// File: contracts/TokenInterface.sol



pragma solidity ^0.7.3;

interface TokenInterface{
    function burnFrom(address _from, uint _amount) external;
    function mintTo(address _to, uint _amount) external;
}

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



pragma solidity ^0.7.0;

/**
 * @dev Library for managing
 * https://en.wikipedia.org/wiki/Set_(abstract_data_type)[sets] of primitive
 * types.
 *
 * Sets have the following properties:
 *
 * - Elements are added, removed, and checked for existence in constant time
 * (O(1)).
 * - Elements are enumerated in O(n). No guarantees are made on the ordering.
 *
 * ```
 * contract Example {
 *     // Add the library methods
 *     using EnumerableSet for EnumerableSet.AddressSet;
 *
 *     // Declare a set state variable
 *     EnumerableSet.AddressSet private mySet;
 * }
 * ```
 *
 * As of v3.0.0, only sets of type `address` (`AddressSet`) and `uint256`
 * (`UintSet`) are supported.
 */
library EnumerableSet {
    // To implement this library for multiple types with as little code
    // repetition as possible, we write it in terms of a generic Set type with
    // bytes32 values.
    // The Set implementation uses private functions, and user-facing
    // implementations (such as AddressSet) are just wrappers around the
    // underlying Set.
    // This means that we can only create new EnumerableSets for types that fit
    // in bytes32.

    struct Set {
        // Storage of set values
        bytes32[] _values;

        // Position of the value in the `values` array, plus 1 because index 0
        // means a value is not in the set.
        mapping (bytes32 => uint256) _indexes;
    }

    /**
     * @dev Add a value to a set. O(1).
     *
     * Returns true if the value was added to the set, that is if it was not
     * already present.
     */
    function _add(Set storage set, bytes32 value) private returns (bool) {
        if (!_contains(set, value)) {
            set._values.push(value);
            // The value is stored at length-1, but we add 1 to all indexes
            // and use 0 as a sentinel value
            set._indexes[value] = set._values.length;
            return true;
        } else {
            return false;
        }
    }

    /**
     * @dev Removes a value from a set. O(1).
     *
     * Returns true if the value was removed from the set, that is if it was
     * present.
     */
    function _remove(Set storage set, bytes32 value) private returns (bool) {
        // We read and store the value's index to prevent multiple reads from the same storage slot
        uint256 valueIndex = set._indexes[value];

        if (valueIndex != 0) { // Equivalent to contains(set, value)
            // To delete an element from the _values array in O(1), we swap the element to delete with the last one in
            // the array, and then remove the last element (sometimes called as 'swap and pop').
            // This modifies the order of the array, as noted in {at}.

            uint256 toDeleteIndex = valueIndex - 1;
            uint256 lastIndex = set._values.length - 1;

            // When the value to delete is the last one, the swap operation is unnecessary. However, since this occurs
            // so rarely, we still do the swap anyway to avoid the gas cost of adding an 'if' statement.

            bytes32 lastvalue = set._values[lastIndex];

            // Move the last value to the index where the value to delete is
            set._values[toDeleteIndex] = lastvalue;
            // Update the index for the moved value
            set._indexes[lastvalue] = toDeleteIndex + 1; // All indexes are 1-based

            // Delete the slot where the moved value was stored
            set._values.pop();

            // Delete the index for the deleted slot
            delete set._indexes[value];

            return true;
        } else {
            return false;
        }
    }

    /**
     * @dev Returns true if the value is in the set. O(1).
     */
    function _contains(Set storage set, bytes32 value) private view returns (bool) {
        return set._indexes[value] != 0;
    }

    /**
     * @dev Returns the number of values on the set. O(1).
     */
    function _length(Set storage set) private view returns (uint256) {
        return set._values.length;
    }

   /**
    * @dev Returns the value stored at position `index` in the set. O(1).
    *
    * Note that there are no guarantees on the ordering of values inside the
    * array, and it may change when more values are added or removed.
    *
    * Requirements:
    *
    * - `index` must be strictly less than {length}.
    */
    function _at(Set storage set, uint256 index) private view returns (bytes32) {
        require(set._values.length > index, "EnumerableSet: index out of bounds");
        return set._values[index];
    }

    // AddressSet

    struct AddressSet {
        Set _inner;
    }

    /**
     * @dev Add a value to a set. O(1).
     *
     * Returns true if the value was added to the set, that is if it was not
     * already present.
     */
    function add(AddressSet storage set, address value) internal returns (bool) {
        return _add(set._inner, bytes32(uint256(value)));
    }

    /**
     * @dev Removes a value from a set. O(1).
     *
     * Returns true if the value was removed from the set, that is if it was
     * present.
     */
    function remove(AddressSet storage set, address value) internal returns (bool) {
        return _remove(set._inner, bytes32(uint256(value)));
    }

    /**
     * @dev Returns true if the value is in the set. O(1).
     */
    function contains(AddressSet storage set, address value) internal view returns (bool) {
        return _contains(set._inner, bytes32(uint256(value)));
    }

    /**
     * @dev Returns the number of values in the set. O(1).
     */
    function length(AddressSet storage set) internal view returns (uint256) {
        return _length(set._inner);
    }

   /**
    * @dev Returns the value stored at position `index` in the set. O(1).
    *
    * Note that there are no guarantees on the ordering of values inside the
    * array, and it may change when more values are added or removed.
    *
    * Requirements:
    *
    * - `index` must be strictly less than {length}.
    */
    function at(AddressSet storage set, uint256 index) internal view returns (address) {
        return address(uint256(_at(set._inner, index)));
    }


    // UintSet

    struct UintSet {
        Set _inner;
    }

    /**
     * @dev Add a value to a set. O(1).
     *
     * Returns true if the value was added to the set, that is if it was not
     * already present.
     */
    function add(UintSet storage set, uint256 value) internal returns (bool) {
        return _add(set._inner, bytes32(value));
    }

    /**
     * @dev Removes a value from a set. O(1).
     *
     * Returns true if the value was removed from the set, that is if it was
     * present.
     */
    function remove(UintSet storage set, uint256 value) internal returns (bool) {
        return _remove(set._inner, bytes32(value));
    }

    /**
     * @dev Returns true if the value is in the set. O(1).
     */
    function contains(UintSet storage set, uint256 value) internal view returns (bool) {
        return _contains(set._inner, bytes32(value));
    }

    /**
     * @dev Returns the number of values on the set. O(1).
     */
    function length(UintSet storage set) internal view returns (uint256) {
        return _length(set._inner);
    }

   /**
    * @dev Returns the value stored at position `index` in the set. O(1).
    *
    * Note that there are no guarantees on the ordering of values inside the
    * array, and it may change when more values are added or removed.
    *
    * Requirements:
    *
    * - `index` must be strictly less than {length}.
    */
    function at(UintSet storage set, uint256 index) internal view returns (uint256) {
        return uint256(_at(set._inner, index));
    }
}

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



pragma solidity ^0.7.0;

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

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

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

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

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

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

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

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

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

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

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



pragma solidity ^0.7.0;

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

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

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



pragma solidity ^0.7.0;




/**
 * @dev Contract module that allows children to implement role-based access
 * control mechanisms.
 *
 * Roles are referred to by their `bytes32` identifier. These should be exposed
 * in the external API and be unique. The best way to achieve this is by
 * using `public constant` hash digests:
 *
 * ```
 * bytes32 public constant MY_ROLE = keccak256("MY_ROLE");
 * ```
 *
 * Roles can be used to represent a set of permissions. To restrict access to a
 * function call, use {hasRole}:
 *
 * ```
 * function foo() public {
 *     require(hasRole(MY_ROLE, msg.sender));
 *     ...
 * }
 * ```
 *
 * Roles can be granted and revoked dynamically via the {grantRole} and
 * {revokeRole} functions. Each role has an associated admin role, and only
 * accounts that have a role's admin role can call {grantRole} and {revokeRole}.
 *
 * By default, the admin role for all roles is `DEFAULT_ADMIN_ROLE`, which means
 * that only accounts with this role will be able to grant or revoke other
 * roles. More complex role relationships can be created by using
 * {_setRoleAdmin}.
 *
 * WARNING: The `DEFAULT_ADMIN_ROLE` is also its own admin: it has permission to
 * grant and revoke this role. Extra precautions should be taken to secure
 * accounts that have been granted it.
 */
abstract contract AccessControl is Context {
    using EnumerableSet for EnumerableSet.AddressSet;
    using Address for address;

    struct RoleData {
        EnumerableSet.AddressSet members;
        bytes32 adminRole;
    }

    mapping (bytes32 => RoleData) private _roles;

    bytes32 public constant DEFAULT_ADMIN_ROLE = 0x00;

    /**
     * @dev Emitted when `newAdminRole` is set as ``role``'s admin role, replacing `previousAdminRole`
     *
     * `DEFAULT_ADMIN_ROLE` is the starting admin for all roles, despite
     * {RoleAdminChanged} not being emitted signaling this.
     *
     * _Available since v3.1._
     */
    event RoleAdminChanged(bytes32 indexed role, bytes32 indexed previousAdminRole, bytes32 indexed newAdminRole);

    /**
     * @dev Emitted when `account` is granted `role`.
     *
     * `sender` is the account that originated the contract call, an admin role
     * bearer except when using {_setupRole}.
     */
    event RoleGranted(bytes32 indexed role, address indexed account, address indexed sender);

    /**
     * @dev Emitted when `account` is revoked `role`.
     *
     * `sender` is the account that originated the contract call:
     *   - if using `revokeRole`, it is the admin role bearer
     *   - if using `renounceRole`, it is the role bearer (i.e. `account`)
     */
    event RoleRevoked(bytes32 indexed role, address indexed account, address indexed sender);

    /**
     * @dev Returns `true` if `account` has been granted `role`.
     */
    function hasRole(bytes32 role, address account) public view returns (bool) {
        return _roles[role].members.contains(account);
    }

    /**
     * @dev Returns the number of accounts that have `role`. Can be used
     * together with {getRoleMember} to enumerate all bearers of a role.
     */
    function getRoleMemberCount(bytes32 role) public view returns (uint256) {
        return _roles[role].members.length();
    }

    /**
     * @dev Returns one of the accounts that have `role`. `index` must be a
     * value between 0 and {getRoleMemberCount}, non-inclusive.
     *
     * Role bearers are not sorted in any particular way, and their ordering may
     * change at any point.
     *
     * WARNING: When using {getRoleMember} and {getRoleMemberCount}, make sure
     * you perform all queries on the same block. See the following
     * https://forum.openzeppelin.com/t/iterating-over-elements-on-enumerableset-in-openzeppelin-contracts/2296[forum post]
     * for more information.
     */
    function getRoleMember(bytes32 role, uint256 index) public view returns (address) {
        return _roles[role].members.at(index);
    }

    /**
     * @dev Returns the admin role that controls `role`. See {grantRole} and
     * {revokeRole}.
     *
     * To change a role's admin, use {_setRoleAdmin}.
     */
    function getRoleAdmin(bytes32 role) public view returns (bytes32) {
        return _roles[role].adminRole;
    }

    /**
     * @dev Grants `role` to `account`.
     *
     * If `account` had not been already granted `role`, emits a {RoleGranted}
     * event.
     *
     * Requirements:
     *
     * - the caller must have ``role``'s admin role.
     */
    function grantRole(bytes32 role, address account) public virtual {
        require(hasRole(_roles[role].adminRole, _msgSender()), "AccessControl: sender must be an admin to grant");

        _grantRole(role, account);
    }

    /**
     * @dev Revokes `role` from `account`.
     *
     * If `account` had been granted `role`, emits a {RoleRevoked} event.
     *
     * Requirements:
     *
     * - the caller must have ``role``'s admin role.
     */
    function revokeRole(bytes32 role, address account) public virtual {
        require(hasRole(_roles[role].adminRole, _msgSender()), "AccessControl: sender must be an admin to revoke");

        _revokeRole(role, account);
    }

    /**
     * @dev Revokes `role` from the calling account.
     *
     * Roles are often managed via {grantRole} and {revokeRole}: this function's
     * purpose is to provide a mechanism for accounts to lose their privileges
     * if they are compromised (such as when a trusted device is misplaced).
     *
     * If the calling account had been granted `role`, emits a {RoleRevoked}
     * event.
     *
     * Requirements:
     *
     * - the caller must be `account`.
     */
    function renounceRole(bytes32 role, address account) public virtual {
        require(account == _msgSender(), "AccessControl: can only renounce roles for self");

        _revokeRole(role, account);
    }

    /**
     * @dev Grants `role` to `account`.
     *
     * If `account` had not been already granted `role`, emits a {RoleGranted}
     * event. Note that unlike {grantRole}, this function doesn't perform any
     * checks on the calling account.
     *
     * [WARNING]
     * ====
     * This function should only be called from the constructor when setting
     * up the initial roles for the system.
     *
     * Using this function in any other way is effectively circumventing the admin
     * system imposed by {AccessControl}.
     * ====
     */
    function _setupRole(bytes32 role, address account) internal virtual {
        _grantRole(role, account);
    }

    /**
     * @dev Sets `adminRole` as ``role``'s admin role.
     *
     * Emits a {RoleAdminChanged} event.
     */
    function _setRoleAdmin(bytes32 role, bytes32 adminRole) internal virtual {
        emit RoleAdminChanged(role, _roles[role].adminRole, adminRole);
        _roles[role].adminRole = adminRole;
    }

    function _grantRole(bytes32 role, address account) private {
        if (_roles[role].members.add(account)) {
            emit RoleGranted(role, account, _msgSender());
        }
    }

    function _revokeRole(bytes32 role, address account) private {
        if (_roles[role].members.remove(account)) {
            emit RoleRevoked(role, account, _msgSender());
        }
    }
}

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



pragma solidity ^0.7.0;

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

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

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

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

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

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

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

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

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



pragma solidity ^0.7.0;

/**
 * @dev Wrappers over Solidity's arithmetic operations with added overflow
 * checks.
 *
 * Arithmetic operations in Solidity wrap on overflow. This can easily result
 * in bugs, because programmers usually assume that an overflow raises an
 * error, which is the standard behavior in high level programming languages.
 * `SafeMath` restores this intuition by reverting the transaction when an
 * operation overflows.
 *
 * Using this library instead of the unchecked operations eliminates an entire
 * class of bugs, so it's recommended to use it always.
 */
library SafeMath {
    /**
     * @dev Returns the addition of two unsigned integers, 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/SafeERC20.sol



pragma solidity ^0.7.0;




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

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

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

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

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

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

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

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

// File: contracts/TokenStaking.sol

// SPDX-License-Identifier: GPL-3.0

// Author: Matt Hooft 
// https://github.com/Civitas-Fundamenta
// mhooft@fundamenta.network

// A simple token Staking Contract that uses a configurable `stakeCap` to limit inflation.
// Employs the use of Role Based Access Control (RBAC) so allow outside accounts and contracts
// to interact with it securely allowing for future extensibility.

pragma solidity ^0.7.3;






contract Staking is AccessControl {

    using SafeMath for uint256;
    using SafeERC20 for IERC20;
    
    TokenInterface private fundamenta;  
    
    /**
     * @dev Smart Contract uses Role Based Access Control to 
     * 
     * alllow for secure access as well as enabling the ability 
     *
     * for other contracts such as oracles to interact with ifundamenta.
     */

    //-------RBAC---------------------------

    bytes32 public constant _STAKING = keccak256("_STAKING");
    bytes32 public constant _RESCUE = keccak256("_RESCUE");
    bytes32 public constant _ADMIN = keccak256("_ADMIN");

    //-------Staking Vars-------------------
    
    uint public stakeCalc;
    uint public stakeCap;
    uint public rewardsWindow;
    uint public stakeLockMultiplier;
    bool public stakingOff;
    bool public paused;
    bool public emergencyWDoff;
    
    //--------Staking mapping/Arrays----------

    address[] internal stakeholders;
    mapping(address => uint) internal stakes;
    mapping(address => uint) internal rewards;
    mapping(address => uint) internal lastWithdraw;
    
    //----------Events----------------------
    
    event StakeCreated(address _stakeholder, uint _stakes, uint _blockHeight);
    event StakeRemoved(address _stakeholder, uint _stakes, uint rewards, uint _blockHeight);
    event RewardsWithdrawn(address _stakeholder, uint _rewards, uint blockHeight);
    event TokensRescued (address _pebcak, address _ERC20, uint _ERC20Amount, uint _blockHeightRescued);
    event ETHRescued (address _pebcak, uint _ETHAmount, uint _blockHeightRescued);

    //-------Constructor----------------------

    constructor(){
        stakingOff = true;
        emergencyWDoff = true;
        stakeCalc = 500;
        stakeCap = 3e22;
        rewardsWindow = 6500;
        stakeLockMultiplier = 2;
        _setupRole(DEFAULT_ADMIN_ROLE, msg.sender);
    }

    //-------Set Token Address----------------
    
    function setAddress(TokenInterface _token) public {
        require(hasRole(_ADMIN, msg.sender));
        fundamenta = _token;
    }
    
    //-------Modifiers--------------------------

    modifier pause() {
        require(!paused, "TokenStaking: Contract is Paused");
        _;
    }

    modifier stakeToggle() {
        require(!stakingOff, "TokenStaking: Staking is not currently active");
        _;
    }
    
    modifier emergency() {
        require(!emergencyWDoff, "TokenStaking: Emergency Withdraw is not enabled");
        _;
    }

    //--------Staking Functions-------------------

    /**
     * @dev allows a user to create a staking positon. Users will
     * 
     * not be allowed to stake more than the `stakeCap` which is 
     *
     * a settable variable by Admins/Contrcats with the `_STAKING` 
     * 
     * Role.
     */

    function createStake(uint _stake) public pause stakeToggle {
        lastWithdraw[msg.sender] = block.number;
        rewards[msg.sender] = rewards[msg.sender].add(rewardsAccrued());
        if(stakes[msg.sender] == 0) addStakeholder(msg.sender);
        stakes[msg.sender] = stakes[msg.sender].add(_stake);
        fundamenta.mintTo(msg.sender, rewardsAccrued());
        fundamenta.burnFrom(msg.sender, _stake);
        require(stakes[msg.sender] <= stakeCap, "TokenStaking: Can't Stake More than allowed moneybags"); 
        lastWithdraw[msg.sender] = block.number;
        emit StakeCreated(msg.sender, _stake, block.number);
    }
    
    /**
     * @dev removes a users staked positon if the required lock
     * 
     * window is satisfied. Also pays out any `_rewardsAccrued` to
     *
     * the user if any rewards are pending.
     */
    
    function removeStake(uint _stake) public pause {
        uint unlockWindow = rewardsWindow.mul(stakeLockMultiplier);
        require(block.number >= lastWithdraw[msg.sender].add(unlockWindow), "TokenStaking: FMTA has not been staked for long enough");
        rewards[msg.sender] = rewards[msg.sender].add(rewardsAccrued());
        if(stakes[msg.sender] == 0 && _stake != 0 ) {
            revert("TokenStaking: You don't have any tokens staked");
        }else if (stakes[msg.sender] != 0 && _stake != 0) {
            fundamenta.mintTo(msg.sender, rewardsAccrued());
            fundamenta.mintTo(msg.sender, _stake);
            stakes[msg.sender] = stakes[msg.sender].sub(_stake);
            lastWithdraw[msg.sender] = block.number;
        }else if (stakes[msg.sender] == 0) {
            fundamenta.mintTo(msg.sender, rewardsAccrued());
            fundamenta.mintTo(msg.sender, _stake);
            stakes[msg.sender] = stakes[msg.sender].sub(_stake);
            removeStakeholder(msg.sender);
            lastWithdraw[msg.sender] = block.number;
        }
        emit StakeRemoved(msg.sender, _stake, rewardsAccrued(), block.number);
        
    }
    
    /**
     * @dev returns the amount of rewards a user as accrued.
     */
    
    function rewardsAccrued() public view returns (uint) {
        uint _rewardsAccrued;
        uint multiplier;
        multiplier = block.number.sub(lastWithdraw[msg.sender]).div(rewardsWindow);
        _rewardsAccrued = calculateReward(msg.sender).mul(multiplier);
        return _rewardsAccrued;
        
    }
    
    /**
     * @dev allows user to withrdraw any pending rewards as
     * 
     * long as the `rewardsWindow` is satisfied.
     */
     
    function withdrawReward() public pause stakeToggle {
        rewards[msg.sender] = rewards[msg.sender].add(rewardsAccrued());
        if(lastWithdraw[msg.sender] == 0) {
           revert("TokenStaking: You cannot withdraw if you hve never staked");
        } else if (lastWithdraw[msg.sender] != 0){
            require(block.number > lastWithdraw[msg.sender].add(rewardsWindow), "TokenStaking: It hasn't been enough time since your last withdrawl");
            fundamenta.mintTo(msg.sender, rewardsAccrued());
            lastWithdraw[msg.sender] = block.number;
            emit RewardsWithdrawn(msg.sender, rewardsAccrued(), block.number);
        }
    }
    
    /**
     * @dev allows user to withrdraw any pending rewards and
     * 
     * staking position if `emergencyWDoff` is false enabling 
     * 
     * emergency withdraw situtaions when staking is off and 
     * 
     * the contract is paused.  This will likely never be used.
     */
    
    function emergencyWithdrawRewardAndStakes() public emergency {
        rewards[msg.sender] = rewards[msg.sender].add(rewardsAccrued());
        fundamenta.mintTo(msg.sender, rewardsAccrued());
        fundamenta.mintTo(msg.sender, stakes[msg.sender]);
        stakes[msg.sender] = stakes[msg.sender].sub(stakes[msg.sender]);
        removeStakeholder(msg.sender);
    }
    
    /**
     * @dev returns a users `lastWithdraw` which is the last block
     * 
     * height that the user last withdrew rewards.
     */
    
    function lastWdHeight() public view returns (uint) {
        return lastWithdraw[msg.sender];
    }
    
    /**
     * @dev returns to the user the amount of blocks that they must
     * 
     * have their stake locked before they are able to unstake their
     * 
     * positon.
     */
    
    function stakeUnlockWindow() external view returns (uint) {
        uint unlockWindow = rewardsWindow.mul(stakeLockMultiplier);
        uint stakeWindow = lastWithdraw[msg.sender].add(unlockWindow);
        return stakeWindow;
    }
    
    /**
     * @dev allows admin with the `_STAKING` role to set the 
     * 
     * `stakeMultiplier` which is used in the calculation that
     *
     * determines how long a user must have a staked positon 
     * 
     * before they are able to unstake said positon.
     */
    
    function setStakeMultiplier(uint _newMultiplier) public pause stakeToggle {
        require(hasRole(_STAKING, msg.sender));
        stakeLockMultiplier = _newMultiplier;
    }
    
    /**
     * @dev returns a users staked position.
     */
    
    function stakeOf (address _stakeholder) public view returns(uint) {
        return stakes[_stakeholder];
    }
    
    /**
     * @dev returns the total amount of FMTA that has been 
     * 
     * placed in staking postions by users.
     */
    
    function totalStakes() public view returns(uint) {
        uint _totalStakes = 0;
        for (uint s = 0; s < stakeholders.length; s += 1) {
            _totalStakes = _totalStakes.add(stakes[stakeholders[s]]);
        }
        
        return _totalStakes;
    }
    
    /**
     * @dev returns if an account is a stakeholder and holds
     * 
     * a staked position.
     */

    function isStakeholder(address _address) public view returns(bool, uint) {
        for (uint s = 0; s < stakeholders.length; s += 1) {
            if (_address == stakeholders[s]) return (true, s);
        }
        
        return (false, 0);
    }
    
    /**
     * @dev internal function that adds accounts as stakeholders.
     */
    
    function addStakeholder(address _stakeholder) internal pause stakeToggle {
        (bool _isStakeholder, ) = isStakeholder(_stakeholder);
        if(!_isStakeholder) stakeholders.push(_stakeholder);
    }
    
    /**
     * @dev internal function that removes accounts as stakeholders.
     */
    
    function removeStakeholder(address _stakeholder) internal {
        (bool _isStakeholder, uint s) = isStakeholder(_stakeholder);
        if(_isStakeholder){
            stakeholders[s] = stakeholders[stakeholders.length - 1];
            stakeholders.pop();
        }
    }
    
    /**
     * @dev returns an accounts total rewards paid over the
     * 
     * Staking Contracts lifetime.
     */
    
    function totalRewardsOf(address _stakeholder) external view returns(uint) {
        return rewards[_stakeholder];
    }
    
    /**
     * @dev returns the amount of total rewards paid to all
     * 
     * accounts over the Staking Contracts lifetime.
     */
    
    function totalRewardsPaid() external view returns(uint) {
        uint _totalRewards = 0;
        for (uint s = 0; s < stakeholders.length; s += 1){
            _totalRewards = _totalRewards.add(rewards[stakeholders[s]]);
        }
        
        return _totalRewards;
    }
    
     /**
     * @dev allows admin with the `_STAKING` role to set the
     * 
     * Staking Contracts `stakeCalc` which is the divisor used
     * 
     * in `calculateReward` to determine the reward during each 
     * 
     * `rewardsWindow`.
     */
    
    function setStakeCalc(uint _stakeCalc) external pause stakeToggle {
        require(hasRole(_STAKING, msg.sender));
        stakeCalc = _stakeCalc;
    }
    
     /**
     * @dev allows admin with the `_STAKING` role to set the
     * 
     * Staking Contracts `stakeCap` which determines how many
     * 
     * tokens total can be staked per accounfundamenta.
     */
    
    function setStakeCap(uint _stakeCap) external pause stakeToggle {
        require(hasRole(_STAKING, msg.sender));
        stakeCap = _stakeCap;
    }
    
     /**
     * @dev allows admin with the `_STAKING` role to set the
     * 
     * Staking Contracts `stakeOff` bool to true ot false 
     * 
     * effecively turning staking on or off. The only function 
     * 
     * that is not effected is removng stake 
     */
    
    function stakeOff(bool _stakingOff) public {
        require(hasRole(_STAKING, msg.sender));
        stakingOff = _stakingOff;
    }
    
    /**
     * @dev allows admin with the `_STAKING` role to set the
     * 
     * Staking Contracts `rewardsWindow` which determines how
     * 
     * long a user must wait before they can with draw in the 
     * 
     * form of a number of blocks that must pass since the users
     * 
     * `lastWithdraw`.
     */
    
    function setRewardsWindow(uint _newWindow) external pause stakeToggle {
        require(hasRole(_STAKING, msg.sender));
        rewardsWindow = _newWindow;
    }
    
    /**
     * @dev simple function help track and calculate the rewards
     * 
     * accrued between rewards windows. it uses `stakeCalc` which
     * 
     * is settable by admins with the `_STAKING` role.
     */
    
    function calculateReward(address _stakeholder) public view returns(uint) {
        return stakes[_stakeholder] / stakeCalc;
    }
    
    /**
     * @dev turns on the emergencyWD function which is used for 
     * 
     * when the staking contract is paused or stopped for some
     * 
     * unforseeable reason and we still need to let users withdraw.
     */
    
    function setEmergencyWDoff(bool _emergencyWD) external {
        require(hasRole(_ADMIN, msg.sender));
        emergencyWDoff = _emergencyWD;
    }
    

    //----------Pause----------------------

    /**
     * @dev pauses the Smart Contract.
     */

    function setPaused(bool _paused) external {
        require(hasRole(_ADMIN, msg.sender));
        paused = _paused;
    }
    
    //----Emergency PEBCAK Functions-------
    
    function mistakenERC20DepositRescue(address _ERC20, address _pebcak, uint _ERC20Amount) public {
        require(hasRole(_RESCUE, msg.sender),"TokenStaking: Message Sender must be _RESCUE");
        IERC20(_ERC20).safeTransfer(_pebcak, _ERC20Amount);
        emit TokensRescued (_pebcak, _ERC20, _ERC20Amount, block.number);
    }

    function mistakenDepositRescue(address payable _pebcak, uint _etherAmount) public {
        require(hasRole(_RESCUE, msg.sender),"TokenStaking: Message Sender must be _RESCUE");
        _pebcak.transfer(_etherAmount);
        emit ETHRescued (_pebcak, _etherAmount, block.number);
    }

}

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