// SPDX-License-Identifier: MIT
// File: @openzeppelin/contracts/GSN/Context.sol

pragma solidity ^0.6.0;

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

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

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

pragma solidity ^0.6.0;

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

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

    /**
     * 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);

    /**
     * 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);

    /**
     * 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);

    /**
     * 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);
    
    function decimals() external view returns (uint8);

    /**
     * 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);

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

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

pragma solidity ^0.6.0;

/**
 * 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 {
    /**
     * 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;
    }

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

    /**
     * Returns the subtraction of two unsigned integers, reverting with custom message on
     * overflow (when the result is negative).
     *
     * Counterpart to Solidity's `-` operator.
     *
     * Requirements:
     *
     * - Subtraction cannot overflow.
     */
    function sub(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b <= a, errorMessage);
        uint256 c = a - b;

        return c;
    }

    /**
     * Returns the multiplication of two unsigned integers, reverting on
     * overflow.
     *
     * Counterpart to Solidity's `*` operator.
     *
     * Requirements:
     *
     * - Multiplication cannot overflow.
     */
    function mul(uint256 a, uint256 b) internal pure returns (uint256) {
        // Gas optimization: this is cheaper than requiring 'a' not being zero, but the
        // benefit is lost if 'b' is also tested.
        // See: https://github.com/OpenZeppelin/openzeppelin-contracts/pull/522
        if (a == 0) {
            return 0;
        }

        uint256 c = a * b;
        require(c / a == b, "SafeMath: multiplication overflow");

        return c;
    }

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

    /**
     * Returns the integer division of two unsigned integers. Reverts with custom message on
     * division by zero. The result is rounded towards zero.
     *
     * Counterpart to Solidity's `/` operator. Note: this function uses a
     * `revert` opcode (which leaves remaining gas untouched) while Solidity
     * uses an invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function div(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b > 0, errorMessage);
        uint256 c = a / b;
        // assert(a == b * c + a % b); // There is no case in which this doesn't hold

        return c;
    }

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

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

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

pragma solidity ^0.6.2;

/**
 * Collection of functions related to the address type
 */
library Address {
    /**
     * Returns true if `account` is a contract.
     *
     * [IMPORTANT]
     * ====
     * It is unsafe to assume that an address for which this function returns
     * false is an externally-owned account (EOA) and not a contract.
     *
     * Among others, `isContract` will return false for the following
     * types of addresses:
     *
     *  - an externally-owned account
     *  - a contract in construction
     *  - an address where a contract will be created
     *  - an address where a contract lived, but was destroyed
     * ====
     */
    function isContract(address account) internal view returns (bool) {
        // According to EIP-1052, 0x0 is the value returned for not-yet created accounts
        // and 0xc5d2460186f7233c927e7db2dcc703c0e500b653ca82273b7bfad8045d85a470 is returned
        // for accounts without code, i.e. `keccak256('')`
        bytes32 codehash;
        bytes32 accountHash = 0xc5d2460186f7233c927e7db2dcc703c0e500b653ca82273b7bfad8045d85a470;
        // solhint-disable-next-line no-inline-assembly
        assembly { codehash := extcodehash(account) }
        return (codehash != accountHash && codehash != 0x0);
    }

    /**
     * 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");
    }

    /**
     * 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");
    }

    /**
     * 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);
    }

    /**
     * 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");
    }

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

    function _functionCallWithValue(address target, bytes memory data, uint256 weiValue, string memory errorMessage) private returns (bytes memory) {
        require(isContract(target), "Address: call to non-contract");

        // solhint-disable-next-line avoid-low-level-calls
        (bool success, bytes memory returndata) = target.call{ value: weiValue }(data);
        if (success) {
            return returndata;
        } else {
            // Look for revert reason and bubble it up if present
            if (returndata.length > 0) {
                // The easiest way to bubble the revert reason is using memory via assembly

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

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

pragma solidity ^0.6.0;

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

    mapping (address => uint256) private _balances;

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

    uint256 private _totalSupply;

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

    /**
     * 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;
    }

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

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

    /**
     * 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 override returns (uint8) {
        return _decimals;
    }

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

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

    /**
     * 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;
    }

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

    /**
     * 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;
    }

    /**
     * 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;
    }

    /**
     * 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;
    }

    /**
     * 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;
    }

    /**
     * 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");

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

    /** 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");

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

    /**
     * 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");

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

    /**
     * Sets `amount` as the allowance of `spender` over the `owner`s tokens.
     *
     * This is 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);
    }

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

}

// File: @openzeppelin/contracts/access/Ownable.sol

pragma solidity ^0.6.0;

/**
 * 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.
 */
contract Ownable is Context {
    address private _owner;

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

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

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

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

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

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");
        }
    }
}

contract ReentrancyGuard {
    // Booleans are more expensive than uint256 or any type that takes up a full
    // word because each write operation emits an extra SLOAD to first read the
    // slot's contents, replace the bits taken up by the boolean, and then write
    // back. This is the compiler's defense against contract upgrades and
    // pointer aliasing, and it cannot be disabled.

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

    uint256 private _status;

    constructor () internal {
        _status = _NOT_ENTERED;
    }

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

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

        _;

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

// File: contracts/zs-BMSGR.sol
// zsTokens are Stabilize proxy tokens that serve as receipts for deposits into Stabilize strategies
// zsTokens should increase in value if the strategy it uses is profitable
// When someone deposits into the zsToken contract, tokens are minted and when they redeem, tokens are burned

interface StabilizeStrategy {
    function rewardTokensCount() external view returns (uint256);
    function rewardTokenAddress(uint256) external view returns (address);
    function withdrawTokenReserves() external view returns (address, uint256);
    function balance() external view returns (uint256);
    function pricePerToken() external view returns (uint256);
    function enter() external;
    function exit() external;
    function deposit(bool) external;
    function withdraw(address, uint256, uint256, bool) external returns (uint256); // Will withdraw to the address specified a percent of total shares
}

pragma solidity ^0.6.6;

contract zsToken is ERC20("Stabilize Strategy BAC-MIC-Seigniorage ", "zs-BMSGR"), Ownable, ReentrancyGuard {
    using SafeERC20 for IERC20;

    // Variables
    uint256 constant divisionFactor = 100000;
    
    // There are no fees to deposit and withdraw from the zs-Tokens
    
    // Info of each user.
    struct UserInfo {
        uint256 depositTime; // The time the user made the last deposit
        uint256 shareEstimate;
    }
    
    mapping(address => UserInfo) private userInfo;
    
    // Token information
    // This wrapped token accepts multiple sgr coins
    // BAC, MIC
    struct TokenInfo {
        IERC20 token; // Reference of token
        uint256 decimals; // Decimals of token
    }
    
    TokenInfo[] private tokenList; // An array of tokens accepted as deposits
    address private _underlyingPriceAsset; // Token from which the price is derived for STBZ staking
    bool public depositsOpen = true; // Governance can open or close deposits without timelock, cannot block withdrawals
    
    // Strategy information
    StabilizeStrategy private currentStrategy; // This will be the contract for the strategy
    address private _pendingStrategy;
    
    // Events
    event Wrapped(address indexed user, uint256 amount);
    event Unwrapped(address indexed user, uint256 amount);

    constructor (address _priceAsset) public {
        _underlyingPriceAsset = _priceAsset;
        setupWithdrawTokens();
    }
    
    function setupWithdrawTokens() internal {
        // Start with BAC
        IERC20 _token = IERC20(address(0x3449FC1Cd036255BA1EB19d65fF4BA2b8903A69a));
        tokenList.push(
            TokenInfo({
                token: _token,
                decimals: _token.decimals()
            })
        );   
        
        // MIC
        _token = IERC20(address(0x368B3a58B5f49392e5C9E4C998cb0bB966752E51));
        tokenList.push(
            TokenInfo({
                token: _token,
                decimals: _token.decimals()
            })
        );
    }
    
    function getCurrentStrategy() external view returns (address) {
        return address(currentStrategy);
    }
    
    function getPendingStrategy() external view returns (address) {
        return _pendingStrategy;
    }

    function underlyingAsset() public view returns (address) {
        // Can be used if staking in the STBZ pool
        return address(_underlyingPriceAsset);
    }
    
    function underlyingDepositAssets() public view returns (address, address, address) {
        // Returns all addresses accepted by this token vault
        return (address(tokenList[0].token), address(tokenList[1].token), address(tokenList[2].token));
    }
    
    function pricePerToken() public view returns (uint256) {
        if(totalSupply() == 0){
            return 1e18; // Shown in Wei units
        }else{
            return uint256(1e18).mul(valueOfVaultAndStrategy()).div(totalSupply());      
        }
    }
    
    function getNormalizedTotalBalance(address _address) public view returns (uint256) {
        uint256 _balance = 0;
        for(uint256 i = 0; i < tokenList.length; i++){
            uint256 _bal = tokenList[i].token.balanceOf(_address);
            _bal = _bal.mul(1e18).div(10**tokenList[i].decimals);
            _balance = _balance.add(_bal); // This has been normalized to 1e18 decimals
        }
        return _balance;
    }
    
    function valueOfVaultAndStrategy() public view returns (uint256) { // The total value of the tokens
        uint256 balance = getNormalizedTotalBalance(address(this)); // Get tokens stored in this contract
        if(currentStrategy != StabilizeStrategy(address(0))){
            balance += currentStrategy.balance(); // And tokens stored at the strategy
        }
        return balance;
    }
    
    function withdrawTokenReserves() public view returns (address, uint256) {
        // This function will return the address and amount of the token with the highest balance
        if(currentStrategy != StabilizeStrategy(address(0))){
            return currentStrategy.withdrawTokenReserves();
        }else{
            uint256 length = tokenList.length;
            uint256 targetID = 0;
            uint256 targetNormBalance = 0;
            for(uint256 i = 0; i < length; i++){
                uint256 _normBal = tokenList[i].token.balanceOf(address(this)).mul(1e18).div(10**tokenList[i].decimals);
                if(_normBal > 0){
                    if(targetNormBalance == 0 || _normBal >= targetNormBalance){
                        targetNormBalance = _normBal;
                        targetID = i;
                    }
                }
            }
            if(targetNormBalance > 0){
                return (address(tokenList[targetID].token), tokenList[targetID].token.balanceOf(address(this)));
            }else{
                return (address(0), 0); // No balance
            }
        }
    }
    
    
    // Now handle deposits into the strategy
    function deposit(uint256 amount, uint256 _tokenID) public nonReentrant {
        uint256 total = valueOfVaultAndStrategy(); // Get token equivalent at strategy and here if applicable
        
        require(depositsOpen == true, "Deposits have been suspended, but you can still withdraw");
        require(currentStrategy != StabilizeStrategy(address(0)),"No strategy contract has been selected yet");
        require(_tokenID < tokenList.length, "Token ID is outside range of tokens in contract");
        
        IERC20 _token = tokenList[_tokenID].token; // Trusted tokens
        uint256 _before = _token.balanceOf(address(this));
        _token.safeTransferFrom(_msgSender(), address(this), amount); // Transfer token to this address
        amount = _token.balanceOf(address(this)).sub(_before); // Some tokens lose amount (transfer fee) upon transfer
        require(amount > 0, "Cannot deposit 0");
        bool nonContract = false;
        if(tx.origin == _msgSender()){
            nonContract = true; // The sender is not a contract
        }
        uint256 _strategyBalance = currentStrategy.balance(); // Will get the balance of the value of the main tokens at the strategy
        // Now call the strategy to deposit
        pushTokensToStrategy(); // Push any strategy tokens here into the strategy
        currentStrategy.deposit(nonContract); // Activate strategy deposit
        require(currentStrategy.balance() > _strategyBalance, "No change in strategy balance"); // Balance should increase
        uint256 normalizedAmount = amount.mul(1e18).div(10**tokenList[_tokenID].decimals); // Make sure everything is same units
        uint256 mintAmount = normalizedAmount;
        if(totalSupply() > 0){
            // There is already a balance here, calculate our share
            mintAmount = normalizedAmount.mul(totalSupply()).div(total); // Our share of the total
        }
        _mint(_msgSender(),mintAmount); // Now mint new zs-token to the depositor
        
        // Add the user information
        userInfo[_msgSender()].depositTime = now;
        userInfo[_msgSender()].shareEstimate = userInfo[_msgSender()].shareEstimate.add(mintAmount);

        emit Wrapped(_msgSender(), amount);
    }
    
    function redeem(uint256 share) public nonReentrant {
        // Essentially withdraw our equivalent share of the pool based on share value
        // Users cannot choose which token they get. They get the largest quantity coin up to the lowest quantity
        require(share > 0, "Cannot withdraw 0");
        require(totalSupply() > 0, "No value redeemable");
        uint256 tokenTotal = totalSupply();
        // Now burn the token
        _burn(_msgSender(),share); // Burn the amount, will fail if user doesn't have enough
        
        bool nonContract = false;
        if(tx.origin == _msgSender()){
            nonContract = true; // The sender is not a contract, we will allow market sells and buys
        }else{
            // This is a contract redeeming
            require(userInfo[_msgSender()].depositTime < now && userInfo[_msgSender()].depositTime > 0, "Contract depositor cannot redeem in same transaction");
        }
        
        // Update user information
        if(share <= userInfo[_msgSender()].shareEstimate){
            userInfo[_msgSender()].shareEstimate = userInfo[_msgSender()].shareEstimate.sub(share);
        }else{
            // Share is greater than our share estimate, can happen if tokens are transferred
            userInfo[_msgSender()].shareEstimate = 0;
            require(nonContract == true, "Contract depositors cannot take out more than what they put in");
        }

        uint256 withdrawAmount = 0;
        if(currentStrategy != StabilizeStrategy(address(0))){
            withdrawAmount = currentStrategy.withdraw(_msgSender(), share, tokenTotal, nonContract); // Returns the amount of underlying removed
            require(withdrawAmount > 0, "Failed to withdraw from the strategy");
        }else{
            // Pull directly from this contract the token amount in relation to the share if strategy not used
            if(share < tokenTotal){
                uint256 _balance = getNormalizedTotalBalance(address(this));
                uint256 _myBalance = _balance.mul(share).div(tokenTotal);
                withdrawPerBalance(_msgSender(), _myBalance, false); // This will withdraw based on token balanace
                withdrawAmount = _myBalance;
            }else{
                // We are all shares, transfer all
                uint256 _balance = getNormalizedTotalBalance(address(this));
                withdrawPerBalance(_msgSender(), _balance, true);
                withdrawAmount = _balance;
            }
        }
        
        emit Unwrapped(_msgSender(), withdrawAmount);
    }
    
    // This will withdraw the tokens from the contract based on their balance, from highest balance to lowest
    function withdrawPerBalance(address _receiver, uint256 _withdrawAmount, bool _takeAll) internal {
        uint256 length = tokenList.length;
        if(_takeAll == true){
            // Send the entire balance
            for(uint256 i = 0; i < length; i++){
                uint256 _bal = tokenList[i].token.balanceOf(address(this));
                if(_bal > 0){
                    tokenList[i].token.safeTransfer(_receiver, _bal);
                }
            }
            return;
        }
        bool[4] memory done;
        uint256 targetID = 0;
        uint256 targetNormBalance = 0;
        for(uint256 i = 0; i < length; i++){
            
            targetNormBalance = 0; // Reset the target balance
            // Find the highest balanced token to withdraw
            for(uint256 i2 = 0; i2 < length; i2++){
                if(done[i2] == false){
                    uint256 _normBal = tokenList[i2].token.balanceOf(address(this)).mul(1e18).div(10**tokenList[i2].decimals);
                    if(targetNormBalance == 0 || _normBal >= targetNormBalance){
                        targetNormBalance = _normBal;
                        targetID = i2;
                    }
                }
            }
            done[targetID] = true;
            
            // Determine the balance left
            uint256 _normalizedBalance = tokenList[targetID].token.balanceOf(address(this)).mul(1e18).div(10**tokenList[targetID].decimals);
            if(_normalizedBalance <= _withdrawAmount){
                // Withdraw the entire balance of this token
                if(_normalizedBalance > 0){
                    _withdrawAmount = _withdrawAmount.sub(_normalizedBalance);
                    tokenList[targetID].token.safeTransfer(_receiver, tokenList[targetID].token.balanceOf(address(this)));                    
                }
            }else{
                // Withdraw a partial amount of this token
                if(_withdrawAmount > 0){
                    // Convert the withdraw amount to the token's decimal amount
                    uint256 _balance = _withdrawAmount.mul(10**tokenList[targetID].decimals).div(1e18);
                    _withdrawAmount = 0;
                    tokenList[targetID].token.safeTransfer(_receiver, _balance);
                }
                break; // Nothing more to withdraw
            }
        }
    }
    
    // Governance functions
    
    // Stop/start all deposits, no timelock required
    // --------------------
    function stopDeposits() external onlyGovernance {
        depositsOpen = false;
    }

    function startDeposits() external onlyGovernance {
        depositsOpen = true;
    }

    // A function used in case of strategy failure, possibly due to bug in the platform our strategy is using, governance can stop using it quick
    function emergencyStopStrategy() external onlyGovernance {
        depositsOpen = false;
        if(currentStrategy != StabilizeStrategy(address(0)) && totalSupply() > 0){
            currentStrategy.exit(); // Pulls all the tokens and accessory tokens from the strategy 
        }
        currentStrategy = StabilizeStrategy(address(0));
        _timelockType = 0; // Prevent governance from changing to new strategy without timelock
    }

    // --------------------
    
    // Timelock variables
    
    uint256 private _timelockStart; // The start of the timelock to change governance variables
    uint256 private _timelockType; // The function that needs to be changed
    uint256 constant _timelockDuration = 86400; // Timelock is 24 hours
    
    // Reusable timelock variables
    address private _timelock_address;
    
    modifier timelockConditionsMet(uint256 _type) {
        require(_timelockType == _type, "Timelock not acquired for this function");
        _timelockType = 0; // Reset the type once the timelock is used
        if(totalSupply() > 0){
            // Timelock is only required after tokens exist
            require(now >= _timelockStart + _timelockDuration, "Timelock time not met");
        }
        _;
    }
    
    // Change the owner of the token contract
    // --------------------
    function startGovernanceChange(address _address) external onlyGovernance {
        _timelockStart = now;
        _timelockType = 1;
        _timelock_address = _address;       
    }
    
    function finishGovernanceChange() external onlyGovernance timelockConditionsMet(1) {
        transferGovernance(_timelock_address);
    }
    // --------------------
    
    
    // Change the treasury address
    // --------------------
    function startChangeStrategy(address _address) external onlyGovernance {
        _timelockStart = now;
        _timelockType = 2;
        _timelock_address = _address;
        _pendingStrategy = _address;
        if(totalSupply() == 0){
            // Can change strategy with one call in this case
            finishChangeStrategy();
        }
    }
    
    function finishChangeStrategy() public onlyGovernance timelockConditionsMet(2) {
        if(currentStrategy != StabilizeStrategy(address(0)) && totalSupply() > 0){
            currentStrategy.exit(); // Pulls all the tokens and accessory tokens from the strategy 
        }
        currentStrategy = StabilizeStrategy(_timelock_address);
        if(currentStrategy != StabilizeStrategy(address(0)) && totalSupply() > 0){
            pushTokensToStrategy(); // It will push any strategy reward tokens here to the new strategy
            currentStrategy.enter(); // Puts all the tokens and accessory tokens into the new strategy 
        }
        _pendingStrategy = address(0);
    }
    
    function pushTokensToStrategy() internal {
        uint256 tokenCount = currentStrategy.rewardTokensCount();
        for(uint256 i = 0; i < tokenCount; i++){
            IERC20 _token = IERC20(address(currentStrategy.rewardTokenAddress(i)));
            uint256 _balance = _token.balanceOf(address(this));
            if(_balance > 0){
                _token.safeTransfer(address(currentStrategy), _balance);
            }
        }
    }
    // --------------------

}

{
  "compilationTarget": {
    "zsToken.sol": "zsToken"
  },
  "evmVersion": "istanbul",
  "libraries": {},
  "metadata": {
    "bytecodeHash": "ipfs"
  },
  "optimizer": {
    "enabled": true,
    "runs": 200
  },
  "remappings": []
}