pragma solidity ^0.5.0;


/**
 * @dev Interface of the ERC20 standard as defined in the EIP. Does not include
 * the optional functions; to access them see {ERC20Detailed}.
 */
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);
}

/**
 * @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.
     *
     * _Available since v2.4.0._
     */
    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.
     *
     * _Available since v2.4.0._
     */
    function div(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        // Solidity only automatically asserts when dividing by 0
        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.
     *
     * _Available since v2.4.0._
     */
    function mod(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b != 0, errorMessage);
        return a % b;
    }
}


/**
 * @dev Standard math utilities missing in the Solidity language.
 */
library Math {
    /**
     * @dev Returns the largest of two numbers.
     */
    function max(uint256 a, uint256 b) internal pure returns (uint256) {
        return a >= b ? a : b;
    }

    /**
     * @dev Returns the smallest of two numbers.
     */
    function min(uint256 a, uint256 b) internal pure returns (uint256) {
        return a < b ? a : b;
    }

    /**
     * @dev Returns the average of two numbers. The result is rounded towards
     * zero.
     */
    function average(uint256 a, uint256 b) internal pure returns (uint256) {
        // (a + b) / 2 can overflow, so we distribute
        return (a / 2) + (b / 2) + ((a % 2 + b % 2) / 2);
    }
}


/**
 * @dev Collection of functions related to array types.
 */
library Arrays {
   /**
     * @dev Searches a sorted `array` and returns the first index that contains
     * a value greater or equal to `element`. If no such index exists (i.e. all
     * values in the array are strictly less than `element`), the array length is
     * returned. Time complexity O(log n).
     *
     * `array` is expected to be sorted in ascending order, and to contain no
     * repeated elements.
     */
    function findUpperBound(uint256[] storage array, uint256 element) internal view returns (uint256) {
        if (array.length == 0) {
            return 0;
        }

        uint256 low = 0;
        uint256 high = array.length;

        while (low < high) {
            uint256 mid = Math.average(low, high);

            // Note that mid will always be strictly less than high (i.e. it will be a valid array index)
            // because Math.average rounds down (it does integer division with truncation).
            if (array[mid] > element) {
                high = mid;
            } else {
                low = mid + 1;
            }
        }

        // At this point `low` is the exclusive upper bound. We will return the inclusive upper bound.
        if (low > 0 && array[low - 1] == element) {
            return low - 1;
        } else {
            return low;
        }
    }
}


/**
 * @title Counters
 * @author Matt Condon (@shrugs)
 * @dev Provides counters that can only be incremented or decremented by one. This can be used e.g. to track the number
 * of elements in a mapping, issuing ERC721 ids, or counting request ids.
 *
 * Include with `using Counters for Counters.Counter;`
 * Since it is not possible to overflow a 256 bit integer with increments of one, `increment` can skip the {SafeMath}
 * overflow check, thereby saving gas. This does assume however correct usage, in that the underlying `_value` is never
 * directly accessed.
 */
library Counters {
    using SafeMath for uint256;

    struct Counter {
        // This variable should never be directly accessed by users of the library: interactions must be restricted to
        // the library's function. As of Solidity v0.5.2, this cannot be enforced, though there is a proposal to add
        // this feature: see https://github.com/ethereum/solidity/issues/4637
        uint256 _value; // default: 0
    }

    function current(Counter storage counter) internal view returns (uint256) {
        return counter._value;
    }

    function increment(Counter storage counter) internal {
        counter._value += 1;
    }

    function decrement(Counter storage counter) internal {
        counter._value = counter._value.sub(1);
    }
}


/*
 * @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.
 */
contract Context {
    // Empty internal constructor, to prevent people from mistakenly deploying
    // an instance of this contract, which should be used via inheritance.
    constructor () internal { }
    // solhint-disable-previous-line no-empty-blocks

    function _msgSender() internal view returns (address payable) {
        return msg.sender;
    }

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


/**
 * @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 {ERC20Mintable}.
 *
 * TIP: For a detailed writeup see our guide
 * https://forum.zeppelin.solutions/t/how-to-implement-erc20-supply-mechanisms/226[How
 * to implement supply mechanisms].
 *
 * We have followed general OpenZeppelin guidelines: functions revert instead
 * of returning `false` on failure. This behavior is nonetheless conventional
 * and does not conflict with the expectations of ERC20 applications.
 *
 * Additionally, an {Approval} event is emitted on calls to {transferFrom}.
 * This allows applications to reconstruct the allowance for all accounts just
 * by listening to said events. Other implementations of the EIP may not emit
 * these events, as it isn't required by the specification.
 *
 * Finally, the non-standard {decreaseAllowance} and {increaseAllowance}
 * functions have been added to mitigate the well-known issues around setting
 * allowances. See {IERC20-approve}.
 */
contract ERC20 is Context, IERC20 {
    using SafeMath for uint256;

    mapping (address => uint256) private _balances;

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

    uint256 private _totalSupply;

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

    /**
     * @dev See {IERC20-balanceOf}.
     */
    function balanceOf(address account) public view 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 returns (bool) {
        _transfer(_msgSender(), recipient, amount);
        return true;
    }

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

    /**
     * @dev See {IERC20-approve}.
     *
     * Requirements:
     *
     * - `spender` cannot be the zero address.
     */
    function approve(address spender, uint256 amount) public 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 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 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 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 {
        require(sender != address(0), "ERC20: transfer from the zero address");
        require(recipient != address(0), "ERC20: transfer to the zero address");

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

    /** @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 {
        require(account != address(0), "ERC20: mint to the zero address");

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

     /**
     * @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 {
        require(account != address(0), "ERC20: burn from the zero address");

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

    /**
     * @dev Sets `amount` as the allowance of `spender` over the `owner`s tokens.
     *
     * This is internal function is equivalent to `approve`, and can be used to
     * e.g. set automatic allowances for certain subsystems, etc.
     *
     * Emits an {Approval} event.
     *
     * Requirements:
     *
     * - `owner` cannot be the zero address.
     * - `spender` cannot be the zero address.
     */
    function _approve(address owner, address spender, uint256 amount) internal {
        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 Destroys `amount` tokens from `account`.`amount` is then deducted
     * from the caller's allowance.
     *
     * See {_burn} and {_approve}.
     */
    function _burnFrom(address account, uint256 amount) internal {
        _burn(account, amount);
        _approve(account, _msgSender(), _allowances[account][_msgSender()].sub(amount, "ERC20: burn amount exceeds allowance"));
    }
}


/**
 * @title ERC20 token with snapshots.
 * @dev Inspired by Jordi Baylina's
 * https://github.com/Giveth/minimd/blob/ea04d950eea153a04c51fa510b068b9dded390cb/contracts/MiniMeToken.sol[MiniMeToken]
 * to record historical balances.
 *
 * When a snapshot is made, the balances and total supply at the time of the snapshot are recorded for later
 * access.
 *
 * To make a snapshot, call the {snapshot} function, which will emit the {Snapshot} event and return a snapshot id.
 * To get the total supply from a snapshot, call the function {totalSupplyAt} with the snapshot id.
 * To get the balance of an account from a snapshot, call the {balanceOfAt} function with the snapshot id and the
 * account address.
 * @author Validity Labs AG <[email protected]>
 */
contract ERC20Snapshot is ERC20 {
    using SafeMath for uint256;
    using Arrays for uint256[];
    using Counters for Counters.Counter;

    // Snapshotted values have arrays of ids and the value corresponding to that id. These could be an array of a
    // Snapshot struct, but that would impede usage of functions that work on an array.
    struct Snapshots {
        uint256[] ids;
        uint256[] values;
    }

    mapping (address => Snapshots) private _accountBalanceSnapshots;
    Snapshots private _totalSupplySnapshots;

    // Snapshot ids increase monotonically, with the first value being 1. An id of 0 is invalid.
    Counters.Counter private _currentSnapshotId;

    event Snapshot(uint256 id);

    // Creates a new snapshot id. Balances are only stored in snapshots on demand: unless a snapshot was taken, a
    // balance change will not be recorded. This means the extra added cost of storing snapshotted balances is only paid
    // when required, but is also flexible enough that it allows for e.g. daily snapshots.
    function snapshot() public returns (uint256) {
        _currentSnapshotId.increment();

        uint256 currentId = _currentSnapshotId.current();
        emit Snapshot(currentId);
        return currentId;
    }

    function balanceOfAt(address account, uint256 snapshotId) public view returns (uint256) {
        (bool snapshotted, uint256 value) = _valueAt(snapshotId, _accountBalanceSnapshots[account]);

        return snapshotted ? value : balanceOf(account);
    }

    function totalSupplyAt(uint256 snapshotId) public view returns(uint256) {
        (bool snapshotted, uint256 value) = _valueAt(snapshotId, _totalSupplySnapshots);

        return snapshotted ? value : totalSupply();
    }

    // _transfer, _mint and _burn are the only functions where the balances are modified, so it is there that the
    // snapshots are updated. Note that the update happens _before_ the balance change, with the pre-modified value.
    // The same is true for the total supply and _mint and _burn.
    function _transfer(address from, address to, uint256 value) internal {
        _updateAccountSnapshot(from);
        _updateAccountSnapshot(to);

        super._transfer(from, to, value);
    }

    function _mint(address account, uint256 value) internal {
        _updateAccountSnapshot(account);
        _updateTotalSupplySnapshot();

        super._mint(account, value);
    }

    function _burn(address account, uint256 value) internal {
        _updateAccountSnapshot(account);
        _updateTotalSupplySnapshot();

        super._burn(account, value);
    }

    // When a valid snapshot is queried, there are three possibilities:
    //  a) The queried value was not modified after the snapshot was taken. Therefore, a snapshot entry was never
    //  created for this id, and all stored snapshot ids are smaller than the requested one. The value that corresponds
    //  to this id is the current one.
    //  b) The queried value was modified after the snapshot was taken. Therefore, there will be an entry with the
    //  requested id, and its value is the one to return.
    //  c) More snapshots were created after the requested one, and the queried value was later modified. There will be
    //  no entry for the requested id: the value that corresponds to it is that of the smallest snapshot id that is
    //  larger than the requested one.
    //
    // In summary, we need to find an element in an array, returning the index of the smallest value that is larger if
    // it is not found, unless said value doesn't exist (e.g. when all values are smaller). Arrays.findUpperBound does
    // exactly this.
    function _valueAt(uint256 snapshotId, Snapshots storage snapshots)
        private view returns (bool, uint256)
    {
        require(snapshotId > 0, "ERC20Snapshot: id is 0");
        // solhint-disable-next-line max-line-length
        require(snapshotId <= _currentSnapshotId.current(), "ERC20Snapshot: nonexistent id");

        uint256 index = snapshots.ids.findUpperBound(snapshotId);

        if (index == snapshots.ids.length) {
            return (false, 0);
        } else {
            return (true, snapshots.values[index]);
        }
    }

    function _updateAccountSnapshot(address account) private {
        _updateSnapshot(_accountBalanceSnapshots[account], balanceOf(account));
    }

    function _updateTotalSupplySnapshot() private {
        _updateSnapshot(_totalSupplySnapshots, totalSupply());
    }

    function _updateSnapshot(Snapshots storage snapshots, uint256 currentValue) private {
        uint256 currentId = _currentSnapshotId.current();
        if (_lastSnapshotId(snapshots.ids) < currentId) {
            snapshots.ids.push(currentId);
            snapshots.values.push(currentValue);
        }
    }

    function _lastSnapshotId(uint256[] storage ids) private view returns (uint256) {
        if (ids.length == 0) {
            return 0;
        } else {
            return ids[ids.length - 1];
        }
    }
}

/**
 * @title ERC20 interface that includes burn and mint methods.
 */
contract ExpandedIERC20 is IERC20 {
    /**
     * @notice Burns a specific amount of the caller's tokens.
     * @dev Only burns the caller's tokens, so it is safe to leave this method permissionless.
     */
    function burn(uint value) external;

    /**
     * @notice Mints tokens and adds them to the balance of the `to` address.
     * @dev This method should be permissioned to only allow designated parties to mint tokens.
     */
    function mint(address to, uint value) external returns (bool);
}


library Exclusive {
    struct RoleMembership {
        address member;
    }

    function isMember(RoleMembership storage roleMembership, address memberToCheck) internal view returns (bool) {
        return roleMembership.member == memberToCheck;
    }

    function resetMember(RoleMembership storage roleMembership, address newMember) internal {
        require(newMember != address(0x0), "Cannot set an exclusive role to 0x0");
        roleMembership.member = newMember;
    }

    function getMember(RoleMembership storage roleMembership) internal view returns (address) {
        return roleMembership.member;
    }

    function init(RoleMembership storage roleMembership, address initialMember) internal {
        resetMember(roleMembership, initialMember);
    }
}


library Shared {
    struct RoleMembership {
        mapping(address => bool) members;
    }

    function isMember(RoleMembership storage roleMembership, address memberToCheck) internal view returns (bool) {
        return roleMembership.members[memberToCheck];
    }

    function addMember(RoleMembership storage roleMembership, address memberToAdd) internal {
        roleMembership.members[memberToAdd] = true;
    }

    function removeMember(RoleMembership storage roleMembership, address memberToRemove) internal {
        roleMembership.members[memberToRemove] = false;
    }

    function init(RoleMembership storage roleMembership, address[] memory initialMembers) internal {
        for (uint i = 0; i < initialMembers.length; i++) {
            addMember(roleMembership, initialMembers[i]);
        }
    }
}


/**
 * @title Base class to manage permissions for the derived class.
 */
contract MultiRole {
    using Exclusive for Exclusive.RoleMembership;
    using Shared for Shared.RoleMembership;

    enum RoleType { Invalid, Exclusive, Shared }

    struct Role {
        uint managingRole;
        RoleType roleType;
        Exclusive.RoleMembership exclusiveRoleMembership;
        Shared.RoleMembership sharedRoleMembership;
    }

    mapping(uint => Role) private roles;

    /**
     * @notice Reverts unless the caller is a member of the specified roleId.
     */
    modifier onlyRoleHolder(uint roleId) {
        require(holdsRole(roleId, msg.sender), "Sender does not hold required role");
        _;
    }

    /**
     * @notice Reverts unless the caller is a member of the manager role for the specified roleId.
     */
    modifier onlyRoleManager(uint roleId) {
        require(holdsRole(roles[roleId].managingRole, msg.sender), "Can only be called by a role manager");
        _;
    }

    /**
     * @notice Reverts unless the roleId represents an initialized, exclusive roleId.
     */
    modifier onlyExclusive(uint roleId) {
        require(roles[roleId].roleType == RoleType.Exclusive, "Must be called on an initialized Exclusive role");
        _;
    }

    /**
     * @notice Reverts unless the roleId represents an initialized, shared roleId.
     */
    modifier onlyShared(uint roleId) {
        require(roles[roleId].roleType == RoleType.Shared, "Must be called on an initialized Shared role");
        _;
    }

    /**
     * @notice Whether `memberToCheck` is a member of roleId.
     * @dev Reverts if roleId does not correspond to an initialized role.
     */
    function holdsRole(uint roleId, address memberToCheck) public view returns (bool) {
        Role storage role = roles[roleId];
        if (role.roleType == RoleType.Exclusive) {
            return role.exclusiveRoleMembership.isMember(memberToCheck);
        } else if (role.roleType == RoleType.Shared) {
            return role.sharedRoleMembership.isMember(memberToCheck);
        }
        require(false, "Invalid roleId");
    }

    /**
     * @notice Changes the exclusive role holder of `roleId` to `newMember`.
     * @dev Reverts if the caller is not a member of the managing role for `roleId` or if `roleId` is not an
     * initialized, exclusive role.
     */
    function resetMember(uint roleId, address newMember) public onlyExclusive(roleId) onlyRoleManager(roleId) {
        roles[roleId].exclusiveRoleMembership.resetMember(newMember);
    }

    /**
     * @notice Gets the current holder of the exclusive role, `roleId`.
     * @dev Reverts if `roleId` does not represent an initialized, exclusive role.
     */
    function getMember(uint roleId) public view onlyExclusive(roleId) returns (address) {
        return roles[roleId].exclusiveRoleMembership.getMember();
    }

    /**
     * @notice Adds `newMember` to the shared role, `roleId`.
     * @dev Reverts if `roleId` does not represent an initialized, shared role or if the caller is not a member of the
     * managing role for `roleId`.
     */
    function addMember(uint roleId, address newMember) public onlyShared(roleId) onlyRoleManager(roleId) {
        roles[roleId].sharedRoleMembership.addMember(newMember);
    }

    /**
     * @notice Removes `memberToRemove` from the shared role, `roleId`.
     * @dev Reverts if `roleId` does not represent an initialized, shared role or if the caller is not a member of the
     * managing role for `roleId`.
     */
    function removeMember(uint roleId, address memberToRemove) public onlyShared(roleId) onlyRoleManager(roleId) {
        roles[roleId].sharedRoleMembership.removeMember(memberToRemove);
    }

    /**
     * @notice Reverts if `roleId` is not initialized.
     */
    modifier onlyValidRole(uint roleId) {
        require(roles[roleId].roleType != RoleType.Invalid, "Attempted to use an invalid roleId");
        _;
    }

    /**
     * @notice Reverts if `roleId` is initialized.
     */
    modifier onlyInvalidRole(uint roleId) {
        require(roles[roleId].roleType == RoleType.Invalid, "Cannot use a pre-existing role");
        _;
    }

    /**
     * @notice Internal method to initialize a shared role, `roleId`, which will be managed by `managingRoleId`.
     * `initialMembers` will be immediately added to the role.
     * @dev Should be called by derived contracts, usually at construction time. Will revert if the role is already
     * initialized.
     */
    function _createSharedRole(uint roleId, uint managingRoleId, address[] memory initialMembers)
        internal
        onlyInvalidRole(roleId)
    {
        Role storage role = roles[roleId];
        role.roleType = RoleType.Shared;
        role.managingRole = managingRoleId;
        role.sharedRoleMembership.init(initialMembers);
        require(roles[managingRoleId].roleType != RoleType.Invalid,
            "Attempted to use an invalid role to manage a shared role");
    }

    /**
     * @notice Internal method to initialize a exclusive role, `roleId`, which will be managed by `managingRoleId`.
     * `initialMembers` will be immediately added to the role.
     * @dev Should be called by derived contracts, usually at construction time. Will revert if the role is already
     * initialized.
     */
    function _createExclusiveRole(uint roleId, uint managingRoleId, address initialMember)
        internal
        onlyInvalidRole(roleId)
    {
        Role storage role = roles[roleId];
        role.roleType = RoleType.Exclusive;
        role.managingRole = managingRoleId;
        role.exclusiveRoleMembership.init(initialMember);
        require(roles[managingRoleId].roleType != RoleType.Invalid,
            "Attempted to use an invalid role to manage an exclusive role");
    }
}


/**
 * @title Ownership of this token allows a voter to respond to price requests.
 * @dev Supports snapshotting and allows the Oracle to mint new tokens as rewards.
 */
contract VotingToken is ExpandedIERC20, ERC20Snapshot, MultiRole {

    enum Roles {
        // Can set the minter and burner.
        Owner,
        // Addresses that can mint new tokens.
        Minter,
        // Addresses that can burn tokens that address owns.
        Burner
    }

    // Standard ERC20 metadata.
    string public constant name = "UMA Voting Token v1"; // solhint-disable-line const-name-snakecase
    string public constant symbol = "UMA"; // solhint-disable-line const-name-snakecase
    uint8 public constant decimals = 18; // solhint-disable-line const-name-snakecase

    constructor() public {
        _createExclusiveRole(uint(Roles.Owner), uint(Roles.Owner), msg.sender);
        _createSharedRole(uint(Roles.Minter), uint(Roles.Owner), new address[](0));
        _createSharedRole(uint(Roles.Burner), uint(Roles.Owner), new address[](0));
    }

    /**
     * @dev Mints `value` tokens to `recipient`, returning true on success.
     */
    function mint(address recipient, uint value) external onlyRoleHolder(uint(Roles.Minter)) returns (bool) {
        _mint(recipient, value);
        return true;
    }

    /**
     * @dev Burns `value` tokens owned by `msg.sender`.
     */
    function burn(uint value) external onlyRoleHolder(uint(Roles.Burner)) {
        _burn(msg.sender, value);
    }
}