/*
   ____            __   __        __   _
  / __/__ __ ___  / /_ / /  ___  / /_ (_)__ __
 _\ \ / // // _ \/ __// _ \/ -_)/ __// / \ \ /
/___/ \_, //_//_/\__//_//_/\__/ \__//_/ /_\_\
     /___/

* Synthetix: ExchangeRatesWithDexPricing.sol
*
* Latest source (may be newer): https://github.com/Synthetixio/synthetix/blob/master/contracts/ExchangeRatesWithDexPricing.sol
* Docs: https://docs.synthetix.io/contracts/ExchangeRatesWithDexPricing
*
* Contract Dependencies: 
*	- ExchangeRates
*	- IAddressResolver
*	- IExchangeRates
*	- MixinResolver
*	- MixinSystemSettings
*	- Owned
* Libraries: 
*	- SafeDecimalMath
*	- SafeMath
*
* MIT License
* ===========
*
* Copyright (c) 2022 Synthetix
*
* 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.synthetix.io/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.synthetix.io/contracts/source/interfaces/iaddressresolver
interface IAddressResolver {
    function getAddress(bytes32 name) external view returns (address);

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

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


// https://docs.synthetix.io/contracts/source/interfaces/isynth
interface ISynth {
    // Views
    function currencyKey() external view returns (bytes32);

    function transferableSynths(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 Synthetix
    function burn(address account, uint amount) external;

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


// https://docs.synthetix.io/contracts/source/interfaces/iissuer
interface IIssuer {
    // Views
    function anySynthOrSNXRateIsInvalid() external view returns (bool anyRateInvalid);

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

    function availableSynthCount() external view returns (uint);

    function availableSynths(uint index) external view returns (ISynth);

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

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

    function minimumStakeTime() external view returns (uint);

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

    function synths(bytes32 currencyKey) external view returns (ISynth);

    function getSynths(bytes32[] calldata currencyKeys) external view returns (ISynth[] memory);

    function synthsByAddress(address synthAddress) external view returns (bytes32);

    function totalIssuedSynths(bytes32 currencyKey, bool excludeOtherCollateral) external view returns (uint);

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

    // Restricted: used internally to Synthetix
    function issueSynths(address from, uint amount) external;

    function issueSynthsOnBehalf(
        address issueFor,
        address from,
        uint amount
    ) external;

    function issueMaxSynths(address from) external;

    function issueMaxSynthsOnBehalf(address issueFor, address from) external;

    function burnSynths(address from, uint amount) external;

    function burnSynthsOnBehalf(
        address burnForAddress,
        address from,
        uint amount
    ) external;

    function burnSynthsToTarget(address from) external;

    function burnSynthsToTargetOnBehalf(address burnForAddress, address from) external;

    function burnForRedemption(
        address deprecatedSynthProxy,
        address account,
        uint balance
    ) external;

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

    function setCurrentPeriodId(uint128 periodId) external;

    function issueSynthsWithoutDebt(
        bytes32 currencyKey,
        address to,
        uint amount
    ) external returns (bool rateInvalid);

    function burnSynthsWithoutDebt(
        bytes32 currencyKey,
        address to,
        uint amount
    ) external returns (bool rateInvalid);
}


// Inheritance


// Internal references


// https://docs.synthetix.io/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 getSynth(bytes32 key) external view returns (address) {
        IIssuer issuer = IIssuer(repository["Issuer"]);
        require(address(issuer) != address(0), "Cannot find Issuer address");
        return address(issuer.synths(key));
    }

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

    event AddressImported(bytes32 name, address destination);
}


// Internal references


// https://docs.synthetix.io/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.synthetix.io/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.synthetix.io/contracts/source/contracts/mixinsystemsettings
contract MixinSystemSettings is MixinResolver {
    // must match the one defined SystemSettingsLib, defined in both places due to sol v0.5 limitations
    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";
    /* ========== Exchange Fees Related ========== */
    bytes32 internal constant SETTING_EXCHANGE_FEE_RATE = "exchangeFeeRate";
    bytes32 internal constant SETTING_EXCHANGE_DYNAMIC_FEE_THRESHOLD = "exchangeDynamicFeeThreshold";
    bytes32 internal constant SETTING_EXCHANGE_DYNAMIC_FEE_WEIGHT_DECAY = "exchangeDynamicFeeWeightDecay";
    bytes32 internal constant SETTING_EXCHANGE_DYNAMIC_FEE_ROUNDS = "exchangeDynamicFeeRounds";
    bytes32 internal constant SETTING_EXCHANGE_MAX_DYNAMIC_FEE = "exchangeMaxDynamicFee";
    /* ========== End Exchange Fees Related ========== */
    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_CROSS_DOMAIN_FEE_PERIOD_CLOSE_GAS_LIMIT = "crossDomainCloseGasLimit";
    bytes32 internal constant SETTING_CROSS_DOMAIN_RELAY_GAS_LIMIT = "crossDomainRelayGasLimit";
    bytes32 internal constant SETTING_ETHER_WRAPPER_MAX_ETH = "etherWrapperMaxETH";
    bytes32 internal constant SETTING_ETHER_WRAPPER_MINT_FEE_RATE = "etherWrapperMintFeeRate";
    bytes32 internal constant SETTING_ETHER_WRAPPER_BURN_FEE_RATE = "etherWrapperBurnFeeRate";
    bytes32 internal constant SETTING_WRAPPER_MAX_TOKEN_AMOUNT = "wrapperMaxTokens";
    bytes32 internal constant SETTING_WRAPPER_MINT_FEE_RATE = "wrapperMintFeeRate";
    bytes32 internal constant SETTING_WRAPPER_BURN_FEE_RATE = "wrapperBurnFeeRate";
    bytes32 internal constant SETTING_INTERACTION_DELAY = "interactionDelay";
    bytes32 internal constant SETTING_COLLAPSE_FEE_RATE = "collapseFeeRate";
    bytes32 internal constant SETTING_ATOMIC_MAX_VOLUME_PER_BLOCK = "atomicMaxVolumePerBlock";
    bytes32 internal constant SETTING_ATOMIC_TWAP_WINDOW = "atomicTwapWindow";
    bytes32 internal constant SETTING_ATOMIC_EQUIVALENT_FOR_DEX_PRICING = "atomicEquivalentForDexPricing";
    bytes32 internal constant SETTING_ATOMIC_EXCHANGE_FEE_RATE = "atomicExchangeFeeRate";
    bytes32 internal constant SETTING_ATOMIC_VOLATILITY_CONSIDERATION_WINDOW = "atomicVolConsiderationWindow";
    bytes32 internal constant SETTING_ATOMIC_VOLATILITY_UPDATE_THRESHOLD = "atomicVolUpdateThreshold";
    bytes32 internal constant SETTING_PURE_CHAINLINK_PRICE_FOR_ATOMIC_SWAPS_ENABLED = "pureChainlinkForAtomicsEnabled";
    bytes32 internal constant SETTING_CROSS_SYNTH_TRANSFER_ENABLED = "crossChainSynthTransferEnabled";

    bytes32 internal constant CONTRACT_FLEXIBLESTORAGE = "FlexibleStorage";

    enum CrossDomainMessageGasLimits {Deposit, Escrow, Reward, Withdrawal, CloseFeePeriod, Relay}

    struct DynamicFeeConfig {
        uint threshold;
        uint weightDecay;
        uint rounds;
        uint maxFee;
    }

    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 if (gasLimitType == CrossDomainMessageGasLimits.Relay) {
            return SETTING_CROSS_DOMAIN_RELAY_GAS_LIMIT;
        } else if (gasLimitType == CrossDomainMessageGasLimits.CloseFeePeriod) {
            return SETTING_CROSS_DOMAIN_FEE_PERIOD_CLOSE_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);
    }

    /* ========== Exchange Related Fees ========== */
    function getExchangeFeeRate(bytes32 currencyKey) internal view returns (uint) {
        return
            flexibleStorage().getUIntValue(
                SETTING_CONTRACT_NAME,
                keccak256(abi.encodePacked(SETTING_EXCHANGE_FEE_RATE, currencyKey))
            );
    }

    /// @notice Get exchange dynamic fee related keys
    /// @return threshold, weight decay, rounds, and max fee
    function getExchangeDynamicFeeConfig() internal view returns (DynamicFeeConfig memory) {
        bytes32[] memory keys = new bytes32[](4);
        keys[0] = SETTING_EXCHANGE_DYNAMIC_FEE_THRESHOLD;
        keys[1] = SETTING_EXCHANGE_DYNAMIC_FEE_WEIGHT_DECAY;
        keys[2] = SETTING_EXCHANGE_DYNAMIC_FEE_ROUNDS;
        keys[3] = SETTING_EXCHANGE_MAX_DYNAMIC_FEE;
        uint[] memory values = flexibleStorage().getUIntValues(SETTING_CONTRACT_NAME, keys);
        return DynamicFeeConfig({threshold: values[0], weightDecay: values[1], rounds: values[2], maxFee: values[3]});
    }

    /* ========== End Exchange Related Fees ========== */

    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 getEtherWrapperMaxETH() internal view returns (uint) {
        return flexibleStorage().getUIntValue(SETTING_CONTRACT_NAME, SETTING_ETHER_WRAPPER_MAX_ETH);
    }

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

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

    function getWrapperMaxTokenAmount(address wrapper) internal view returns (uint) {
        return
            flexibleStorage().getUIntValue(
                SETTING_CONTRACT_NAME,
                keccak256(abi.encodePacked(SETTING_WRAPPER_MAX_TOKEN_AMOUNT, wrapper))
            );
    }

    function getWrapperMintFeeRate(address wrapper) internal view returns (int) {
        return
            flexibleStorage().getIntValue(
                SETTING_CONTRACT_NAME,
                keccak256(abi.encodePacked(SETTING_WRAPPER_MINT_FEE_RATE, wrapper))
            );
    }

    function getWrapperBurnFeeRate(address wrapper) internal view returns (int) {
        return
            flexibleStorage().getIntValue(
                SETTING_CONTRACT_NAME,
                keccak256(abi.encodePacked(SETTING_WRAPPER_BURN_FEE_RATE, wrapper))
            );
    }

    function getInteractionDelay(address collateral) internal view returns (uint) {
        return
            flexibleStorage().getUIntValue(
                SETTING_CONTRACT_NAME,
                keccak256(abi.encodePacked(SETTING_INTERACTION_DELAY, collateral))
            );
    }

    function getCollapseFeeRate(address collateral) internal view returns (uint) {
        return
            flexibleStorage().getUIntValue(
                SETTING_CONTRACT_NAME,
                keccak256(abi.encodePacked(SETTING_COLLAPSE_FEE_RATE, collateral))
            );
    }

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

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

    function getAtomicEquivalentForDexPricing(bytes32 currencyKey) internal view returns (address) {
        return
            flexibleStorage().getAddressValue(
                SETTING_CONTRACT_NAME,
                keccak256(abi.encodePacked(SETTING_ATOMIC_EQUIVALENT_FOR_DEX_PRICING, currencyKey))
            );
    }

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

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

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

    function getPureChainlinkPriceForAtomicSwapsEnabled(bytes32 currencyKey) internal view returns (bool) {
        return
            flexibleStorage().getBoolValue(
                SETTING_CONTRACT_NAME,
                keccak256(abi.encodePacked(SETTING_PURE_CHAINLINK_PRICE_FOR_ATOMIC_SWAPS_ENABLED, currencyKey))
            );
    }

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


// https://docs.synthetix.io/contracts/source/interfaces/ierc20
interface IERC20 {
    // ERC20 Optional Views
    function name() external view returns (string memory);

    function symbol() external view returns (string memory);

    function decimals() external view returns (uint8);

    // Views
    function totalSupply() external view returns (uint);

    function balanceOf(address owner) external view returns (uint);

    function allowance(address owner, address spender) external view returns (uint);

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

    function approve(address spender, uint value) external returns (bool);

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

    // Events
    event Transfer(address indexed from, address indexed to, uint value);

    event Approval(address indexed owner, address indexed spender, uint value);
}


// https://docs.synthetix.io/contracts/source/interfaces/iexchangerates
interface IExchangeRates {
    // Structs
    struct RateAndUpdatedTime {
        uint216 rate;
        uint40 time;
    }

    // Views
    function aggregators(bytes32 currencyKey) external view returns (address);

    function aggregatorWarningFlags() external view returns (address);

    function anyRateIsInvalid(bytes32[] calldata currencyKeys) external view returns (bool);

    function anyRateIsInvalidAtRound(bytes32[] calldata currencyKeys, uint[] calldata roundIds) external view returns (bool);

    function currenciesUsingAggregator(address aggregator) external view returns (bytes32[] memory);

    function effectiveValue(
        bytes32 sourceCurrencyKey,
        uint sourceAmount,
        bytes32 destinationCurrencyKey
    ) external view returns (uint value);

    function effectiveValueAndRates(
        bytes32 sourceCurrencyKey,
        uint sourceAmount,
        bytes32 destinationCurrencyKey
    )
        external
        view
        returns (
            uint value,
            uint sourceRate,
            uint destinationRate
        );

    function effectiveValueAndRatesAtRound(
        bytes32 sourceCurrencyKey,
        uint sourceAmount,
        bytes32 destinationCurrencyKey,
        uint roundIdForSrc,
        uint roundIdForDest
    )
        external
        view
        returns (
            uint value,
            uint sourceRate,
            uint destinationRate
        );

    function effectiveAtomicValueAndRates(
        bytes32 sourceCurrencyKey,
        uint sourceAmount,
        bytes32 destinationCurrencyKey
    )
        external
        view
        returns (
            uint value,
            uint systemValue,
            uint systemSourceRate,
            uint systemDestinationRate
        );

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

    function getLastRoundIdBeforeElapsedSecs(
        bytes32 currencyKey,
        uint startingRoundId,
        uint startingTimestamp,
        uint timediff
    ) external view returns (uint);

    function lastRateUpdateTimes(bytes32 currencyKey) external view returns (uint256);

    function rateAndTimestampAtRound(bytes32 currencyKey, uint roundId) external view returns (uint rate, uint time);

    function rateAndUpdatedTime(bytes32 currencyKey) external view returns (uint rate, uint time);

    function rateAndInvalid(bytes32 currencyKey) external view returns (uint rate, bool isInvalid);

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

    function rateIsFlagged(bytes32 currencyKey) external view returns (bool);

    function rateIsInvalid(bytes32 currencyKey) external view returns (bool);

    function rateIsStale(bytes32 currencyKey) external view returns (bool);

    function rateStalePeriod() external view returns (uint);

    function ratesAndUpdatedTimeForCurrencyLastNRounds(
        bytes32 currencyKey,
        uint numRounds,
        uint roundId
    ) external view returns (uint[] memory rates, uint[] memory times);

    function ratesAndInvalidForCurrencies(bytes32[] calldata currencyKeys)
        external
        view
        returns (uint[] memory rates, bool anyRateInvalid);

    function ratesForCurrencies(bytes32[] calldata currencyKeys) external view returns (uint[] memory);

    function synthTooVolatileForAtomicExchange(bytes32 currencyKey) external view returns (bool);
}


/**
 * @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.synthetix.io/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;
    }

    // Computes `a - b`, setting the value to 0 if b > a.
    function floorsub(uint a, uint b) internal pure returns (uint) {
        return b >= a ? 0 : a - b;
    }

    /* ---------- Utilities ---------- */
    /*
     * Absolute value of the input, returned as a signed number.
     */
    function signedAbs(int x) internal pure returns (int) {
        return x < 0 ? -x : x;
    }

    /*
     * Absolute value of the input, returned as an unsigned number.
     */
    function abs(int x) internal pure returns (uint) {
        return uint(signedAbs(x));
    }
}


interface AggregatorInterface {
  function latestAnswer() external view returns (int256);
  function latestTimestamp() external view returns (uint256);
  function latestRound() external view returns (uint256);
  function getAnswer(uint256 roundId) external view returns (int256);
  function getTimestamp(uint256 roundId) external view returns (uint256);

  event AnswerUpdated(int256 indexed current, uint256 indexed roundId, uint256 timestamp);
  event NewRound(uint256 indexed roundId, address indexed startedBy, uint256 startedAt);
}


interface AggregatorV3Interface {

  function decimals() external view returns (uint8);
  function description() external view returns (string memory);
  function version() external view returns (uint256);

  // getRoundData and latestRoundData should both raise "No data present"
  // if they do not have data to report, instead of returning unset values
  // which could be misinterpreted as actual reported values.
  function getRoundData(uint80 _roundId)
    external
    view
    returns (
      uint80 roundId,
      int256 answer,
      uint256 startedAt,
      uint256 updatedAt,
      uint80 answeredInRound
    );
  function latestRoundData()
    external
    view
    returns (
      uint80 roundId,
      int256 answer,
      uint256 startedAt,
      uint256 updatedAt,
      uint80 answeredInRound
    );

}


/**
 * @title The V2 & V3 Aggregator Interface
 * @notice Solidity V0.5 does not allow interfaces to inherit from other
 * interfaces so this contract is a combination of v0.5 AggregatorInterface.sol
 * and v0.5 AggregatorV3Interface.sol.
 */
interface AggregatorV2V3Interface {
  //
  // V2 Interface:
  //
  function latestAnswer() external view returns (int256);
  function latestTimestamp() external view returns (uint256);
  function latestRound() external view returns (uint256);
  function getAnswer(uint256 roundId) external view returns (int256);
  function getTimestamp(uint256 roundId) external view returns (uint256);

  event AnswerUpdated(int256 indexed current, uint256 indexed roundId, uint256 timestamp);
  event NewRound(uint256 indexed roundId, address indexed startedBy, uint256 startedAt);

  //
  // V3 Interface:
  //
  function decimals() external view returns (uint8);
  function description() external view returns (string memory);
  function version() external view returns (uint256);

  // getRoundData and latestRoundData should both raise "No data present"
  // if they do not have data to report, instead of returning unset values
  // which could be misinterpreted as actual reported values.
  function getRoundData(uint80 _roundId)
    external
    view
    returns (
      uint80 roundId,
      int256 answer,
      uint256 startedAt,
      uint256 updatedAt,
      uint80 answeredInRound
    );
  function latestRoundData()
    external
    view
    returns (
      uint80 roundId,
      int256 answer,
      uint256 startedAt,
      uint256 updatedAt,
      uint80 answeredInRound
    );

}


interface FlagsInterface {
  function getFlag(address) external view returns (bool);
  function getFlags(address[] calldata) external view returns (bool[] memory);
  function raiseFlag(address) external;
  function raiseFlags(address[] calldata) external;
  function lowerFlags(address[] calldata) external;
  function setRaisingAccessController(address) external;
}


// https://docs.synthetix.io/contracts/source/interfaces/IExchangeCircuitBreaker
interface IExchangeCircuitBreaker {
    // Views

    function exchangeRates() external view returns (address);

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

    function priceDeviationThresholdFactor() external view returns (uint);

    function isDeviationAboveThreshold(uint base, uint comparison) external view returns (bool);

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

    // Mutative functions
    function resetLastExchangeRate(bytes32[] calldata currencyKeys) external;

    function rateWithBreakCircuit(bytes32 currencyKey) external returns (uint lastValidRate, bool circuitBroken);
}


// Inheritance


// Libraries


// Internal references
// AggregatorInterface from Chainlink represents a decentralized pricing network for a single currency key

// FlagsInterface from Chainlink addresses SIP-76


// https://docs.synthetix.io/contracts/source/contracts/exchangerates
contract ExchangeRates is Owned, MixinSystemSettings, IExchangeRates {
    using SafeMath for uint;
    using SafeDecimalMath for uint;

    bytes32 public constant CONTRACT_NAME = "ExchangeRates";
    //slither-disable-next-line naming-convention
    bytes32 internal constant sUSD = "sUSD";

    // Decentralized oracle networks that feed into pricing aggregators
    mapping(bytes32 => AggregatorV2V3Interface) public aggregators;

    mapping(bytes32 => uint8) public currencyKeyDecimals;

    // List of aggregator keys for convenient iteration
    bytes32[] public aggregatorKeys;

    // ========== CONSTRUCTOR ==========

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

    /* ========== MUTATIVE FUNCTIONS ========== */

    function addAggregator(bytes32 currencyKey, address aggregatorAddress) external onlyOwner {
        AggregatorV2V3Interface aggregator = AggregatorV2V3Interface(aggregatorAddress);
        // This check tries to make sure that a valid aggregator is being added.
        // It checks if the aggregator is an existing smart contract that has implemented `latestTimestamp` function.

        require(aggregator.latestRound() >= 0, "Given Aggregator is invalid");
        uint8 decimals = aggregator.decimals();
        require(decimals <= 18, "Aggregator decimals should be lower or equal to 18");
        if (address(aggregators[currencyKey]) == address(0)) {
            aggregatorKeys.push(currencyKey);
        }
        aggregators[currencyKey] = aggregator;
        currencyKeyDecimals[currencyKey] = decimals;
        emit AggregatorAdded(currencyKey, address(aggregator));
    }

    function removeAggregator(bytes32 currencyKey) external onlyOwner {
        address aggregator = address(aggregators[currencyKey]);
        require(aggregator != address(0), "No aggregator exists for key");
        delete aggregators[currencyKey];
        delete currencyKeyDecimals[currencyKey];

        bool wasRemoved = removeFromArray(currencyKey, aggregatorKeys);

        if (wasRemoved) {
            emit AggregatorRemoved(currencyKey, aggregator);
        }
    }

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

    function currenciesUsingAggregator(address aggregator) external view returns (bytes32[] memory currencies) {
        uint count = 0;
        currencies = new bytes32[](aggregatorKeys.length);
        for (uint i = 0; i < aggregatorKeys.length; i++) {
            bytes32 currencyKey = aggregatorKeys[i];
            if (address(aggregators[currencyKey]) == aggregator) {
                currencies[count++] = currencyKey;
            }
        }
    }

    function rateStalePeriod() external view returns (uint) {
        return getRateStalePeriod();
    }

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

    function rateAndUpdatedTime(bytes32 currencyKey) external view returns (uint rate, uint time) {
        RateAndUpdatedTime memory rateAndTime = _getRateAndUpdatedTime(currencyKey);
        return (rateAndTime.rate, rateAndTime.time);
    }

    function getLastRoundIdBeforeElapsedSecs(
        bytes32 currencyKey,
        uint startingRoundId,
        uint startingTimestamp,
        uint timediff
    ) external view returns (uint) {
        uint roundId = startingRoundId;
        uint nextTimestamp = 0;
        while (true) {
            (, nextTimestamp) = _getRateAndTimestampAtRound(currencyKey, roundId + 1);
            // if there's no new round, then the previous roundId was the latest
            if (nextTimestamp == 0 || nextTimestamp > startingTimestamp + timediff) {
                return roundId;
            }
            roundId++;
        }
        return roundId;
    }

    function getCurrentRoundId(bytes32 currencyKey) external view returns (uint) {
        return _getCurrentRoundId(currencyKey);
    }

    function effectiveValueAndRatesAtRound(
        bytes32 sourceCurrencyKey,
        uint sourceAmount,
        bytes32 destinationCurrencyKey,
        uint roundIdForSrc,
        uint roundIdForDest
    )
        external
        view
        returns (
            uint value,
            uint sourceRate,
            uint destinationRate
        )
    {
        (sourceRate, ) = _getRateAndTimestampAtRound(sourceCurrencyKey, roundIdForSrc);
        // If there's no change in the currency, then just return the amount they gave us
        if (sourceCurrencyKey == destinationCurrencyKey) {
            destinationRate = sourceRate;
            value = sourceAmount;
        } else {
            (destinationRate, ) = _getRateAndTimestampAtRound(destinationCurrencyKey, roundIdForDest);
            // prevent divide-by 0 error (this happens if the dest is not a valid rate)
            if (destinationRate > 0) {
                // Calculate the effective value by going from source -> USD -> destination
                value = sourceAmount.multiplyDecimalRound(sourceRate).divideDecimalRound(destinationRate);
            }
        }
    }

    function rateAndTimestampAtRound(bytes32 currencyKey, uint roundId) external view returns (uint rate, uint time) {
        return _getRateAndTimestampAtRound(currencyKey, roundId);
    }

    function lastRateUpdateTimes(bytes32 currencyKey) external view returns (uint256) {
        return _getUpdatedTime(currencyKey);
    }

    function lastRateUpdateTimesForCurrencies(bytes32[] calldata currencyKeys) external view returns (uint[] memory) {
        uint[] memory lastUpdateTimes = new uint[](currencyKeys.length);

        for (uint i = 0; i < currencyKeys.length; i++) {
            lastUpdateTimes[i] = _getUpdatedTime(currencyKeys[i]);
        }

        return lastUpdateTimes;
    }

    function effectiveValue(
        bytes32 sourceCurrencyKey,
        uint sourceAmount,
        bytes32 destinationCurrencyKey
    ) external view returns (uint value) {
        (value, , ) = _effectiveValueAndRates(sourceCurrencyKey, sourceAmount, destinationCurrencyKey);
    }

    function effectiveValueAndRates(
        bytes32 sourceCurrencyKey,
        uint sourceAmount,
        bytes32 destinationCurrencyKey
    )
        external
        view
        returns (
            uint value,
            uint sourceRate,
            uint destinationRate
        )
    {
        return _effectiveValueAndRates(sourceCurrencyKey, sourceAmount, destinationCurrencyKey);
    }

    // SIP-120 Atomic exchanges
    function effectiveAtomicValueAndRates(
        bytes32,
        uint,
        bytes32
    )
        external
        view
        returns (
            uint,
            uint,
            uint,
            uint
        )
    {
        _notImplemented();
    }

    function rateForCurrency(bytes32 currencyKey) external view returns (uint) {
        return _getRateAndUpdatedTime(currencyKey).rate;
    }

    /// @notice getting N rounds of rates for a currency at a specific round
    /// @param currencyKey the currency key
    /// @param numRounds the number of rounds to get
    /// @param roundId the round id
    /// @return a list of rates and a list of times
    function ratesAndUpdatedTimeForCurrencyLastNRounds(
        bytes32 currencyKey,
        uint numRounds,
        uint roundId
    ) external view returns (uint[] memory rates, uint[] memory times) {
        rates = new uint[](numRounds);
        times = new uint[](numRounds);

        roundId = roundId > 0 ? roundId : _getCurrentRoundId(currencyKey);
        for (uint i = 0; i < numRounds; i++) {
            // fetch the rate and treat is as current, so inverse limits if frozen will always be applied
            // regardless of current rate
            (rates[i], times[i]) = _getRateAndTimestampAtRound(currencyKey, roundId);

            if (roundId == 0) {
                // if we hit the last round, then return what we have
                return (rates, times);
            } else {
                roundId--;
            }
        }
    }

    function ratesForCurrencies(bytes32[] calldata currencyKeys) external view returns (uint[] memory) {
        uint[] memory _localRates = new uint[](currencyKeys.length);

        for (uint i = 0; i < currencyKeys.length; i++) {
            _localRates[i] = _getRate(currencyKeys[i]);
        }

        return _localRates;
    }

    function rateAndInvalid(bytes32 currencyKey) external view returns (uint rate, bool isInvalid) {
        RateAndUpdatedTime memory rateAndTime = _getRateAndUpdatedTime(currencyKey);

        if (currencyKey == sUSD) {
            return (rateAndTime.rate, false);
        }
        return (
            rateAndTime.rate,
            _rateIsStaleWithTime(getRateStalePeriod(), rateAndTime.time) ||
                _rateIsFlagged(currencyKey, FlagsInterface(getAggregatorWarningFlags()))
        );
    }

    function ratesAndInvalidForCurrencies(bytes32[] calldata currencyKeys)
        external
        view
        returns (uint[] memory rates, bool anyRateInvalid)
    {
        rates = new uint[](currencyKeys.length);

        uint256 _rateStalePeriod = getRateStalePeriod();

        // fetch all flags at once
        bool[] memory flagList = getFlagsForRates(currencyKeys);

        for (uint i = 0; i < currencyKeys.length; i++) {
            // do one lookup of the rate & time to minimize gas
            RateAndUpdatedTime memory rateEntry = _getRateAndUpdatedTime(currencyKeys[i]);
            rates[i] = rateEntry.rate;
            if (!anyRateInvalid && currencyKeys[i] != sUSD) {
                anyRateInvalid = flagList[i] || _rateIsStaleWithTime(_rateStalePeriod, rateEntry.time);
            }
        }
    }

    function rateIsStale(bytes32 currencyKey) external view returns (bool) {
        return _rateIsStale(currencyKey, getRateStalePeriod());
    }

    function rateIsInvalid(bytes32 currencyKey) external view returns (bool) {
        return
            _rateIsStale(currencyKey, getRateStalePeriod()) ||
            _rateIsFlagged(currencyKey, FlagsInterface(getAggregatorWarningFlags()));
    }

    function rateIsFlagged(bytes32 currencyKey) external view returns (bool) {
        return _rateIsFlagged(currencyKey, FlagsInterface(getAggregatorWarningFlags()));
    }

    function anyRateIsInvalid(bytes32[] calldata currencyKeys) external view returns (bool) {
        // Loop through each key and check whether the data point is stale.

        uint256 _rateStalePeriod = getRateStalePeriod();
        bool[] memory flagList = getFlagsForRates(currencyKeys);

        for (uint i = 0; i < currencyKeys.length; i++) {
            if (flagList[i] || _rateIsStale(currencyKeys[i], _rateStalePeriod)) {
                return true;
            }
        }

        return false;
    }

    /// this method checks whether any rate is:
    /// 1. flagged
    /// 2. stale with respect to current time (now)
    function anyRateIsInvalidAtRound(bytes32[] calldata currencyKeys, uint[] calldata roundIds)
        external
        view
        returns (bool)
    {
        // Loop through each key and check whether the data point is stale.

        require(roundIds.length == currencyKeys.length, "roundIds must be the same length as currencyKeys");

        uint256 _rateStalePeriod = getRateStalePeriod();
        bool[] memory flagList = getFlagsForRates(currencyKeys);

        for (uint i = 0; i < currencyKeys.length; i++) {
            if (flagList[i] || _rateIsStaleAtRound(currencyKeys[i], roundIds[i], _rateStalePeriod)) {
                return true;
            }
        }

        return false;
    }

    function synthTooVolatileForAtomicExchange(bytes32) external view returns (bool) {
        _notImplemented();
    }

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

    function getFlagsForRates(bytes32[] memory currencyKeys) internal view returns (bool[] memory flagList) {
        FlagsInterface _flags = FlagsInterface(getAggregatorWarningFlags());

        // fetch all flags at once
        if (_flags != FlagsInterface(0)) {
            address[] memory _aggregators = new address[](currencyKeys.length);

            for (uint i = 0; i < currencyKeys.length; i++) {
                _aggregators[i] = address(aggregators[currencyKeys[i]]);
            }

            flagList = _flags.getFlags(_aggregators);
        } else {
            flagList = new bool[](currencyKeys.length);
        }
    }

    function removeFromArray(bytes32 entry, bytes32[] storage array) internal returns (bool) {
        for (uint i = 0; i < array.length; i++) {
            if (array[i] == entry) {
                delete array[i];

                // Copy the last key into the place of the one we just deleted
                // If there's only one key, this is array[0] = array[0].
                // If we're deleting the last one, it's also a NOOP in the same way.
                array[i] = array[array.length - 1];

                // Decrease the size of the array by one.
                array.length--;

                return true;
            }
        }
        return false;
    }

    function _formatAggregatorAnswer(bytes32 currencyKey, int256 rate) internal view returns (uint) {
        require(rate >= 0, "Negative rate not supported");
        if (currencyKeyDecimals[currencyKey] > 0) {
            uint multiplier = 10**uint(SafeMath.sub(18, currencyKeyDecimals[currencyKey]));
            return uint(uint(rate).mul(multiplier));
        }
        return uint(rate);
    }

    function _getRateAndUpdatedTime(bytes32 currencyKey) internal view returns (RateAndUpdatedTime memory) {
        // sUSD rate is 1.0
        if (currencyKey == sUSD) {
            return RateAndUpdatedTime({rate: uint216(SafeDecimalMath.unit()), time: 0});
        } else {
            AggregatorV2V3Interface aggregator = aggregators[currencyKey];
            if (aggregator != AggregatorV2V3Interface(0)) {
                // this view from the aggregator is the most gas efficient but it can throw when there's no data,
                // so let's call it low-level to suppress any reverts
                bytes memory payload = abi.encodeWithSignature("latestRoundData()");
                // solhint-disable avoid-low-level-calls
                // slither-disable-next-line low-level-calls
                (bool success, bytes memory returnData) = address(aggregator).staticcall(payload);

                if (success) {
                    (, int256 answer, , uint256 updatedAt, ) =
                        abi.decode(returnData, (uint80, int256, uint256, uint256, uint80));
                    return
                        RateAndUpdatedTime({
                            rate: uint216(_formatAggregatorAnswer(currencyKey, answer)),
                            time: uint40(updatedAt)
                        });
                } // else return defaults, to avoid reverting in views
            } // else return defaults, to avoid reverting in views
        }
    }

    function _getCurrentRoundId(bytes32 currencyKey) internal view returns (uint) {
        if (currencyKey == sUSD) {
            return 0;
        }
        AggregatorV2V3Interface aggregator = aggregators[currencyKey];
        if (aggregator != AggregatorV2V3Interface(0)) {
            return aggregator.latestRound();
        } // else return defaults, to avoid reverting in views
    }

    function _getRateAndTimestampAtRound(bytes32 currencyKey, uint roundId) internal view returns (uint rate, uint time) {
        // short circuit sUSD
        if (currencyKey == sUSD) {
            // sUSD has no rounds, and 0 time is preferrable for "volatility" heuristics
            // which are used in atomic swaps and fee reclamation
            return (SafeDecimalMath.unit(), 0);
        } else {
            AggregatorV2V3Interface aggregator = aggregators[currencyKey];
            if (aggregator != AggregatorV2V3Interface(0)) {
                // this view from the aggregator is the most gas efficient but it can throw when there's no data,
                // so let's call it low-level to suppress any reverts
                bytes memory payload = abi.encodeWithSignature("getRoundData(uint80)", roundId);
                // solhint-disable avoid-low-level-calls
                (bool success, bytes memory returnData) = address(aggregator).staticcall(payload);

                if (success) {
                    (, int256 answer, , uint256 updatedAt, ) =
                        abi.decode(returnData, (uint80, int256, uint256, uint256, uint80));
                    return (_formatAggregatorAnswer(currencyKey, answer), updatedAt);
                } // else return defaults, to avoid reverting in views
            } // else return defaults, to avoid reverting in views
        }
    }

    function _getRate(bytes32 currencyKey) internal view returns (uint256) {
        return _getRateAndUpdatedTime(currencyKey).rate;
    }

    function _getUpdatedTime(bytes32 currencyKey) internal view returns (uint256) {
        return _getRateAndUpdatedTime(currencyKey).time;
    }

    function _effectiveValueAndRates(
        bytes32 sourceCurrencyKey,
        uint sourceAmount,
        bytes32 destinationCurrencyKey
    )
        internal
        view
        returns (
            uint value,
            uint sourceRate,
            uint destinationRate
        )
    {
        sourceRate = _getRate(sourceCurrencyKey);
        // If there's no change in the currency, then just return the amount they gave us
        if (sourceCurrencyKey == destinationCurrencyKey) {
            destinationRate = sourceRate;
            value = sourceAmount;
        } else {
            // Calculate the effective value by going from source -> USD -> destination
            destinationRate = _getRate(destinationCurrencyKey);
            // prevent divide-by 0 error (this happens if the dest is not a valid rate)
            if (destinationRate > 0) {
                value = sourceAmount.multiplyDecimalRound(sourceRate).divideDecimalRound(destinationRate);
            }
        }
    }

    function _rateIsStale(bytes32 currencyKey, uint _rateStalePeriod) internal view returns (bool) {
        // sUSD is a special case and is never stale (check before an SLOAD of getRateAndUpdatedTime)
        if (currencyKey == sUSD) {
            return false;
        }
        return _rateIsStaleWithTime(_rateStalePeriod, _getUpdatedTime(currencyKey));
    }

    function _rateIsStaleAtRound(
        bytes32 currencyKey,
        uint roundId,
        uint _rateStalePeriod
    ) internal view returns (bool) {
        // sUSD is a special case and is never stale (check before an SLOAD of getRateAndUpdatedTime)
        if (currencyKey == sUSD) {
            return false;
        }
        (, uint time) = _getRateAndTimestampAtRound(currencyKey, roundId);
        return _rateIsStaleWithTime(_rateStalePeriod, time);
    }

    function _rateIsStaleWithTime(uint _rateStalePeriod, uint _time) internal view returns (bool) {
        return _time.add(_rateStalePeriod) < now;
    }

    function _rateIsFlagged(bytes32 currencyKey, FlagsInterface flags) internal view returns (bool) {
        // sUSD is a special case and is never invalid
        if (currencyKey == sUSD) {
            return false;
        }
        address aggregator = address(aggregators[currencyKey]);
        // when no aggregator or when the flags haven't been setup
        if (aggregator == address(0) || flags == FlagsInterface(0)) {
            return false;
        }
        return flags.getFlag(aggregator);
    }

    function _notImplemented() internal pure {
        // slither-disable-next-line dead-code
        revert("Cannot be run on this layer");
    }

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

    event AggregatorAdded(bytes32 currencyKey, address aggregator);
    event AggregatorRemoved(bytes32 currencyKey, address aggregator);
}


// https://sips.synthetix.io/sips/sip-120/
// Uniswap V3 based DecPriceAggregator (unaudited) e.g. https://etherscan.io/address/0xf120f029ac143633d1942e48ae2dfa2036c5786c#code
// https://github.com/sohkai/uniswap-v3-spot-twap-oracle
//  inteface: https://github.com/sohkai/uniswap-v3-spot-twap-oracle/blob/8f9777a6160a089c99f39f2ee297119ee293bc4b/contracts/interfaces/IDexPriceAggregator.sol
//  implementation: https://github.com/sohkai/uniswap-v3-spot-twap-oracle/blob/8f9777a6160a089c99f39f2ee297119ee293bc4b/contracts/DexPriceAggregatorUniswapV3.sol
interface IDexPriceAggregator {
    function assetToAsset(
        address tokenIn,
        uint amountIn,
        address tokenOut,
        uint twapPeriod
    ) external view returns (uint amountOut);
}


// Inheritance


// https://docs.synthetix.io/contracts/source/contracts/exchangerateswithdexpricing
contract ExchangeRatesWithDexPricing is ExchangeRates {
    bytes32 public constant CONTRACT_NAME = "ExchangeRatesWithDexPricing";

    bytes32 internal constant SETTING_DEX_PRICE_AGGREGATOR = "dexPriceAggregator";

    constructor(address _owner, address _resolver) public ExchangeRates(_owner, _resolver) {}

    /* ========== SETTERS ========== */

    function setDexPriceAggregator(IDexPriceAggregator _dexPriceAggregator) external onlyOwner {
        flexibleStorage().setAddressValue(
            ExchangeRates.CONTRACT_NAME,
            SETTING_DEX_PRICE_AGGREGATOR,
            address(_dexPriceAggregator)
        );
        emit DexPriceAggregatorUpdated(address(_dexPriceAggregator));
    }

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

    function dexPriceAggregator() public view returns (IDexPriceAggregator) {
        return
            IDexPriceAggregator(
                flexibleStorage().getAddressValue(ExchangeRates.CONTRACT_NAME, SETTING_DEX_PRICE_AGGREGATOR)
            );
    }

    function atomicTwapWindow() external view returns (uint) {
        return getAtomicTwapWindow();
    }

    function atomicEquivalentForDexPricing(bytes32 currencyKey) external view returns (address) {
        return getAtomicEquivalentForDexPricing(currencyKey);
    }

    function atomicVolatilityConsiderationWindow(bytes32 currencyKey) external view returns (uint) {
        return getAtomicVolatilityConsiderationWindow(currencyKey);
    }

    function atomicVolatilityUpdateThreshold(bytes32 currencyKey) external view returns (uint) {
        return getAtomicVolatilityUpdateThreshold(currencyKey);
    }

    // SIP-120 Atomic exchanges
    // Note that the returned systemValue, systemSourceRate, and systemDestinationRate are based on
    // the current system rate, which may not be the atomic rate derived from value / sourceAmount
    function effectiveAtomicValueAndRates(
        bytes32 sourceCurrencyKey,
        uint sourceAmount,
        bytes32 destinationCurrencyKey
    )
        external
        view
        returns (
            uint value,
            uint systemValue,
            uint systemSourceRate,
            uint systemDestinationRate
        )
    {
        (systemValue, systemSourceRate, systemDestinationRate) = _effectiveValueAndRates(
            sourceCurrencyKey,
            sourceAmount,
            destinationCurrencyKey
        );

        bool usePureChainlinkPriceForSource = getPureChainlinkPriceForAtomicSwapsEnabled(sourceCurrencyKey);
        bool usePureChainlinkPriceForDest = getPureChainlinkPriceForAtomicSwapsEnabled(destinationCurrencyKey);
        uint sourceRate;
        uint destRate;

        // Handle the different scenarios that may arise when trading currencies with or without the PureChainlinkPrice set.
        // outlined here: https://sips.synthetix.io/sips/sip-198/#computation-methodology-in-atomic-pricing
        if (usePureChainlinkPriceForSource && usePureChainlinkPriceForDest) {
            // SRC and DEST are both set to trade at the PureChainlinkPrice
            sourceRate = systemSourceRate;
            destRate = systemDestinationRate;
        } else if (!usePureChainlinkPriceForSource && usePureChainlinkPriceForDest) {
            // SRC is NOT set to PureChainlinkPrice and DEST is set to PureChainlinkPrice
            sourceRate = _getMinValue(systemSourceRate, _getPriceFromDexAggregator(sourceCurrencyKey, sourceAmount));
            destRate = systemDestinationRate;
        } else if (usePureChainlinkPriceForSource && !usePureChainlinkPriceForDest) {
            // SRC is set to PureChainlinkPrice and DEST is NOT set to PureChainlinkPrice
            sourceRate = systemSourceRate;
            destRate = _getMaxValue(systemDestinationRate, _getPriceFromDexAggregator(destinationCurrencyKey, sourceAmount));
        } else {
            // Otherwise, neither SRC nor DEST is set to PureChainlinkPrice.
            sourceRate = _getMinValue(systemSourceRate, _getPriceFromDexAggregator(sourceCurrencyKey, sourceAmount));
            destRate = _getMaxValue(systemDestinationRate, _getPriceFromDexAggregator(destinationCurrencyKey, sourceAmount));
        }
        value = sourceAmount.mul(sourceRate).div(destRate);
    }

    function _getMinValue(uint x, uint y) internal pure returns (uint) {
        return x < y ? x : y;
    }

    function _getMaxValue(uint x, uint y) internal pure returns (uint) {
        return x > y ? x : y;
    }

    /// @notice Retrieve the TWAP (time-weighted average price) of an asset from its Uniswap V3-equivalent pool
    /// @dev By default, the TWAP oracle 'hops' through the wETH pool. This can be overridden. See DexPriceAggregator for more information.
    /// @dev The TWAP oracle doesn't take into account variable slippage due to trade amounts, as Uniswap's OracleLibary doesn't cross ticks based on their liquidity. See: https://docs.uniswap.org/protocol/concepts/V3-overview/oracle#deriving-price-from-a-tick
    /// @param currencyKey The currency key of the synth we're retrieving the price for
    /// @param amount The amount of the asset we're interested in
    /// @return The price of the asset
    function _getPriceFromDexAggregator(bytes32 currencyKey, uint amount) internal view returns (uint) {
        require(amount != 0, "Amount must be greater than 0");

        IERC20 inputEquivalent = IERC20(getAtomicEquivalentForDexPricing(currencyKey));
        require(address(inputEquivalent) != address(0), "No atomic equivalent for input");

        IERC20 susdEquivalent = IERC20(getAtomicEquivalentForDexPricing("sUSD"));
        require(address(susdEquivalent) != address(0), "No atomic equivalent for sUSD");

        uint result =
            _dexPriceDestinationValue(inputEquivalent, susdEquivalent, amount).mul(SafeDecimalMath.unit()).div(amount);
        require(result != 0, "Result must be greater than 0");

        return result;
    }

    function _dexPriceDestinationValue(
        IERC20 sourceEquivalent,
        IERC20 destEquivalent,
        uint sourceAmount
    ) internal view returns (uint) {
        // Normalize decimals in case equivalent asset uses different decimals from internal unit
        uint sourceAmountInEquivalent =
            (sourceAmount.mul(10**uint(sourceEquivalent.decimals()))).div(SafeDecimalMath.unit());

        uint twapWindow = getAtomicTwapWindow();
        require(twapWindow != 0, "Uninitialized atomic twap window");

        uint twapValueInEquivalent =
            dexPriceAggregator().assetToAsset(
                address(sourceEquivalent),
                sourceAmountInEquivalent,
                address(destEquivalent),
                twapWindow
            );
        require(twapValueInEquivalent > 0, "dex price returned 0");

        // Similar to source amount, normalize decimals back to internal unit for output amount
        return (twapValueInEquivalent.mul(SafeDecimalMath.unit())).div(10**uint(destEquivalent.decimals()));
    }

    function synthTooVolatileForAtomicExchange(bytes32 currencyKey) external view returns (bool) {
        // sUSD is a special case and is never volatile
        if (currencyKey == "sUSD") return false;

        uint considerationWindow = getAtomicVolatilityConsiderationWindow(currencyKey);
        uint updateThreshold = getAtomicVolatilityUpdateThreshold(currencyKey);

        if (considerationWindow == 0 || updateThreshold == 0) {
            // If either volatility setting is not set, never judge an asset to be volatile
            return false;
        }

        // Go back through the historical oracle update rounds to see if there have been more
        // updates in the consideration window than the allowed threshold.
        // If there have, consider the asset volatile--by assumption that many close-by oracle
        // updates is a good proxy for price volatility.
        uint considerationWindowStart = block.timestamp.sub(considerationWindow);
        uint roundId = _getCurrentRoundId(currencyKey);
        for (updateThreshold; updateThreshold > 0; updateThreshold--) {
            (uint rate, uint time) = _getRateAndTimestampAtRound(currencyKey, roundId);
            if (time != 0 && time < considerationWindowStart) {
                // Round was outside consideration window so we can stop querying further rounds
                return false;
            } else if (rate == 0 || time == 0) {
                // Either entire round or a rate inside consideration window was not available
                // Consider the asset volatile
                break;
            }

            if (roundId == 0) {
                // Not enough historical data to continue further
                // Consider the asset volatile
                break;
            }
            roundId--;
        }

        return true;
    }

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

    event DexPriceAggregatorUpdated(address newDexPriceAggregator);
}