Contract Source Code:

// SPDX-License-Identifier: Apache-2.0
pragma solidity 0.6.12;

contract Ownable {
    // Owner of the contract
    address private _owner;

    /**
     * @dev Event to show ownership has been transferred
     * @param previousOwner representing the address of the previous owner
     * @param newOwner representing the address of the new owner
     */
    event OwnershipTransferred(address previousOwner, address newOwner);

    /**
     * @dev The constructor sets the original owner of the contract to the sender account.
     */
    constructor() public {
        setOwner(msg.sender);
    }

    /**
     * @dev Tells the address of the owner
     * @return the address of the owner
     */
    function owner() external view returns (address) {
        return _owner;
    }

    /**
     * @dev Sets a new owner address
     */
    function setOwner(address newOwner) internal {
        _owner = newOwner;
    }

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

    /**
     * @dev Allows the current owner to transfer control of the contract to a newOwner.
     * @param newOwner The address to transfer ownership to.
     */
    function transferOwnership(address newOwner) external onlyOwner {
        require(
            newOwner != address(0),
            "Ownable: new owner is the zero address"
        );
        emit OwnershipTransferred(_owner, newOwner);
        setOwner(newOwner);
    }
}


library SafeMath {
    /**
     * @dev Returns the addition of two unsigned integers, with an overflow flag.
     *
     * _Available since v3.4._
     */
    function tryAdd(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        uint256 c = a + b;
        if (c < a) return (false, 0);
        return (true, c);
    }

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

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

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

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

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

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

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

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

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

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

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

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


contract Controller is Ownable {
    /**
     * @dev A controller manages a single worker address.
     * controllers[controller] = worker
     */
    mapping(address => address) internal controllers;

    event ControllerConfigured(
        address indexed _controller,
        address indexed _worker
    );
    event ControllerRemoved(address indexed _controller);

    /**
     * @notice Ensures that caller is the controller of a non-zero worker
     * address.
     */
    modifier onlyController() {
        require(
            controllers[msg.sender] != address(0),
            "The value of controllers[msg.sender] must be non-zero"
        );
        _;
    }

    /**
     * @notice Gets the worker at address _controller.
     */
    function getWorker(address _controller) external view returns (address) {
        return controllers[_controller];
    }

    // onlyOwner functions

    /**
     * @notice Configure a controller with the given worker.
     * @param _controller The controller to be configured with a worker.
     * @param _worker The worker to be set for the newly configured controller.
     * _worker must not be a non-zero address. To disable a worker,
     * use removeController instead.
     */
    function configureController(address _controller, address _worker)
        public
        onlyOwner
    {
        require(
            _controller != address(0),
            "Controller must be a non-zero address"
        );
        require(_worker != address(0), "Worker must be a non-zero address");
        controllers[_controller] = _worker;
        emit ControllerConfigured(_controller, _worker);
    }

    /**
     * @notice disables a controller by setting its worker to address(0).
     * @param _controller The controller to disable.
     */
    function removeController(address _controller) public onlyOwner {
        require(
            _controller != address(0),
            "Controller must be a non-zero address"
        );
        require(
            controllers[_controller] != address(0),
            "Worker must be a non-zero address"
        );
        controllers[_controller] = address(0);
        emit ControllerRemoved(_controller);
    }
}


interface MinterManagementInterface {
    function isMinter(address _account) external view returns (bool);

    function minterAllowance(address _minter) external view returns (uint256);

    function configureMinter(address _minter, uint256 _minterAllowedAmount)
        external
        returns (bool);

    function removeMinter(address _minter) external returns (bool);
}


contract MintController is Controller {
    using SafeMath for uint256;

    /**
     * @dev MintController calls the minterManager to execute/record minter
     * management tasks, as well as to query the status of a minter address.
     */
    MinterManagementInterface internal minterManager;

    event MinterManagerSet(
        address indexed _oldMinterManager,
        address indexed _newMinterManager
    );
    event MinterConfigured(
        address indexed _msgSender,
        address indexed _minter,
        uint256 _allowance
    );
    event MinterRemoved(address indexed _msgSender, address indexed _minter);
    event MinterAllowanceIncremented(
        address indexed _msgSender,
        address indexed _minter,
        uint256 _increment,
        uint256 _newAllowance
    );

    event MinterAllowanceDecremented(
        address indexed msgSender,
        address indexed minter,
        uint256 decrement,
        uint256 newAllowance
    );

    /**
     * @notice Initializes the minterManager.
     * @param _minterManager The address of the minterManager contract.
     */
    constructor(address _minterManager) public {
        minterManager = MinterManagementInterface(_minterManager);
    }

    /**
     * @notice gets the minterManager
     */
    function getMinterManager()
        external
        view
        returns (MinterManagementInterface)
    {
        return minterManager;
    }

    // onlyOwner functions

    /**
     * @notice Sets the minterManager.
     * @param _newMinterManager The address of the new minterManager contract.
     */
    function setMinterManager(address _newMinterManager) public onlyOwner {
        emit MinterManagerSet(address(minterManager), _newMinterManager);
        minterManager = MinterManagementInterface(_newMinterManager);
    }

    // onlyController functions

    /**
     * @notice Removes the controller's own minter.
     */
    function removeMinter() public onlyController returns (bool) {
        address minter = controllers[msg.sender];
        emit MinterRemoved(msg.sender, minter);
        return minterManager.removeMinter(minter);
    }

    /**
     * @notice Enables the minter and sets its allowance.
     * @param _newAllowance New allowance to be set for minter.
     */
    function configureMinter(uint256 _newAllowance)
        public
        onlyController
        returns (bool)
    {
        address minter = controllers[msg.sender];
        emit MinterConfigured(msg.sender, minter, _newAllowance);
        return internal_setMinterAllowance(minter, _newAllowance);
    }

    /**
     * @notice Increases the minter's allowance if and only if the minter is an
     * active minter.
     * @dev An minter is considered active if minterManager.isMinter(minter)
     * returns true.
     */
    function incrementMinterAllowance(uint256 _allowanceIncrement)
        public
        onlyController
        returns (bool)
    {
        require(
            _allowanceIncrement > 0,
            "Allowance increment must be greater than 0"
        );
        address minter = controllers[msg.sender];
        require(
            minterManager.isMinter(minter),
            "Can only increment allowance for minters in minterManager"
        );

        uint256 currentAllowance = minterManager.minterAllowance(minter);
        uint256 newAllowance = currentAllowance.add(_allowanceIncrement);

        emit MinterAllowanceIncremented(
            msg.sender,
            minter,
            _allowanceIncrement,
            newAllowance
        );

        return internal_setMinterAllowance(minter, newAllowance);
    }

    /**
     * @notice decreases the minter allowance if and only if the minter is
     * currently active. The controller can safely send a signed
     * decrementMinterAllowance() transaction to a minter and not worry
     * about it being used to undo a removeMinter() transaction.
     */
    function decrementMinterAllowance(uint256 _allowanceDecrement)
        public
        onlyController
        returns (bool)
    {
        require(
            _allowanceDecrement > 0,
            "Allowance decrement must be greater than 0"
        );
        address minter = controllers[msg.sender];
        require(
            minterManager.isMinter(minter),
            "Can only decrement allowance for minters in minterManager"
        );

        uint256 currentAllowance = minterManager.minterAllowance(minter);
        uint256 actualAllowanceDecrement = (
            currentAllowance > _allowanceDecrement
                ? _allowanceDecrement
                : currentAllowance
        );
        uint256 newAllowance = currentAllowance.sub(actualAllowanceDecrement);

        emit MinterAllowanceDecremented(
            msg.sender,
            minter,
            actualAllowanceDecrement,
            newAllowance
        );

        return internal_setMinterAllowance(minter, newAllowance);
    }

    // Internal functions

    /**
     * @notice Uses the MinterManagementInterface to enable the minter and
     * set its allowance.
     * @param _minter Minter to set new allowance of.
     * @param _newAllowance New allowance to be set for minter.
     */
    function internal_setMinterAllowance(address _minter, uint256 _newAllowance)
        internal
        returns (bool)
    {
        return minterManager.configureMinter(_minter, _newAllowance);
    }
}


contract MasterMinter is MintController {
    constructor(address _minterManager) public MintController(_minterManager) {}
}