// File: @openzeppelin/contracts-upgradeable/access/OwnableUpgradeable.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

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

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

    /**
     * @dev Initializes the contract setting the deployer as the initial owner.
     */
    function __Ownable_init() internal initializer {
        __Context_init_unchained();
        __Ownable_init_unchained();
    }

    function __Ownable_init_unchained() internal initializer {
        address msgSender = _msgSender();
        _owner = msgSender;
        emit OwnershipTransferred(address(0), msgSender);
    }

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

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

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

    /**
     * @dev Transfers ownership of the contract to a new account (`newOwner`).
     * Can only be called by the current owner.
     */
    function transferOwnership(address newOwner) public virtual onlyOwner {
        require(newOwner != address(0), "Ownable: new owner is the zero address");
        emit OwnershipTransferred(_owner, newOwner);
        _owner = newOwner;
    }
    uint256[49] private __gap;
}

// File: @openzeppelin/contracts-upgradeable/math/SafeMathUpgradeable.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

/**
 * @dev Wrappers over Solidity's arithmetic operations with added overflow
 * checks.
 *
 * Arithmetic operations in Solidity wrap on overflow. This can easily result
 * in bugs, because programmers usually assume that an overflow raises an
 * error, which is the standard behavior in high level programming languages.
 * `SafeMath` restores this intuition by reverting the transaction when an
 * operation overflows.
 *
 * Using this library instead of the unchecked operations eliminates an entire
 * class of bugs, so it's recommended to use it always.
 */
library SafeMathUpgradeable {
    /**
     * @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-upgradeable/proxy/Initializable.sol



// SPDX-License-Identifier: MIT

// solhint-disable-next-line compiler-version
pragma solidity >=0.4.24 <0.8.0;

import "../utils/AddressUpgradeable.sol";

/**
 * @dev This is a base contract to aid in writing upgradeable contracts, or any kind of contract that will be deployed
 * behind a proxy. Since a proxied contract can't have a constructor, it's common to move constructor logic to an
 * external initializer function, usually called `initialize`. It then becomes necessary to protect this initializer
 * function so it can only be called once. The {initializer} modifier provided by this contract will have this effect.
 *
 * TIP: To avoid leaving the proxy in an uninitialized state, the initializer function should be called as early as
 * possible by providing the encoded function call as the `_data` argument to {UpgradeableProxy-constructor}.
 *
 * CAUTION: When used with inheritance, manual care must be taken to not invoke a parent initializer twice, or to ensure
 * that all initializers are idempotent. This is not verified automatically as constructors are by Solidity.
 */
abstract contract Initializable {

    /**
     * @dev Indicates that the contract has been initialized.
     */
    bool private _initialized;

    /**
     * @dev Indicates that the contract is in the process of being initialized.
     */
    bool private _initializing;

    /**
     * @dev Modifier to protect an initializer function from being invoked twice.
     */
    modifier initializer() {
        require(_initializing || _isConstructor() || !_initialized, "Initializable: contract is already initialized");

        bool isTopLevelCall = !_initializing;
        if (isTopLevelCall) {
            _initializing = true;
            _initialized = true;
        }

        _;

        if (isTopLevelCall) {
            _initializing = false;
        }
    }

    /// @dev Returns true if and only if the function is running in the constructor
    function _isConstructor() private view returns (bool) {
        return !AddressUpgradeable.isContract(address(this));
    }
}

// File: @openzeppelin/contracts-upgradeable/token/ERC20/ERC20BurnableUpgradeable.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

import "../../utils/ContextUpgradeable.sol";
import "./ERC20Upgradeable.sol";
import "../../proxy/Initializable.sol";

/**
 * @dev Extension of {ERC20} that allows token holders to destroy both their own
 * tokens and those that they have an allowance for, in a way that can be
 * recognized off-chain (via event analysis).
 */
abstract contract ERC20BurnableUpgradeable is Initializable, ContextUpgradeable, ERC20Upgradeable {
    function __ERC20Burnable_init() internal initializer {
        __Context_init_unchained();
        __ERC20Burnable_init_unchained();
    }

    function __ERC20Burnable_init_unchained() internal initializer {
    }
    using SafeMathUpgradeable for uint256;

    /**
     * @dev Destroys `amount` tokens from the caller.
     *
     * See {ERC20-_burn}.
     */
    function burn(uint256 amount) public virtual {
        _burn(_msgSender(), amount);
    }

    /**
     * @dev Destroys `amount` tokens from `account`, deducting from the caller's
     * allowance.
     *
     * See {ERC20-_burn} and {ERC20-allowance}.
     *
     * Requirements:
     *
     * - the caller must have allowance for ``accounts``'s tokens of at least
     * `amount`.
     */
    function burnFrom(address account, uint256 amount) public virtual {
        uint256 decreasedAllowance = allowance(account, _msgSender()).sub(amount, "ERC20: burn amount exceeds allowance");

        _approve(account, _msgSender(), decreasedAllowance);
        _burn(account, amount);
    }
    uint256[50] private __gap;
}

// File: @openzeppelin/contracts-upgradeable/token/ERC20/ERC20Upgradeable.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

import "../../utils/ContextUpgradeable.sol";
import "./IERC20Upgradeable.sol";
import "../../math/SafeMathUpgradeable.sol";
import "../../proxy/Initializable.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 ERC20Upgradeable is Initializable, ContextUpgradeable, IERC20Upgradeable {
    using SafeMathUpgradeable 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.
     */
    function __ERC20_init(string memory name_, string memory symbol_) internal initializer {
        __Context_init_unchained();
        __ERC20_init_unchained(name_, symbol_);
    }

    function __ERC20_init_unchained(string memory name_, string memory symbol_) internal initializer {
        _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 { }
    uint256[44] private __gap;
}

// File: @openzeppelin/contracts-upgradeable/token/ERC20/IERC20Upgradeable.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

/**
 * @dev Interface of the ERC20 standard as defined in the EIP.
 */
interface IERC20Upgradeable {
    /**
     * @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-upgradeable/utils/AddressUpgradeable.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.2 <0.8.0;

/**
 * @dev Collection of functions related to the address type
 */
library AddressUpgradeable {
    /**
     * @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);
    }

    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-upgradeable/utils/ContextUpgradeable.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;
import "../proxy/Initializable.sol";

/*
 * @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 ContextUpgradeable is Initializable {
    function __Context_init() internal initializer {
        __Context_init_unchained();
    }

    function __Context_init_unchained() internal initializer {
    }
    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;
    }
    uint256[50] private __gap;
}

// File: @openzeppelin/contracts-upgradeable/utils/ReentrancyGuardUpgradeable.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;
import "../proxy/Initializable.sol";

/**
 * @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 ReentrancyGuardUpgradeable is Initializable {
    // 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;

    function __ReentrancyGuard_init() internal initializer {
        __ReentrancyGuard_init_unchained();
    }

    function __ReentrancyGuard_init_unchained() internal initializer {
        _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;
    }
    uint256[49] private __gap;
}

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



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

/**
 * @dev Wrappers over Solidity's arithmetic operations with added overflow
 * checks.
 *
 * Arithmetic operations in Solidity wrap on overflow. This can easily result
 * in bugs, because programmers usually assume that an overflow raises an
 * error, which is the standard behavior in high level programming languages.
 * `SafeMath` restores this intuition by reverting the transaction when an
 * operation overflows.
 *
 * Using this library instead of the unchecked operations eliminates an entire
 * class of bugs, so it's recommended to use it always.
 */
library SafeMath {
    /**
     * @dev Returns the addition of two unsigned integers, with an overflow flag.
     *
     * _Available since v3.4._
     */
    function tryAdd(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        uint256 c = a + b;
        if (c < a) return (false, 0);
        return (true, c);
    }

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

    /**
     * @dev Returns the multiplication of two unsigned integers, with an overflow flag.
     *
     * _Available since v3.4._
     */
    function tryMul(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        // Gas optimization: this is cheaper than requiring 'a' not being zero, but the
        // benefit is lost if 'b' is also tested.
        // See: https://github.com/OpenZeppelin/openzeppelin-contracts/pull/522
        if (a == 0) return (true, 0);
        uint256 c = a * b;
        if (c / a != b) return (false, 0);
        return (true, c);
    }

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

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

    /**
     * @dev Returns the addition of two unsigned integers, reverting on
     * overflow.
     *
     * Counterpart to Solidity's `+` operator.
     *
     * Requirements:
     *
     * - Addition cannot overflow.
     */
    function add(uint256 a, uint256 b) internal pure returns (uint256) {
        uint256 c = a + b;
        require(c >= a, "SafeMath: addition overflow");
        return c;
    }

    /**
     * @dev Returns the subtraction of two unsigned integers, reverting on
     * overflow (when the result is negative).
     *
     * Counterpart to Solidity's `-` operator.
     *
     * Requirements:
     *
     * - Subtraction cannot overflow.
     */
    function sub(uint256 a, uint256 b) internal pure returns (uint256) {
        require(b <= a, "SafeMath: subtraction overflow");
        return a - b;
    }

    /**
     * @dev Returns the multiplication of two unsigned integers, reverting on
     * overflow.
     *
     * Counterpart to Solidity's `*` operator.
     *
     * Requirements:
     *
     * - Multiplication cannot overflow.
     */
    function mul(uint256 a, uint256 b) internal pure returns (uint256) {
        if (a == 0) return 0;
        uint256 c = a * b;
        require(c / a == b, "SafeMath: multiplication overflow");
        return c;
    }

    /**
     * @dev Returns the integer division of two unsigned integers, reverting on
     * division by zero. The result is rounded towards zero.
     *
     * Counterpart to Solidity's `/` operator. Note: this function uses a
     * `revert` opcode (which leaves remaining gas untouched) while Solidity
     * uses an invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function div(uint256 a, uint256 b) internal pure returns (uint256) {
        require(b > 0, "SafeMath: division by zero");
        return a / b;
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * reverting when dividing by zero.
     *
     * Counterpart to Solidity's `%` operator. This function uses a `revert`
     * opcode (which leaves remaining gas untouched) while Solidity uses an
     * invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function mod(uint256 a, uint256 b) internal pure returns (uint256) {
        require(b > 0, "SafeMath: modulo by zero");
        return a % b;
    }

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

    /**
     * @dev Returns the integer division of two unsigned integers, reverting with custom message on
     * division by zero. The result is rounded towards zero.
     *
     * CAUTION: This function is deprecated because it requires allocating memory for the error
     * message unnecessarily. For custom revert reasons use {tryDiv}.
     *
     * Counterpart to Solidity's `/` operator. Note: this function uses a
     * `revert` opcode (which leaves remaining gas untouched) while Solidity
     * uses an invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function div(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b > 0, errorMessage);
        return a / b;
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * reverting with custom message when dividing by zero.
     *
     * CAUTION: This function is deprecated because it requires allocating memory for the error
     * message unnecessarily. For custom revert reasons use {tryMod}.
     *
     * Counterpart to Solidity's `%` operator. This function uses a `revert`
     * opcode (which leaves remaining gas untouched) while Solidity uses an
     * invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function mod(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b > 0, errorMessage);
        return a % b;
    }
}

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



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

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

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

    mapping (address => uint256) private _balances;

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

    uint256 private _totalSupply;

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

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

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

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

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

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

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

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

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

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

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

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

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

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

        _beforeTokenTransfer(sender, recipient, amount);

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

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

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

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

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

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

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

    /**
     * @dev Sets `amount` as the allowance of `spender` over the `owner` s tokens.
     *
     * This internal function is equivalent to `approve`, and can be used to
     * e.g. set automatic allowances for certain subsystems, etc.
     *
     * Emits an {Approval} event.
     *
     * Requirements:
     *
     * - `owner` cannot be the zero address.
     * - `spender` cannot be the zero address.
     */
    function _approve(address owner, address spender, uint256 amount) internal virtual {
        require(owner != address(0), "ERC20: approve from the zero address");
        require(spender != address(0), "ERC20: approve to the zero address");

        _allowances[owner][spender] = amount;
        emit Approval(owner, spender, amount);
    }

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

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

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



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

/**
 * @dev Interface of the ERC20 standard as defined in the EIP.
 */
interface IERC20 {
    /**
     * @dev Returns the amount of tokens in existence.
     */
    function totalSupply() external view returns (uint256);

    /**
     * @dev Returns the amount of tokens owned by `account`.
     */
    function balanceOf(address account) external view returns (uint256);

    /**
     * @dev Moves `amount` tokens from the caller's account to `recipient`.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * Emits a {Transfer} event.
     */
    function transfer(address recipient, uint256 amount) external returns (bool);

    /**
     * @dev Returns the remaining number of tokens that `spender` will be
     * allowed to spend on behalf of `owner` through {transferFrom}. This is
     * zero by default.
     *
     * This value changes when {approve} or {transferFrom} are called.
     */
    function allowance(address owner, address spender) external view returns (uint256);

    /**
     * @dev Sets `amount` as the allowance of `spender` over the caller's tokens.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * IMPORTANT: Beware that changing an allowance with this method brings the risk
     * that someone may use both the old and the new allowance by unfortunate
     * transaction ordering. One possible solution to mitigate this race
     * condition is to first reduce the spender's allowance to 0 and set the
     * desired value afterwards:
     * https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729
     *
     * Emits an {Approval} event.
     */
    function approve(address spender, uint256 amount) external returns (bool);

    /**
     * @dev Moves `amount` tokens from `sender` to `recipient` using the
     * allowance mechanism. `amount` is then deducted from the caller's
     * allowance.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * Emits a {Transfer} event.
     */
    function transferFrom(address sender, address recipient, uint256 amount) external returns (bool);

    /**
     * @dev Emitted when `value` tokens are moved from one account (`from`) to
     * another (`to`).
     *
     * Note that `value` may be zero.
     */
    event Transfer(address indexed from, address indexed to, uint256 value);

    /**
     * @dev Emitted when the allowance of a `spender` for an `owner` is set by
     * a call to {approve}. `value` is the new allowance.
     */
    event Approval(address indexed owner, address indexed spender, uint256 value);
}

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



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

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

/**
 * @title SafeERC20
 * @dev Wrappers around ERC20 operations that throw on failure (when the token
 * contract returns false). Tokens that return no value (and instead revert or
 * throw on failure) are also supported, non-reverting calls are assumed to be
 * successful.
 * To use this library you can add a `using SafeERC20 for IERC20;` statement to your contract,
 * which allows you to call the safe operations as `token.safeTransfer(...)`, etc.
 */
library SafeERC20 {
    using SafeMath for uint256;
    using Address for address;

    function safeTransfer(IERC20 token, address to, uint256 value) internal {
        _callOptionalReturn(token, abi.encodeWithSelector(token.transfer.selector, to, value));
    }

    function safeTransferFrom(IERC20 token, address from, address to, uint256 value) internal {
        _callOptionalReturn(token, abi.encodeWithSelector(token.transferFrom.selector, from, to, value));
    }

    /**
     * @dev Deprecated. This function has issues similar to the ones found in
     * {IERC20-approve}, and its usage is discouraged.
     *
     * Whenever possible, use {safeIncreaseAllowance} and
     * {safeDecreaseAllowance} instead.
     */
    function safeApprove(IERC20 token, address spender, uint256 value) internal {
        // safeApprove should only be called when setting an initial allowance,
        // or when resetting it to zero. To increase and decrease it, use
        // 'safeIncreaseAllowance' and 'safeDecreaseAllowance'
        // solhint-disable-next-line max-line-length
        require((value == 0) || (token.allowance(address(this), spender) == 0),
            "SafeERC20: approve from non-zero to non-zero allowance"
        );
        _callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, value));
    }

    function safeIncreaseAllowance(IERC20 token, address spender, uint256 value) internal {
        uint256 newAllowance = token.allowance(address(this), spender).add(value);
        _callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, newAllowance));
    }

    function safeDecreaseAllowance(IERC20 token, address spender, uint256 value) internal {
        uint256 newAllowance = token.allowance(address(this), spender).sub(value, "SafeERC20: decreased allowance below zero");
        _callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, newAllowance));
    }

    /**
     * @dev Imitates a Solidity high-level call (i.e. a regular function call to a contract), relaxing the requirement
     * on the return value: the return value is optional (but if data is returned, it must not be false).
     * @param token The token targeted by the call.
     * @param data The call data (encoded using abi.encode or one of its variants).
     */
    function _callOptionalReturn(IERC20 token, bytes memory data) private {
        // We need to perform a low level call here, to bypass Solidity's return data size checking mechanism, since
        // we're implementing it ourselves. We use {Address.functionCall} to perform this call, which verifies that
        // the target address contains contract code and also asserts for success in the low-level call.

        bytes memory returndata = address(token).functionCall(data, "SafeERC20: low-level call failed");
        if (returndata.length > 0) { // Return data is optional
            // solhint-disable-next-line max-line-length
            require(abi.decode(returndata, (bool)), "SafeERC20: ERC20 operation did not succeed");
        }
    }
}

// File: @openzeppelin/contracts/utils/Address.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.2 <0.8.0;

/**
 * @dev Collection of functions related to the address type
 */
library Address {
    /**
     * @dev Returns true if `account` is a contract.
     *
     * [IMPORTANT]
     * ====
     * It is unsafe to assume that an address for which this function returns
     * false is an externally-owned account (EOA) and not a contract.
     *
     * Among others, `isContract` will return false for the following
     * types of addresses:
     *
     *  - an externally-owned account
     *  - a contract in construction
     *  - an address where a contract will be created
     *  - an address where a contract lived, but was destroyed
     * ====
     */
    function isContract(address account) internal view returns (bool) {
        // This method relies on extcodesize, which returns 0 for contracts in
        // construction, since the code is only stored at the end of the
        // constructor execution.

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

    /**
     * @dev Replacement for Solidity's `transfer`: sends `amount` wei to
     * `recipient`, forwarding all available gas and reverting on errors.
     *
     * https://eips.ethereum.org/EIPS/eip-1884[EIP1884] increases the gas cost
     * of certain opcodes, possibly making contracts go over the 2300 gas limit
     * imposed by `transfer`, making them unable to receive funds via
     * `transfer`. {sendValue} removes this limitation.
     *
     * https://diligence.consensys.net/posts/2019/09/stop-using-soliditys-transfer-now/[Learn more].
     *
     * IMPORTANT: because control is transferred to `recipient`, care must be
     * taken to not create reentrancy vulnerabilities. Consider using
     * {ReentrancyGuard} or the
     * https://solidity.readthedocs.io/en/v0.5.11/security-considerations.html#use-the-checks-effects-interactions-pattern[checks-effects-interactions pattern].
     */
    function sendValue(address payable recipient, uint256 amount) internal {
        require(address(this).balance >= amount, "Address: insufficient balance");

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

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

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

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

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

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

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

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

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

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

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

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

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

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

// File: @openzeppelin/contracts/utils/Context.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

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

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

// File: contracts/LPToken.sol



// SPDX-License-Identifier: MIT

pragma solidity 0.6.12;

import "@openzeppelin/contracts-upgradeable/token/ERC20/ERC20BurnableUpgradeable.sol";
import "@openzeppelin/contracts-upgradeable/access/OwnableUpgradeable.sol";
import "./interfaces/ISwap.sol";

/**
 * @title Liquidity Provider Token
 * @notice This token is an ERC20 detailed token with added capability to be minted by the owner.
 * It is used to represent user's shares when providing liquidity to swap contracts.
 * @dev Only Swap contracts should initialize and own LPToken contracts.
 */
contract LPToken is ERC20BurnableUpgradeable, OwnableUpgradeable {
    using SafeMathUpgradeable for uint256;

    /**
     * @notice Initializes this LPToken contract with the given name and symbol
     * @dev The caller of this function will become the owner. A Swap contract should call this
     * in its initializer function.
     * @param name name of this token
     * @param symbol symbol of this token
     */
    function initialize(string memory name, string memory symbol)
        external
        initializer
        returns (bool)
    {
        __Context_init_unchained();
        __ERC20_init_unchained(name, symbol);
        __Ownable_init_unchained();
        return true;
    }

    /**
     * @notice Mints the given amount of LPToken to the recipient.
     * @dev only owner can call this mint function
     * @param recipient address of account to receive the tokens
     * @param amount amount of tokens to mint
     */
    function mint(address recipient, uint256 amount) external onlyOwner {
        require(amount != 0, "LPToken: cannot mint 0");
        _mint(recipient, amount);
    }

    /**
     * @dev Overrides ERC20._beforeTokenTransfer() which get called on every transfers including
     * minting and burning. * This assumes the owner is set to a Swap contract's address.
     */
    function _beforeTokenTransfer(
        address from,
        address to,
        uint256 amount
    ) internal virtual override(ERC20Upgradeable) {
        super._beforeTokenTransfer(from, to, amount);
        require(to != address(this), "LPToken: cannot send to itself");
    }
}

// File: contracts/interfaces/IMetaSwap.sol



// SPDX-License-Identifier: MIT

pragma solidity 0.6.12;

import "@openzeppelin/contracts/token/ERC20/ERC20.sol";

interface IMetaSwap {
    // pool data view functions
    function getA() external view returns (uint256);

    function getToken(uint8 index) external view returns (IERC20);

    function getTokenIndex(address tokenAddress) external view returns (uint8);

    function getTokenBalance(uint8 index) external view returns (uint256);

    function getVirtualPrice() external view returns (uint256);

    function isGuarded() external view returns (bool);

    // min return calculation functions
    function calculateSwap(
        uint8 tokenIndexFrom,
        uint8 tokenIndexTo,
        uint256 dx
    ) external view returns (uint256);

    function calculateSwapUnderlying(
        uint8 tokenIndexFrom,
        uint8 tokenIndexTo,
        uint256 dx
    ) external view returns (uint256);

    function calculateTokenAmount(uint256[] calldata amounts, bool deposit)
        external
        view
        returns (uint256);

    function calculateRemoveLiquidity(uint256 amount)
        external
        view
        returns (uint256[] memory);

    function calculateRemoveLiquidityOneToken(
        uint256 tokenAmount,
        uint8 tokenIndex
    ) external view returns (uint256 availableTokenAmount);

    // state modifying functions
    function initializeMetaSwap(
        IERC20[] memory pooledTokens,
        uint8[] memory decimals,
        string memory lpTokenName,
        string memory lpTokenSymbol,
        uint256 a,
        uint256 fee,
        uint256 adminFee,
        address lpTokenTargetAddress,
        address baseSwap
    ) external;

    function swap(
        uint8 tokenIndexFrom,
        uint8 tokenIndexTo,
        uint256 dx,
        uint256 minDy,
        uint256 deadline
    ) external returns (uint256);

    function swapUnderlying(
        uint8 tokenIndexFrom,
        uint8 tokenIndexTo,
        uint256 dx,
        uint256 minDy,
        uint256 deadline
    ) external returns (uint256);

    function addLiquidity(
        uint256[] calldata amounts,
        uint256 minToMint,
        uint256 deadline
    ) external returns (uint256);

    function removeLiquidity(
        uint256 amount,
        uint256[] calldata minAmounts,
        uint256 deadline
    ) external returns (uint256[] memory);

    function removeLiquidityOneToken(
        uint256 tokenAmount,
        uint8 tokenIndex,
        uint256 minAmount,
        uint256 deadline
    ) external returns (uint256);

    function removeLiquidityImbalance(
        uint256[] calldata amounts,
        uint256 maxBurnAmount,
        uint256 deadline
    ) external returns (uint256);

    function swapStorage()
        external
        view
        returns (
            uint256 initialA,
            uint256 futureA,
            uint256 initialATime,
            uint256 futureATime,
            uint256 swapFee,
            uint256 adminFee,
            address lpToken
        );
}

// File: contracts/interfaces/ISwap.sol



// SPDX-License-Identifier: MIT

pragma solidity 0.6.12;

import "@openzeppelin/contracts/token/ERC20/ERC20.sol";

interface ISwap {
    // pool data view functions
    function getA() external view returns (uint256);

    function getToken(uint8 index) external view returns (IERC20);

    function getTokenIndex(address tokenAddress) external view returns (uint8);

    function getTokenBalance(uint8 index) external view returns (uint256);

    function getVirtualPrice() external view returns (uint256);

    // min return calculation functions
    function calculateSwap(
        uint8 tokenIndexFrom,
        uint8 tokenIndexTo,
        uint256 dx
    ) external view returns (uint256);

    function calculateTokenAmount(uint256[] calldata amounts, bool deposit)
        external
        view
        returns (uint256);

    function calculateRemoveLiquidity(uint256 amount)
        external
        view
        returns (uint256[] memory);

    function calculateRemoveLiquidityOneToken(
        uint256 tokenAmount,
        uint8 tokenIndex
    ) external view returns (uint256 availableTokenAmount);

    // state modifying functions
    function initialize(
        IERC20[] memory pooledTokens,
        uint8[] memory decimals,
        string memory lpTokenName,
        string memory lpTokenSymbol,
        uint256 a,
        uint256 fee,
        uint256 adminFee,
        address lpTokenTargetAddress
    ) external;

    function swap(
        uint8 tokenIndexFrom,
        uint8 tokenIndexTo,
        uint256 dx,
        uint256 minDy,
        uint256 deadline
    ) external returns (uint256);

    function addLiquidity(
        uint256[] calldata amounts,
        uint256 minToMint,
        uint256 deadline
    ) external returns (uint256);

    function removeLiquidity(
        uint256 amount,
        uint256[] calldata minAmounts,
        uint256 deadline
    ) external returns (uint256[] memory);

    function removeLiquidityOneToken(
        uint256 tokenAmount,
        uint8 tokenIndex,
        uint256 minAmount,
        uint256 deadline
    ) external returns (uint256);

    function removeLiquidityImbalance(
        uint256[] calldata amounts,
        uint256 maxBurnAmount,
        uint256 deadline
    ) external returns (uint256);
}

// File: contracts/meta/MetaSwapDeposit.sol



// SPDX-License-Identifier: MIT

pragma solidity 0.6.12;

import "@openzeppelin/contracts/math/SafeMath.sol";
import "@openzeppelin/contracts/token/ERC20/SafeERC20.sol";
import "@openzeppelin/contracts-upgradeable/proxy/Initializable.sol";
import "@openzeppelin/contracts-upgradeable/utils/ReentrancyGuardUpgradeable.sol";
import "../LPToken.sol";
import "../interfaces/ISwap.sol";
import "../interfaces/IMetaSwap.sol";

/**
 * @title MetaSwapDeposit
 * @notice This contract flattens the LP token in a MetaSwap pool for easier user access. MetaSwap must be
 * deployed before this contract can be initialized successfully.
 *
 * For example, suppose there exists a base Swap pool consisting of [DAI, USDC, USDT].
 * Then a MetaSwap pool can be created with [sUSD, BaseSwapLPToken] to allow trades between either
 * the LP token or the underlying tokens and sUSD.
 *
 * MetaSwapDeposit flattens the LP token and remaps them to a single array, allowing users
 * to ignore the dependency on BaseSwapLPToken. Using the above example, MetaSwapDeposit can act
 * as a Swap containing [sUSD, DAI, USDC, USDT] tokens.
 */
contract MetaSwapDeposit is Initializable, ReentrancyGuardUpgradeable {
    using SafeERC20 for IERC20;
    using SafeMath for uint256;

    ISwap public baseSwap;
    IMetaSwap public metaSwap;
    IERC20[] public baseTokens;
    IERC20[] public metaTokens;
    IERC20[] public tokens;
    IERC20 public metaLPToken;

    uint256 constant MAX_UINT256 = 2**256 - 1;

    struct RemoveLiquidityImbalanceInfo {
        ISwap baseSwap;
        IMetaSwap metaSwap;
        IERC20 metaLPToken;
        uint8 baseLPTokenIndex;
        bool withdrawFromBase;
        uint256 leftoverMetaLPTokenAmount;
    }

    /**
     * @notice Sets the address for the base Swap contract, MetaSwap contract, and the
     * MetaSwap LP token contract.
     * @param _baseSwap the address of the base Swap contract
     * @param _metaSwap the address of the MetaSwap contract
     * @param _metaLPToken the address of the MetaSwap LP token contract
     */
    function initialize(
        ISwap _baseSwap,
        IMetaSwap _metaSwap,
        IERC20 _metaLPToken
    ) external initializer {
        __ReentrancyGuard_init();
        // Check and approve base level tokens to be deposited to the base Swap contract
        {
            uint8 i;
            for (; i < 32; i++) {
                try _baseSwap.getToken(i) returns (IERC20 token) {
                    baseTokens.push(token);
                    token.safeApprove(address(_baseSwap), MAX_UINT256);
                    token.safeApprove(address(_metaSwap), MAX_UINT256);
                } catch {
                    break;
                }
            }
            require(i > 1, "baseSwap must have at least 2 tokens");
        }

        // Check and approve meta level tokens to be deposited to the MetaSwap contract
        IERC20 baseLPToken;
        {
            uint8 i;
            for (; i < 32; i++) {
                try _metaSwap.getToken(i) returns (IERC20 token) {
                    baseLPToken = token;
                    metaTokens.push(token);
                    tokens.push(token);
                    token.safeApprove(address(_metaSwap), MAX_UINT256);
                } catch {
                    break;
                }
            }
            require(i > 1, "metaSwap must have at least 2 tokens");
        }

        // Flatten baseTokens and append it to tokens array
        tokens[tokens.length - 1] = baseTokens[0];
        for (uint8 i = 1; i < baseTokens.length; i++) {
            tokens.push(baseTokens[i]);
        }

        // Approve base Swap LP token to be burned by the base Swap contract for withdrawing
        baseLPToken.safeApprove(address(_baseSwap), MAX_UINT256);
        // Approve MetaSwap LP token to be burned by the MetaSwap contract for withdrawing
        _metaLPToken.safeApprove(address(_metaSwap), MAX_UINT256);

        // Initialize storage variables
        baseSwap = _baseSwap;
        metaSwap = _metaSwap;
        metaLPToken = _metaLPToken;
    }

    // Mutative functions

    /**
     * @notice Swap two underlying tokens using the meta pool and the base pool
     * @param tokenIndexFrom the token the user wants to swap from
     * @param tokenIndexTo the token the user wants to swap to
     * @param dx the amount of tokens the user wants to swap from
     * @param minDy the min amount the user would like to receive, or revert.
     * @param deadline latest timestamp to accept this transaction
     */
    function swap(
        uint8 tokenIndexFrom,
        uint8 tokenIndexTo,
        uint256 dx,
        uint256 minDy,
        uint256 deadline
    ) external nonReentrant returns (uint256) {
        tokens[tokenIndexFrom].safeTransferFrom(msg.sender, address(this), dx);
        uint256 tokenToAmount =
            metaSwap.swapUnderlying(
                tokenIndexFrom,
                tokenIndexTo,
                dx,
                minDy,
                deadline
            );
        tokens[tokenIndexTo].safeTransfer(msg.sender, tokenToAmount);
        return tokenToAmount;
    }

    /**
     * @notice Add liquidity to the pool with the given amounts of tokens
     * @param amounts the amounts of each token to add, in their native precision
     * @param minToMint the minimum LP tokens adding this amount of liquidity
     * should mint, otherwise revert. Handy for front-running mitigation
     * @param deadline latest timestamp to accept this transaction
     * @return amount of LP token user minted and received
     */
    function addLiquidity(
        uint256[] calldata amounts,
        uint256 minToMint,
        uint256 deadline
    ) external nonReentrant returns (uint256) {
        // Read to memory to save on gas
        IERC20[] memory memBaseTokens = baseTokens;
        IERC20[] memory memMetaTokens = metaTokens;
        uint256 baseLPTokenIndex = memMetaTokens.length - 1;

        require(amounts.length == memBaseTokens.length + baseLPTokenIndex);

        uint256 baseLPTokenAmount;
        {
            // Transfer base tokens from the caller and deposit to the base Swap pool
            uint256[] memory baseAmounts = new uint256[](memBaseTokens.length);
            bool shouldDepositBaseTokens;
            for (uint8 i = 0; i < memBaseTokens.length; i++) {
                IERC20 token = memBaseTokens[i];
                uint256 depositAmount = amounts[baseLPTokenIndex + i];
                if (depositAmount > 0) {
                    token.safeTransferFrom(
                        msg.sender,
                        address(this),
                        depositAmount
                    );
                    baseAmounts[i] = token.balanceOf(address(this)); // account for any fees on transfer
                    // if there are any base Swap level tokens, flag it for deposits
                    shouldDepositBaseTokens = true;
                }
            }
            if (shouldDepositBaseTokens) {
                // Deposit any base Swap level tokens and receive baseLPToken
                baseLPTokenAmount = baseSwap.addLiquidity(
                    baseAmounts,
                    0,
                    deadline
                );
            }
        }

        uint256 metaLPTokenAmount;
        {
            // Transfer remaining meta level tokens from the caller
            uint256[] memory metaAmounts = new uint256[](metaTokens.length);
            for (uint8 i = 0; i < baseLPTokenIndex; i++) {
                IERC20 token = memMetaTokens[i];
                uint256 depositAmount = amounts[i];
                if (depositAmount > 0) {
                    token.safeTransferFrom(
                        msg.sender,
                        address(this),
                        depositAmount
                    );
                    metaAmounts[i] = token.balanceOf(address(this)); // account for any fees on transfer
                }
            }
            // Update the baseLPToken amount that will be deposited
            metaAmounts[baseLPTokenIndex] = baseLPTokenAmount;

            // Deposit the meta level tokens and the baseLPToken
            metaLPTokenAmount = metaSwap.addLiquidity(
                metaAmounts,
                minToMint,
                deadline
            );
        }

        // Transfer the meta lp token to the caller
        metaLPToken.safeTransfer(msg.sender, metaLPTokenAmount);

        return metaLPTokenAmount;
    }

    /**
     * @notice Burn LP tokens to remove liquidity from the pool. Withdraw fee that decays linearly
     * over period of 4 weeks since last deposit will apply.
     * @dev Liquidity can always be removed, even when the pool is paused.
     * @param amount the amount of LP tokens to burn
     * @param minAmounts the minimum amounts of each token in the pool
     *        acceptable for this burn. Useful as a front-running mitigation
     * @param deadline latest timestamp to accept this transaction
     * @return amounts of tokens user received
     */
    function removeLiquidity(
        uint256 amount,
        uint256[] calldata minAmounts,
        uint256 deadline
    ) external nonReentrant returns (uint256[] memory) {
        IERC20[] memory memBaseTokens = baseTokens;
        IERC20[] memory memMetaTokens = metaTokens;
        uint256[] memory totalRemovedAmounts;

        {
            uint256 numOfAllTokens =
                memBaseTokens.length + memMetaTokens.length - 1;
            require(minAmounts.length == numOfAllTokens, "out of range");
            totalRemovedAmounts = new uint256[](numOfAllTokens);
        }

        // Transfer meta lp token from the caller to this
        metaLPToken.safeTransferFrom(msg.sender, address(this), amount);

        uint256 baseLPTokenAmount;
        {
            // Remove liquidity from the MetaSwap pool
            uint256[] memory removedAmounts;
            uint256 baseLPTokenIndex = memMetaTokens.length - 1;
            {
                uint256[] memory metaMinAmounts =
                    new uint256[](memMetaTokens.length);
                for (uint8 i = 0; i < baseLPTokenIndex; i++) {
                    metaMinAmounts[i] = minAmounts[i];
                }
                removedAmounts = metaSwap.removeLiquidity(
                    amount,
                    metaMinAmounts,
                    deadline
                );
            }

            // Send the meta level tokens to the caller
            for (uint8 i = 0; i < baseLPTokenIndex; i++) {
                totalRemovedAmounts[i] = removedAmounts[i];
                memMetaTokens[i].safeTransfer(msg.sender, removedAmounts[i]);
            }
            baseLPTokenAmount = removedAmounts[baseLPTokenIndex];

            // Remove liquidity from the base Swap pool
            {
                uint256[] memory baseMinAmounts =
                    new uint256[](memBaseTokens.length);
                for (uint8 i = 0; i < baseLPTokenIndex; i++) {
                    baseMinAmounts[i] = minAmounts[baseLPTokenIndex + i];
                }
                removedAmounts = baseSwap.removeLiquidity(
                    baseLPTokenAmount,
                    baseMinAmounts,
                    deadline
                );
            }

            // Send the base level tokens to the caller
            for (uint8 i = 0; i < memBaseTokens.length; i++) {
                totalRemovedAmounts[baseLPTokenIndex + i] = removedAmounts[i];
                memBaseTokens[i].safeTransfer(msg.sender, removedAmounts[i]);
            }
        }

        return totalRemovedAmounts;
    }

    /**
     * @notice Remove liquidity from the pool all in one token. Withdraw fee that decays linearly
     * over period of 4 weeks since last deposit will apply.
     * @param tokenAmount the amount of the token you want to receive
     * @param tokenIndex the index of the token you want to receive
     * @param minAmount the minimum amount to withdraw, otherwise revert
     * @param deadline latest timestamp to accept this transaction
     * @return amount of chosen token user received
     */
    function removeLiquidityOneToken(
        uint256 tokenAmount,
        uint8 tokenIndex,
        uint256 minAmount,
        uint256 deadline
    ) external nonReentrant returns (uint256) {
        uint8 baseLPTokenIndex = uint8(metaTokens.length - 1);
        uint8 baseTokensLength = uint8(baseTokens.length);

        // Transfer metaLPToken from the caller
        metaLPToken.safeTransferFrom(msg.sender, address(this), tokenAmount);

        IERC20 token;
        if (tokenIndex < baseLPTokenIndex) {
            // When the desired token is meta level token, we can just call `removeLiquidityOneToken` directly
            metaSwap.removeLiquidityOneToken(
                tokenAmount,
                tokenIndex,
                minAmount,
                deadline
            );
            token = metaTokens[tokenIndex];
        } else if (tokenIndex < baseLPTokenIndex + baseTokensLength) {
            // When the desired token is a base level token, we need to first withdraw via baseLPToken, then withdraw
            // the desired token from the base Swap contract.
            uint256 removedBaseLPTokenAmount =
                metaSwap.removeLiquidityOneToken(
                    tokenAmount,
                    baseLPTokenIndex,
                    0,
                    deadline
                );

            baseSwap.removeLiquidityOneToken(
                removedBaseLPTokenAmount,
                tokenIndex - baseLPTokenIndex,
                minAmount,
                deadline
            );
            token = baseTokens[tokenIndex - baseLPTokenIndex];
        } else {
            revert("out of range");
        }

        uint256 amountWithdrawn = token.balanceOf(address(this));
        token.safeTransfer(msg.sender, amountWithdrawn);
        return amountWithdrawn;
    }

    /**
     * @notice Remove liquidity from the pool, weighted differently than the
     * pool's current balances. Withdraw fee that decays linearly
     * over period of 4 weeks since last deposit will apply.
     * @param amounts how much of each token to withdraw
     * @param maxBurnAmount the max LP token provider is willing to pay to
     * remove liquidity. Useful as a front-running mitigation.
     * @param deadline latest timestamp to accept this transaction
     * @return amount of LP tokens burned
     */
    function removeLiquidityImbalance(
        uint256[] calldata amounts,
        uint256 maxBurnAmount,
        uint256 deadline
    ) external nonReentrant returns (uint256) {
        IERC20[] memory memBaseTokens = baseTokens;
        IERC20[] memory memMetaTokens = metaTokens;
        uint256[] memory metaAmounts = new uint256[](memMetaTokens.length);
        uint256[] memory baseAmounts = new uint256[](memBaseTokens.length);

        require(
            amounts.length == memBaseTokens.length + memMetaTokens.length - 1,
            "out of range"
        );

        RemoveLiquidityImbalanceInfo memory v =
            RemoveLiquidityImbalanceInfo(
                baseSwap,
                metaSwap,
                metaLPToken,
                uint8(metaAmounts.length - 1),
                false,
                0
            );

        for (uint8 i = 0; i < v.baseLPTokenIndex; i++) {
            metaAmounts[i] = amounts[i];
        }

        for (uint8 i = 0; i < baseAmounts.length; i++) {
            baseAmounts[i] = amounts[v.baseLPTokenIndex + i];
            if (baseAmounts[i] > 0) {
                v.withdrawFromBase = true;
            }
        }

        // Calculate how much base LP token we need to get the desired amount of underlying tokens
        if (v.withdrawFromBase) {
            metaAmounts[v.baseLPTokenIndex] = v
                .baseSwap
                .calculateTokenAmount(baseAmounts, false)
                .mul(10005)
                .div(10000);
        }

        // Transfer MetaSwap LP token from the caller to this contract
        v.metaLPToken.safeTransferFrom(
            msg.sender,
            address(this),
            maxBurnAmount
        );

        // Withdraw the paired meta level tokens and the base LP token from the MetaSwap pool
        uint256 burnedMetaLPTokenAmount =
            v.metaSwap.removeLiquidityImbalance(
                metaAmounts,
                maxBurnAmount,
                deadline
            );
        v.leftoverMetaLPTokenAmount = maxBurnAmount.sub(
            burnedMetaLPTokenAmount
        );

        // If underlying tokens are desired, withdraw them from the base Swap pool
        if (v.withdrawFromBase) {
            v.baseSwap.removeLiquidityImbalance(
                baseAmounts,
                metaAmounts[v.baseLPTokenIndex],
                deadline
            );

            // Base Swap may require LESS base LP token than the amount we have
            // In that case, deposit it to the MetaSwap pool.
            uint256[] memory leftovers = new uint256[](metaAmounts.length);
            IERC20 baseLPToken = memMetaTokens[v.baseLPTokenIndex];
            uint256 leftoverBaseLPTokenAmount =
                baseLPToken.balanceOf(address(this));
            if (leftoverBaseLPTokenAmount > 0) {
                leftovers[v.baseLPTokenIndex] = leftoverBaseLPTokenAmount;
                v.leftoverMetaLPTokenAmount = v.leftoverMetaLPTokenAmount.add(
                    v.metaSwap.addLiquidity(leftovers, 0, deadline)
                );
            }
        }

        // Transfer all withdrawn tokens to the caller
        for (uint8 i = 0; i < amounts.length; i++) {
            IERC20 token;
            if (i < v.baseLPTokenIndex) {
                token = memMetaTokens[i];
            } else {
                token = memBaseTokens[i - v.baseLPTokenIndex];
            }
            if (amounts[i] > 0) {
                token.safeTransfer(msg.sender, amounts[i]);
            }
        }

        // If there were any extra meta lp token, transfer them back to the caller as well
        if (v.leftoverMetaLPTokenAmount > 0) {
            v.metaLPToken.safeTransfer(msg.sender, v.leftoverMetaLPTokenAmount);
        }

        return maxBurnAmount - v.leftoverMetaLPTokenAmount;
    }

    // VIEW FUNCTIONS

    /**
     * @notice A simple method to calculate prices from deposits or
     * withdrawals, excluding fees but including slippage. This is
     * helpful as an input into the various "min" parameters on calls
     * to fight front-running. When withdrawing from the base pool in imbalanced
     * fashion, the recommended slippage setting is 0.2% or higher.
     *
     * @dev This shouldn't be used outside frontends for user estimates.
     *
     * @param amounts an array of token amounts to deposit or withdrawal,
     * corresponding to pooledTokens. The amount should be in each
     * pooled token's native precision. If a token charges a fee on transfers,
     * use the amount that gets transferred after the fee.
     * @param deposit whether this is a deposit or a withdrawal
     * @return token amount the user will receive
     */
    function calculateTokenAmount(uint256[] calldata amounts, bool deposit)
        external
        view
        returns (uint256)
    {
        uint256[] memory metaAmounts = new uint256[](metaTokens.length);
        uint256[] memory baseAmounts = new uint256[](baseTokens.length);
        uint256 baseLPTokenIndex = metaAmounts.length - 1;

        for (uint8 i = 0; i < baseLPTokenIndex; i++) {
            metaAmounts[i] = amounts[i];
        }

        for (uint8 i = 0; i < baseAmounts.length; i++) {
            baseAmounts[i] = amounts[baseLPTokenIndex + i];
        }

        uint256 baseLPTokenAmount =
            baseSwap.calculateTokenAmount(baseAmounts, deposit);
        metaAmounts[baseLPTokenIndex] = baseLPTokenAmount;

        return metaSwap.calculateTokenAmount(metaAmounts, deposit);
    }

    /**
     * @notice A simple method to calculate amount of each underlying
     * tokens that is returned upon burning given amount of LP tokens
     * @param amount the amount of LP tokens that would be burned on withdrawal
     * @return array of token balances that the user will receive
     */
    function calculateRemoveLiquidity(uint256 amount)
        external
        view
        returns (uint256[] memory)
    {
        uint256[] memory metaAmounts =
            metaSwap.calculateRemoveLiquidity(amount);
        uint8 baseLPTokenIndex = uint8(metaAmounts.length - 1);
        uint256[] memory baseAmounts =
            baseSwap.calculateRemoveLiquidity(metaAmounts[baseLPTokenIndex]);

        uint256[] memory totalAmounts =
            new uint256[](baseLPTokenIndex + baseAmounts.length);
        for (uint8 i = 0; i < baseLPTokenIndex; i++) {
            totalAmounts[i] = metaAmounts[i];
        }
        for (uint8 i = 0; i < baseAmounts.length; i++) {
            totalAmounts[baseLPTokenIndex + i] = baseAmounts[i];
        }

        return totalAmounts;
    }

    /**
     * @notice Calculate the amount of underlying token available to withdraw
     * when withdrawing via only single token
     * @param tokenAmount the amount of LP token to burn
     * @param tokenIndex index of which token will be withdrawn
     * @return availableTokenAmount calculated amount of underlying token
     * available to withdraw
     */
    function calculateRemoveLiquidityOneToken(
        uint256 tokenAmount,
        uint8 tokenIndex
    ) external view returns (uint256) {
        uint8 baseLPTokenIndex = uint8(metaTokens.length - 1);

        if (tokenIndex < baseLPTokenIndex) {
            return
                metaSwap.calculateRemoveLiquidityOneToken(
                    tokenAmount,
                    tokenIndex
                );
        } else {
            uint256 baseLPTokenAmount =
                metaSwap.calculateRemoveLiquidityOneToken(
                    tokenAmount,
                    baseLPTokenIndex
                );
            return
                baseSwap.calculateRemoveLiquidityOneToken(
                    baseLPTokenAmount,
                    tokenIndex - baseLPTokenIndex
                );
        }
    }

    /**
     * @notice Returns the address of the pooled token at given index. Reverts if tokenIndex is out of range.
     * This is a flattened representation of the pooled tokens.
     * @param index the index of the token
     * @return address of the token at given index
     */
    function getToken(uint256 index) external view returns (IERC20) {
        require(index < tokens.length, "index out of range");
        return tokens[index];
    }

    /**
     * @notice Calculate amount of tokens you receive on swap
     * @param tokenIndexFrom the token the user wants to sell
     * @param tokenIndexTo the token the user wants to buy
     * @param dx the amount of tokens the user wants to sell. If the token charges
     * a fee on transfers, use the amount that gets transferred after the fee.
     * @return amount of tokens the user will receive
     */
    function calculateSwap(
        uint8 tokenIndexFrom,
        uint8 tokenIndexTo,
        uint256 dx
    ) external view returns (uint256) {
        return
            metaSwap.calculateSwapUnderlying(tokenIndexFrom, tokenIndexTo, dx);
    }
}