// File: @openzeppelin/contracts/math/SafeMath.sol

pragma solidity ^0.6.0;

/**
 * @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/GSN/Context.sol

pragma solidity ^0.6.0;

/*
 * @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/Ownable.sol

pragma solidity ^0.6.0;

/**
 * @dev Contract module which provides a basic access control mechanism, where
 * there is an account (an owner) that can be granted exclusive access to
 * specific functions.
 *
 * By default, the owner account will be the one that deploys the contract. This
 * can later be changed with {transferOwnership}.
 *
 * This module is used through inheritance. It will make available the modifier
 * `onlyOwner`, which can be applied to your functions to restrict their use to
 * the owner.
 */
contract Ownable is Context {
    address private _owner;

    event OwnershipTransferred(
        address indexed previousOwner,
        address indexed newOwner
    );

    /**
     * @dev Initializes the contract setting the deployer as the initial owner.
     */
    constructor() internal {
        address msgSender = _msgSender();
        _owner = msgSender;
        emit OwnershipTransferred(address(0), msgSender);
    }

    /**
     * @dev Returns the address of the current owner.
     */
    function owner() public view returns (address) {
        return _owner;
    }

    /**
     * @dev Throws if called by any account other than the owner.
     */
    modifier onlyOwner() {
        require(_owner == _msgSender(), 'Ownable: caller is not the owner');
        _;
    }

    /**
     * @dev Leaves the contract without owner. It will not be possible to call
     * `onlyOwner` functions anymore. Can only be called by the current owner.
     *
     * NOTE: Renouncing ownership will leave the contract without an owner,
     * thereby removing any functionality that is only available to the owner.
     */
    function renounceOwnership() public virtual onlyOwner {
        emit OwnershipTransferred(_owner, address(0));
        _owner = address(0);
    }

    /**
     * @dev Transfers ownership of the contract to a new account (`newOwner`).
     * Can only be called by the current owner.
     */
    function transferOwnership(address newOwner) public virtual onlyOwner {
        require(
            newOwner != address(0),
            'Ownable: new owner is the zero address'
        );
        emit OwnershipTransferred(_owner, newOwner);
        _owner = newOwner;
    }
}

// File: contracts/owner/Operator.sol

pragma solidity ^0.6.0;

contract Operator is Context, Ownable {
    address private _operator;

    event OperatorTransferred(
        address indexed previousOperator,
        address indexed newOperator
    );

    constructor() internal {
        _operator = _msgSender();
        emit OperatorTransferred(address(0), _operator);
    }

    function operator() public view returns (address) {
        return _operator;
    }

    modifier onlyOperator() {
        require(
            _operator == msg.sender,
            'operator: caller is not the operator'
        );
        _;
    }

    function isOperator() public view returns (bool) {
        return _msgSender() == _operator;
    }

    function transferOperator(address newOperator_) public onlyOwner {
        _transferOperator(newOperator_);
    }

    function _transferOperator(address newOperator_) internal {
        require(
            newOperator_ != address(0),
            'operator: zero address given for new operator'
        );
        emit OperatorTransferred(address(0), newOperator_);
        _operator = newOperator_;
    }
}

// File: contracts/curve/Curve.sol

pragma solidity ^0.6.0;

interface ICurve {
    function minSupply() external view returns (uint256);

    function maxSupply() external view returns (uint256);

    function minCeiling() external view returns (uint256);

    function maxCeiling() external view returns (uint256);

    function calcCeiling(uint256 _supply) external view returns (uint256);
}

abstract contract Curve is ICurve {
    /* ========== EVENTS ========== */

    event MinSupplyChanged(
        address indexed operator,
        uint256 _old,
        uint256 _new
    );

    event MaxSupplyChanged(
        address indexed operator,
        uint256 _old,
        uint256 _new
    );

    event MinCeilingChanged(
        address indexed operator,
        uint256 _old,
        uint256 _new
    );

    event MaxCeilingChanged(
        address indexed operator,
        uint256 _old,
        uint256 _new
    );

    /* ========== STATE VARIABLES ========== */

    uint256 public override minSupply;
    uint256 public override maxSupply;

    uint256 public override minCeiling;
    uint256 public override maxCeiling;

    /* ========== GOVERNANCE ========== */

    function setMinSupply(uint256 _newMinSupply) public virtual {
        uint256 oldMinSupply = minSupply;
        minSupply = _newMinSupply;
        emit MinSupplyChanged(msg.sender, oldMinSupply, _newMinSupply);
    }

    function setMaxSupply(uint256 _newMaxSupply) public virtual {
        uint256 oldMaxSupply = maxSupply;
        maxSupply = _newMaxSupply;
        emit MaxSupplyChanged(msg.sender, oldMaxSupply, _newMaxSupply);
    }

    function setMinCeiling(uint256 _newMinCeiling) public virtual {
        uint256 oldMinCeiling = _newMinCeiling;
        minCeiling = _newMinCeiling;
        emit MinCeilingChanged(msg.sender, oldMinCeiling, _newMinCeiling);
    }

    function setMaxCeiling(uint256 _newMaxCeiling) public virtual {
        uint256 oldMaxCeiling = _newMaxCeiling;
        maxCeiling = _newMaxCeiling;
        emit MaxCeilingChanged(msg.sender, oldMaxCeiling, _newMaxCeiling);
    }

    function calcCeiling(uint256 _supply)
        external
        view
        virtual
        override
        returns (uint256);
}

// File: contracts/curve/Linear.sol

pragma solidity ^0.6.0;

contract LinearThreshold is Operator, Curve {
    using SafeMath for uint256;

    /* ========== CONSTRUCTOR ========== */

    constructor(
        uint256 _minSupply,
        uint256 _maxSupply,
        uint256 _minCeiling,
        uint256 _maxCeiling
    ) public {
        minSupply = _minSupply;
        maxSupply = _maxSupply;
        minCeiling = _minCeiling;
        maxCeiling = _maxCeiling;
    }

    /* ========== GOVERNANCE ========== */

    function setMinSupply(uint256 _newMinSupply) public override onlyOperator {
        super.setMinSupply(_newMinSupply);
    }

    function setMaxSupply(uint256 _newMaxSupply) public override onlyOperator {
        super.setMaxSupply(_newMaxSupply);
    }

    function setMinCeiling(uint256 _newMinCeiling)
        public
        override
        onlyOperator
    {
        super.setMinCeiling(_newMinCeiling);
    }

    function setMaxCeiling(uint256 _newMaxCeiling)
        public
        override
        onlyOperator
    {
        super.setMaxCeiling(_newMaxCeiling);
    }

    /* ========== VIEW FUNCTIONS ========== */

    function calcCeiling(uint256 _supply)
        public
        view
        override
        returns (uint256)
    {
        if (_supply <= minSupply) {
            return maxCeiling;
        }
        if (_supply >= maxSupply) {
            return minCeiling;
        }

        uint256 slope =
            maxCeiling.sub(minCeiling).mul(1e18).div(maxSupply.sub(minSupply));
        uint256 ceiling =
            maxCeiling.sub(slope.mul(_supply.sub(minSupply)).div(1e18));

        return ceiling;
    }
}