from curvePool
   * @param _share is the number of vault shares to be burned
   */
  function withdrawETH(uint256 _share, uint256 minEth) external nonReentrant {
    notEmergency();
    actionsInitialized();
    uint256 currentSdecrvBalance = _balance();
    uint256 sdecrvToWithdraw = _getWithdrawAmountByShares(_share);
    require(sdecrvToWithdraw <= currentSdecrvBalance, 'O8');

    _burn(msg.sender, _share);

    // withdraw from stakedao and curvePool
    IStakeDao sdecrv = IStakeDao(sdecrvAddress);
    sdecrv.withdraw(sdecrvToWithdraw);
    uint256 ecrvBalance = sdecrv.token().balanceOf(address(this));
    uint256 ethReceived = curvePool.remove_liquidity_one_coin(ecrvBalance, 0, minEth);

    // calculate fees
    uint256 fee = _getWithdrawFee(ethReceived);
    uint256 ethOwedToUser = ethReceived.sub(fee);

    // send fee to recipient 
    (bool success1, ) = feeRecipient.call{ value: fee }('');
    require(success1, 'O9');

    // send ETH to user
    (bool success2, ) = msg.sender.call{ value: ethOwedToUser }('');
    require(success2, 'O10');

    emit Withdraw(msg.sender, ethOwedToUser, fee, _share);
  }

  /**
   * @notice anyone can call this to close out the previous round by calling "closePositions" on all actions. 
   * @dev iterrate through each action, close position and withdraw funds
   */
  function closePositions() public {
    actionsInitialized();
    require(state == VaultState.Locked, "O11");
    state = VaultState.Unlocked;

    address cacheAddress = sdecrvAddress;
    for (uint8 i = 0; i < actions.length; i = i + 1) {
      // 1. close position. this should revert if any position is not ready to be closed.
      IAction(actions[i]).closePosition();

      // 2. withdraw sdecrv
      uint256 actionBalance = IERC20(cacheAddress).balanceOf(actions[i]);
      if (actionBalance > 0)
        IERC20(cacheAddress).safeTransferFrom(actions[i], address(this), actionBalance);
    }

    emit StateUpdated(VaultState.Unlocked);
  }

  /**
   * @notice can only be called when the vault is unlocked. It sets the state to locked and distributes funds to each action.
   */
  function rollOver(uint256[] calldata _allocationPercentages) external onlyOwner nonReentrant {
    actionsInitialized();
    require(_allocationPercentages.length == actions.length, 'O12');
    require(state == VaultState.Unlocked, "O13");
    state = VaultState.Locked;

    uint256 cacheTotalAsset = totalStakedaoAsset();
    uint256 cacheBase = BASE;

    // keep track of total percentage to make sure we're summing up to 100%
    uint256 sumPercentage = withdrawReserve;
    address cacheAddress = sdecrvAddress;

    for (uint8 i = 0; i < _allocationPercentages.length; i = i + 1) {
      sumPercentage = sumPercentage.add(_allocationPercentages[i]);
      require(sumPercentage <= cacheBase, 'O14');

      uint256 newAmount = cacheTotalAsset.mul(_allocationPercentages[i]).div(cacheBase);

      if (newAmount > 0) IERC20(cacheAddress).safeTransfer(actions[i], newAmount);
      IAction(actions[i]).rolloverPosition();
    }

    require(sumPercentage == cacheBase, 'O15');

    emit Rollover(_allocationPercentages);
    emit StateUpdated(VaultState.Locked);
  }

  /**
   * @dev set the vault withdrawal fee recipient
   */
  function setWithdrawalFeeRecipient(address _newWithdrawalFeeRecipient) external onlyOwner {
    feeRecipient = _newWithdrawalFeeRecipient;
  }

  /**
   * @dev set the percentage that should be reserved in vault for withdraw
   */
  function setWithdrawalFeePercentage(uint256 _newWithdrawalFeePercentage) external onlyOwner {
    withdrawalFeePercentage = _newWithdrawalFeePercentage;
  }

  /**
   * @dev set the percentage that should be reserved in vault for withdraw
   */
  function setWithdrawReserve(uint256 _reserve) external onlyOwner {
    require(_reserve < 5000, "O16");
    withdrawReserve = _reserve;
  }

  /**
   * @dev set the state to "Emergency", which disable all withdraw and deposit
   */
  function emergencyPause() external onlyOwner {
    require(state != VaultState.Emergency, "O17");

    stateBeforePause = state;
    state = VaultState.Emergency;

    emit StateUpdated(VaultState.Emergency);
  }

  /**
   * @dev set the state from "Emergency", which disable all withdraw and deposit
   */
  function resumeFromPause() external onlyOwner {
    require(state == VaultState.Emergency, "O18");

    state = stateBeforePause;

    emit StateUpdated(stateBeforePause);
  }

   /**
   * @dev return how many shares you can get if you deposit {_amount} sdecrv
   * @param _amount amount of token depositing
   */
  function getSharesByDepositAmount(uint256 _amount) external view returns (uint256) {
    return _getSharesByDepositAmount(_amount, totalStakedaoAsset());
  }

  /*=====================
   * Internal functions *
   *====================*/

  /**
   * @dev returns remaining sdecrv balance in the vault.
   */
  function _balance() internal view returns (uint256) {
    return IERC20(sdecrvAddress).balanceOf(address(this));
  }

  /**
   * @dev return how many shares you can get if you deposit {_amount} sdecrv
   * @param _amount amount of token depositing
   * @param _totalAssetAmount amont of sdecrv already in the pool before deposit
   */
  function _getSharesByDepositAmount(uint256 _amount, uint256 _totalAssetAmount) internal view returns (uint256) {
    uint256 shareSupply = totalSupply();

    // share amount
    return shareSupply == 0 ? _amount : _amount.mul(shareSupply).div(_totalAssetAmount);
  }

  /**
   * @dev return how many sdecrv you can get if you burn the number of shares
   */
  function _getWithdrawAmountByShares(uint256 _share) internal view returns (uint256) {
    // withdrawal amount
    return _share.mul(totalStakedaoAsset()).div(totalSupply());
  }

  /**
   * @dev get amount of fee charged based on total amount of weth withdrawing.
   */
  function _getWithdrawFee(uint256 _withdrawAmount) internal view returns (uint256) {
    return _withdrawAmount.mul(withdrawalFeePercentage).div(BASE);
  }

  /**
    * @notice the receive ether function is called whenever the call data is empty
    */
  receive() external payable {
    require(msg.sender == address(curvePool), "O19");
  }
}

// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

import "../utils/Context.sol";
/**
 * @dev Contract module which provides a basic access control mechanism, where
 * there is an account (an owner) that can be granted exclusive access to
 * specific functions.
 *
 * By default, the owner account will be the one that deploys the contract. This
 * can later be changed with {transferOwnership}.
 *
 * This module is used through inheritance. It will make available the modifier
 * `onlyOwner`, which can be applied to your functions to restrict their use to
 * the owner.
 */
abstract contract Ownable is Context {
    address private _owner;

    event OwnershipTransferred(address indexed previousOwner, address indexed newOwner);

    /**
     * @dev Initializes the contract setting the deployer as the initial owner.
     */
    constructor () internal {
        address msgSender = _msgSender();
        _owner = msgSender;
        emit OwnershipTransferred(address(0), msgSender);
    }

    /**
     * @dev Returns the address of the current owner.
     */
    function owner() public view virtual returns (address) {
        return _owner;
    }

    /**
     * @dev Throws if called by any account other than the owner.
     */
    modifier onlyOwner() {
        require(owner() == _msgSender(), "Ownable: caller is not the owner");
        _;
    }

    /**
     * @dev Leaves the contract without owner. It will not be possible to call
     * `onlyOwner` functions anymore. Can only be called by the current owner.
     *
     * NOTE: Renouncing ownership will leave the contract without an owner,
     * thereby removing any functionality that is only available to the owner.
     */
    function renounceOwnership() public virtual onlyOwner {
        emit OwnershipTransferred(_owner, address(0));
        _owner = address(0);
    }

    /**
     * @dev Transfers ownership of the contract to a new account (`newOwner`).
     * Can only be called by the current owner.
     */
    function transferOwnership(address newOwner) public virtual onlyOwner {
        require(newOwner != address(0), "Ownable: new owner is the zero address");
        emit OwnershipTransferred(_owner, newOwner);
        _owner = newOwner;
    }
}

// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

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

/**
 * @dev Implementation of the {IERC20} interface.
 *
 * This implementation is agnostic to the way tokens are created. This means
 * that a supply mechanism has to be added in a derived contract using {_mint}.
 * For a generic mechanism see {ERC20PresetMinterPauser}.
 *
 * TIP: For a detailed writeup see our guide
 * https://forum.zeppelin.solutions/t/how-to-implement-erc20-supply-mechanisms/226[How
 * to implement supply mechanisms].
 *
 * We have followed general OpenZeppelin guidelines: functions revert instead
 * of returning `false` on failure. This behavior is nonetheless conventional
 * and does not conflict with the expectations of ERC20 applications.
 *
 * Additionally, an {Approval} event is emitted on calls to {transferFrom}.
 * This allows applications to reconstruct the allowance for all accounts just
 * by listening to said events. Other implementations of the EIP may not emit
 * these events, as it isn't required by the specification.
 *
 * Finally, the non-standard {decreaseAllowance} and {increaseAllowance}
 * functions have been added to mitigate the well-known issues around setting
 * allowances. See {IERC20-approve}.
 */
contract ERC20 is Context, IERC20 {
    using SafeMath for uint256;

    mapping (address => uint256) private _balances;

    mapping (address => mapping (address => uint256)) private _allowances;

    uint256 private _totalSupply;

    string private _name;
    string private _symbol;
    uint8 private _decimals;

    /**
     * @dev Sets the values for {name} and {symbol}, initializes {decimals} with
     * a default value of 18.
     *
     * To select a different value for {decimals}, use {_setupDecimals}.
     *
     * All three of these values are immutable: they can only be set once during
     * construction.
     */
    constructor (string memory name_, string memory symbol_) public {
        _name = name_;
        _symbol = symbol_;
        _decimals = 18;
    }

    /**
     * @dev Returns the name of the token.
     */
    function name() public view virtual returns (string memory) {
        return _name;
    }

    /**
     * @dev Returns the symbol of the token, usually a shorter version of the
     * name.
     */
    function symbol() public view virtual returns (string memory) {
        return _symbol;
    }

    /**
     * @dev Returns the number of decimals used to get its user representation.
     * For example, if `decimals` equals `2`, a balance of `505` tokens should
     * be displayed to a user as `5,05` (`505 / 10 ** 2`).
     *
     * Tokens usually opt for a value of 18, imitating the relationship between
     * Ether and Wei. This is the value {ERC20} uses, unless {_setupDecimals} is
     * called.
     *
     * NOTE: This information is only used for _display_ purposes: it in
     * no way affects any of the arithmetic of the contract, including
     * {IERC20-balanceOf} and {IERC20-transfer}.
     */
    function decimals() public view virtual returns (uint8) {
        return _decimals;
    }

    /**
     * @dev See {IERC20-totalSupply}.
     */
    function totalSupply() public view virtual override returns (uint256) {
        return _totalSupply;
    }

    /**
     * @dev See {IERC20-balanceOf}.
     */
    function balanceOf(address account) public view virtual override returns (uint256) {
        return _balances[account];
    }

    /**
     * @dev See {IERC20-transfer}.
     *
     * Requirements:
     *
     * - `recipient` cannot be the zero address.
     * - the caller must have a balance of at least `amount`.
     */
    function transfer(address recipient, uint256 amount) public virtual override returns (bool) {
        _transfer(_msgSender(), recipient, amount);
        return true;
    }

    /**
     * @dev See {IERC20-allowance}.
     */
    function allowance(address owner, address spender) public view virtual override returns (uint256) {
        return _allowances[owner][spender];
    }

    /**
     * @dev See {IERC20-approve}.
     *
     * Requirements:
     *
     * - `spender` cannot be the zero address.
     */
    function approve(address spender, uint256 amount) public virtual override returns (bool) {
        _approve(_msgSender(), spender, amount);
        return true;
    }

    /**
     * @dev See {IERC20-transferFrom}.
     *
     * Emits an {Approval} event indicating the updated allowance. This is not
     * required by the EIP. See the note at the beginning of {ERC20}.
     *
     * Requirements:
     *
     * - `sender` and `recipient` cannot be the zero address.
     * - `sender` must have a balance of at least `amount`.
     * - the caller must have allowance for ``sender``'s tokens of at least
     * `amount`.
     */
    function transferFrom(address sender, address recipient, uint256 amount) public virtual override returns (bool) {
        _transfer(sender, recipient, amount);
        _approve(sender, _msgSender(), _allowances[sender][_msgSender()].sub(amount, "ERC20: transfer amount exceeds allowance"));
        return true;
    }

    /**
     * @dev Atomically increases the allowance granted to `spender` by the caller.
     *
     * This is an alternative to {approve} that can be used as a mitigation for
     * problems described in {IERC20-approve}.
     *
     * Emits an {Approval} event indicating the updated allowance.
     *
     * Requirements:
     *
     * - `spender` cannot be the zero address.
     */
    function increaseAllowance(address spender, uint256 addedValue) public virtual returns (bool) {
        _approve(_msgSender(), spender, _allowances[_msgSender()][spender].add(addedValue));
        return true;
    }

    /**
     * @dev Atomically decreases the allowance granted to `spender` by the caller.
     *
     * This is an alternative to {approve} that can be used as a mitigation for
     * problems described in {IERC20-approve}.
     *
     * Emits an {Approval} event indicating the updated allowance.
     *
     * Requirements:
     *
     * - `spender` cannot be the zero address.
     * - `spender` must have allowance for the caller of at least
     * `subtractedValue`.
     */
    function decreaseAllowance(address spender, uint256 subtractedValue) public virtual returns (bool) {
        _approve(_msgSender(), spender, _allowances[_msgSender()][spender].sub(subtractedValue, "ERC20: decreased allowance below zero"));
        return true;
    }

    /**
     * @dev Moves tokens `amount` from `sender` to `recipient`.
     *
     * This is internal function is equivalent to {transfer}, and can be used to
     * e.g. implement automatic token fees, slashing mechanisms, etc.
     *
     * Emits a {Transfer} event.
     *
     * Requirements:
     *
     * - `sender` cannot be the zero address.
     * - `recipient` cannot be the zero address.
     * - `sender` must have a balance of at least `amount`.
     */
    function _transfer(address sender, address recipient, uint256 amount) internal virtual {
        require(sender != address(0), "ERC20: transfer from the zero address");
        require(recipient != address(0), "ERC20: transfer to the zero address");

        _beforeTokenTransfer(sender, recipient, amount);

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

    /** @dev Creates `amount` tokens and assigns them to `account`, increasing
     * the total supply.
     *
     * Emits a {Transfer} event with `from` set to the zero address.
     *
     * Requirements:
     *
     * - `to` cannot be the zero address.
     */
    function _mint(address account, uint256 amount) internal virtual {
        require(account != address(0), "ERC20: mint to the zero address");

        _beforeTokenTransfer(address(0), account, amount);

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

    /**
     * @dev Destroys `amount` tokens from `account`, reducing the
     * total supply.
     *
     * Emits a {Transfer} event with `to` set to the zero address.
     *
     * Requirements:
     *
     * - `account` cannot be the zero address.
     * - `account` must have at least `amount` tokens.
     */
    function _burn(address account, uint256 amount) internal virtual {
        require(account != address(0), "ERC20: burn from the zero address");

        _beforeTokenTransfer(account, address(0), amount);

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

    /**
     * @dev Sets `amount` as the allowance of `spender` over the `owner` s tokens.
     *
     * This internal function is equivalent to `approve`, and can be used to
     * e.g. set automatic allowances for certain subsystems, etc.
     *
     * Emits an {Approval} event.
     *
     * Requirements:
     *
     * - `owner` cannot be the zero address.
     * - `spender` cannot be the zero address.
     */
    function _approve(address owner, address spender, uint256 amount) internal virtual {
        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);
    }

    /**
     * @dev Sets {decimals} to a value other than the default one of 18.
     *
     * WARNING: This function should only be called from the constructor. Most
     * applications that interact with token contracts will not expect
     * {decimals} to ever change, and may work incorrectly if it does.
     */
    function _setupDecimals(uint8 decimals_) internal virtual {
        _decimals = decimals_;
    }

    /**
     * @dev Hook that is called before any transfer of tokens. This includes
     * minting and burning.
     *
     * Calling conditions:
     *
     * - when `from` and `to` are both non-zero, `amount` of ``from``'s tokens
     * will be to transferred to `to`.
     * - when `from` is zero, `amount` tokens will be minted for `to`.
     * - when `to` is zero, `amount` of ``from``'s tokens will be burned.
     * - `from` and `to` are never both zero.
     *
     * To learn more about hooks, head to xref:ROOT:extending-contracts.adoc#using-hooks[Using Hooks].
     */
    function _beforeTokenTransfer(address from, address to, uint256 amount) internal virtual { }
}

// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

/**
 * @dev Contract module that helps prevent reentrant calls to a function.
 *
 * Inheriting from `ReentrancyGuard` will make the {nonReentrant} modifier
 * available, which can be applied to functions to make sure there are no nested
 * (reentrant) calls to them.
 *
 * Note that because there is a single `nonReentrant` guard, functions marked as
 * `nonReentrant` may not call one another. This can be worked around by making
 * those functions `private`, and then adding `external` `nonReentrant` entry
 * points to them.
 *
 * TIP: If you would like to learn more about reentrancy and alternative ways
 * to protect against it, check out our blog post
 * https://blog.openzeppelin.com/reentrancy-after-istanbul/[Reentrancy After Istanbul].
 */
abstract contract ReentrancyGuard {
    // Booleans are more expensive than uint256 or any type that takes up a full
    // word because each write operation emits an extra SLOAD to first read the
    // slot's contents, replace the bits taken up by the boolean, and then write
    // back. This is the compiler's defense against contract upgrades and
    // pointer aliasing, and it cannot be disabled.

    // The values being non-zero value makes deployment a bit more expensive,
    // but in exchange the refund on every call to nonReentrant will be lower in
    // amount. Since refunds are capped to a percentage of the total
    // transaction's gas, it is best to keep them low in cases like this one, to
    // increase the likelihood of the full refund coming into effect.
    uint256 private constant _NOT_ENTERED = 1;
    uint256 private constant _ENTERED = 2;

    uint256 private _status;

    constructor () internal {
        _status = _NOT_ENTERED;
    }

    /**
     * @dev Prevents a contract from calling itself, directly or indirectly.
     * Calling a `nonReentrant` function from another `nonReentrant`
     * function is not supported. It is possible to prevent this from happening
     * by making the `nonReentrant` function external, and make it call a
     * `private` function that does the actual work.
     */
    modifier nonReentrant() {
        // On the first call to nonReentrant, _notEntered will be true
        require(_status != _ENTERED, "ReentrancyGuard: reentrant call");

        // Any calls to nonReentrant after this point will fail
        _status = _ENTERED;

        _;

        // By storing the original value once again, a refund is triggered (see
        // https://eips.ethereum.org/EIPS/eip-2200)
        _status = _NOT_ENTERED;
    }
}

// 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;
    }
}

// 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);
}

// 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");
        }
    }
}

// SPDX-License-Identifier: MIT
pragma solidity >=0.7.2;

interface IAction {
  /**
   * The function used to determin how much asset the current action is controlling.
   * this will impact the withdraw and deposit amount calculated from the vault.
   */
  function currentValue() external view returns (uint256);

  /**
   * The function for the vault to call at the end of each vault's round.
   * after calling this function, the vault will try to pull assets back from the action and enable withdraw.
   */
  function closePosition() external;

  /**
   * The function for the vault to call when the vault is ready to start the next round.
   * the vault will push assets to action before calling this function, but the amount can change compare to 
   * the last round. So each action should check their asset balance instead of using any cached balance.
   *
   * Each action can also add additional checks and revert the `rolloverPosition` call if the action 
   * is not ready to go into the next round.
   */
  function rolloverPosition() external;
}

// SPDX-License-Identifier: MIT

pragma solidity ^0.7.2;
pragma experimental ABIEncoderV2;

interface ICurve {
  function add_liquidity(uint256[2] memory amounts, uint256 minAmount) external payable returns (uint256);

  function remove_liquidity_one_coin(uint256 _token_amount, int128 i, uint256 _minAmount) external returns (uint256);

  function get_virtual_price() external view returns (uint256);
}

// SPDX-License-Identifier: MIT

import { IERC20 } from '@openzeppelin/contracts/token/ERC20/IERC20.sol';

pragma solidity ^0.7.2;
pragma experimental ABIEncoderV2;

interface IStakeDao {
  function depositAll() external;

  function deposit(uint256 amount) external;

  function withdrawAll() external;

  function withdraw(uint256 _shares) external;

  function token() external returns (IERC20);

  function balanceOf(address account) external view returns (uint256);

  function approve(address spender, uint256 amount) external returns (bool);

  function transfer(address recipient, uint256 amount) external returns (bool);

  function getPricePerFullShare() external view returns (uint256);
}

// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

/*
 * @dev Provides information about the current execution context, including the
 * sender of the transaction and its data. While these are generally available
 * via msg.sender and msg.data, they should not be accessed in such a direct
 * manner, since when dealing with GSN meta-transactions the account sending and
 * paying for execution may not be the actual sender (as far as an application
 * is concerned).
 *
 * This contract is only required for intermediate, library-like contracts.
 */
abstract contract Context {
    function _msgSender() internal view virtual returns (address payable) {
        return msg.sender;
    }

    function _msgData() internal view virtual returns (bytes memory) {
        this; // silence state mutability warning without generating bytecode - see https://github.com/ethereum/solidity/issues/2691
        return msg.data;
    }
}

// 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);
            }
        }
    }
}