/*
https://powerpool.finance/

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*/

// File @openzeppelin/contracts/utils/Context.sol@v3.4.0

// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;
pragma experimental ABIEncoderV2;

/*
 * @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;
    }
}

// File @openzeppelin/contracts/token/ERC20/IERC20.sol@v3.4.0

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@v3.4.0

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;
    }
}

// File @openzeppelin/contracts/token/ERC20/ERC20.sol@v3.4.0

pragma solidity >=0.6.0 <0.8.0;

/**
 * @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 { }
}

// File @openzeppelin/contracts/utils/Address.sol@v3.4.0

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@v3.4.0

pragma solidity >=0.6.0 <0.8.0;

/**
 * @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/utils/ReentrancyGuard.sol@v3.4.0

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;
    }
}

// File contracts/interfaces/PowerIndexNaiveRouterInterface.sol

pragma solidity 0.6.12;

interface PowerIndexNaiveRouterInterface {
  function migrateToNewRouter(
    address _piToken,
    address payable _newRouter,
    address[] memory _tokens
  ) external;

  function enableRouterCallback(address _piToken, bool _enable) external;

  function piTokenCallback(address sender, uint256 _withdrawAmount) external payable;
}

// File contracts/interfaces/PowerIndexRouterInterface.sol

pragma solidity 0.6.12;

interface PowerIndexRouterInterface {
  enum StakeStatus {
    EQUILIBRIUM,
    EXCESS,
    SHORTAGE
  }

  //  function setVotingAndStaking(address _voting, address _staking) external;

  function setReserveConfig(
    uint256 _reserveRatio,
    uint256 _reserveRatioLowerBound,
    uint256 _reserveRatioUpperBound,
    uint256 _claimRewardsInterval
  ) external;

  function getPiEquivalentForUnderlying(uint256 _underlyingAmount, uint256 _piTotalSupply)
    external
    view
    returns (uint256);

  function getPiEquivalentForUnderlyingPure(
    uint256 _underlyingAmount,
    uint256 _totalUnderlyingWrapped,
    uint256 _piTotalSupply
  ) external pure returns (uint256);

  function getUnderlyingEquivalentForPi(uint256 _piAmount, uint256 _piTotalSupply) external view returns (uint256);

  function getUnderlyingEquivalentForPiPure(
    uint256 _piAmount,
    uint256 _totalUnderlyingWrapped,
    uint256 _piTotalSupply
  ) external pure returns (uint256);
}

// File contracts/interfaces/IERC20Permit.sol

pragma solidity >=0.6.0 <0.8.0;

/**
 * @dev Interface of the ERC20 Permit extension allowing approvals to be made via signatures, as defined in
 * https://eips.ethereum.org/EIPS/eip-2612[EIP-2612].
 *
 * Adds the {permit} method, which can be used to change an account's ERC20 allowance (see {IERC20-allowance}) by
 * presenting a message signed by the account. By not relying on {IERC20-approve}, the token holder account doesn't
 * need to send a transaction, and thus is not required to hold Ether at all.
 */
interface IERC20Permit is IERC20 {
  /**
   * @dev Sets `value` as the allowance of `spender` over ``owner``'s tokens,
   * given ``owner``'s signed approval.
   *
   * IMPORTANT: The same issues {IERC20-approve} has related to transaction
   * ordering also apply here.
   *
   * Emits an {Approval} event.
   *
   * Requirements:
   *
   * - `spender` cannot be the zero address.
   * - `deadline` must be a timestamp in the future.
   * - `v`, `r` and `s` must be a valid `secp256k1` signature from `owner`
   * over the EIP712-formatted function arguments.
   * - the signature must use ``owner``'s current nonce (see {nonces}).
   *
   * For more information on the signature format, see the
   * https://eips.ethereum.org/EIPS/eip-2612#specification[relevant EIP
   * section].
   */
  function permit(
    address owner,
    address spender,
    uint256 value,
    uint256 deadline,
    uint8 v,
    bytes32 r,
    bytes32 s
  ) external;

  /**
   * @dev Returns the current nonce for `owner`. This value must be
   * included whenever a signature is generated for {permit}.
   *
   * Every successful call to {permit} increases ``owner``'s nonce by one. This
   * prevents a signature from being used multiple times.
   */
  function nonces(address owner) external view returns (uint256);

  /**
   * @dev Returns the domain separator used in the encoding of the signature for {permit}, as defined by {EIP712}.
   */
  // solhint-disable-next-line func-name-mixedcase
  function DOMAIN_SEPARATOR() external view returns (bytes32);
}

// File contracts/interfaces/WrappedPiErc20Interface.sol

pragma solidity 0.6.12;

interface WrappedPiErc20Interface is IERC20Permit {
  function deposit(uint256 _amount) external payable returns (uint256);

  function withdraw(uint256 _amount) external payable returns (uint256);

  function withdrawShares(uint256 _burnAmount) external payable returns (uint256);

  function changeRouter(address _newRouter) external;

  function enableRouterCallback(bool _enable) external;

  function setNoFee(address _for, bool _noFee) external;

  function setEthFee(uint256 _newEthFee) external;

  function withdrawEthFee(address payable receiver) external;

  function approveUnderlying(address _to, uint256 _amount) external;

  function getPiEquivalentForUnderlying(uint256 _underlyingAmount) external view returns (uint256);

  function getUnderlyingEquivalentForPi(uint256 _piAmount) external view returns (uint256);

  function balanceOfUnderlying(address account) external view returns (uint256);

  function callExternal(
    address voting,
    bytes4 signature,
    bytes calldata args,
    uint256 value
  ) external payable returns (bytes memory);

  struct ExternalCallData {
    address destination;
    bytes4 signature;
    bytes args;
    uint256 value;
  }

  function callExternalMultiple(ExternalCallData[] calldata calls) external payable returns (bytes[] memory);

  function getUnderlyingBalance() external view returns (uint256);
}


// File contracts/WrappedPiErc20.sol

pragma solidity 0.6.12;

contract WrappedPiErc20 is ERC20, ReentrancyGuard, WrappedPiErc20Interface {
  using SafeMath for uint256;
  using SafeERC20 for IERC20Permit;

  bytes32 public constant PERMIT_TYPEHASH =
    keccak256("Permit(address owner,address spender,uint256 value,uint256 nonce,uint256 deadline)");
  bytes public constant EIP712_REVISION = bytes("1");
  bytes32 internal constant EIP712_DOMAIN =
    keccak256("EIP712Domain(string name,string version,uint256 chainId,address verifyingContract)");

  IERC20Permit public immutable underlying;
  bytes32 public immutable override DOMAIN_SEPARATOR;
  address public router;
  bool public routerCallbackEnabled;
  uint256 public ethFee;
  mapping(address => bool) public noFeeWhitelist;
  mapping(address => uint256) public override nonces;

  event Deposit(address indexed account, uint256 undelyingDeposited, uint256 piMinted);
  event Withdraw(address indexed account, uint256 underlyingWithdrawn, uint256 piBurned);
  event Approve(address indexed to, uint256 amount);
  event ChangeRouter(address indexed newRouter);
  event EnableRouterCallback(bool indexed enabled);
  event SetEthFee(uint256 newEthFee);
  event SetNoFee(address indexed addr, bool noFee);
  event WithdrawEthFee(uint256 value);
  event CallExternal(address indexed destination, bytes4 indexed inputSig, bytes inputData, bytes outputData);

  modifier onlyRouter() {
    require(router == msg.sender, "ONLY_ROUTER");
    _;
  }

  constructor(
    address _token,
    address _router,
    string memory _name,
    string memory _symbol
  ) public ERC20(_name, _symbol) {
    underlying = IERC20Permit(_token);
    router = _router;

    uint256 chainId;

    assembly {
      chainId := chainid()
    }

    DOMAIN_SEPARATOR = keccak256(
      abi.encode(EIP712_DOMAIN, keccak256(bytes(_name)), keccak256(EIP712_REVISION), chainId, address(this))
    );
  }

  /**
   * @notice Deposits underlying ERC20 token to the piToken(piERC20) with permit params
   * @param _amount The amount to deposit in underlying ERC20 tokens.
   * @param _deadline Deadline timestamp of permit
   * @param _v param of permit
   * @param _r param of permit
   * @param _s param of permit
   */
  function depositWithPermit(
    uint256 _amount,
    uint256 _deadline,
    uint8 _v,
    bytes32 _r,
    bytes32 _s
  ) public virtual {
    underlying.permit(msg.sender, address(this), _amount, _deadline, _v, _r, _s);
    deposit(_amount);
  }

  /**
   * @notice Deposits underlying ERC20 token to the piToken(piERC20).
   * @param _depositAmount The amount to deposit in underlying ERC20 tokens.
   */
  function deposit(uint256 _depositAmount) public payable override nonReentrant returns (uint256) {
    if (noFeeWhitelist[msg.sender]) {
      require(msg.value == 0, "NO_FEE_FOR_WL");
    } else {
      require(msg.value >= ethFee, "FEE");
    }

    require(_depositAmount > 0, "ZERO_DEPOSIT");

    uint256 mintAmount = getPiEquivalentForUnderlying(_depositAmount);
    require(mintAmount > 0, "ZERO_PI_FOR_MINT");

    underlying.safeTransferFrom(msg.sender, address(this), _depositAmount);
    _mint(msg.sender, mintAmount);

    emit Deposit(msg.sender, _depositAmount, mintAmount);

    if (routerCallbackEnabled) {
      PowerIndexNaiveRouterInterface(router).piTokenCallback{ value: msg.value }(msg.sender, 0);
    }

    return mintAmount;
  }

  /**
   * @notice Withdraws underlying ERC20 token from the piToken (piERC20).
   * @param _withdrawAmount The amount to withdraw in underlying ERC20 tokens.
   * @return The amount of the burned shares.
   */
  function withdraw(uint256 _withdrawAmount) external payable override nonReentrant returns (uint256) {
    if (noFeeWhitelist[msg.sender]) {
      require(msg.value == 0, "NO_FEE_FOR_WL");
    } else {
      require(msg.value >= ethFee, "FEE");
    }

    require(_withdrawAmount > 0, "ZERO_WITHDRAWAL");

    if (routerCallbackEnabled) {
      PowerIndexNaiveRouterInterface(router).piTokenCallback{ value: msg.value }(msg.sender, _withdrawAmount);
    }

    uint256 burnAmount = getPiEquivalentForUnderlying(_withdrawAmount);
    require(burnAmount > 0, "ZERO_PI_FOR_BURN");

    _burn(msg.sender, burnAmount);
    underlying.safeTransfer(msg.sender, _withdrawAmount);

    emit Withdraw(msg.sender, _withdrawAmount, burnAmount);

    return burnAmount;
  }

  /**
   * @notice Withdraws underlying ERC20 token from the piToken(piERC20).
   * @param _burnAmount The amount of shares to burn.
   * @return The amount of the withdrawn underlying ERC20 token.
   */
  function withdrawShares(uint256 _burnAmount) external payable override nonReentrant returns (uint256) {
    if (noFeeWhitelist[msg.sender]) {
      require(msg.value == 0, "NO_FEE_FOR_WL");
    } else {
      require(msg.value >= ethFee, "FEE");
    }

    require(_burnAmount > 0, "ZERO_WITHDRAWAL");

    uint256 withdrawAmount = getUnderlyingEquivalentForPi(_burnAmount);
    require(withdrawAmount > 0, "ZERO_UNDERLYING_TO_WITHDRAW");

    if (routerCallbackEnabled) {
      PowerIndexNaiveRouterInterface(router).piTokenCallback{ value: msg.value }(msg.sender, withdrawAmount);
    }

    _burn(msg.sender, _burnAmount);
    underlying.safeTransfer(msg.sender, withdrawAmount);

    emit Withdraw(msg.sender, withdrawAmount, _burnAmount);

    return withdrawAmount;
  }

  function getPiEquivalentForUnderlying(uint256 _underlyingAmount) public view override returns (uint256) {
    return PowerIndexRouterInterface(router).getPiEquivalentForUnderlying(_underlyingAmount, totalSupply());
  }

  function getUnderlyingEquivalentForPi(uint256 _piAmount) public view override returns (uint256) {
    return PowerIndexRouterInterface(router).getUnderlyingEquivalentForPi(_piAmount, totalSupply());
  }

  function balanceOfUnderlying(address account) external view override returns (uint256) {
    return getUnderlyingEquivalentForPi(balanceOf(account));
  }

  function totalSupplyUnderlying() external view returns (uint256) {
    return getUnderlyingEquivalentForPi(totalSupply());
  }

  function changeRouter(address _newRouter) external override onlyRouter {
    router = _newRouter;
    emit ChangeRouter(router);
  }

  function enableRouterCallback(bool _enable) external override onlyRouter {
    routerCallbackEnabled = _enable;
    emit EnableRouterCallback(_enable);
  }

  function setNoFee(address _for, bool _noFee) external override onlyRouter {
    noFeeWhitelist[_for] = _noFee;
    emit SetNoFee(_for, _noFee);
  }

  function setEthFee(uint256 _ethFee) external override onlyRouter {
    ethFee = _ethFee;
    emit SetEthFee(_ethFee);
  }

  function withdrawEthFee(address payable _receiver) external override onlyRouter {
    emit WithdrawEthFee(address(this).balance);
    _receiver.transfer(address(this).balance);
  }

  function approveUnderlying(address _to, uint256 _amount) external override onlyRouter {
    underlying.approve(_to, _amount);
    emit Approve(_to, _amount);
  }

  function callExternal(
    address _destination,
    bytes4 _signature,
    bytes calldata _args,
    uint256 _value
  ) external payable override onlyRouter returns (bytes memory) {
    return _callExternal(_destination, _signature, _args, _value);
  }

  function callExternalMultiple(ExternalCallData[] calldata _calls)
    external
    payable
    override
    onlyRouter
    returns (bytes[] memory results)
  {
    uint256 len = _calls.length;
    results = new bytes[](len);
    for (uint256 i = 0; i < len; i++) {
      results[i] = _callExternal(_calls[i].destination, _calls[i].signature, _calls[i].args, _calls[i].value);
    }
  }

  function getUnderlyingBalance() external view override returns (uint256) {
    return underlying.balanceOf(address(this));
  }

  /**
   * @dev implements the permit function as for
   *      https://github.com/ethereum/EIPs/blob/8a34d644aacf0f9f8f00815307fd7dd5da07655f/EIPS/eip-2612.md
   * @param owner the owner of the funds
   * @param spender the spender
   * @param value the amount
   * @param deadline the deadline timestamp, type(uint256).max for no deadline
   * @param v signature param
   * @param s signature param
   * @param r signature param
   */
  function permit(
    address owner,
    address spender,
    uint256 value,
    uint256 deadline,
    uint8 v,
    bytes32 r,
    bytes32 s
  ) external override {
    require(owner != address(0), "INVALID_OWNER");
    require(block.timestamp <= deadline, "INVALID_EXPIRATION");
    uint256 currentValidNonce = nonces[owner];
    bytes32 digest = keccak256(
      abi.encodePacked(
        "\x19\x01",
        DOMAIN_SEPARATOR,
        keccak256(abi.encode(PERMIT_TYPEHASH, owner, spender, value, currentValidNonce, deadline))
      )
    );

    require(owner == ecrecover(digest, v, r, s), "INVALID_SIGNATURE");
    nonces[owner] = currentValidNonce.add(1);
    _approve(owner, spender, value);
  }

  function _callExternal(
    address _destination,
    bytes4 _signature,
    bytes calldata _args,
    uint256 _value
  ) internal returns (bytes memory) {
    (bool success, bytes memory data) = _destination.call{ value: _value }(abi.encodePacked(_signature, _args));

    if (!success) {
      assembly {
        let output := mload(0x40)
        let size := returndatasize()
        switch size
        case 0 {
          // If there is no revert reason string, revert with the default `REVERTED_WITH_NO_REASON_STRING`
          mstore(output, 0x08c379a000000000000000000000000000000000000000000000000000000000) // error identifier
          mstore(add(output, 0x04), 0x0000000000000000000000000000000000000000000000000000000000000020) // offset
          mstore(add(output, 0x24), 0x000000000000000000000000000000000000000000000000000000000000001e) // length
          mstore(add(output, 0x44), 0x52455645525445445f574954485f4e4f5f524541534f4e5f535452494e470000) // reason
          revert(output, 100) // 100 = 4 + 3 * 32 (error identifier + 3 words for the ABI encoded error)
        }
        default {
          // If there is a revert reason string hijacked, revert with it
          revert(add(data, 32), size)
        }
      }
    }

    emit CallExternal(_destination, _signature, _args, data);

    return data;
  }
}