/*
    ___            _       ___  _                          
    | .\ ___  _ _ <_> ___ | __><_>._ _  ___ ._ _  ___  ___ 
    |  _// ._>| '_>| ||___|| _> | || ' |<_> || ' |/ | '/ ._>
    |_|  \___.|_|  |_|     |_|  |_||_|_|<___||_|_|\_|_.\___.
    
* PeriFinance: SystemSettings.sol
*
* Latest source (may be newer): https://github.com/perifinance/peri-finance/blob/master/contracts/SystemSettings.sol
* Docs: Will be added in the future. 
* https://docs.peri.finance/contracts/source/contracts/SystemSettings
*
* Contract Dependencies: 
*	- IAddressResolver
*	- ISystemSettings
*	- MixinResolver
*	- MixinSystemSettings
*	- Owned
* Libraries: 
*	- SafeDecimalMath
*	- SafeMath
*
* MIT License
* ===========
*
* Copyright (c) 2021 PeriFinance
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in all
* copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
*/



pragma solidity 0.5.16;

// https://docs.peri.finance/contracts/source/contracts/owned
contract Owned {
    address public owner;
    address public nominatedOwner;

    constructor(address _owner) public {
        require(_owner != address(0), "Owner address cannot be 0");
        owner = _owner;
        emit OwnerChanged(address(0), _owner);
    }

    function nominateNewOwner(address _owner) external onlyOwner {
        nominatedOwner = _owner;
        emit OwnerNominated(_owner);
    }

    function acceptOwnership() external {
        require(msg.sender == nominatedOwner, "You must be nominated before you can accept ownership");
        emit OwnerChanged(owner, nominatedOwner);
        owner = nominatedOwner;
        nominatedOwner = address(0);
    }

    modifier onlyOwner {
        _onlyOwner();
        _;
    }

    function _onlyOwner() private view {
        require(msg.sender == owner, "Only the contract owner may perform this action");
    }

    event OwnerNominated(address newOwner);
    event OwnerChanged(address oldOwner, address newOwner);
}


// https://docs.peri.finance/contracts/source/interfaces/iaddressresolver
interface IAddressResolver {
    function getAddress(bytes32 name) external view returns (address);

    function getPynth(bytes32 key) external view returns (address);

    function requireAndGetAddress(bytes32 name, string calldata reason) external view returns (address);
}


// https://docs.peri.finance/contracts/source/interfaces/ipynth
interface IPynth {
    // Views
    function currencyKey() external view returns (bytes32);

    function transferablePynths(address account) external view returns (uint);

    // Mutative functions
    function transferAndSettle(address to, uint value) external returns (bool);

    function transferFromAndSettle(
        address from,
        address to,
        uint value
    ) external returns (bool);

    // Restricted: used internally to PeriFinance
    function burn(address account, uint amount) external;

    function issue(address account, uint amount) external;
}


// https://docs.peri.finance/contracts/source/interfaces/iissuer
interface IIssuer {
    // Views
    function anyPynthOrPERIRateIsInvalid() external view returns (bool anyRateInvalid);

    function availableCurrencyKeys() external view returns (bytes32[] memory);

    function availablePynthCount() external view returns (uint);

    function availablePynths(uint index) external view returns (IPynth);

    function canBurnPynths(address account) external view returns (bool);

    function collateral(address account) external view returns (uint);

    function collateralisationRatio(address issuer) external view returns (uint);

    function collateralisationRatioAndAnyRatesInvalid(address _issuer)
        external
        view
        returns (uint cratio, bool anyRateIsInvalid);

    function debtBalanceOf(address issuer, bytes32 currencyKey) external view returns (uint debtBalance);

    function issuanceRatio() external view returns (uint);

    function externalTokenLimit() external view returns (uint);

    function lastIssueEvent(address account) external view returns (uint);

    function maxIssuablePynths(address issuer) external view returns (uint maxIssuable);

    function externalTokenQuota(
        address _account,
        uint _addtionalpUSD,
        uint _addtionalExToken,
        bool _isIssue
    ) external view returns (uint);

    function maxExternalTokenStakeAmount(address _account, bytes32 _currencyKey)
        external
        view
        returns (uint issueAmountToQuota, uint stakeAmountToQuota);

    function minimumStakeTime() external view returns (uint);

    function remainingIssuablePynths(address issuer)
        external
        view
        returns (
            uint maxIssuable,
            uint alreadyIssued,
            uint totalSystemDebt
        );

    function pynths(bytes32 currencyKey) external view returns (IPynth);

    function getPynths(bytes32[] calldata currencyKeys) external view returns (IPynth[] memory);

    function pynthsByAddress(address pynthAddress) external view returns (bytes32);

    function totalIssuedPynths(bytes32 currencyKey, bool excludeEtherCollateral) external view returns (uint);

    function transferablePeriFinanceAndAnyRateIsInvalid(address account, uint balance)
        external
        view
        returns (uint transferable, bool anyRateIsInvalid);

    // Restricted: used internally to PeriFinance
    function issuePynths(
        address _issuer,
        bytes32 _currencyKey,
        uint _issueAmount
    ) external;

    function issueMaxPynths(address _issuer) external;

    function issuePynthsToMaxQuota(address _issuer, bytes32 _currencyKey) external;

    function burnPynths(
        address _from,
        bytes32 _currencyKey,
        uint _burnAmount
    ) external;

    function fitToClaimable(address _from) external;

    function exit(address _from) external;

    function liquidateDelinquentAccount(
        address account,
        uint pusdAmount,
        address liquidator
    ) external returns (uint totalRedeemed, uint amountToLiquidate);
}


// Inheritance


// Internal references


// https://docs.peri.finance/contracts/source/contracts/addressresolver
contract AddressResolver is Owned, IAddressResolver {
    mapping(bytes32 => address) public repository;

    constructor(address _owner) public Owned(_owner) {}

    /* ========== RESTRICTED FUNCTIONS ========== */

    function importAddresses(bytes32[] calldata names, address[] calldata destinations) external onlyOwner {
        require(names.length == destinations.length, "Input lengths must match");

        for (uint i = 0; i < names.length; i++) {
            bytes32 name = names[i];
            address destination = destinations[i];
            repository[name] = destination;
            emit AddressImported(name, destination);
        }
    }

    /* ========= PUBLIC FUNCTIONS ========== */

    function rebuildCaches(MixinResolver[] calldata destinations) external {
        for (uint i = 0; i < destinations.length; i++) {
            destinations[i].rebuildCache();
        }
    }

    /* ========== VIEWS ========== */

    function areAddressesImported(bytes32[] calldata names, address[] calldata destinations) external view returns (bool) {
        for (uint i = 0; i < names.length; i++) {
            if (repository[names[i]] != destinations[i]) {
                return false;
            }
        }
        return true;
    }

    function getAddress(bytes32 name) external view returns (address) {
        return repository[name];
    }

    function requireAndGetAddress(bytes32 name, string calldata reason) external view returns (address) {
        address _foundAddress = repository[name];
        require(_foundAddress != address(0), reason);
        return _foundAddress;
    }

    function getPynth(bytes32 key) external view returns (address) {
        IIssuer issuer = IIssuer(repository["Issuer"]);
        require(address(issuer) != address(0), "Cannot find Issuer address");
        return address(issuer.pynths(key));
    }

    /* ========== EVENTS ========== */

    event AddressImported(bytes32 name, address destination);
}


// solhint-disable payable-fallback

// https://docs.peri.finance/contracts/source/contracts/readproxy
contract ReadProxy is Owned {
    address public target;

    constructor(address _owner) public Owned(_owner) {}

    function setTarget(address _target) external onlyOwner {
        target = _target;
        emit TargetUpdated(target);
    }

    function() external {
        // The basics of a proxy read call
        // Note that msg.sender in the underlying will always be the address of this contract.
        assembly {
            calldatacopy(0, 0, calldatasize)

            // Use of staticcall - this will revert if the underlying function mutates state
            let result := staticcall(gas, sload(target_slot), 0, calldatasize, 0, 0)
            returndatacopy(0, 0, returndatasize)

            if iszero(result) {
                revert(0, returndatasize)
            }
            return(0, returndatasize)
        }
    }

    event TargetUpdated(address newTarget);
}


// Inheritance


// Internal references


// https://docs.peri.finance/contracts/source/contracts/mixinresolver
contract MixinResolver {
    AddressResolver public resolver;

    mapping(bytes32 => address) private addressCache;

    constructor(address _resolver) internal {
        resolver = AddressResolver(_resolver);
    }

    /* ========== INTERNAL FUNCTIONS ========== */

    function combineArrays(bytes32[] memory first, bytes32[] memory second)
        internal
        pure
        returns (bytes32[] memory combination)
    {
        combination = new bytes32[](first.length + second.length);

        for (uint i = 0; i < first.length; i++) {
            combination[i] = first[i];
        }

        for (uint j = 0; j < second.length; j++) {
            combination[first.length + j] = second[j];
        }
    }

    /* ========== PUBLIC FUNCTIONS ========== */

    // Note: this function is public not external in order for it to be overridden and invoked via super in subclasses
    function resolverAddressesRequired() public view returns (bytes32[] memory addresses) {}

    function rebuildCache() public {
        bytes32[] memory requiredAddresses = resolverAddressesRequired();
        // The resolver must call this function whenver it updates its state
        for (uint i = 0; i < requiredAddresses.length; i++) {
            bytes32 name = requiredAddresses[i];
            // Note: can only be invoked once the resolver has all the targets needed added
            address destination =
                resolver.requireAndGetAddress(name, string(abi.encodePacked("Resolver missing target: ", name)));
            addressCache[name] = destination;
            emit CacheUpdated(name, destination);
        }
    }

    /* ========== VIEWS ========== */

    function isResolverCached() external view returns (bool) {
        bytes32[] memory requiredAddresses = resolverAddressesRequired();
        for (uint i = 0; i < requiredAddresses.length; i++) {
            bytes32 name = requiredAddresses[i];
            // false if our cache is invalid or if the resolver doesn't have the required address
            if (resolver.getAddress(name) != addressCache[name] || addressCache[name] == address(0)) {
                return false;
            }
        }

        return true;
    }

    /* ========== INTERNAL FUNCTIONS ========== */

    function requireAndGetAddress(bytes32 name) internal view returns (address) {
        address _foundAddress = addressCache[name];
        require(_foundAddress != address(0), string(abi.encodePacked("Missing address: ", name)));
        return _foundAddress;
    }

    /* ========== EVENTS ========== */

    event CacheUpdated(bytes32 name, address destination);
}


// https://docs.peri.finance/contracts/source/interfaces/iflexiblestorage
interface IFlexibleStorage {
    // Views
    function getUIntValue(bytes32 contractName, bytes32 record) external view returns (uint);

    function getUIntValues(bytes32 contractName, bytes32[] calldata records) external view returns (uint[] memory);

    function getIntValue(bytes32 contractName, bytes32 record) external view returns (int);

    function getIntValues(bytes32 contractName, bytes32[] calldata records) external view returns (int[] memory);

    function getAddressValue(bytes32 contractName, bytes32 record) external view returns (address);

    function getAddressValues(bytes32 contractName, bytes32[] calldata records) external view returns (address[] memory);

    function getBoolValue(bytes32 contractName, bytes32 record) external view returns (bool);

    function getBoolValues(bytes32 contractName, bytes32[] calldata records) external view returns (bool[] memory);

    function getBytes32Value(bytes32 contractName, bytes32 record) external view returns (bytes32);

    function getBytes32Values(bytes32 contractName, bytes32[] calldata records) external view returns (bytes32[] memory);

    // Mutative functions
    function deleteUIntValue(bytes32 contractName, bytes32 record) external;

    function deleteIntValue(bytes32 contractName, bytes32 record) external;

    function deleteAddressValue(bytes32 contractName, bytes32 record) external;

    function deleteBoolValue(bytes32 contractName, bytes32 record) external;

    function deleteBytes32Value(bytes32 contractName, bytes32 record) external;

    function setUIntValue(
        bytes32 contractName,
        bytes32 record,
        uint value
    ) external;

    function setUIntValues(
        bytes32 contractName,
        bytes32[] calldata records,
        uint[] calldata values
    ) external;

    function setIntValue(
        bytes32 contractName,
        bytes32 record,
        int value
    ) external;

    function setIntValues(
        bytes32 contractName,
        bytes32[] calldata records,
        int[] calldata values
    ) external;

    function setAddressValue(
        bytes32 contractName,
        bytes32 record,
        address value
    ) external;

    function setAddressValues(
        bytes32 contractName,
        bytes32[] calldata records,
        address[] calldata values
    ) external;

    function setBoolValue(
        bytes32 contractName,
        bytes32 record,
        bool value
    ) external;

    function setBoolValues(
        bytes32 contractName,
        bytes32[] calldata records,
        bool[] calldata values
    ) external;

    function setBytes32Value(
        bytes32 contractName,
        bytes32 record,
        bytes32 value
    ) external;

    function setBytes32Values(
        bytes32 contractName,
        bytes32[] calldata records,
        bytes32[] calldata values
    ) external;
}


// Internal references


// https://docs.peri.finance/contracts/source/contracts/mixinsystemsettings
contract MixinSystemSettings is MixinResolver {
    bytes32 internal constant SETTING_CONTRACT_NAME = "SystemSettings";

    bytes32 internal constant SETTING_WAITING_PERIOD_SECS = "waitingPeriodSecs";
    bytes32 internal constant SETTING_PRICE_DEVIATION_THRESHOLD_FACTOR = "priceDeviationThresholdFactor";
    bytes32 internal constant SETTING_ISSUANCE_RATIO = "issuanceRatio";
    bytes32 internal constant SETTING_FEE_PERIOD_DURATION = "feePeriodDuration";
    bytes32 internal constant SETTING_TARGET_THRESHOLD = "targetThreshold";
    bytes32 internal constant SETTING_LIQUIDATION_DELAY = "liquidationDelay";
    bytes32 internal constant SETTING_LIQUIDATION_RATIO = "liquidationRatio";
    bytes32 internal constant SETTING_LIQUIDATION_PENALTY = "liquidationPenalty";
    bytes32 internal constant SETTING_RATE_STALE_PERIOD = "rateStalePeriod";
    bytes32 internal constant SETTING_EXCHANGE_FEE_RATE = "exchangeFeeRate";
    bytes32 internal constant SETTING_MINIMUM_STAKE_TIME = "minimumStakeTime";
    bytes32 internal constant SETTING_AGGREGATOR_WARNING_FLAGS = "aggregatorWarningFlags";
    bytes32 internal constant SETTING_TRADING_REWARDS_ENABLED = "tradingRewardsEnabled";
    bytes32 internal constant SETTING_DEBT_SNAPSHOT_STALE_TIME = "debtSnapshotStaleTime";
    bytes32 internal constant SETTING_CROSS_DOMAIN_DEPOSIT_GAS_LIMIT = "crossDomainDepositGasLimit";
    bytes32 internal constant SETTING_CROSS_DOMAIN_ESCROW_GAS_LIMIT = "crossDomainEscrowGasLimit";
    bytes32 internal constant SETTING_CROSS_DOMAIN_REWARD_GAS_LIMIT = "crossDomainRewardGasLimit";
    bytes32 internal constant SETTING_CROSS_DOMAIN_WITHDRAWAL_GAS_LIMIT = "crossDomainWithdrawalGasLimit";
    bytes32 internal constant SETTING_EXTERNAL_TOKEN_QUOTA = "externalTokenQuota";

    bytes32 internal constant CONTRACT_FLEXIBLESTORAGE = "FlexibleStorage";

    enum CrossDomainMessageGasLimits {Deposit, Escrow, Reward, Withdrawal}

    constructor(address _resolver) internal MixinResolver(_resolver) {}

    function resolverAddressesRequired() public view returns (bytes32[] memory addresses) {
        addresses = new bytes32[](1);
        addresses[0] = CONTRACT_FLEXIBLESTORAGE;
    }

    function flexibleStorage() internal view returns (IFlexibleStorage) {
        return IFlexibleStorage(requireAndGetAddress(CONTRACT_FLEXIBLESTORAGE));
    }

    function _getGasLimitSetting(CrossDomainMessageGasLimits gasLimitType) internal pure returns (bytes32) {
        if (gasLimitType == CrossDomainMessageGasLimits.Deposit) {
            return SETTING_CROSS_DOMAIN_DEPOSIT_GAS_LIMIT;
        } else if (gasLimitType == CrossDomainMessageGasLimits.Escrow) {
            return SETTING_CROSS_DOMAIN_ESCROW_GAS_LIMIT;
        } else if (gasLimitType == CrossDomainMessageGasLimits.Reward) {
            return SETTING_CROSS_DOMAIN_REWARD_GAS_LIMIT;
        } else if (gasLimitType == CrossDomainMessageGasLimits.Withdrawal) {
            return SETTING_CROSS_DOMAIN_WITHDRAWAL_GAS_LIMIT;
        } else {
            revert("Unknown gas limit type");
        }
    }

    function getCrossDomainMessageGasLimit(CrossDomainMessageGasLimits gasLimitType) internal view returns (uint) {
        return flexibleStorage().getUIntValue(SETTING_CONTRACT_NAME, _getGasLimitSetting(gasLimitType));
    }

    function getTradingRewardsEnabled() internal view returns (bool) {
        return flexibleStorage().getBoolValue(SETTING_CONTRACT_NAME, SETTING_TRADING_REWARDS_ENABLED);
    }

    function getWaitingPeriodSecs() internal view returns (uint) {
        return flexibleStorage().getUIntValue(SETTING_CONTRACT_NAME, SETTING_WAITING_PERIOD_SECS);
    }

    function getPriceDeviationThresholdFactor() internal view returns (uint) {
        return flexibleStorage().getUIntValue(SETTING_CONTRACT_NAME, SETTING_PRICE_DEVIATION_THRESHOLD_FACTOR);
    }

    function getIssuanceRatio() internal view returns (uint) {
        // lookup on flexible storage directly for gas savings (rather than via SystemSettings)
        return flexibleStorage().getUIntValue(SETTING_CONTRACT_NAME, SETTING_ISSUANCE_RATIO);
    }

    function getFeePeriodDuration() internal view returns (uint) {
        // lookup on flexible storage directly for gas savings (rather than via SystemSettings)
        return flexibleStorage().getUIntValue(SETTING_CONTRACT_NAME, SETTING_FEE_PERIOD_DURATION);
    }

    function getTargetThreshold() internal view returns (uint) {
        // lookup on flexible storage directly for gas savings (rather than via SystemSettings)
        return flexibleStorage().getUIntValue(SETTING_CONTRACT_NAME, SETTING_TARGET_THRESHOLD);
    }

    function getLiquidationDelay() internal view returns (uint) {
        return flexibleStorage().getUIntValue(SETTING_CONTRACT_NAME, SETTING_LIQUIDATION_DELAY);
    }

    function getLiquidationRatio() internal view returns (uint) {
        return flexibleStorage().getUIntValue(SETTING_CONTRACT_NAME, SETTING_LIQUIDATION_RATIO);
    }

    function getLiquidationPenalty() internal view returns (uint) {
        return flexibleStorage().getUIntValue(SETTING_CONTRACT_NAME, SETTING_LIQUIDATION_PENALTY);
    }

    function getRateStalePeriod() internal view returns (uint) {
        return flexibleStorage().getUIntValue(SETTING_CONTRACT_NAME, SETTING_RATE_STALE_PERIOD);
    }

    function getExchangeFeeRate(bytes32 currencyKey) internal view returns (uint) {
        return
            flexibleStorage().getUIntValue(
                SETTING_CONTRACT_NAME,
                keccak256(abi.encodePacked(SETTING_EXCHANGE_FEE_RATE, currencyKey))
            );
    }

    function getMinimumStakeTime() internal view returns (uint) {
        return flexibleStorage().getUIntValue(SETTING_CONTRACT_NAME, SETTING_MINIMUM_STAKE_TIME);
    }

    function getAggregatorWarningFlags() internal view returns (address) {
        return flexibleStorage().getAddressValue(SETTING_CONTRACT_NAME, SETTING_AGGREGATOR_WARNING_FLAGS);
    }

    function getDebtSnapshotStaleTime() internal view returns (uint) {
        return flexibleStorage().getUIntValue(SETTING_CONTRACT_NAME, SETTING_DEBT_SNAPSHOT_STALE_TIME);
    }

    function getExternalTokenQuota() internal view returns (uint) {
        return flexibleStorage().getUIntValue(SETTING_CONTRACT_NAME, SETTING_EXTERNAL_TOKEN_QUOTA);
    }
}


// https://docs.peri.finance/contracts/source/interfaces/isystemsettings
interface ISystemSettings {
    // Views
    function priceDeviationThresholdFactor() external view returns (uint);

    function waitingPeriodSecs() external view returns (uint);

    function issuanceRatio() external view returns (uint);

    function feePeriodDuration() external view returns (uint);

    function targetThreshold() external view returns (uint);

    function liquidationDelay() external view returns (uint);

    function liquidationRatio() external view returns (uint);

    function liquidationPenalty() external view returns (uint);

    function rateStalePeriod() external view returns (uint);

    function exchangeFeeRate(bytes32 currencyKey) external view returns (uint);

    function minimumStakeTime() external view returns (uint);

    function externalTokenQuota() external view returns (uint);
}


/**
 * @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) {
        require(b <= a, "SafeMath: subtraction overflow");
        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-solidity/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) {
        // Solidity only automatically asserts when dividing by 0
        require(b > 0, "SafeMath: division by zero");
        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) {
        require(b != 0, "SafeMath: modulo by zero");
        return a % b;
    }
}


// Libraries


// https://docs.peri.finance/contracts/source/libraries/safedecimalmath
library SafeDecimalMath {
    using SafeMath for uint;

    /* Number of decimal places in the representations. */
    uint8 public constant decimals = 18;
    uint8 public constant highPrecisionDecimals = 27;

    /* The number representing 1.0. */
    uint public constant UNIT = 10**uint(decimals);

    /* The number representing 1.0 for higher fidelity numbers. */
    uint public constant PRECISE_UNIT = 10**uint(highPrecisionDecimals);
    uint private constant UNIT_TO_HIGH_PRECISION_CONVERSION_FACTOR = 10**uint(highPrecisionDecimals - decimals);

    /**
     * @return Provides an interface to UNIT.
     */
    function unit() external pure returns (uint) {
        return UNIT;
    }

    /**
     * @return Provides an interface to PRECISE_UNIT.
     */
    function preciseUnit() external pure returns (uint) {
        return PRECISE_UNIT;
    }

    /**
     * @return The result of multiplying x and y, interpreting the operands as fixed-point
     * decimals.
     *
     * @dev A unit factor is divided out after the product of x and y is evaluated,
     * so that product must be less than 2**256. As this is an integer division,
     * the internal division always rounds down. This helps save on gas. Rounding
     * is more expensive on gas.
     */
    function multiplyDecimal(uint x, uint y) internal pure returns (uint) {
        /* Divide by UNIT to remove the extra factor introduced by the product. */
        return x.mul(y) / UNIT;
    }

    /**
     * @return The result of safely multiplying x and y, interpreting the operands
     * as fixed-point decimals of the specified precision unit.
     *
     * @dev The operands should be in the form of a the specified unit factor which will be
     * divided out after the product of x and y is evaluated, so that product must be
     * less than 2**256.
     *
     * Unlike multiplyDecimal, this function rounds the result to the nearest increment.
     * Rounding is useful when you need to retain fidelity for small decimal numbers
     * (eg. small fractions or percentages).
     */
    function _multiplyDecimalRound(
        uint x,
        uint y,
        uint precisionUnit
    ) private pure returns (uint) {
        /* Divide by UNIT to remove the extra factor introduced by the product. */
        uint quotientTimesTen = x.mul(y) / (precisionUnit / 10);

        if (quotientTimesTen % 10 >= 5) {
            quotientTimesTen += 10;
        }

        return quotientTimesTen / 10;
    }

    /**
     * @return The result of safely multiplying x and y, interpreting the operands
     * as fixed-point decimals of a precise unit.
     *
     * @dev The operands should be in the precise unit factor which will be
     * divided out after the product of x and y is evaluated, so that product must be
     * less than 2**256.
     *
     * Unlike multiplyDecimal, this function rounds the result to the nearest increment.
     * Rounding is useful when you need to retain fidelity for small decimal numbers
     * (eg. small fractions or percentages).
     */
    function multiplyDecimalRoundPrecise(uint x, uint y) internal pure returns (uint) {
        return _multiplyDecimalRound(x, y, PRECISE_UNIT);
    }

    /**
     * @return The result of safely multiplying x and y, interpreting the operands
     * as fixed-point decimals of a standard unit.
     *
     * @dev The operands should be in the standard unit factor which will be
     * divided out after the product of x and y is evaluated, so that product must be
     * less than 2**256.
     *
     * Unlike multiplyDecimal, this function rounds the result to the nearest increment.
     * Rounding is useful when you need to retain fidelity for small decimal numbers
     * (eg. small fractions or percentages).
     */
    function multiplyDecimalRound(uint x, uint y) internal pure returns (uint) {
        return _multiplyDecimalRound(x, y, UNIT);
    }

    /**
     * @return The result of safely dividing x and y. The return value is a high
     * precision decimal.
     *
     * @dev y is divided after the product of x and the standard precision unit
     * is evaluated, so the product of x and UNIT must be less than 2**256. As
     * this is an integer division, the result is always rounded down.
     * This helps save on gas. Rounding is more expensive on gas.
     */
    function divideDecimal(uint x, uint y) internal pure returns (uint) {
        /* Reintroduce the UNIT factor that will be divided out by y. */
        return x.mul(UNIT).div(y);
    }

    /**
     * @return The result of safely dividing x and y. The return value is as a rounded
     * decimal in the precision unit specified in the parameter.
     *
     * @dev y is divided after the product of x and the specified precision unit
     * is evaluated, so the product of x and the specified precision unit must
     * be less than 2**256. The result is rounded to the nearest increment.
     */
    function _divideDecimalRound(
        uint x,
        uint y,
        uint precisionUnit
    ) private pure returns (uint) {
        uint resultTimesTen = x.mul(precisionUnit * 10).div(y);

        if (resultTimesTen % 10 >= 5) {
            resultTimesTen += 10;
        }

        return resultTimesTen / 10;
    }

    /**
     * @return The result of safely dividing x and y. The return value is as a rounded
     * standard precision decimal.
     *
     * @dev y is divided after the product of x and the standard precision unit
     * is evaluated, so the product of x and the standard precision unit must
     * be less than 2**256. The result is rounded to the nearest increment.
     */
    function divideDecimalRound(uint x, uint y) internal pure returns (uint) {
        return _divideDecimalRound(x, y, UNIT);
    }

    /**
     * @return The result of safely dividing x and y. The return value is as a rounded
     * high precision decimal.
     *
     * @dev y is divided after the product of x and the high precision unit
     * is evaluated, so the product of x and the high precision unit must
     * be less than 2**256. The result is rounded to the nearest increment.
     */
    function divideDecimalRoundPrecise(uint x, uint y) internal pure returns (uint) {
        return _divideDecimalRound(x, y, PRECISE_UNIT);
    }

    /**
     * @dev Convert a standard decimal representation to a high precision one.
     */
    function decimalToPreciseDecimal(uint i) internal pure returns (uint) {
        return i.mul(UNIT_TO_HIGH_PRECISION_CONVERSION_FACTOR);
    }

    /**
     * @dev Convert a high precision decimal to a standard decimal representation.
     */
    function preciseDecimalToDecimal(uint i) internal pure returns (uint) {
        uint quotientTimesTen = i / (UNIT_TO_HIGH_PRECISION_CONVERSION_FACTOR / 10);

        if (quotientTimesTen % 10 >= 5) {
            quotientTimesTen += 10;
        }

        return quotientTimesTen / 10;
    }

    /**
     * @dev Round down the value with given number
     */
    function roundDownDecimal(uint x, uint d) internal pure returns (uint) {
        return x.div(10**d).mul(10**d);
    }

    /**
     * @dev Round up the value with given number
     */
    function roundUpDecimal(uint x, uint d) internal pure returns (uint) {
        uint _decimal = 10**d;

        if (x % _decimal > 0) {
            x = x.add(10**d);
        }

        return x.div(_decimal).mul(_decimal);
    }
}


// Inheritance


// Libraries


// https://docs.peri.finance/contracts/source/contracts/systemsettings
contract SystemSettings is Owned, MixinSystemSettings, ISystemSettings {
    using SafeMath for uint;
    using SafeDecimalMath for uint;

    // No more pynths may be issued than the value of PERI backing them.
    uint public constant MAX_ISSUANCE_RATIO = 1e18;

    // The fee period must be between 1 day and 60 days.
    uint public constant MIN_FEE_PERIOD_DURATION = 1 days;
    uint public constant MAX_FEE_PERIOD_DURATION = 60 days;

    uint public constant MAX_TARGET_THRESHOLD = 50;

    uint public constant MAX_LIQUIDATION_RATIO = 1e18; // 100% issuance ratio

    uint public constant MAX_LIQUIDATION_PENALTY = 1e18 / 4; // Max 25% liquidation penalty / bonus

    uint public constant RATIO_FROM_TARGET_BUFFER = 2e18; // 200% - mininimum buffer between issuance ratio and liquidation ratio

    uint public constant MAX_LIQUIDATION_DELAY = 30 days;
    uint public constant MIN_LIQUIDATION_DELAY = 1 days;

    // Exchange fee may not exceed 10%.
    uint public constant MAX_EXCHANGE_FEE_RATE = 1e18 / 10;

    // Minimum Stake time may not exceed 1 weeks.
    uint public constant MAX_MINIMUM_STAKE_TIME = 1 weeks;

    uint public constant MAX_CROSS_DOMAIN_GAS_LIMIT = 8e6;
    uint public constant MIN_CROSS_DOMAIN_GAS_LIMIT = 3e6;

    uint public constant MAX_EXTERNAL_TOKEN_QUOTA = 8e17;

    constructor(address _owner, address _resolver) public Owned(_owner) MixinSystemSettings(_resolver) {}

    // ========== VIEWS ==========

    // SIP-37 Fee Reclamation
    // The number of seconds after an exchange is executed that must be waited
    // before settlement.
    function waitingPeriodSecs() external view returns (uint) {
        return getWaitingPeriodSecs();
    }

    // SIP-65 Decentralized Circuit Breaker
    // The factor amount expressed in decimal format
    // E.g. 3e18 = factor 3, meaning movement up to 3x and above or down to 1/3x and below
    function priceDeviationThresholdFactor() external view returns (uint) {
        return getPriceDeviationThresholdFactor();
    }

    // The raio of collateral
    // Expressed in 18 decimals. So 800% cratio is 100/800 = 0.125 (0.125e18)
    function issuanceRatio() external view returns (uint) {
        return getIssuanceRatio();
    }

    // How long a fee period lasts at a minimum. It is required for
    // anyone to roll over the periods, so they are not guaranteed
    // to roll over at exactly this duration, but the contract enforces
    // that they cannot roll over any quicker than this duration.
    function feePeriodDuration() external view returns (uint) {
        return getFeePeriodDuration();
    }

    // Users are unable to claim fees if their collateralisation ratio drifts out of target threshold
    function targetThreshold() external view returns (uint) {
        return getTargetThreshold();
    }

    // SIP-15 Liquidations
    // liquidation time delay after address flagged (seconds)
    function liquidationDelay() external view returns (uint) {
        return getLiquidationDelay();
    }

    // SIP-15 Liquidations
    // issuance ratio when account can be flagged for liquidation (with 18 decimals), e.g 0.5 issuance ratio
    // when flag means 1/0.5 = 200% cratio
    function liquidationRatio() external view returns (uint) {
        return getLiquidationRatio();
    }

    // SIP-15 Liquidations
    // penalty taken away from target of liquidation (with 18 decimals). E.g. 10% is 0.1e18
    function liquidationPenalty() external view returns (uint) {
        return getLiquidationPenalty();
    }

    // How long will the ExchangeRates contract assume the rate of any asset is correct
    function rateStalePeriod() external view returns (uint) {
        return getRateStalePeriod();
    }

    function exchangeFeeRate(bytes32 currencyKey) external view returns (uint) {
        return getExchangeFeeRate(currencyKey);
    }

    function minimumStakeTime() external view returns (uint) {
        return getMinimumStakeTime();
    }

    function debtSnapshotStaleTime() external view returns (uint) {
        return getDebtSnapshotStaleTime();
    }

    function aggregatorWarningFlags() external view returns (address) {
        return getAggregatorWarningFlags();
    }

    // SIP-63 Trading incentives
    // determines if Exchanger records fee entries in TradingRewards
    function tradingRewardsEnabled() external view returns (bool) {
        return getTradingRewardsEnabled();
    }

    function crossDomainMessageGasLimit(CrossDomainMessageGasLimits gasLimitType) external view returns (uint) {
        return getCrossDomainMessageGasLimit(gasLimitType);
    }

    function externalTokenQuota() external view returns (uint) {
        return getExternalTokenQuota();
    }

    // ========== RESTRICTED ==========

    function setCrossDomainMessageGasLimit(CrossDomainMessageGasLimits _gasLimitType, uint _crossDomainMessageGasLimit)
        external
        onlyOwner
    {
        require(
            _crossDomainMessageGasLimit >= MIN_CROSS_DOMAIN_GAS_LIMIT &&
                _crossDomainMessageGasLimit <= MAX_CROSS_DOMAIN_GAS_LIMIT,
            "Out of range xDomain gasLimit"
        );
        flexibleStorage().setUIntValue(
            SETTING_CONTRACT_NAME,
            _getGasLimitSetting(_gasLimitType),
            _crossDomainMessageGasLimit
        );
        emit CrossDomainMessageGasLimitChanged(_gasLimitType, _crossDomainMessageGasLimit);
    }

    function setTradingRewardsEnabled(bool _tradingRewardsEnabled) external onlyOwner {
        flexibleStorage().setBoolValue(SETTING_CONTRACT_NAME, SETTING_TRADING_REWARDS_ENABLED, _tradingRewardsEnabled);
        emit TradingRewardsEnabled(_tradingRewardsEnabled);
    }

    function setWaitingPeriodSecs(uint _waitingPeriodSecs) external onlyOwner {
        flexibleStorage().setUIntValue(SETTING_CONTRACT_NAME, SETTING_WAITING_PERIOD_SECS, _waitingPeriodSecs);
        emit WaitingPeriodSecsUpdated(_waitingPeriodSecs);
    }

    function setPriceDeviationThresholdFactor(uint _priceDeviationThresholdFactor) external onlyOwner {
        flexibleStorage().setUIntValue(
            SETTING_CONTRACT_NAME,
            SETTING_PRICE_DEVIATION_THRESHOLD_FACTOR,
            _priceDeviationThresholdFactor
        );
        emit PriceDeviationThresholdUpdated(_priceDeviationThresholdFactor);
    }

    function setIssuanceRatio(uint _issuanceRatio) external onlyOwner {
        require(_issuanceRatio <= MAX_ISSUANCE_RATIO, "New issuance ratio cannot exceed MAX_ISSUANCE_RATIO");
        flexibleStorage().setUIntValue(SETTING_CONTRACT_NAME, SETTING_ISSUANCE_RATIO, _issuanceRatio);
        emit IssuanceRatioUpdated(_issuanceRatio);
    }

    function setFeePeriodDuration(uint _feePeriodDuration) external onlyOwner {
        require(_feePeriodDuration >= MIN_FEE_PERIOD_DURATION, "value < MIN_FEE_PERIOD_DURATION");
        require(_feePeriodDuration <= MAX_FEE_PERIOD_DURATION, "value > MAX_FEE_PERIOD_DURATION");

        flexibleStorage().setUIntValue(SETTING_CONTRACT_NAME, SETTING_FEE_PERIOD_DURATION, _feePeriodDuration);

        emit FeePeriodDurationUpdated(_feePeriodDuration);
    }

    function setTargetThreshold(uint _percent) external onlyOwner {
        require(_percent <= MAX_TARGET_THRESHOLD, "Threshold too high");

        uint _targetThreshold = _percent.mul(SafeDecimalMath.unit()).div(100);

        flexibleStorage().setUIntValue(SETTING_CONTRACT_NAME, SETTING_TARGET_THRESHOLD, _targetThreshold);

        emit TargetThresholdUpdated(_targetThreshold);
    }

    function setLiquidationDelay(uint time) external onlyOwner {
        require(time <= MAX_LIQUIDATION_DELAY, "Must be less than 30 days");
        require(time >= MIN_LIQUIDATION_DELAY, "Must be greater than 1 day");

        flexibleStorage().setUIntValue(SETTING_CONTRACT_NAME, SETTING_LIQUIDATION_DELAY, time);

        emit LiquidationDelayUpdated(time);
    }

    // The collateral / issuance ratio ( debt / collateral ) is higher when there is less collateral backing their debt
    // Upper bound liquidationRatio is 1 + penalty (100% + 10% = 110%) to allow collateral value to cover debt and liquidation penalty
    function setLiquidationRatio(uint _liquidationRatio) external onlyOwner {
        require(
            _liquidationRatio <= MAX_LIQUIDATION_RATIO.divideDecimal(SafeDecimalMath.unit().add(getLiquidationPenalty())),
            "liquidationRatio > MAX_LIQUIDATION_RATIO / (1 + penalty)"
        );

        // MIN_LIQUIDATION_RATIO is a product of target issuance ratio * RATIO_FROM_TARGET_BUFFER
        // Ensures that liquidation ratio is set so that there is a buffer between the issuance ratio and liquidation ratio.
        uint MIN_LIQUIDATION_RATIO = getIssuanceRatio().multiplyDecimal(RATIO_FROM_TARGET_BUFFER);
        require(_liquidationRatio >= MIN_LIQUIDATION_RATIO, "liquidationRatio < MIN_LIQUIDATION_RATIO");

        flexibleStorage().setUIntValue(SETTING_CONTRACT_NAME, SETTING_LIQUIDATION_RATIO, _liquidationRatio);

        emit LiquidationRatioUpdated(_liquidationRatio);
    }

    function setLiquidationPenalty(uint penalty) external onlyOwner {
        require(penalty <= MAX_LIQUIDATION_PENALTY, "penalty > MAX_LIQUIDATION_PENALTY");

        flexibleStorage().setUIntValue(SETTING_CONTRACT_NAME, SETTING_LIQUIDATION_PENALTY, penalty);

        emit LiquidationPenaltyUpdated(penalty);
    }

    function setRateStalePeriod(uint period) external onlyOwner {
        flexibleStorage().setUIntValue(SETTING_CONTRACT_NAME, SETTING_RATE_STALE_PERIOD, period);

        emit RateStalePeriodUpdated(period);
    }

    function setExchangeFeeRateForPynths(bytes32[] calldata pynthKeys, uint256[] calldata exchangeFeeRates)
        external
        onlyOwner
    {
        require(pynthKeys.length == exchangeFeeRates.length, "Array lengths dont match");
        for (uint i = 0; i < pynthKeys.length; i++) {
            require(exchangeFeeRates[i] <= MAX_EXCHANGE_FEE_RATE, "MAX_EXCHANGE_FEE_RATE exceeded");
            flexibleStorage().setUIntValue(
                SETTING_CONTRACT_NAME,
                keccak256(abi.encodePacked(SETTING_EXCHANGE_FEE_RATE, pynthKeys[i])),
                exchangeFeeRates[i]
            );
            emit ExchangeFeeUpdated(pynthKeys[i], exchangeFeeRates[i]);
        }
    }

    function setMinimumStakeTime(uint _seconds) external onlyOwner {
        require(_seconds <= MAX_MINIMUM_STAKE_TIME, "stake time exceed maximum 1 week");
        flexibleStorage().setUIntValue(SETTING_CONTRACT_NAME, SETTING_MINIMUM_STAKE_TIME, _seconds);
        emit MinimumStakeTimeUpdated(_seconds);
    }

    function setDebtSnapshotStaleTime(uint _seconds) external onlyOwner {
        flexibleStorage().setUIntValue(SETTING_CONTRACT_NAME, SETTING_DEBT_SNAPSHOT_STALE_TIME, _seconds);
        emit DebtSnapshotStaleTimeUpdated(_seconds);
    }

    function setAggregatorWarningFlags(address _flags) external onlyOwner {
        require(_flags != address(0), "Valid address must be given");
        flexibleStorage().setAddressValue(SETTING_CONTRACT_NAME, SETTING_AGGREGATOR_WARNING_FLAGS, _flags);
        emit AggregatorWarningFlagsUpdated(_flags);
    }

    function setExternalTokenQuota(uint _newQuota) external onlyOwner {
        require(_newQuota <= MAX_EXTERNAL_TOKEN_QUOTA, "new quota exceeds maximum 100 percentage");

        flexibleStorage().setUIntValue(SETTING_CONTRACT_NAME, SETTING_EXTERNAL_TOKEN_QUOTA, _newQuota);

        emit ExternalTokenQuotaUpdated(_newQuota);
    }

    // ========== EVENTS ==========
    event CrossDomainMessageGasLimitChanged(CrossDomainMessageGasLimits gasLimitType, uint newLimit);
    event TradingRewardsEnabled(bool enabled);
    event WaitingPeriodSecsUpdated(uint waitingPeriodSecs);
    event PriceDeviationThresholdUpdated(uint threshold);
    event IssuanceRatioUpdated(uint newRatio);
    event FeePeriodDurationUpdated(uint newFeePeriodDuration);
    event TargetThresholdUpdated(uint newTargetThreshold);
    event LiquidationDelayUpdated(uint newDelay);
    event LiquidationRatioUpdated(uint newRatio);
    event LiquidationPenaltyUpdated(uint newPenalty);
    event RateStalePeriodUpdated(uint rateStalePeriod);
    event ExchangeFeeUpdated(bytes32 pynthKey, uint newExchangeFeeRate);
    event MinimumStakeTimeUpdated(uint minimumStakeTime);
    event DebtSnapshotStaleTimeUpdated(uint debtSnapshotStaleTime);
    event AggregatorWarningFlagsUpdated(address flags);
    event ExternalTokenQuotaUpdated(uint quota);
}