pragma solidity ^0.6.2;


// SPDX-License-Identifier: MIT
/**
 * @dev Wrappers over Solidity's arithmetic operations with added overflow
 * checks.
 *
 * Arithmetic operations in Solidity wrap on overflow. This can easily result
 * in bugs, because programmers usually assume that an overflow raises an
 * error, which is the standard behavior in high level programming languages.
 * `SafeMath` restores this intuition by reverting the transaction when an
 * operation overflows.
 *
 * Using this library instead of the unchecked operations eliminates an entire
 * class of bugs, so it's recommended to use it always.
 */
library SafeMath {
    /**
     * @dev Returns the addition of two unsigned integers, reverting on
     * overflow.
     *
     * Counterpart to Solidity's `+` operator.
     *
     * Requirements:
     *
     * - Addition cannot overflow.
     */
    function add(uint256 a, uint256 b) internal pure returns (uint256) {
        uint256 c = a + b;
        require(c >= a, "SafeMath: addition overflow");

        return c;
    }

    /**
     * @dev Returns the subtraction of two unsigned integers, reverting on
     * overflow (when the result is negative).
     *
     * Counterpart to Solidity's `-` operator.
     *
     * Requirements:
     *
     * - Subtraction cannot overflow.
     */
    function sub(uint256 a, uint256 b) internal pure returns (uint256) {
        return sub(a, b, "SafeMath: subtraction overflow");
    }

    /**
     * @dev Returns the subtraction of two unsigned integers, reverting with custom message on
     * overflow (when the result is negative).
     *
     * Counterpart to Solidity's `-` operator.
     *
     * Requirements:
     *
     * - Subtraction cannot overflow.
     */
    function sub(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b <= a, errorMessage);
        uint256 c = a - b;

        return c;
    }

    /**
     * @dev Returns the multiplication of two unsigned integers, reverting on
     * overflow.
     *
     * Counterpart to Solidity's `*` operator.
     *
     * Requirements:
     *
     * - Multiplication cannot overflow.
     */
    function mul(uint256 a, uint256 b) internal pure returns (uint256) {
        // Gas optimization: this is cheaper than requiring 'a' not being zero, but the
        // benefit is lost if 'b' is also tested.
        // See: https://github.com/OpenZeppelin/openzeppelin-contracts/pull/522
        if (a == 0) {
            return 0;
        }

        uint256 c = a * b;
        require(c / a == b, "SafeMath: multiplication overflow");

        return c;
    }

    /**
     * @dev Returns the integer division of two unsigned integers. Reverts on
     * division by zero. The result is rounded towards zero.
     *
     * Counterpart to Solidity's `/` operator. Note: this function uses a
     * `revert` opcode (which leaves remaining gas untouched) while Solidity
     * uses an invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function div(uint256 a, uint256 b) internal pure returns (uint256) {
        return div(a, b, "SafeMath: division by zero");
    }

    /**
     * @dev Returns the integer division of two unsigned integers. Reverts with custom message on
     * division by zero. The result is rounded towards zero.
     *
     * Counterpart to Solidity's `/` operator. Note: this function uses a
     * `revert` opcode (which leaves remaining gas untouched) while Solidity
     * uses an invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function div(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b > 0, errorMessage);
        uint256 c = a / b;
        // assert(a == b * c + a % b); // There is no case in which this doesn't hold

        return c;
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * Reverts when dividing by zero.
     *
     * Counterpart to Solidity's `%` operator. This function uses a `revert`
     * opcode (which leaves remaining gas untouched) while Solidity uses an
     * invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function mod(uint256 a, uint256 b) internal pure returns (uint256) {
        return mod(a, b, "SafeMath: modulo by zero");
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * Reverts with custom message when dividing by zero.
     *
     * Counterpart to Solidity's `%` operator. This function uses a `revert`
     * opcode (which leaves remaining gas untouched) while Solidity uses an
     * invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function mod(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b != 0, errorMessage);
        return a % b;
    }
}

// SPDX-License-Identifier: MIT
/*
 * @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: contracts/GSN/Context.sol
// SPDX-License-Identifier: MIT
// File: contracts/token/ERC20/IERC20.sol
/**
 * @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: contracts/utils/Address.sol
/**
 * @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) {
        // According to EIP-1052, 0x0 is the value returned for not-yet created accounts
        // and 0xc5d2460186f7233c927e7db2dcc703c0e500b653ca82273b7bfad8045d85a470 is returned
        // for accounts without code, i.e. `keccak256('')`
        bytes32 codehash;
        bytes32 accountHash = 0xc5d2460186f7233c927e7db2dcc703c0e500b653ca82273b7bfad8045d85a470;
        // solhint-disable-next-line no-inline-assembly
        assembly { codehash := extcodehash(account) }
        return (codehash != accountHash && codehash != 0x0);
    }

    /**
     * @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");
        return _functionCallWithValue(target, data, value, errorMessage);
    }

    function _functionCallWithValue(address target, bytes memory data, uint256 weiValue, string memory errorMessage) private returns (bytes memory) {
        require(isContract(target), "Address: call to non-contract");

        // solhint-disable-next-line avoid-low-level-calls
        (bool success, bytes memory returndata) = target.call{ value: weiValue }(data);
        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: contracts/token/ERC20/ERC20.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;
    using Address for address;

    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 returns (string memory) {
        return _name;
    }

    /**
     * @dev Returns the symbol of the token, usually a shorter version of the
     * name.
     */
    function symbol() public view 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 returns (uint8) {
        return _decimals;
    }

    /**
     * @dev See {IERC20-totalSupply}.
     */
    function totalSupply() public view override returns (uint256) {
        return _totalSupply;
    }

    /**
     * @dev See {IERC20-balanceOf}.
     */
    function balanceOf(address account) public view 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 {
        _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 { }
}

/**
 * @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
interface IVault is IERC20 {
    function token() external view returns (address);

    function claimInsurance() external; // NOTE: Only yDelegatedVault implements this

    function getRatio() external view returns (uint256);

    function deposit(uint256) external;

    function withdraw(uint256) external;

    function earn() external;
}

// SPDX-License-Identifier: MIT
interface IStakingRewards {
    function balanceOf(address account) external view returns (uint256);

    function earned(address account) external view returns (uint256);

    function exit() external;

    function getReward() external;

    function getRewardForDuration() external view returns (uint256);

    function lastTimeRewardApplicable() external view returns (uint256);

    function lastUpdateTime() external view returns (uint256);

    function notifyRewardAmount(uint256 reward) external;

    function periodFinish() external view returns (uint256);

    function rewardPerToken() external view returns (uint256);

    function rewardPerTokenStored() external view returns (uint256);

    function rewardRate() external view returns (uint256);

    function rewards(address) external view returns (uint256);

    function rewardsDistribution() external view returns (address);

    function rewardsDuration() external view returns (uint256);

    function rewardsToken() external view returns (address);

    function stake(uint256 amount) external;

    function stakeWithPermit(
        uint256 amount,
        uint256 deadline,
        uint8 v,
        bytes32 r,
        bytes32 s
    ) external;

    function stakingToken() external view returns (address);

    function totalSupply() external view returns (uint256);

    function userRewardPerTokenPaid(address) external view returns (uint256);

    function withdraw(uint256 amount) external;
}

interface IStakingRewardsFactory {
    function deploy(address stakingToken, uint256 rewardAmount) external;

    function isOwner() external view returns (bool);

    function notifyRewardAmount(address stakingToken) external;

    function notifyRewardAmounts() external;

    function owner() external view returns (address);

    function renounceOwnership() external;

    function rewardsToken() external view returns (address);

    function stakingRewardsGenesis() external view returns (uint256);

    function stakingRewardsInfoByStakingToken(address)
        external
        view
        returns (address stakingRewards, uint256 rewardAmount);

    function stakingTokens(uint256) external view returns (address);

    function transferOwnership(address newOwner) external;
}

// SPDX-License-Identifier: MIT
// SPDX-License-Identifier: MIT
interface UniswapRouterV2 {
    function swapExactTokensForTokens(
        uint256 amountIn,
        uint256 amountOutMin,
        address[] calldata path,
        address to,
        uint256 deadline
    ) external returns (uint256[] memory amounts);

    function addLiquidity(
        address tokenA,
        address tokenB,
        uint256 amountADesired,
        uint256 amountBDesired,
        uint256 amountAMin,
        uint256 amountBMin,
        address to,
        uint256 deadline
    )
        external
        returns (
            uint256 amountA,
            uint256 amountB,
            uint256 liquidity
        );

    function addLiquidityETH(
        address token,
        uint256 amountTokenDesired,
        uint256 amountTokenMin,
        uint256 amountETHMin,
        address to,
        uint256 deadline
    )
        external
        payable
        returns (
            uint256 amountToken,
            uint256 amountETH,
            uint256 liquidity
        );

    function removeLiquidity(
        address tokenA,
        address tokenB,
        uint256 liquidity,
        uint256 amountAMin,
        uint256 amountBMin,
        address to,
        uint256 deadline
    ) external returns (uint256 amountA, uint256 amountB);

    function getAmountsOut(uint256 amountIn, address[] calldata path)
        external
        view
        returns (uint256[] memory amounts);

    function getAmountsIn(uint256 amountOut, address[] calldata path)
        external
        view
        returns (uint256[] memory amounts);

    function swapETHForExactTokens(
        uint256 amountOut,
        address[] calldata path,
        address to,
        uint256 deadline
    ) external payable returns (uint256[] memory amounts);

    function swapExactETHForTokens(
        uint256 amountOutMin,
        address[] calldata path,
        address to,
        uint256 deadline
    ) external payable returns (uint256[] memory amounts);
}

interface IUniswapV2Pair {
    event Approval(
        address indexed owner,
        address indexed spender,
        uint256 value
    );
    event Transfer(address indexed from, address indexed to, uint256 value);

    function name() external pure returns (string memory);

    function symbol() external pure returns (string memory);

    function decimals() external pure returns (uint8);

    function totalSupply() external view returns (uint256);

    function balanceOf(address owner) external view returns (uint256);

    function allowance(address owner, address spender)
        external
        view
        returns (uint256);

    function approve(address spender, uint256 value) external returns (bool);

    function transfer(address to, uint256 value) external returns (bool);

    function transferFrom(
        address from,
        address to,
        uint256 value
    ) external returns (bool);

    function DOMAIN_SEPARATOR() external view returns (bytes32);

    function PERMIT_TYPEHASH() external pure returns (bytes32);

    function nonces(address owner) external view returns (uint256);

    function permit(
        address owner,
        address spender,
        uint256 value,
        uint256 deadline,
        uint8 v,
        bytes32 r,
        bytes32 s
    ) external;

    event Mint(address indexed sender, uint256 amount0, uint256 amount1);
    event Burn(
        address indexed sender,
        uint256 amount0,
        uint256 amount1,
        address indexed to
    );
    event Swap(
        address indexed sender,
        uint256 amount0In,
        uint256 amount1In,
        uint256 amount0Out,
        uint256 amount1Out,
        address indexed to
    );
    event Sync(uint112 reserve0, uint112 reserve1);

    function MINIMUM_LIQUIDITY() external pure returns (uint256);

    function factory() external view returns (address);

    function token0() external view returns (address);

    function token1() external view returns (address);

    function getReserves()
        external
        view
        returns (
            uint112 reserve0,
            uint112 reserve1,
            uint32 blockTimestampLast
        );

    function price0CumulativeLast() external view returns (uint256);

    function price1CumulativeLast() external view returns (uint256);

    function kLast() external view returns (uint256);

    function mint(address to) external returns (uint256 liquidity);

    function burn(address to)
        external
        returns (uint256 amount0, uint256 amount1);

    function swap(
        uint256 amount0Out,
        uint256 amount1Out,
        address to,
        bytes calldata data
    ) external;

    function skim(address to) external;

    function sync() external;
}

interface IUniswapV2Factory {
    event PairCreated(
        address indexed token0,
        address indexed token1,
        address pair,
        uint256
    );

    function getPair(address tokenA, address tokenB)
        external
        view
        returns (address pair);

    function allPairs(uint256) external view returns (address pair);

    function allPairsLength() external view returns (uint256);

    function feeTo() external view returns (address);

    function feeToSetter() external view returns (address);

    function createPair(address tokenA, address tokenB)
        external
        returns (address pair);
}

// SPDX-License-Identifier: MIT
interface IController {
    function vaults(address) external view returns (address);

    function rewards() external view returns (address);

    function devfund() external view returns (address);

    function treasury() external view returns (address);

    function balanceOf(address) external view returns (uint256);

    function withdraw(address, uint256) external;

    function earn(address, uint256) external;
}

// SPDX-License-Identifier: MIT
interface IMasterchef {
    function BONUS_MULTIPLIER() external view returns (uint256);

    function add(
        uint256 _allocPoint,
        address _lpToken,
        bool _withUpdate
    ) external;

    function bonusEndBlock() external view returns (uint256);

    function deposit(uint256 _pid, uint256 _amount) external;

    function dev(address _devaddr) external;

    function devFundDivRate() external view returns (uint256);

    function devaddr() external view returns (address);

    function emergencyWithdraw(uint256 _pid) external;

    function getMultiplier(uint256 _from, uint256 _to)
        external
        view
        returns (uint256);

    function massUpdatePools() external;

    function owner() external view returns (address);

    function pendingMM(uint256 _pid, address _user)
        external
        view
        returns (uint256);

    function mm() external view returns (address);

    function mmPerBlock() external view returns (uint256);

    function poolInfo(uint256)
        external
        view
        returns (
            address lpToken,
            uint256 allocPoint,
            uint256 lastRewardBlock,
            uint256 accMMPerShare
        );

    function poolLength() external view returns (uint256);

    function renounceOwnership() external;

    function set(
        uint256 _pid,
        uint256 _allocPoint,
        bool _withUpdate
    ) external;

    function setBonusEndBlock(uint256 _bonusEndBlock) external;

    function setDevFundDivRate(uint256 _devFundDivRate) external;

    function setMMPerBlock(uint256 _mmPerBlock) external;

    function startBlock() external view returns (uint256);

    function totalAllocPoint() external view returns (uint256);

    function transferOwnership(address newOwner) external;

    function updatePool(uint256 _pid) external;

    function userInfo(uint256, address)
        external
        view
        returns (uint256 amount, uint256 rewardDebt);

    function withdraw(uint256 _pid, uint256 _amount) external;

    function notifyBuybackReward(uint256 _amount) external;
}

// Strategy Contract Basics
abstract contract StrategyBase {
    using SafeERC20 for IERC20;
    using Address for address;
    using SafeMath for uint256;

    // Perfomance fee 30% to buyback
    uint256 public performanceFee = 30000;
    uint256 public constant performanceMax = 100000;

    // Withdrawal fee 0.2% to buyback
    // - 0.14% to treasury
    // - 0.06% to dev fund
    uint256 public treasuryFee = 140;
    uint256 public constant treasuryMax = 100000;

    uint256 public devFundFee = 60;
    uint256 public constant devFundMax = 100000;

    // buyback ready
    bool public buybackEnabled = false;
    address public mmToken;
    address public masterChef;
	
    // Tokens
    address public want;
    address public constant weth = 0xC02aaA39b223FE8D0A0e5C4F27eAD9083C756Cc2;

    // buyback coins
    address public constant usdcBuyback = 0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48;
    address public constant usdtBuyback = 0xdAC17F958D2ee523a2206206994597C13D831ec7;
    address public constant wbtcBuyback = 0x2260FAC5E5542a773Aa44fBCfeDf7C193bc2C599;
    address public constant renbtcBuyback = 0xEB4C2781e4ebA804CE9a9803C67d0893436bB27D;
    address public constant mirBuyback = 0x09a3EcAFa817268f77BE1283176B946C4ff2E608;
    address public constant ustBuyback = 0xa47c8bf37f92aBed4A126BDA807A7b7498661acD;

    // User accounts
    address public governance;
    address public controller;
    address public strategist;
    address public timelock;

    // Dex
    address public univ2Router2 = 0x7a250d5630B4cF539739dF2C5dAcb4c659F2488D;

    constructor(
        address _want,
        address _governance,
        address _strategist,
        address _controller,
        address _timelock
    ) public {
        require(_want != address(0));
        require(_governance != address(0));
        require(_strategist != address(0));
        require(_controller != address(0));
        require(_timelock != address(0));

        want = _want;
        governance = _governance;
        strategist = _strategist;
        controller = _controller;
        timelock = _timelock;
    }

    // **** Modifiers **** //

    modifier onlyBenevolent {
        require(
            msg.sender == tx.origin ||
                msg.sender == governance ||
                msg.sender == strategist
        );
        _;
    }

    // **** Views **** //

    function balanceOfWant() public view returns (uint256) {
        return IERC20(want).balanceOf(address(this));
    }

    function balanceOfPool() public virtual view returns (uint256);

    function balanceOf() public view returns (uint256) {
        return balanceOfWant().add(balanceOfPool());
    }

    function getName() external virtual pure returns (string memory);

    // **** Setters **** //

    function setDevFundFee(uint256 _devFundFee) external {
        require(msg.sender == timelock, "!timelock");
        devFundFee = _devFundFee;
    }

    function setTreasuryFee(uint256 _treasuryFee) external {
        require(msg.sender == timelock, "!timelock");
        treasuryFee = _treasuryFee;
    }

    function setPerformanceFee(uint256 _performanceFee) external {
        require(msg.sender == timelock, "!timelock");
        performanceFee = _performanceFee;
    }

    function setStrategist(address _strategist) external {
        require(msg.sender == governance, "!governance");
        strategist = _strategist;
    }

    function setGovernance(address _governance) external {
        require(msg.sender == governance, "!governance");
        governance = _governance;
    }

    function setTimelock(address _timelock) external {
        require(msg.sender == timelock, "!timelock");
        timelock = _timelock;
    }

    function setController(address _controller) external {
        require(msg.sender == timelock, "!timelock");
        controller = _controller;
    }

    function setMmToken(address _mmToken) external {
        require(msg.sender == governance, "!governance");
        mmToken = _mmToken;
    }

    function setBuybackEnabled(bool _buybackEnabled) external {
        require(msg.sender == governance, "!governance");
        buybackEnabled = _buybackEnabled;
    }

    function setMasterChef(address _masterChef) external {
        require(msg.sender == governance, "!governance");
        masterChef = _masterChef;
    }

    // **** State mutations **** //
    function deposit() public virtual;

    // Controller only function for creating additional rewards from dust
    function withdraw(IERC20 _asset) external returns (uint256 balance) {
        require(msg.sender == controller, "!controller");
        require(want != address(_asset), "want");
        balance = _asset.balanceOf(address(this));
        _asset.safeTransfer(controller, balance);
    }

    // Withdraw partial funds, normally used with a vault withdrawal
    function withdraw(uint256 _amount) external {
        require(msg.sender == controller, "!controller");
        uint256 _balance = IERC20(want).balanceOf(address(this));
        if (_balance < _amount) {
            _amount = _withdrawSome(_amount.sub(_balance));
            _amount = _amount.add(_balance);
        }
				
        uint256 _feeDev = _amount.mul(devFundFee).div(devFundMax);
        uint256 _feeTreasury = _amount.mul(treasuryFee).div(treasuryMax);

        if (buybackEnabled == true) {            
            // we want buyback mm using LP token
            (address _buybackPrinciple, uint256 _buybackAmount) = _convertWantToBuyback(_feeDev.add(_feeTreasury));
            buybackAndNotify(_buybackPrinciple, _buybackAmount);			
        } else {
            IERC20(want).safeTransfer(IController(controller).devfund(), _feeDev);
            IERC20(want).safeTransfer(IController(controller).treasury(), _feeTreasury);
        }        

        address _vault = IController(controller).vaults(address(want));
        require(_vault != address(0), "!vault"); // additional protection so we don't burn the funds

        IERC20(want).safeTransfer(_vault, _amount.sub(_feeDev).sub(_feeTreasury));
    }
	
    // buyback MM and notify MasterChef
    function buybackAndNotify(address _buybackPrinciple, uint256 _buybackAmount) internal {
        if (buybackEnabled == true) {
            _swapUniswap(_buybackPrinciple, mmToken, _buybackAmount);
            uint256 _mmBought = IERC20(mmToken).balanceOf(address(this));
            IERC20(mmToken).safeTransfer(masterChef, _mmBought);
            IMasterchef(masterChef).notifyBuybackReward(_mmBought);
        }
    }

    // Withdraw all funds, normally used when migrating strategies
    function withdrawAll() external returns (uint256 balance) {
        require(msg.sender == controller, "!controller");
        _withdrawAll();

        balance = IERC20(want).balanceOf(address(this));

        address _vault = IController(controller).vaults(address(want));
        require(_vault != address(0), "!vault"); // additional protection so we don't burn the funds
        IERC20(want).safeTransfer(_vault, balance);
    }

    function _withdrawAll() internal {
        _withdrawSome(balanceOfPool());
    }

    function _withdrawSome(uint256 _amount) internal virtual returns (uint256);	
	
    // convert LP to buyback principle token
    function _convertWantToBuyback(uint256 _lpAmount) internal virtual returns (address, uint256);

    function harvest() public virtual;

    // **** Emergency functions ****

    function execute(address _target, bytes memory _data)
        public
        payable
        returns (bytes memory response)
    {
        require(msg.sender == timelock, "!timelock");
        require(_target != address(0), "!target");

        // call contract in current context
        assembly {
            let succeeded := delegatecall(
                sub(gas(), 5000),
                _target,
                add(_data, 0x20),
                mload(_data),
                0,
                0
            )
            let size := returndatasize()

            response := mload(0x40)
            mstore(
                0x40,
                add(response, and(add(add(size, 0x20), 0x1f), not(0x1f)))
            )
            mstore(response, size)
            returndatacopy(add(response, 0x20), 0, size)

            switch iszero(succeeded)
                case 1 {
                    // throw if delegatecall failed
                    revert(add(response, 0x20), size)
                }
        }
    }

    // **** Internal functions ****
    function _swapUniswap(
        address _from,
        address _to,
        uint256 _amount
    ) internal {
        require(_to != address(0));

        // Swap with uniswap
        IERC20(_from).safeApprove(univ2Router2, 0);
        IERC20(_from).safeApprove(univ2Router2, _amount);

        address[] memory path;

        if (_to == mmToken && buybackEnabled == true) {
            if (_from == usdcBuyback){
                path = new address[](2);
                path[0] = _from;
                path[1] = _to;			   
            }else if(_from == renbtcBuyback || _from == wbtcBuyback){
                path = new address[](4);
                path[0] = _from;
                path[1] = weth;
                path[2] = usdcBuyback;
                path[3] = _to;
            }else if(_from == ustBuyback){
                path = new address[](4);
                path[0] = _from;
                path[1] = usdtBuyback;
                path[2] = usdcBuyback;
                path[3] = _to;
            }else{
                path = new address[](3);
                path[0] = _from;
                path[1] = usdcBuyback;
                path[2] = _to;
            }
        } else{		
            if (_from == weth || _to == weth || _to == ustBuyback) {
                path = new address[](2);
                path[0] = _from;
                path[1] = _to;
            } else if (_from == mirBuyback) {
                path = new address[](3);
                path[0] = _from;
                path[1] = ustBuyback;
                path[2] = _to;
            } else {
                path = new address[](3);
                path[0] = _from;
                path[1] = weth;
                path[2] = _to;
            }		
        }

        UniswapRouterV2(univ2Router2).swapExactTokensForTokens(
            _amount,
            0,
            path,
            address(this),
            now.add(60)
        );
    }
}

// Base contract for SNX Staking rewards contract interfaces
abstract contract StrategyStakingRewardsBase is StrategyBase {
    address public rewards;

    // **** Getters ****
    constructor(
        address _rewards,
        address _want,
        address _governance,
        address _strategist,
        address _controller,
        address _timelock
    )
        public
        StrategyBase(_want, _governance, _strategist, _controller, _timelock)
    {
        rewards = _rewards;
    }

    function balanceOfPool() public override view returns (uint256) {
        return IStakingRewards(rewards).balanceOf(address(this));
    }

    function getHarvestable() external view returns (uint256) {
        return IStakingRewards(rewards).earned(address(this));
    }

    // **** Setters ****

    function deposit() public override {
        uint256 _want = IERC20(want).balanceOf(address(this));
        if (_want > 0) {
            IERC20(want).safeApprove(rewards, 0);
            IERC20(want).safeApprove(rewards, _want);
            IStakingRewards(rewards).stake(_want);
        }
    }

    function _withdrawSome(uint256 _amount)
        internal
        override
        returns (uint256)
    {
        IStakingRewards(rewards).withdraw(_amount);
        return _amount;
    }
}

// SPDX-License-Identifier: MIT
abstract contract StrategyMirFarmBase is StrategyStakingRewardsBase {
    // Token addresses
    address public mir = 0x09a3EcAFa817268f77BE1283176B946C4ff2E608;

    // UST/<token1> pair
    address public token1;
    address public token0 = 0xa47c8bf37f92aBed4A126BDA807A7b7498661acD;

    // How much MIR tokens to keep?
    uint256 public keepMIR = 0;
    uint256 public constant keepMIRMax = 10000;

    constructor(
        address _token1,
        address _rewards,
        address _lp,
        address _governance,
        address _strategist,
        address _controller,
        address _timelock
    )
        public
        StrategyStakingRewardsBase(
            _rewards,
            _lp,
            _governance,
            _strategist,
            _controller,
            _timelock
        )
    {
        token1 = _token1;
    }

    // **** Setters ****

    function setKeepMIR(uint256 _keepMIR) external {
        require(msg.sender == timelock, "!timelock");
        keepMIR = _keepMIR;
    }

    // **** State Mutations ****
	
    function _convertWantToBuyback(uint256 _lpAmount) internal override returns (address, uint256){
        require(_lpAmount > 0, '!_lpAmount');		

        IERC20(want).safeApprove(univ2Router2, 0);
        IERC20(want).safeApprove(univ2Router2, _lpAmount);
		
        UniswapRouterV2(univ2Router2).removeLiquidity(
            token0,
            token1,
            _lpAmount,
            0,
            0,
            address(this),
            now + 60
        );	        

        // Swap token1 for UST
        uint256 _token1 = IERC20(token1).balanceOf(address(this));	
        if (_token1 > 0) {
            _swapUniswap(token1, token0, _token1);
        }
        uint256 _ust = IERC20(token0).balanceOf(address(this));	
        return (token0, _ust);
    }

    function harvest() public override onlyBenevolent {
        // Anyone can harvest it at any given time.
        // I understand the possibility of being frontrun
        // But ETH is a dark forest, and I wanna see how this plays out
        // i.e. will be be heavily frontrunned?
        //      if so, a new strategy will be deployed.

        // Collects MIR tokens
        IStakingRewards(rewards).getReward();
        uint256 _mir = IERC20(mir).balanceOf(address(this));
        if (_mir > 0) {
            // in case some mir is locked up for future gov
            uint256 _keepMIR = _mir.mul(keepMIR).div(keepMIRMax);
            if(_keepMIR > 0){
               IERC20(mir).safeTransfer(IController(controller).treasury(), _keepMIR);		
            }		
        }

        // Swap half MIR for UST
        _mir = IERC20(mir).balanceOf(address(this));
        if (_mir > 0) {
            _swapUniswap(mir, token0, _mir.div(2));
        }

        // Swap rest MIR for token1
        _mir = IERC20(mir).balanceOf(address(this));
        if (_mir > 0 && mir != token1) {
            _swapUniswap(mir, token1, _mir);
        }

        // Adds in liquidity for UST/MIR
        uint256 _ust = IERC20(token0).balanceOf(address(this));
        uint256 _token1 = IERC20(token1).balanceOf(address(this));
        if (_ust > 0 && _token1 > 0) {
            IERC20(token0).safeApprove(univ2Router2, 0);
            IERC20(token0).safeApprove(univ2Router2, _ust);

            IERC20(token1).safeApprove(univ2Router2, 0);
            IERC20(token1).safeApprove(univ2Router2, _token1);

            UniswapRouterV2(univ2Router2).addLiquidity(
                token0,
                token1,
                _ust,
                _token1,
                0,
                0,
                address(this),
                now + 60
            );
        }

        // We want to get back UNI LP tokens
        uint256 _want = IERC20(want).balanceOf(address(this));
        uint256 _buybackLpAmount = _want.mul(performanceFee).div(performanceMax);
        if (_want > 0) {
            if(buybackEnabled == true && _buybackLpAmount > 0){
                (address _buybackPrinciple, uint256 _buybackAmount) = _convertWantToBuyback(_buybackLpAmount);
                buybackAndNotify(_buybackPrinciple, _buybackAmount);
            }else{
                // Performance fee
                IERC20(want).safeTransfer(IController(controller).treasury(), _want.mul(performanceFee).div(performanceMax));			
            }
            deposit();
        }
    }
}

// SPDX-License-Identifier: MIT
contract StrategyMirUstLpV1 is StrategyMirFarmBase {
    // Token addresses
    address public mir_rewards = 0x5d447Fc0F8965cED158BAB42414Af10139Edf0AF;
    address public uni_mir_ust_lp = 0x87dA823B6fC8EB8575a235A824690fda94674c88;

    constructor(
        address _governance,
        address _strategist,
        address _controller,
        address _timelock
    )
        public
        StrategyMirFarmBase(
            mir,
            mir_rewards,
            uni_mir_ust_lp,
            _governance,
            _strategist,
            _controller,
            _timelock
        )
    {}

    // **** Views ****

    function getName() external override pure returns (string memory) {
        return "StrategyMirUstLpV1";
    }
}