// Contract: AggregatorDataProvider
// Target function: function _updateExchangeRate()
 Calculator Contract
    IRateCalculatorV2 public rateContract; // For complex rate calculations

    // Swapper
    mapping(address => bool) public swappers; // approved swapper addresses

    // ERC20 Metadata
    string internal nameOfContract;
    string internal symbolOfContract;
    uint8 internal immutable decimalsOfContract;

    // ============================================================================================
    // Storage
    // ============================================================================================

    /// @notice Stores information about the current interest rate
    /// @dev struct is packed to reduce SLOADs. feeToProtocolRate is 1e5 precision, ratePerSec & fullUtilizationRate is 1e18 precision
    CurrentRateInfo public currentRateInfo;

    struct CurrentRateInfo {
        uint32 lastBlock;
        uint32 feeToProtocolRate; // Fee amount 1e5 precision
        uint64 lastTimestamp;
        uint64 ratePerSec;
        uint64 fullUtilizationRate;
    }

    /// @notice Stores information about the current exchange rate. Collateral:Asset ratio
    /// @dev Struct packed to save SLOADs. Amount of Collateral Token to buy 1e18 Asset Token
    ExchangeRateInfo public exchangeRateInfo;

    struct ExchangeRateInfo {
        address oracle;
        uint32 maxOracleDeviation; // % of larger number, 1e5 precision
        uint184 lastTimestamp;
        uint256 lowExchangeRate;
        uint256 highExchangeRate;
    }

    // Contract Level Accounting
    VaultAccount public totalAsset; // amount = total amount of assets, shares = total shares outstanding
    VaultAccount public totalBorrow; // amount = total borrow amount with interest accrued, shares = total shares outstanding
    uint256 public totalCollateral; // total amount of collateral in contract

    // User Level Accounting
    /// @notice Stores the balance of collateral for each user
    mapping(address => uint256) public userCollateralBalance; // amount of collateral each user is backed
    /// @notice Stores the balance of borrow shares for each user
    mapping(address => uint256) public userBorrowShares; // represents the shares held by individuals
    /// @notice Stores the borrow allowance of the user
    mapping(address => mapping(address => uint256)) public userBorrowAllowances;  // represent the borrowable amount on behalfof user
    /// @notice Stores the whitelisted delegators who call the removeCollateralFrom(), ex: Leverage contracts
    mapping(address => bool) public whitelistedDelegators;  // represent the leverage contract who call the removeCollateralFrom()

    // NOTE: user shares of assets are represented as ERC-20 tokens and accessible via balanceOf()

    // ============================================================================================
    // Constructor
    // ============================================================================================

    /// @notice The ```constructor``` function is called on deployment
    /// @param _configData abi.encode(address _asset, address _collateral, address _oracle, uint32 _maxOracleDeviation, address _rateContract, uint64 _fullUtilizationRate, uint256 _maxLTV, uint256 _cleanLiquidationFee, uint256 _dirtyLiquidationFee, uint256 _protocolLiquidationFee)
    /// @param _immutables abi.encode(address _circuitBreakerAddress, address _comptrollerAddress, address _timelockAddress)
    /// @param _customConfigData abi.encode(string memory _nameOfContract, string memory _symbolOfContract, uint8 _decimalsOfContract)
    constructor(
        bytes memory _configData,
        bytes memory _immutables,
        bytes memory _customConfigData
    ) SturdyPairAccessControl(_immutables) ERC20("", "") {
        {
            (
                address _asset,
                address _collateral,
                address _oracle,
                uint32 _maxOracleDeviation,
                address _rateContract,
                uint64 _fullUtilizationRate,
                uint256 _maxLTV,
                uint256 _liquidationFee,
                uint256 _protocolLiquidationFee
            ) = abi.decode(
                    _configData,
                    (address, address, address, uint32, address, uint64, uint256, uint256, uint256)
                );

            // Pair Settings
            assetContract = IERC20(_asset);
            collateralContract = IERC20(_collateral);

            currentRateInfo.feeToProtocolRate = 0;
            currentRateInfo.fullUtilizationRate = _fullUtilizationRate;
            currentRateInfo.lastTimestamp = uint64(block.timestamp - 1);
            currentRateInfo.lastBlock = uint32(block.number - 1);

            exchangeRateInfo.oracle = _oracle;
            exchangeRateInfo.maxOracleDeviation = _maxOracleDeviation;

            rateContract = IRateCalculatorV2(_rateContract);

            //Liquidation Fee Settings
            cleanLiquidationFee = _liquidationFee;
            dirtyLiquidationFee = (_liquidationFee * 90_000) / LIQ_PRECISION; // 90% of clean fee
            protocolLiquidationFee = _protocolLiquidationFee;

            // set maxLTV
            maxLTV = _maxLTV;
        }

        {
            (string memory _nameOfContract, string memory _symbolOfContract, uint8 _decimalsOfContract) = abi.decode(
                _customConfigData,
                (string, string, uint8)
            );

            // ERC20 Metadata
            nameOfContract = _nameOfContract;
            symbolOfContract = _symbolOfContract;
            decimalsOfContract = _decimalsOfContract;

            // Instantiate Interest
            _addInterest();
            // Instantiate Exchange Rate
            _updateExchangeRate();
        }
    }

    // ============================================================================================
    // Internal Helpers
    // ============================================================================================

    /// @notice The ```_totalAssetAvailable``` function returns the total balance of Asset Tokens in the contract
    /// @param _totalAsset VaultAccount struct which stores total amount and shares for assets
    /// @param _totalBorrow VaultAccount struct which stores total amount and shares for borrows
    /// @return The balance of Asset Tokens held by contract
    function _totalAssetAvailable(
        VaultAccount memory _totalAsset,
        VaultAccount memory _totalBorrow
    ) internal pure returns (uint256) {
        return _totalAsset.amount - _totalBorrow.amount;
    }

    /// @notice The ```_isSolvent``` function determines if a given borrower is solvent given an exchange rate
    /// @param _borrower The borrower address to check
    /// @param _exchangeRate The exchange rate, i.e. the amount of collateral to buy 1e18 asset
    /// @return Whether borrower is solvent
    function _isSolvent(address _borrower, uint256 _exchangeRate) internal view returns (bool) {
        if (maxLTV == 0) return true;
        uint256 _borrowerAmount = totalBorrow.toAmount(userBorrowShares[_borrower], true);
        if (_borrowerAmount == 0) return true;
        uint256 _collateralAmount = userCollateralBalance[_borrower];
        if (_collateralAmount == 0) return false;

        uint256 _ltv = (((_borrowerAmount * _exchangeRate) / EXCHANGE_PRECISION) * LTV_PRECISION) / _collateralAmount;
        return _ltv <= maxLTV;
    }

    // ============================================================================================
    // Modifiers
    // ============================================================================================

    /// @notice Checks for solvency AFTER executing contract code
    /// @param _borrower The borrower whose solvency we will check
    modifier isSolvent(address _borrower) {
        _;
        ExchangeRateInfo memory _exchangeRateInfo = exchangeRateInfo;

        if (!_isSolvent(_borrower, exchangeRateInfo.highExchangeRate)) {
            revert Insolvent(
                totalBorrow.toAmount(userBorrowShares[_borrower], true),
                userCollateralBalance[_borrower],
                exchangeRateInfo.highExchangeRate
            );
        }
    }

    // ============================================================================================
    // Functions: Interest Accumulation and Adjustment
    // ============================================================================================

    /// @notice The ```AddInterest``` event is emitted when interest is accrued by borrowers
    /// @param interestEarned The total interest accrued by all borrowers
    /// @param rate The interest rate used to calculate accrued interest
    /// @param feesAmount The amount of fees paid to protocol
    /// @param feesShare The amount of shares distributed to protocol
    event AddInterest(uint256 interestEarned, uint256 rate, uint256 feesAmount, uint256 feesShare);

    /// @notice The ```UpdateRate``` event is emitted when the interest rate is updated
    /// @param oldRatePerSec The old interest rate (per second)
    /// @param oldFullUtilizationRate The old full utilization rate
    /// @param newRatePerSec The new interest rate (per second)
    /// @param newFullUtilizationRate The new full utilization rate
    event UpdateRate(
        uint256 oldRatePerSec,
        uint256 oldFullUtilizationRate,
        uint256 newRatePerSec,
        uint256 newFullUtilizationRate
    );

    /// @notice The ```addInterest``` function is a public implementation of _addInterest and allows 3rd parties to trigger interest accrual
    /// @return _interestEarned The amount of interest accrued by all borrowers
    /// @return _feesAmount The amount of fees paid to protocol
    /// @return _feesShare The amount of shares distributed to protocol
    /// @return _currentRateInfo The new rate info struct
    /// @return _totalAsset The new total asset struct
    /// @return _totalBorrow The new total borrow struct
    function addInterest(
        bool _returnAccounting
    )
        external
        nonReentrant
        returns (
            uint256 _interestEarned,
            uint256 _feesAmount,
            uint256 _feesShare,
            CurrentRateInfo memory _currentRateInfo,
            VaultAccount memory _totalAsset,
            VaultAccount memory _totalBorrow
        )
    {
        (, _interestEarned, _feesAmount, _feesShare, _currentRateInfo) = _addInterest();
        if (_returnAccounting) {
            _totalAsset = totalAsset;
            _totalBorrow = totalBorrow;
        }
    }

    /// @notice The ```previewAddInterest``` function
    /// @return _interestEarned The amount of interest accrued by all borrowers
    /// @return _feesAmount The amount of fees paid to protocol
    /// @return _feesShare The amount of shares distributed to protocol
    /// @return _newCurrentRateInfo The new rate info struct
    /// @return _totalAsset The new total asset struct
    /// @return _totalBorrow The new total borrow struct
    function previewAddInterest()
        public
        view
        returns (
            uint256 _interestEarned,
            uint256 _feesAmount,
            uint256 _feesShare,
            CurrentRateInfo memory _newCurrentRateInfo,
            VaultAccount memory _totalAsset,
            VaultAccount memory _totalBorrow
        )
    {
        _newCurrentRateInfo = currentRateInfo;
        // Write return values
        InterestCalculationResults memory _results = _calculateInterest(_newCurrentRateInfo);

        if (_results.isInterestUpdated) {
            _interestEarned = _results.interestEarned;
            _feesAmount = _results.feesAmount;
            _feesShare = _results.feesShare;

            _newCurrentRateInfo.ratePerSec = _results.newRate;
            _newCurrentRateInfo.fullUtilizationRate = _results.newFullUtilizationRate;

            _totalAsset = _results.totalAsset;
            _totalBorrow = _results.totalBorrow;
        } else {
            _totalAsset = totalAsset;
            _totalBorrow = totalBorrow;
        }
    }

    struct InterestCalculationResults {
        bool isInterestUpdated;
        uint64 newRate;
        uint64 newFullUtilizationRate;
        uint256 interestEarned;
        uint256 feesAmount;
        uint256 feesShare;
        VaultAccount totalAsset;
        VaultAccount totalBorrow;
    }

    /// @notice The ```_calculateInterest``` function calculates the interest to be accrued and the new interest rate info
    /// @param _currentRateInfo The current rate info
    /// @return _results The results of the interest calculation
    function _calculateInterest(
        CurrentRateInfo memory _currentRateInfo
    ) internal view returns (InterestCalculationResults memory _results) {
        // Short circuit if interest already calculated this block OR if interest is paused
        if (_currentRateInfo.lastTimestamp != block.timestamp && !isInterestPaused) {
            // Indicate that interest is updated and calculated
            _results.isInterestUpdated = true;

            // Write return values and use these to save gas
            _results.totalAsset = totalAsset;
            _results.totalBorrow = totalBorrow;

            // Time elapsed since last interest update
            uint256 _deltaTime = block.timestamp - _currentRateInfo.lastTimestamp;

            // Get the utilization rate
            uint256 _utilizationRate = _results.totalAsset.amount == 0
                ? 0
                : (UTIL_PREC * _results.totalBorrow.amount) / _results.totalAsset.amount;

            // Request new interest rate and full utilization rate from the rate calculator
            (_results.newRate, _results.newFullUtilizationRate) = IRateCalculatorV2(rateContract).getNewRate(
                _deltaTime,
                _utilizationRate,
                _currentRateInfo.fullUtilizationRate
            );

            // Calculate interest accrued
            _results.interestEarned = (_deltaTime * _results.totalBorrow.amount * _results.newRate) / RATE_PRECISION;

            // Accrue interest (if any) and fees iff no overflow
            if (
                _results.interestEarned > 0 &&
                _results.interestEarned + _results.totalBorrow.amount <= type(uint128).max &&
                _results.interestEarned + _results.totalAsset.amount <= type(uint128).max
            ) {
                // Increment totalBorrow and totalAsset by interestEarned
                _results.totalBorrow.amount += uint128(_results.interestEarned);
                _results.totalAsset.amount += uint128(_results.interestEarned);
                if (_currentRateInfo.feeToProtocolRate > 0) {
                    _results.feesAmount =
                        (_results.interestEarned * _currentRateInfo.feeToProtocolRate) /
                        FEE_PRECISION;

                    _results.feesShare =
                        (_results.feesAmount * _results.totalAsset.shares) /
                        (_results.totalAsset.amount - _results.feesAmount);

                    // Effects: Give new shares to this contract, effectively diluting lenders an amount equal to the fees
                    // We can safely cast because _feesShare < _feesAmount < interestEarned which is always less than uint128
                    _results.totalAsset.shares += uint128(_results.feesShare);
                }
            }
        }
    }

    /// @notice The ```_addInterest``` function is invoked prior to every external function and is used to accrue interest and update interest rate
    /// @dev Can only called once per block
    /// @return _isInterestUpdated True if interest was calculated
    /// @return _interestEarned The amount of interest accrued by all borrowers
    /// @return _feesAmount The amount of fees paid to protocol
    /// @return _feesShare The amount of shares distributed to protocol
    /// @return _currentRateInfo The new rate info struct
    function _addInterest()
        internal
        returns (
            bool _isInterestUpdated,
            uint256 _interestEarned,
            uint256 _feesAmount,
            uint256 _feesShare,
            CurrentRateInfo memory _currentRateInfo
        )
    {
        // Pull from storage and set default return values
        _currentRateInfo = currentRateInfo;

        // Calc interest
        InterestCalculationResults memory _results = _calculateInterest(_currentRateInfo);

        // Write return values only if interest was updated and calculated
        if (_results.isInterestUpdated) {
            _isInterestUpdated = _results.isInterestUpdated;
            _interestEarned = _results.interestEarned;
            _feesAmount = _results.feesAmount;
            _feesShare = _results.feesShare;

            // emit here so that we have access to the old values
            emit UpdateRate(
                _currentRateInfo.ratePerSec,
                _currentRateInfo.fullUtilizationRate,
                _results.newRate,
                _results.newFullUtilizationRate
            );
            emit AddInterest(_interestEarned, _results.newRate, _feesAmount, _feesShare);

            // overwrite original values
            _currentRateInfo.ratePerSec = _results.newRate;
            _currentRateInfo.fullUtilizationRate = _results.newFullUtilizationRate;
            _currentRateInfo.lastTimestamp = uint64(block.timestamp);
            _currentRateInfo.lastBlock = uint32(block.number);

            // Effects: write to state
            currentRateInfo = _currentRateInfo;
            totalAsset = _results.totalAsset;
            totalBorrow = _results.totalBorrow;
            if (_feesShare > 0) _mint(address(this), _feesShare);
        }
    }

    // ============================================================================================
    // Functions: ExchangeRate
    // ============================================================================================

    /// @notice The ```UpdateExchangeRate``` event is emitted when the Collateral:Asset exchange rate is updated
    /// @param lowExchangeRate The low exchange rate
    /// @param highExchangeRate The high exchange rate
    event UpdateExchangeRate(uint256 lowExchangeRate, uint256 highExchangeRate);

    /// @notice The ```WarnOracleData``` event is emitted when one of the oracles has stale or otherwise problematic data
    /// @param oracle The oracle address
    event WarnOracleData(address oracle);

    /// @notice The ```updateExchangeRate``` function is the external implementation of _updateExchangeRate.
    /// @dev This function is invoked at most once per block as these queries can be expensive
    /// @return _isBorrowAllowed True if deviation is within bounds
    /// @return _lowExchangeRate The low exchange rate
    /// @return _highExchangeRate The high exchange rate
    function updateExchangeRate()
        external
        nonReentrant
        returns (bool _isBorrowAllowed, uint256 _lowExchangeRate, uint256 _highExchangeRate)
    {
        return _updateExchangeRate();
    }