// File: @openzeppelin\contracts\math\SafeMath.sol

// SPDX-License-Identifier: MIT
pragma solidity 0.6.12;

/**
 * @dev Wrappers over Solidity's arithmetic operations with added overflow
 * checks.
 *
 * Arithmetic operations in Solidity wrap on overflow. This can easily result
 * in bugs, because programmers usually assume that an overflow raises an
 * error, which is the standard behavior in high level programming languages.
 * `SafeMath` restores this intuition by reverting the transaction when an
 * operation overflows.
 *
 * Using this library instead of the unchecked operations eliminates an entire
 * class of bugs, so it's recommended to use it always.
 */
library SafeMath {
    /**
     * @dev Returns the addition of two unsigned integers, reverting on
     * overflow.
     *
     * Counterpart to Solidity's `+` operator.
     *
     * Requirements:
     *
     * - Addition cannot overflow.
     */
    function add(uint256 a, uint256 b) internal pure returns (uint256) {
        uint256 c = a + b;
        require(c >= a, "SafeMath: addition overflow");

        return c;
    }

    /**
     * @dev Returns the subtraction of two unsigned integers, reverting on
     * overflow (when the result is negative).
     *
     * Counterpart to Solidity's `-` operator.
     *
     * Requirements:
     *
     * - Subtraction cannot overflow.
     */
    function sub(uint256 a, uint256 b) internal pure returns (uint256) {
        return sub(a, b, "SafeMath: subtraction overflow");
    }

    /**
     * @dev Returns the subtraction of two unsigned integers, reverting with custom message on
     * overflow (when the result is negative).
     *
     * Counterpart to Solidity's `-` operator.
     *
     * Requirements:
     *
     * - Subtraction cannot overflow.
     */
    function sub(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b <= a, errorMessage);
        uint256 c = a - b;

        return c;
    }

    /**
     * @dev Returns the multiplication of two unsigned integers, reverting on
     * overflow.
     *
     * Counterpart to Solidity's `*` operator.
     *
     * Requirements:
     *
     * - Multiplication cannot overflow.
     */
    function mul(uint256 a, uint256 b) internal pure returns (uint256) {
        // Gas optimization: this is cheaper than requiring 'a' not being zero, but the
        // benefit is lost if 'b' is also tested.
        // See: https://github.com/OpenZeppelin/openzeppelin-contracts/pull/522
        if (a == 0) {
            return 0;
        }

        uint256 c = a * b;
        require(c / a == b, "SafeMath: multiplication overflow");

        return c;
    }

    /**
     * @dev Returns the integer division of two unsigned integers. Reverts on
     * division by zero. The result is rounded towards zero.
     *
     * Counterpart to Solidity's `/` operator. Note: this function uses a
     * `revert` opcode (which leaves remaining gas untouched) while Solidity
     * uses an invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function div(uint256 a, uint256 b) internal pure returns (uint256) {
        return div(a, b, "SafeMath: division by zero");
    }

    /**
     * @dev Returns the integer division of two unsigned integers. Reverts with custom message on
     * division by zero. The result is rounded towards zero.
     *
     * Counterpart to Solidity's `/` operator. Note: this function uses a
     * `revert` opcode (which leaves remaining gas untouched) while Solidity
     * uses an invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function div(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b > 0, errorMessage);
        uint256 c = a / b;
        // assert(a == b * c + a % b); // There is no case in which this doesn't hold

        return c;
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * Reverts when dividing by zero.
     *
     * Counterpart to Solidity's `%` operator. This function uses a `revert`
     * opcode (which leaves remaining gas untouched) while Solidity uses an
     * invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function mod(uint256 a, uint256 b) internal pure returns (uint256) {
        return mod(a, b, "SafeMath: modulo by zero");
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * Reverts with custom message when dividing by zero.
     *
     * Counterpart to Solidity's `%` operator. This function uses a `revert`
     * opcode (which leaves remaining gas untouched) while Solidity uses an
     * invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function mod(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b != 0, errorMessage);
        return a % b;
    }
}

// File: @openzeppelin\contracts\token\ERC20\IERC20.sol


/**
 * @dev Interface of the ERC20 standard as defined in the EIP.
 */
interface IERC20 {
    /**
     * @dev Returns the amount of tokens in existence.
     */
    function totalSupply() external view returns (uint256);

    /**
     * @dev Returns the amount of tokens owned by `account`.
     */
    function balanceOf(address account) external view returns (uint256);

    /**
     * @dev Moves `amount` tokens from the caller's account to `recipient`.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * Emits a {Transfer} event.
     */
    function transfer(address recipient, uint256 amount) external returns (bool);

    /**
     * @dev Returns the remaining number of tokens that `spender` will be
     * allowed to spend on behalf of `owner` through {transferFrom}. This is
     * zero by default.
     *
     * This value changes when {approve} or {transferFrom} are called.
     */
    function allowance(address owner, address spender) external view returns (uint256);

    /**
     * @dev Sets `amount` as the allowance of `spender` over the caller's tokens.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * IMPORTANT: Beware that changing an allowance with this method brings the risk
     * that someone may use both the old and the new allowance by unfortunate
     * transaction ordering. One possible solution to mitigate this race
     * condition is to first reduce the spender's allowance to 0 and set the
     * desired value afterwards:
     * https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729
     *
     * Emits an {Approval} event.
     */
    function approve(address spender, uint256 amount) external returns (bool);

    /**
     * @dev Moves `amount` tokens from `sender` to `recipient` using the
     * allowance mechanism. `amount` is then deducted from the caller's
     * allowance.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * Emits a {Transfer} event.
     */
    function transferFrom(address sender, address recipient, uint256 amount) external returns (bool);

    /**
     * @dev Emitted when `value` tokens are moved from one account (`from`) to
     * another (`to`).
     *
     * Note that `value` may be zero.
     */
    event Transfer(address indexed from, address indexed to, uint256 value);

    /**
     * @dev Emitted when the allowance of a `spender` for an `owner` is set by
     * a call to {approve}. `value` is the new allowance.
     */
    event Approval(address indexed owner, address indexed spender, uint256 value);
}




// File: node_modules\@openzeppelin\contracts\utils\Address.sol


/**
 * @dev Collection of functions related to the address type
 */
library Address {
    /**
     * @dev Returns true if `account` is a contract.
     *
     * [IMPORTANT]
     * ====
     * It is unsafe to assume that an address for which this function returns
     * false is an externally-owned account (EOA) and not a contract.
     *
     * Among others, `isContract` will return false for the following
     * types of addresses:
     *
     *  - an externally-owned account
     *  - a contract in construction
     *  - an address where a contract will be created
     *  - an address where a contract lived, but was destroyed
     * ====
     */
    function isContract(address account) internal view returns (bool) {
        // This method relies in 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");
        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\SafeERC20.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: node_modules\@openzeppelin\contracts\GSN\Context.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 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\utils\Pausable.sol



/**
 * @dev Contract module which allows children to implement an emergency stop
 * mechanism that can be triggered by an authorized account.
 *
 * This module is used through inheritance. It will make available the
 * modifiers `whenNotPaused` and `whenPaused`, which can be applied to
 * the functions of your contract. Note that they will not be pausable by
 * simply including this module, only once the modifiers are put in place.
 */
contract Pausable is Context {
    /**
     * @dev Emitted when the pause is triggered by `account`.
     */
    event Paused(address account);

    /**
     * @dev Emitted when the pause is lifted by `account`.
     */
    event Unpaused(address account);

    bool private _paused;

    /**
     * @dev Initializes the contract in unpaused state.
     */
    constructor () internal {
        _paused = false;
    }

    /**
     * @dev Returns true if the contract is paused, and false otherwise.
     */
    function paused() public view returns (bool) {
        return _paused;
    }

    /**
     * @dev Modifier to make a function callable only when the contract is not paused.
     *
     * Requirements:
     *
     * - The contract must not be paused.
     */
    modifier whenNotPaused() {
        require(!_paused, "Pausable: paused");
        _;
    }

    /**
     * @dev Modifier to make a function callable only when the contract is paused.
     *
     * Requirements:
     *
     * - The contract must be paused.
     */
    modifier whenPaused() {
        require(_paused, "Pausable: not paused");
        _;
    }

    /**
     * @dev Triggers stopped state.
     *
     * Requirements:
     *
     * - The contract must not be paused.
     */
    function _pause() internal virtual whenNotPaused {
        _paused = true;
        emit Paused(_msgSender());
    }

    /**
     * @dev Returns to normal state.
     *
     * Requirements:
     *
     * - The contract must be paused.
     */
    function _unpause() internal virtual whenPaused {
        _paused = false;
        emit Unpaused(_msgSender());
    }
}

// File: @openzeppelin\contracts\utils\ReentrancyGuard.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].
 */
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: @openzeppelin\contracts\access\Ownable.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.
 */
contract Ownable is Context {
    address private _owner;

    event OwnershipTransferred(address indexed previousOwner, address indexed newOwner);

    /**
     * @dev Initializes the contract setting the deployer as the initial owner.
     */
    constructor () internal {
        address msgSender = _msgSender();
        _owner = msgSender;
        emit OwnershipTransferred(address(0), msgSender);
    }

    /**
     * @dev Returns the address of the current owner.
     */
    function owner() public view 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;
    }
    
    /**
     * @dev Internal function that forces an ownership change. Can be used to
     * implement custom ownership management logic in childs contracts.
     */
    function _setOwner(address newOwner) internal virtual {
        emit OwnershipTransferred(_owner, newOwner);
        _owner = newOwner;
    }
}

// File: @openzeppelin\contracts\proxy\Initializable.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) {
        // extcodesize checks the size of the code stored in an address, and
        // address returns the current address. Since the code is still not
        // deployed when running a constructor, any checks on its code size will
        // yield zero, making it an effective way to detect if a contract is
        // under construction or not.
        address self = address(this);
        uint256 cs;
        // solhint-disable-next-line no-inline-assembly
        assembly { cs := extcodesize(self) }
        return cs == 0;
    }
}



// File: node_modules\@openzeppelin\contracts\proxy\Proxy.sol


/**
 * @dev This abstract contract provides a fallback function that delegates all calls to another contract using the EVM
 * instruction `delegatecall`. We refer to the second contract as the _implementation_ behind the proxy, and it has to
 * be specified by overriding the virtual {_implementation} function.
 * 
 * Additionally, delegation to the implementation can be triggered manually through the {_fallback} function, or to a
 * different contract through the {_delegate} function.
 * 
 * The success and return data of the delegated call will be returned back to the caller of the proxy.
 */
abstract contract Proxy {
    /**
     * @dev Delegates the current call to `implementation`.
     * 
     * This function does not return to its internall call site, it will return directly to the external caller.
     */
    function _delegate(address implementation) internal {
        // solhint-disable-next-line no-inline-assembly
        assembly {
            // Copy msg.data. We take full control of memory in this inline assembly
            // block because it will not return to Solidity code. We overwrite the
            // Solidity scratch pad at memory position 0.
            calldatacopy(0, 0, calldatasize())

            // Call the implementation.
            // out and outsize are 0 because we don't know the size yet.
            let result := delegatecall(gas(), implementation, 0, calldatasize(), 0, 0)

            // Copy the returned data.
            returndatacopy(0, 0, returndatasize())

            switch result
            // delegatecall returns 0 on error.
            case 0 { revert(0, returndatasize()) }
            default { return(0, returndatasize()) }
        }
    }

    /**
     * @dev This is a virtual function that should be overriden so it returns the address to which the fallback function
     * and {_fallback} should delegate.
     */
    function _implementation() internal virtual view returns (address);

    /**
     * @dev Delegates the current call to the address returned by `_implementation()`.
     * 
     * This function does not return to its internall call site, it will return directly to the external caller.
     */
    function _fallback() internal {
        _beforeFallback();
        _delegate(_implementation());
    }

    /**
     * @dev Fallback function that delegates calls to the address returned by `_implementation()`. Will run if no other
     * function in the contract matches the call data.
     */
    fallback () payable external {
        _fallback();
    }

    /**
     * @dev Fallback function that delegates calls to the address returned by `_implementation()`. Will run if call data
     * is empty.
     */
    receive () payable external {
        _fallback();
    }

    /**
     * @dev Hook that is called before falling back to the implementation. Can happen as part of a manual `_fallback`
     * call, or as part of the Solidity `fallback` or `receive` functions.
     * 
     * If overriden should call `super._beforeFallback()`.
     */
    function _beforeFallback() internal virtual {
    }
}

// File: node_modules\@openzeppelin\contracts\proxy\UpgradeableProxy.sol




/**
 * @dev This contract implements an upgradeable proxy. It is upgradeable because calls are delegated to an
 * implementation address that can be changed. This address is stored in storage in the location specified by
 * https://eips.ethereum.org/EIPS/eip-1967[EIP1967], so that it doesn't conflict with the storage layout of the
 * implementation behind the proxy.
 * 
 * Upgradeability is only provided internally through {_upgradeTo}. For an externally upgradeable proxy see
 * {TransparentUpgradeableProxy}.
 */
contract UpgradeableProxy is Proxy {
    /**
     * @dev Initializes the upgradeable proxy with an initial implementation specified by `_logic`.
     * 
     * If `_data` is nonempty, it's used as data in a delegate call to `_logic`. This will typically be an encoded
     * function call, and allows initializating the storage of the proxy like a Solidity constructor.
     */
    constructor(address _logic, bytes memory _data) public payable {
        assert(_IMPLEMENTATION_SLOT == bytes32(uint256(keccak256("eip1967.proxy.implementation")) - 1));
        _setImplementation(_logic);
        if(_data.length > 0) {
            // solhint-disable-next-line avoid-low-level-calls
            (bool success,) = _logic.delegatecall(_data);
            require(success);
        }
    }

    /**
     * @dev Emitted when the implementation is upgraded.
     */
    event Upgraded(address indexed implementation);

    /**
     * @dev Storage slot with the address of the current implementation.
     * This is the keccak-256 hash of "eip1967.proxy.implementation" subtracted by 1, and is
     * validated in the constructor.
     */
    bytes32 private constant _IMPLEMENTATION_SLOT = 0x360894a13ba1a3210667c828492db98dca3e2076cc3735a920a3ca505d382bbc;

    /**
     * @dev Returns the current implementation address.
     */
    function _implementation() internal override view returns (address impl) {
        bytes32 slot = _IMPLEMENTATION_SLOT;
        // solhint-disable-next-line no-inline-assembly
        assembly {
            impl := sload(slot)
        }
    }

    /**
     * @dev Upgrades the proxy to a new implementation.
     * 
     * Emits an {Upgraded} event.
     */
    function _upgradeTo(address newImplementation) internal {
        _setImplementation(newImplementation);
        emit Upgraded(newImplementation);
    }

    /**
     * @dev Stores a new address in the EIP1967 implementation slot.
     */
    function _setImplementation(address newImplementation) private {
        require(Address.isContract(newImplementation), "UpgradeableProxy: new implementation is not a contract");

        bytes32 slot = _IMPLEMENTATION_SLOT;

        // solhint-disable-next-line no-inline-assembly
        assembly {
            sstore(slot, newImplementation)
        }
    }
}

// File: node_modules\@openzeppelin\contracts\proxy\TransparentUpgradeableProxy.sol



/**
 * @dev This contract implements a proxy that is upgradeable by an admin.
 * 
 * To avoid https://medium.com/nomic-labs-blog/malicious-backdoors-in-ethereum-proxies-62629adf3357[proxy selector
 * clashing], which can potentially be used in an attack, this contract uses the
 * https://blog.openzeppelin.com/the-transparent-proxy-pattern/[transparent proxy pattern]. This pattern implies two
 * things that go hand in hand:
 * 
 * 1. If any account other than the admin calls the proxy, the call will be forwarded to the implementation, even if
 * that call matches one of the admin functions exposed by the proxy itself.
 * 2. If the admin calls the proxy, it can access the admin functions, but its calls will never be forwarded to the
 * implementation. If the admin tries to call a function on the implementation it will fail with an error that says
 * "admin cannot fallback to proxy target".
 * 
 * These properties mean that the admin account can only be used for admin actions like upgrading the proxy or changing
 * the admin, so it's best if it's a dedicated account that is not used for anything else. This will avoid headaches due
 * to sudden errors when trying to call a function from the proxy implementation.
 * 
 * Our recommendation is for the dedicated account to be an instance of the {ProxyAdmin} contract. If set up this way,
 * you should think of the `ProxyAdmin` instance as the real administrative inerface of your proxy.
 */
contract TransparentUpgradeableProxy is UpgradeableProxy {
    /**
     * @dev Initializes an upgradeable proxy managed by `_admin`, backed by the implementation at `_logic`, and
     * optionally initialized with `_data` as explained in {UpgradeableProxy-constructor}.
     */
    constructor(address _logic, address _admin, bytes memory _data) public payable UpgradeableProxy(_logic, _data) {
        assert(_ADMIN_SLOT == bytes32(uint256(keccak256("eip1967.proxy.admin")) - 1));
        _setAdmin(_admin);
    }

    /**
     * @dev Emitted when the admin account has changed.
     */
    event AdminChanged(address previousAdmin, address newAdmin);

    /**
     * @dev Storage slot with the admin of the contract.
     * This is the keccak-256 hash of "eip1967.proxy.admin" subtracted by 1, and is
     * validated in the constructor.
     */
    bytes32 private constant _ADMIN_SLOT = 0xb53127684a568b3173ae13b9f8a6016e243e63b6e8ee1178d6a717850b5d6103;

    /**
     * @dev Modifier used internally that will delegate the call to the implementation unless the sender is the admin.
     */
    modifier ifAdmin() {
        if (msg.sender == _admin()) {
            _;
        } else {
            _fallback();
        }
    }

    /**
     * @dev Returns the current admin.
     * 
     * NOTE: Only the admin can call this function. See {ProxyAdmin-getProxyAdmin}.
     * 
     * TIP: To get this value clients can read directly from the storage slot shown below (specified by EIP1967) using the
     * https://eth.wiki/json-rpc/API#eth_getstorageat[`eth_getStorageAt`] RPC call.
     * `0xb53127684a568b3173ae13b9f8a6016e243e63b6e8ee1178d6a717850b5d6103`
     */
    function admin() external ifAdmin returns (address) {
        return _admin();
    }

    /**
     * @dev Returns the current implementation.
     * 
     * NOTE: Only the admin can call this function. See {ProxyAdmin-getProxyImplementation}.
     * 
     * TIP: To get this value clients can read directly from the storage slot shown below (specified by EIP1967) using the
     * https://eth.wiki/json-rpc/API#eth_getstorageat[`eth_getStorageAt`] RPC call.
     * `0x360894a13ba1a3210667c828492db98dca3e2076cc3735a920a3ca505d382bbc`
     */
    function implementation() external ifAdmin returns (address) {
        return _implementation();
    }

    /**
     * @dev Changes the admin of the proxy.
     * 
     * Emits an {AdminChanged} event.
     * 
     * NOTE: Only the admin can call this function. See {ProxyAdmin-changeProxyAdmin}.
     */
    function changeAdmin(address newAdmin) external ifAdmin {
        require(newAdmin != address(0), "TransparentUpgradeableProxy: new admin is the zero address");
        emit AdminChanged(_admin(), newAdmin);
        _setAdmin(newAdmin);
    }

    /**
     * @dev Upgrade the implementation of the proxy.
     * 
     * NOTE: Only the admin can call this function. See {ProxyAdmin-upgrade}.
     */
    function upgradeTo(address newImplementation) external ifAdmin {
        _upgradeTo(newImplementation);
    }

    /**
     * @dev Upgrade the implementation of the proxy, and then call a function from the new implementation as specified
     * by `data`, which should be an encoded function call. This is useful to initialize new storage variables in the
     * proxied contract.
     * 
     * NOTE: Only the admin can call this function. See {ProxyAdmin-upgradeAndCall}.
     */
    function upgradeToAndCall(address newImplementation, bytes calldata data) external payable ifAdmin {
        _upgradeTo(newImplementation);
        // solhint-disable-next-line avoid-low-level-calls
        (bool success,) = newImplementation.delegatecall(data);
        require(success);
    }

    /**
     * @dev Returns the current admin.
     */
    function _admin() internal view returns (address adm) {
        bytes32 slot = _ADMIN_SLOT;
        // solhint-disable-next-line no-inline-assembly
        assembly {
            adm := sload(slot)
        }
    }

    /**
     * @dev Stores a new address in the EIP1967 admin slot.
     */
    function _setAdmin(address newAdmin) private {
        bytes32 slot = _ADMIN_SLOT;

        // solhint-disable-next-line no-inline-assembly
        assembly {
            sstore(slot, newAdmin)
        }
    }

    /**
     * @dev Makes sure the admin cannot access the fallback function. See {Proxy-_beforeFallback}.
     */
    function _beforeFallback() internal override virtual {
        require(msg.sender != _admin(), "TransparentUpgradeableProxy: admin cannot fallback to proxy target");
        super._beforeFallback();
    }
}

// File: @openzeppelin\contracts\proxy\ProxyAdmin.sol




/**
 * @dev This is an auxiliary contract meant to be assigned as the admin of a {TransparentUpgradeableProxy}. For an
 * explanation of why you would want to use this see the documentation for {TransparentUpgradeableProxy}.
 */
contract ProxyAdmin is Ownable {

    /**
     * @dev Returns the current implementation of `proxy`.
     * 
     * Requirements:
     * 
     * - This contract must be the admin of `proxy`.
     */
    function getProxyImplementation(TransparentUpgradeableProxy proxy) public view returns (address) {
        // We need to manually run the static call since the getter cannot be flagged as view
        // bytes4(keccak256("implementation()")) == 0x5c60da1b
        (bool success, bytes memory returndata) = address(proxy).staticcall(hex"5c60da1b");
        require(success);
        return abi.decode(returndata, (address));
    }

    /**
     * @dev Returns the current admin of `proxy`.
     * 
     * Requirements:
     * 
     * - This contract must be the admin of `proxy`.
     */
    function getProxyAdmin(TransparentUpgradeableProxy proxy) public view returns (address) {
        // We need to manually run the static call since the getter cannot be flagged as view
        // bytes4(keccak256("admin()")) == 0xf851a440
        (bool success, bytes memory returndata) = address(proxy).staticcall(hex"f851a440");
        require(success);
        return abi.decode(returndata, (address));
    }

    /**
     * @dev Changes the admin of `proxy` to `newAdmin`.
     * 
     * Requirements:
     * 
     * - This contract must be the current admin of `proxy`.
     */
    function changeProxyAdmin(TransparentUpgradeableProxy proxy, address newAdmin) public onlyOwner {
        proxy.changeAdmin(newAdmin);
    }

    /**
     * @dev Upgrades `proxy` to `implementation`. See {TransparentUpgradeableProxy-upgradeTo}.
     * 
     * Requirements:
     * 
     * - This contract must be the admin of `proxy`.
     */
    function upgrade(TransparentUpgradeableProxy proxy, address implementation) public onlyOwner {
        proxy.upgradeTo(implementation);
    }

    /**
     * @dev Upgrades `proxy` to `implementation` and calls a function on the new implementation. See
     * {TransparentUpgradeableProxy-upgradeToAndCall}.
     * 
     * Requirements:
     * 
     * - This contract must be the admin of `proxy`.
     */
    function upgradeAndCall(TransparentUpgradeableProxy proxy, address implementation, bytes memory data) public payable onlyOwner {
        proxy.upgradeToAndCall{value: msg.value}(implementation, data);
    }
}

// File: @openzeppelin\contracts\token\ERC20\ERC20.sol






/**
 * @dev Implementation of the {IERC20} interface.
 *
 * This implementation is agnostic to the way tokens are created. This means
 * that a supply mechanism has to be added in a derived contract using {_mint}.
 * For a generic mechanism see {ERC20PresetMinterPauser}.
 *
 * TIP: For a detailed writeup see our guide
 * https://forum.zeppelin.solutions/t/how-to-implement-erc20-supply-mechanisms/226[How
 * to implement supply mechanisms].
 *
 * We have followed general OpenZeppelin guidelines: functions revert instead
 * of returning `false` on failure. This behavior is nonetheless conventional
 * and does not conflict with the expectations of ERC20 applications.
 *
 * Additionally, an {Approval} event is emitted on calls to {transferFrom}.
 * This allows applications to reconstruct the allowance for all accounts just
 * by listening to said events. Other implementations of the EIP may not emit
 * these events, as it isn't required by the specification.
 *
 * Finally, the non-standard {decreaseAllowance} and {increaseAllowance}
 * functions have been added to mitigate the well-known issues around setting
 * allowances. See {IERC20-approve}.
 */
contract ERC20 is Context, IERC20 {
    using SafeMath for uint256;
    using Address for address;

    mapping (address => uint256) private _balances;

    mapping (address => mapping (address => uint256)) private _allowances;

    uint256 private _totalSupply;

    string private _name;
    string private _symbol;
    uint8 private _decimals;

    /**
     * @dev Sets the values for {name} and {symbol}, initializes {decimals} with
     * a default value of 18.
     *
     * To select a different value for {decimals}, use {_setupDecimals}.
     *
     * All three of these values are immutable: they can only be set once during
     * construction.
     */
    constructor (string memory name, string memory symbol) public {
        _name = name;
        _symbol = symbol;
        _decimals = 18;
    }

    /**
     * @dev Returns the name of the token.
     */
    function name() public view returns (string memory) {
        return _name;
    }

    /**
     * @dev Returns the symbol of the token, usually a shorter version of the
     * name.
     */
    function symbol() public view returns (string memory) {
        return _symbol;
    }

    /**
     * @dev Returns the number of decimals used to get its user representation.
     * For example, if `decimals` equals `2`, a balance of `505` tokens should
     * be displayed to a user as `5,05` (`505 / 10 ** 2`).
     *
     * Tokens usually opt for a value of 18, imitating the relationship between
     * Ether and Wei. This is the value {ERC20} uses, unless {_setupDecimals} is
     * called.
     *
     * NOTE: This information is only used for _display_ purposes: it in
     * no way affects any of the arithmetic of the contract, including
     * {IERC20-balanceOf} and {IERC20-transfer}.
     */
    function decimals() public view returns (uint8) {
        return _decimals;
    }

    /**
     * @dev See {IERC20-totalSupply}.
     */
    function totalSupply() public view override returns (uint256) {
        return _totalSupply;
    }

    /**
     * @dev See {IERC20-balanceOf}.
     */
    function balanceOf(address account) public view override returns (uint256) {
        return _balances[account];
    }

    /**
     * @dev See {IERC20-transfer}.
     *
     * Requirements:
     *
     * - `recipient` cannot be the zero address.
     * - the caller must have a balance of at least `amount`.
     */
    function transfer(address recipient, uint256 amount) public virtual override returns (bool) {
        _transfer(_msgSender(), recipient, amount);
        return true;
    }

    /**
     * @dev See {IERC20-allowance}.
     */
    function allowance(address owner, address spender) public view virtual override returns (uint256) {
        return _allowances[owner][spender];
    }

    /**
     * @dev See {IERC20-approve}.
     *
     * Requirements:
     *
     * - `spender` cannot be the zero address.
     */
    function approve(address spender, uint256 amount) public virtual override returns (bool) {
        _approve(_msgSender(), spender, amount);
        return true;
    }

    /**
     * @dev See {IERC20-transferFrom}.
     *
     * Emits an {Approval} event indicating the updated allowance. This is not
     * required by the EIP. See the note at the beginning of {ERC20};
     *
     * Requirements:
     * - `sender` and `recipient` cannot be the zero address.
     * - `sender` must have a balance of at least `amount`.
     * - the caller must have allowance for ``sender``'s tokens of at least
     * `amount`.
     */
    function transferFrom(address sender, address recipient, uint256 amount) public virtual override returns (bool) {
        _transfer(sender, recipient, amount);
        _approve(sender, _msgSender(), _allowances[sender][_msgSender()].sub(amount, "ERC20: transfer amount exceeds allowance"));
        return true;
    }

    /**
     * @dev Atomically increases the allowance granted to `spender` by the caller.
     *
     * This is an alternative to {approve} that can be used as a mitigation for
     * problems described in {IERC20-approve}.
     *
     * Emits an {Approval} event indicating the updated allowance.
     *
     * Requirements:
     *
     * - `spender` cannot be the zero address.
     */
    function increaseAllowance(address spender, uint256 addedValue) public virtual returns (bool) {
        _approve(_msgSender(), spender, _allowances[_msgSender()][spender].add(addedValue));
        return true;
    }

    /**
     * @dev Atomically decreases the allowance granted to `spender` by the caller.
     *
     * This is an alternative to {approve} that can be used as a mitigation for
     * problems described in {IERC20-approve}.
     *
     * Emits an {Approval} event indicating the updated allowance.
     *
     * Requirements:
     *
     * - `spender` cannot be the zero address.
     * - `spender` must have allowance for the caller of at least
     * `subtractedValue`.
     */
    function decreaseAllowance(address spender, uint256 subtractedValue) public virtual returns (bool) {
        _approve(_msgSender(), spender, _allowances[_msgSender()][spender].sub(subtractedValue, "ERC20: decreased allowance below zero"));
        return true;
    }

    /**
     * @dev Moves tokens `amount` from `sender` to `recipient`.
     *
     * This is internal function is equivalent to {transfer}, and can be used to
     * e.g. implement automatic token fees, slashing mechanisms, etc.
     *
     * Emits a {Transfer} event.
     *
     * Requirements:
     *
     * - `sender` cannot be the zero address.
     * - `recipient` cannot be the zero address.
     * - `sender` must have a balance of at least `amount`.
     */
    function _transfer(address sender, address recipient, uint256 amount) internal virtual {
        require(sender != address(0), "ERC20: transfer from the zero address");
        require(recipient != address(0), "ERC20: transfer to the zero address");

        _beforeTokenTransfer(sender, recipient, amount);

        _balances[sender] = _balances[sender].sub(amount, "ERC20: transfer amount exceeds balance");
        _balances[recipient] = _balances[recipient].add(amount);
        emit Transfer(sender, recipient, amount);
    }

    /** @dev Creates `amount` tokens and assigns them to `account`, increasing
     * the total supply.
     *
     * Emits a {Transfer} event with `from` set to the zero address.
     *
     * Requirements
     *
     * - `to` cannot be the zero address.
     */
    function _mint(address account, uint256 amount) internal virtual {
        require(account != address(0), "ERC20: mint to the zero address");

        _beforeTokenTransfer(address(0), account, amount);

        _totalSupply = _totalSupply.add(amount);
        _balances[account] = _balances[account].add(amount);
        emit Transfer(address(0), account, amount);
    }

    /**
     * @dev Destroys `amount` tokens from `account`, reducing the
     * total supply.
     *
     * Emits a {Transfer} event with `to` set to the zero address.
     *
     * Requirements
     *
     * - `account` cannot be the zero address.
     * - `account` must have at least `amount` tokens.
     */
    function _burn(address account, uint256 amount) internal virtual {
        require(account != address(0), "ERC20: burn from the zero address");

        _beforeTokenTransfer(account, address(0), amount);

        _balances[account] = _balances[account].sub(amount, "ERC20: burn amount exceeds balance");
        _totalSupply = _totalSupply.sub(amount);
        emit Transfer(account, address(0), amount);
    }

    /**
     * @dev Sets `amount` as the allowance of `spender` over the `owner` s tokens.
     *
     * This internal function is equivalent to `approve`, and can be used to
     * e.g. set automatic allowances for certain subsystems, etc.
     *
     * Emits an {Approval} event.
     *
     * Requirements:
     *
     * - `owner` cannot be the zero address.
     * - `spender` cannot be the zero address.
     */
    function _approve(address owner, address spender, uint256 amount) internal virtual {
        require(owner != address(0), "ERC20: approve from the zero address");
        require(spender != address(0), "ERC20: approve to the zero address");

        _allowances[owner][spender] = amount;
        emit Approval(owner, spender, amount);
    }

    /**
     * @dev Sets {decimals} to a value other than the default one of 18.
     *
     * WARNING: This function should only be called from the constructor. Most
     * applications that interact with token contracts will not expect
     * {decimals} to ever change, and may work incorrectly if it does.
     */
    function _setupDecimals(uint8 decimals_) internal {
        _decimals = decimals_;
    }

    /**
     * @dev Hook that is called before any transfer of tokens. This includes
     * minting and burning.
     *
     * Calling conditions:
     *
     * - when `from` and `to` are both non-zero, `amount` of ``from``'s tokens
     * will be to transferred to `to`.
     * - when `from` is zero, `amount` tokens will be minted for `to`.
     * - when `to` is zero, `amount` of ``from``'s tokens will be burned.
     * - `from` and `to` are never both zero.
     *
     * To learn more about hooks, head to xref:ROOT:extending-contracts.adoc#using-hooks[Using Hooks].
     */
    function _beforeTokenTransfer(address from, address to, uint256 amount) internal virtual { }
}

// File: contracts\SeeleToken.sol



contract SeeleERC20 is ERC20 {
    uint256 MAX_UINT = 2**256 - 1;

    constructor(
        address bridgeAddress_,
        string memory name_,
        string memory symbol_,
        uint8 decimals_
    ) public ERC20(name_, symbol_) {
        _setupDecimals(decimals_);
        _mint(bridgeAddress_, MAX_UINT);
    }
}

// File: contracts\SeeleBridge.sol





pragma experimental ABIEncoderV2;

// This is being used purely to avoid stack too deep errors
struct LogicCallArgs {
    // Transfers out to the logic contract
    uint256[] transferAmounts;
    address[] transferTokenContracts;
    // The fees (transferred to msg.sender)
    uint256[] feeAmounts;
    address[] feeTokenContracts;
    // The arbitrary logic call
    address logicContractAddress;
    bytes payload;
    // Invalidation metadata
    uint256 timeOut;
    bytes32 invalidationId;
    uint256 invalidationNonce;
}

contract SeeleBridge is Initializable, Pausable, Ownable, ReentrancyGuard {
    using SafeMath for uint256;
    using SafeERC20 for IERC20;

    // These are updated often
    bytes32 public state_lastValsetCheckpoint;
    mapping(address => uint256) public state_lastBatchNonces;
    mapping(bytes32 => uint256) public state_invalidationMapping;
    uint256 public state_lastValsetNonce = 0;
    // event nonce zero is reserved by the bridge module as a special
    // value indicating that no events have yet been submitted
    uint256 public state_lastEventNonce = 1;

    // These are set once at initialization
    bytes32 public state_bridgeId;
    uint256 public state_powerThreshold;

    /*
     * @notice mapping to keep track of whitelisted tokens
     */
    mapping(address => bool) private _ethereumTokenWhiteList;

    event WhiteListUpdateEvent(address _token, bool _value);
    // TransactionBatchExecutedEvent and SendToSeeleEvent both include the field _eventNonce.
    // This is incremented every time one of these events is emitted. It is checked by the
    // bridge module to ensure that all events are received in order, and that none are lost.
    //
    // ValsetUpdatedEvent does not include the field _eventNonce because it is never submitted to the Bridge
    // module. It is purely for the use of relayers to allow them to successfully submit batches.
    event TransactionBatchExecutedEvent(
        uint256 indexed _batchNonce,
        address indexed _token,
        uint256 _eventNonce
    );
    event SendToSeeleEvent(
        address indexed _tokenContract,
        address indexed _sender,
        address indexed _destination,
        uint256 _amount,
        uint256 _eventNonce
    );
    event ERC20DeployedEvent(
        // FYI: Can't index on a string without doing a bunch of weird stuff
        string _seeleDenom,
        address indexed _tokenContract,
        string _name,
        string _symbol,
        uint8 _decimals,
        uint256 _eventNonce
    );
    event ValsetUpdatedEvent(
        uint256 indexed _newValsetNonce,
        uint256 _eventNonce,
        address[] _validators,
        uint256[] _powers
    );
    event LogicCallEvent(
        bytes32 _invalidationId,
        uint256 _invalidationNonce,
        bytes _returnData,
        uint256 _eventNonce
    );

    function initialize() external initializer {
        _setOwner(msg.sender);
    }
    
    function initialize(
        // A unique identifier for this bridge instance to use in signatures
        bytes32 _bridgeId,
        // How much voting power is needed to approve operations
        uint256 _powerThreshold,
        // The validator set, not in valset args format since many of it's
        // arguments would never be used in this case
        address[] calldata _validators,
        uint256[] memory _powers
    ) external onlyOwner {
        // CHECKS

        // Check that validators, powers, and signatures (v,r,s) set is well-formed
        require(
            _validators.length == _powers.length,
            "Malformed current validator set"
        );

        // Check cumulative power to ensure the contract has sufficient power to actually
        // pass a vote
        uint256 cumulativePower = 0;
        for (uint256 i = 0; i < _powers.length; i++) {
            cumulativePower = cumulativePower + _powers[i];
            if (cumulativePower > _powerThreshold) {
                break;
            }
        }

        require(
            cumulativePower > _powerThreshold,
            "Submitted validator set signatures do not have enough power."
        );

        bytes32 newCheckpoint = makeCheckpoint(
            _validators,
            _powers,
            0,
            _bridgeId
        );

        // ACTIONS

        state_bridgeId = _bridgeId;
        state_powerThreshold = _powerThreshold;
        state_lastValsetCheckpoint = newCheckpoint;
        //_ethereumTokenWhiteList[address(0)] = true;
        // LOGS

        emit ValsetUpdatedEvent(
            state_lastValsetNonce,
            state_lastEventNonce,
            _validators,
            _powers
        );
    }

    function lastBatchNonce(address _erc20Address)
        public
        view
        returns (uint256)
    {
        return state_lastBatchNonces[_erc20Address];
    }

    function lastLogicCallNonce(bytes32 _invalidation_id)
        public
        view
        returns (uint256)
    {
        return state_invalidationMapping[_invalidation_id];
    }

    // Utility function to verify geth style signatures
    function verifySig(
        address _signer,
        bytes32 _theHash,
        uint8 _v,
        bytes32 _r,
        bytes32 _s
    ) private pure returns (bool) {
        bytes32 messageDigest = keccak256(
            abi.encodePacked("\x19Ethereum Signed Message:\n32", _theHash)
        );
        return _signer == ecrecover(messageDigest, _v, _r, _s);
    }

    // Make a new checkpoint from the supplied validator set
    // A checkpoint is a hash of all relevant information about the valset. This is stored by the contract,
    // instead of storing the information directly. This saves on storage and gas.
    // The format of the checkpoint is:
    // h(gravityId, "checkpoint", valsetNonce, validators[], powers[])
    // Where h is the keccak256 hash function.
    // The validator powers must be decreasing or equal. This is important for checking the signatures on the
    // next valset, since it allows the caller to stop verifying signatures once a quorum of signatures have been verified.
    function makeCheckpoint(
        address[] memory _validators,
        uint256[] memory _powers,
        uint256 _valsetNonce,
        bytes32 _gravityId
    ) private pure returns (bytes32) {
        // bytes32 encoding of the string "checkpoint"
        bytes32 methodName = 0x636865636b706f696e7400000000000000000000000000000000000000000000;

        bytes32 checkpoint = keccak256(
            abi.encode(
                _gravityId,
                methodName,
                _valsetNonce,
                _validators,
                _powers
            )
        );

        return checkpoint;
    }

    function checkValidatorSignatures(
        // The current validator set and their powers
        address[] memory _currentValidators,
        uint256[] memory _currentPowers,
        // The current validator's signatures
        uint8[] memory _v,
        bytes32[] memory _r,
        bytes32[] memory _s,
        // This is what we are checking they have signed
        bytes32 _theHash,
        uint256 _powerThreshold
    ) private pure {
        uint256 cumulativePower = 0;

        for (uint256 i = 0; i < _currentValidators.length; i++) {
            // If v is set to 0, this signifies that it was not possible to get a signature from this validator and we skip evaluation
            // (In a valid signature, it is either 27 or 28)
            if (_v[i] != 0) {
                // Check that the current validator has signed off on the hash
                require(
                    verifySig(
                        _currentValidators[i],
                        _theHash,
                        _v[i],
                        _r[i],
                        _s[i]
                    ),
                    "Validator signature does not match."
                );

                // Sum up cumulative power
                cumulativePower = cumulativePower + _currentPowers[i];

                // Break early to avoid wasting gas
                if (cumulativePower > _powerThreshold) {
                    break;
                }
            }
        }

        // Check that there was enough power
        require(
            cumulativePower > _powerThreshold,
            "Submitted validator set signatures do not have enough power."
        );
        // Success
    }

    // This updates the valset by checking that the validators in the current valset have signed off on the
    // new valset. The signatures supplied are the signatures of the current valset over the checkpoint hash
    // generated from the new valset.
    // Anyone can call this function, but they must supply valid signatures of state_powerThreshold of the current valset over
    // the new valset.
    function updateValset(
        // The new version of the validator set
        address[] memory _newValidators,
        uint256[] memory _newPowers,
        uint256 _newValsetNonce,
        // The current validators that approve the change
        address[] memory _currentValidators,
        uint256[] memory _currentPowers,
        uint256 _currentValsetNonce,
        // These are arrays of the parts of the current validator's signatures
        uint8[] memory _v,
        bytes32[] memory _r,
        bytes32[] memory _s
    ) external whenNotPaused nonReentrant {
        // CHECKS

        // Check that the valset nonce is greater than the old one
        require(
            _newValsetNonce > _currentValsetNonce,
            "New valset nonce must be greater than the current nonce"
        );

        // Check that new validators and powers set is well-formed
        require(
            _newValidators.length == _newPowers.length,
            "Malformed new validator set"
        );

        // Check that current validators, powers, and signatures (v,r,s) set is well-formed
        require(
            _currentValidators.length == _currentPowers.length &&
                _currentValidators.length == _v.length &&
                _currentValidators.length == _r.length &&
                _currentValidators.length == _s.length,
            "Malformed current validator set"
        );

        // Check that the supplied current validator set matches the saved checkpoint
        require(
            makeCheckpoint(
                _currentValidators,
                _currentPowers,
                _currentValsetNonce,
                state_bridgeId
            ) == state_lastValsetCheckpoint,
            "Supplied current validators and powers do not match checkpoint."
        );

        // Check that enough current validators have signed off on the new validator set
        bytes32 newCheckpoint = makeCheckpoint(
            _newValidators,
            _newPowers,
            _newValsetNonce,
            state_bridgeId
        );

        checkValidatorSignatures(
            _currentValidators,
            _currentPowers,
            _v,
            _r,
            _s,
            newCheckpoint,
            state_powerThreshold
        );

        // ACTIONS

        // Stored to be used next time to validate that the valset
        // supplied by the caller is correct.
        state_lastValsetCheckpoint = newCheckpoint;

        // Store new nonce
        state_lastValsetNonce = _newValsetNonce;

        // LOGS
        state_lastEventNonce = state_lastEventNonce.add(1);
        emit ValsetUpdatedEvent(
            _newValsetNonce,
            state_lastEventNonce,
            _newValidators,
            _newPowers
        );
    }

    // submitBatch processes a batch of Seele -> Ethereum transactions by sending the tokens in the transactions
    // to the destination addresses. It is approved by the current Seele validator set.
    // Anyone can call this function, but they must supply valid signatures of state_powerThreshold of the current valset over
    // the batch.
    function submitBatch(
        // The validators that approve the batch
        address[] memory _currentValidators,
        uint256[] memory _currentPowers,
        uint256 _currentValsetNonce,
        // These are arrays of the parts of the validators signatures
        uint8[] memory _v,
        bytes32[] memory _r,
        bytes32[] memory _s,
        // The batch of transactions
        uint256[] memory _amounts,
        address payable[] memory _destinations,
        uint256[] memory _fees,
        uint256 _batchNonce,
        address _tokenContract,
        // a block height beyond which this batch is not valid
        // used to provide a fee-free timeout
        uint256 _batchTimeout
    ) external nonReentrant whenNotPaused {
        // CHECKS scoped to reduce stack depth
        {
            // Check that the batch nonce is higher than the last nonce for this token
            require(
                state_lastBatchNonces[_tokenContract] < _batchNonce,
                "New batch nonce must be greater than the current nonce"
            );

            // Check that the block height is less than the timeout height
            require(
                block.number < _batchTimeout,
                "Batch timeout must be greater than the current block height"
            );

            // Check that current validators, powers, and signatures (v,r,s) set is well-formed
            require(
                _currentValidators.length == _currentPowers.length &&
                    _currentValidators.length == _v.length &&
                    _currentValidators.length == _r.length &&
                    _currentValidators.length == _s.length,
                "Malformed current validator set"
            );

            // Check that the supplied current validator set matches the saved checkpoint
            require(
                makeCheckpoint(
                    _currentValidators,
                    _currentPowers,
                    _currentValsetNonce,
                    state_bridgeId
                ) == state_lastValsetCheckpoint,
                "Supplied current validators and powers do not match checkpoint."
            );

            // Check that the transaction batch is well-formed
            require(
                _amounts.length == _destinations.length &&
                    _amounts.length == _fees.length,
                "Malformed batch of transactions"
            );

            // Check that enough current validators have signed off on the transaction batch and valset
            checkValidatorSignatures(
                _currentValidators,
                _currentPowers,
                _v,
                _r,
                _s,
                // Get hash of the transaction batch and checkpoint
                keccak256(
                    abi.encode(
                        state_bridgeId,
                        // bytes32 encoding of "transactionBatch"
                        0x7472616e73616374696f6e426174636800000000000000000000000000000000,
                        _amounts,
                        _destinations,
                        _fees,
                        _batchNonce,
                        _tokenContract,
                        _batchTimeout
                    )
                ),
                state_powerThreshold
            );

            // ACTIONS

            // Store batch nonce
            state_lastBatchNonces[_tokenContract] = _batchNonce;

            {
                // Send transaction amounts to destinations
                uint256 totalFee;
                for (uint256 i = 0; i < _amounts.length; i++) {
                    if (_tokenContract == address(0)) {
                        (bool success, ) = _destinations[i].call{
                            value: _amounts[i],
                            gas: 60000
                        }("");
                        require(success, "error sending ether");
                    } else {
                        IERC20(_tokenContract).safeTransfer(
                            _destinations[i],
                            _amounts[i]
                        );
                    }
                    totalFee = totalFee.add(_fees[i]);
                }

                // Send transaction fees to msg.sender
                if (totalFee > 0) {
                    if (_tokenContract == address(0)) {
                        (bool success, ) = msg.sender.call{
                            value: totalFee,
                            gas: 60000
                        }("");
                        require(success, "error sending ether");
                    } else {
                        IERC20(_tokenContract).safeTransfer(
                            msg.sender,
                            totalFee
                        );
                    }
                }
            }
        }

        // LOGS scoped to reduce stack depth
        {
            state_lastEventNonce = state_lastEventNonce.add(1);
            emit TransactionBatchExecutedEvent(
                _batchNonce,
                _tokenContract,
                state_lastEventNonce
            );
        }
    }

    // This makes calls to contracts that execute arbitrary logic
    // First, it gives the logic contract some tokens
    // Then, it gives msg.senders tokens for fees
    // Then, it calls an arbitrary function on the logic contract
    // invalidationId and invalidationNonce are used for replay prevention.
    // They can be used to implement a per-token nonce by setting the token
    // address as the invalidationId and incrementing the nonce each call.
    // They can be used for nonce-free replay prevention by using a different invalidationId
    // for each call.
    function submitLogicCall(
        // The validators that approve the call
        address[] memory _currentValidators,
        uint256[] memory _currentPowers,
        uint256 _currentValsetNonce,
        // These are arrays of the parts of the validators signatures
        uint8[] memory _v,
        bytes32[] memory _r,
        bytes32[] memory _s,
        LogicCallArgs memory _args
    ) public nonReentrant {
        // CHECKS scoped to reduce stack depth
        {
            // Check that the call has not timed out
            require(block.number < _args.timeOut, "Timed out");

            // Check that the invalidation nonce is higher than the last nonce for this invalidation Id
            require(
                state_invalidationMapping[_args.invalidationId] <
                    _args.invalidationNonce,
                "New invalidation nonce must be greater than the current nonce"
            );

            // Check that current validators, powers, and signatures (v,r,s) set is well-formed
            require(
                _currentValidators.length == _currentPowers.length &&
                    _currentValidators.length == _v.length &&
                    _currentValidators.length == _r.length &&
                    _currentValidators.length == _s.length,
                "Malformed current validator set"
            );

            // Check that the supplied current validator set matches the saved checkpoint
            require(
                makeCheckpoint(
                    _currentValidators,
                    _currentPowers,
                    _currentValsetNonce,
                    state_bridgeId
                ) == state_lastValsetCheckpoint,
                "Supplied current validators and powers do not match checkpoint."
            );

            // Check that the token transfer list is well-formed
            require(
                _args.transferAmounts.length ==
                    _args.transferTokenContracts.length,
                "Malformed list of token transfers"
            );

            // Check that the fee list is well-formed
            require(
                _args.feeAmounts.length == _args.feeTokenContracts.length,
                "Malformed list of fees"
            );
        }

        bytes32 argsHash = keccak256(
            abi.encode(
                state_bridgeId,
                // bytes32 encoding of "logicCall"
                0x6c6f67696343616c6c0000000000000000000000000000000000000000000000,
                _args.transferAmounts,
                _args.transferTokenContracts,
                _args.feeAmounts,
                _args.feeTokenContracts,
                _args.logicContractAddress,
                _args.payload,
                _args.timeOut,
                _args.invalidationId,
                _args.invalidationNonce
            )
        );

        {
            // Check that enough current validators have signed off on the transaction batch and valset
            checkValidatorSignatures(
                _currentValidators,
                _currentPowers,
                _v,
                _r,
                _s,
                // Get hash of the transaction batch and checkpoint
                argsHash,
                state_powerThreshold
            );
        }

        // ACTIONS

        // Update invaldiation nonce
        state_invalidationMapping[_args.invalidationId] = _args
            .invalidationNonce;

        // Send tokens to the logic contract
        for (uint256 i = 0; i < _args.transferAmounts.length; i++) {
            IERC20(_args.transferTokenContracts[i]).safeTransfer(
                _args.logicContractAddress,
                _args.transferAmounts[i]
            );
        }

        // Make call to logic contract
        bytes memory returnData = Address.functionCall(
            _args.logicContractAddress,
            _args.payload
        );

        // Send fees to msg.sender
        for (uint256 i = 0; i < _args.feeAmounts.length; i++) {
            IERC20(_args.feeTokenContracts[i]).safeTransfer(
                msg.sender,
                _args.feeAmounts[i]
            );
        }

        // LOGS scoped to reduce stack depth
        {
            state_lastEventNonce = state_lastEventNonce.add(1);
            emit LogicCallEvent(
                _args.invalidationId,
                _args.invalidationNonce,
                returnData,
                state_lastEventNonce
            );
        }
    }

    function sendToSeele(
        address _tokenContract,
        address _destination,
        uint256 _amount
    )
        external
        payable
        onlyEthTokenWhiteList(_tokenContract)
        whenNotPaused
        nonReentrant
    {
        require(_amount > 0, "incorrect amount");
        if (msg.value > 0) {
            // Ethereum deposit
            require(_tokenContract == address(0), "!address(0)");
            require(msg.value == _amount, "incorrect eth amount");
        } else {
            // ERC20 deposit
            IERC20(_tokenContract).safeTransferFrom(
                msg.sender,
                address(this),
                _amount
            );
        }
        state_lastEventNonce = state_lastEventNonce.add(1);
        emit SendToSeeleEvent(
            _tokenContract,
            msg.sender,
            _destination,
            _amount,
            state_lastEventNonce
        );
    }

    function deployERC20(
        string calldata _seeleDenom,
        string calldata _name,
        string calldata _symbol,
        uint8 _decimals
    ) external onlyOwner {
        // Deploy an ERC20 with entire supply granted to SeeleBridge.sol
        SeeleERC20 erc20 = new SeeleERC20(
            address(this),
            _name,
            _symbol,
            _decimals
        );

        // Fire an event to let the Bridge module know
        state_lastEventNonce = state_lastEventNonce.add(1);
        emit ERC20DeployedEvent(
            _seeleDenom,
            address(erc20),
            _name,
            _symbol,
            _decimals,
            state_lastEventNonce
        );
    }

    function emergencyPause() external onlyOwner {
        _pause();
    }

    function emergencyUnpause() external onlyOwner {
        _unpause();
    }

    /*
     * @dev: Modifier to restrict erc20 can be locked
     */
    modifier onlyEthTokenWhiteList(address _token) {
        require(
            getTokenInEthWhiteList(_token),
            "Only token in whitelist can be transferred to cosmos"
        );
        _;
    }

    /*
     * @dev: Set the token address in whitelist
     *
     * @param _token: ERC 20's address
     * @param _inList: set the _token in list or not
     */
    function setTokenInEthWhiteList(address _token, bool _inList)
        external
        onlyOwner
    {
        _ethereumTokenWhiteList[_token] = _inList;
        emit WhiteListUpdateEvent(_token, _inList);
    }

    /*
     * @dev: Get if the token in whitelist
     *
     * @param _token: ERC 20's address
     * @return: if _token in whitelist
     */
    function getTokenInEthWhiteList(address _token) public view returns (bool) {
        return _ethereumTokenWhiteList[_token];
    }
}