// SPDX-License-Identifier: BUSL-1.1
pragma solidity 0.8.15;

import "./CometMainInterface.sol";
import "./interfaces/IERC20NonStandard.sol";
import "./interfaces/IPriceFeed.sol";
import "./interfaces/IAssetListFactory.sol";
import "./interfaces/IAssetListFactoryHolder.sol";
import "./interfaces/IAssetList.sol";

/**
 * @title Compound's Comet Contract
 * @notice An efficient monolithic money market protocol
 * @author Compound
 */
contract CometWithExtendedAssetList is CometMainInterface {
    /** General configuration constants **/

    /// @notice The admin of the protocol
    address public override immutable governor;

    /// @notice The account which may trigger pauses
    address public override immutable pauseGuardian;

    /// @notice The address of the base token contract
    address public override immutable baseToken;

    /// @notice The address of the price feed for the base token
    address public override immutable baseTokenPriceFeed;

    /// @notice The address of the extension contract delegate
    address public override immutable extensionDelegate;

    /// @notice The point in the supply rates separating the low interest rate slope and the high interest rate slope (factor)
    /// @dev uint64
    uint public override immutable supplyKink;

    /// @notice Per second supply interest rate slope applied when utilization is below kink (factor)
    /// @dev uint64
    uint public override immutable supplyPerSecondInterestRateSlopeLow;

    /// @notice Per second supply interest rate slope applied when utilization is above kink (factor)
    /// @dev uint64
    uint public override immutable supplyPerSecondInterestRateSlopeHigh;

    /// @notice Per second supply base interest rate (factor)
    /// @dev uint64
    uint public override immutable supplyPerSecondInterestRateBase;

    /// @notice The point in the borrow rate separating the low interest rate slope and the high interest rate slope (factor)
    /// @dev uint64
    uint public override immutable borrowKink;

    /// @notice Per second borrow interest rate slope applied when utilization is below kink (factor)
    /// @dev uint64
    uint public override immutable borrowPerSecondInterestRateSlopeLow;

    /// @notice Per second borrow interest rate slope applied when utilization is above kink (factor)
    /// @dev uint64
    uint public override immutable borrowPerSecondInterestRateSlopeHigh;

    /// @notice Per second borrow base interest rate (factor)
    /// @dev uint64
    uint public override immutable borrowPerSecondInterestRateBase;

    /// @notice The fraction of the liquidation penalty that goes to buyers of collateral instead of the protocol
    /// @dev uint64
    uint public override immutable storeFrontPriceFactor;

    /// @notice The scale for base token (must be less than 18 decimals)
    /// @dev uint64
    uint public override immutable baseScale;

    /// @notice The scale for reward tracking
    /// @dev uint64
    uint public override immutable trackingIndexScale;

    /// @notice The speed at which supply rewards are tracked (in trackingIndexScale)
    /// @dev uint64
    uint public override immutable baseTrackingSupplySpeed;

    /// @notice The speed at which borrow rewards are tracked (in trackingIndexScale)
    /// @dev uint64
    uint public override immutable baseTrackingBorrowSpeed;

    /// @notice The minimum amount of base principal wei for rewards to accrue
    /// @dev This must be large enough so as to prevent division by base wei from overflowing the 64 bit indices
    /// @dev uint104
    uint public override immutable baseMinForRewards;

    /// @notice The minimum base amount required to initiate a borrow
    uint public override immutable baseBorrowMin;

    /// @notice The minimum base token reserves which must be held before collateral is hodled
    uint public override immutable targetReserves;

    /// @notice The number of decimals for wrapped base token
    uint8 public override immutable decimals;

    /// @notice The number of assets this contract actually supports
    uint8 public override immutable numAssets;

    /// @notice Factor to divide by when accruing rewards in order to preserve 6 decimals (i.e. baseScale / 1e6)
    uint internal immutable accrualDescaleFactor;
    
    /// @notice The address of the asset list
    address immutable public assetList;

    uint8 internal constant MAX_ASSETS_FOR_ASSET_LIST = 24;

    /**
     * @notice Construct a new protocol instance
     * @param config The mapping of initial/constant parameters
     **/
    constructor(Configuration memory config) {
        // Sanity checks
        uint8 decimals_ = IERC20NonStandard(config.baseToken).decimals();
        if (decimals_ > MAX_BASE_DECIMALS) revert BadDecimals();
        if (config.storeFrontPriceFactor > FACTOR_SCALE) revert BadDiscount();
        if (config.assetConfigs.length > MAX_ASSETS_FOR_ASSET_LIST) revert TooManyAssets();
        if (config.baseMinForRewards == 0) revert BadMinimum();
        if (IPriceFeed(config.baseTokenPriceFeed).decimals() != PRICE_FEED_DECIMALS) revert BadDecimals();

        // Copy configuration
        unchecked {
            governor = config.governor;
            pauseGuardian = config.pauseGuardian;
            baseToken = config.baseToken;
            baseTokenPriceFeed = config.baseTokenPriceFeed;
            extensionDelegate = config.extensionDelegate;
            storeFrontPriceFactor = config.storeFrontPriceFactor;

            decimals = decimals_;
            baseScale = uint64(10 ** decimals_);
            trackingIndexScale = config.trackingIndexScale;
            if (baseScale < BASE_ACCRUAL_SCALE) revert BadDecimals();
            accrualDescaleFactor = baseScale / BASE_ACCRUAL_SCALE;

            baseMinForRewards = config.baseMinForRewards;
            baseTrackingSupplySpeed = config.baseTrackingSupplySpeed;
            baseTrackingBorrowSpeed = config.baseTrackingBorrowSpeed;

            baseBorrowMin = config.baseBorrowMin;
            targetReserves = config.targetReserves;
        }

        // Set interest rate model configs
        unchecked {
            supplyKink = config.supplyKink;
            supplyPerSecondInterestRateSlopeLow = config.supplyPerYearInterestRateSlopeLow / SECONDS_PER_YEAR;
            supplyPerSecondInterestRateSlopeHigh = config.supplyPerYearInterestRateSlopeHigh / SECONDS_PER_YEAR;
            supplyPerSecondInterestRateBase = config.supplyPerYearInterestRateBase / SECONDS_PER_YEAR;
            borrowKink = config.borrowKink;
            borrowPerSecondInterestRateSlopeLow = config.borrowPerYearInterestRateSlopeLow / SECONDS_PER_YEAR;
            borrowPerSecondInterestRateSlopeHigh = config.borrowPerYearInterestRateSlopeHigh / SECONDS_PER_YEAR;
            borrowPerSecondInterestRateBase = config.borrowPerYearInterestRateBase / SECONDS_PER_YEAR;
        }

        // Set asset info
        numAssets = uint8(config.assetConfigs.length);

        assetList = IAssetListFactory(IAssetListFactoryHolder(extensionDelegate).assetListFactory()).createAssetList(config.assetConfigs);
    }

    /**
     * @dev Prevents marked functions from being reentered 
     * Note: this restrict contracts from calling comet functions in their hooks.
     * Doing so will cause the transaction to revert.
     */
    modifier nonReentrant() {
        nonReentrantBefore();
        _;
        nonReentrantAfter();
    }

    /**
     * @dev Checks that the reentrancy flag is not set and then sets the flag
     */
    function nonReentrantBefore() internal {
        bytes32 slot = REENTRANCY_GUARD_FLAG_SLOT;
        uint256 status;
        assembly ("memory-safe") {
            status := sload(slot)
        }

        if (status == REENTRANCY_GUARD_ENTERED) revert ReentrantCallBlocked();
        assembly ("memory-safe") {
            sstore(slot, REENTRANCY_GUARD_ENTERED)
        }
    }

    /**
     * @dev Unsets the reentrancy flag
     */
    function nonReentrantAfter() internal {
        bytes32 slot = REENTRANCY_GUARD_FLAG_SLOT;
        uint256 status;
        assembly ("memory-safe") {
            sstore(slot, REENTRANCY_GUARD_NOT_ENTERED)
        }
    }

    /**
     * @notice Initialize storage for the contract
     * @dev Can be used from constructor or proxy
     */
    function initializeStorage() override external {
        if (lastAccrualTime != 0) revert AlreadyInitialized();

        // Initialize aggregates
        lastAccrualTime = getNowInternal();
        baseSupplyIndex = BASE_INDEX_SCALE;
        baseBorrowIndex = BASE_INDEX_SCALE;

        // Implicit initialization (not worth increasing contract size)
        // trackingSupplyIndex = 0;
        // trackingBorrowIndex = 0;
    }

    /**
     * @notice Get the i-th asset info, according to the order they were passed in originally
     * @param i The index of the asset info to get
     * @return The asset info object
     */
    function getAssetInfo(uint8 i) override public view returns (AssetInfo memory) {
        return IAssetList(assetList).getAssetInfo(i);
    }

    /**
     * @dev Determine index of asset that matches given address
     */
    function getAssetInfoByAddress(address asset) override public view returns (AssetInfo memory) {
        for (uint8 i = 0; i < numAssets; ) {
            AssetInfo memory assetInfo = getAssetInfo(i);
            if (assetInfo.asset == asset) {
                return assetInfo;
            }
            unchecked { i++; }
        }
        revert BadAsset();
    }

    /**
     * @return The current timestamp
     **/
    function getNowInternal() virtual internal view returns (uint40) {
        if (block.timestamp >= 2**40) revert TimestampTooLarge();
        return uint40(block.timestamp);
    }

    /**
     * @dev Calculate accrued interest indices for base token supply and borrows
     **/
    function accruedInterestIndices(uint timeElapsed) internal view returns (uint64, uint64) {
        uint64 baseSupplyIndex_ = baseSupplyIndex;
        uint64 baseBorrowIndex_ = baseBorrowIndex;
        if (timeElapsed > 0) {
            uint utilization = getUtilization();
            uint supplyRate = getSupplyRate(utilization);
            uint borrowRate = getBorrowRate(utilization);
            baseSupplyIndex_ += safe64(mulFactor(baseSupplyIndex_, supplyRate * timeElapsed));
            baseBorrowIndex_ += safe64(mulFactor(baseBorrowIndex_, borrowRate * timeElapsed));
        }
        return (baseSupplyIndex_, baseBorrowIndex_);
    }

    /**
     * @dev Accrue interest (and rewards) in base token supply and borrows
     **/
    function accrueInternal() internal {
        uint40 now_ = getNowInternal();
        uint timeElapsed = uint256(now_ - lastAccrualTime);
        if (timeElapsed > 0) {
            (baseSupplyIndex, baseBorrowIndex) = accruedInterestIndices(timeElapsed);
            if (totalSupplyBase >= baseMinForRewards) {
                trackingSupplyIndex += safe64(divBaseWei(baseTrackingSupplySpeed * timeElapsed, totalSupplyBase));
            }
            if (totalBorrowBase >= baseMinForRewards) {
                trackingBorrowIndex += safe64(divBaseWei(baseTrackingBorrowSpeed * timeElapsed, totalBorrowBase));
            }
            lastAccrualTime = now_;
        }
    }

    /**
     * @notice Accrue interest and rewards for an account
     **/
    function accrueAccount(address account) override external {
        accrueInternal();

        UserBasic memory basic = userBasic[account];
        updateBasePrincipal(account, basic, basic.principal);
    }

    /**
     * @dev Note: Does not accrue interest first
     * @param utilization The utilization to check the supply rate for
     * @return The per second supply rate at `utilization`
     */
    function getSupplyRate(uint utilization) override public view returns (uint64) {
        if (utilization <= supplyKink) {
            // interestRateBase + interestRateSlopeLow * utilization
            return safe64(supplyPerSecondInterestRateBase + mulFactor(supplyPerSecondInterestRateSlopeLow, utilization));
        } else {
            // interestRateBase + interestRateSlopeLow * kink + interestRateSlopeHigh * (utilization - kink)
            return safe64(supplyPerSecondInterestRateBase + mulFactor(supplyPerSecondInterestRateSlopeLow, supplyKink) + mulFactor(supplyPerSecondInterestRateSlopeHigh, (utilization - supplyKink)));
        }
    }

    /**
     * @dev Note: Does not accrue interest first
     * @param utilization The utilization to check the borrow rate for
     * @return The per second borrow rate at `utilization`
     */
    function getBorrowRate(uint utilization) override public view returns (uint64) {
        if (utilization <= borrowKink) {
            // interestRateBase + interestRateSlopeLow * utilization
            return safe64(borrowPerSecondInterestRateBase + mulFactor(borrowPerSecondInterestRateSlopeLow, utilization));
        } else {
            // interestRateBase + interestRateSlopeLow * kink + interestRateSlopeHigh * (utilization - kink)
            return safe64(borrowPerSecondInterestRateBase + mulFactor(borrowPerSecondInterestRateSlopeLow, borrowKink) + mulFactor(borrowPerSecondInterestRateSlopeHigh, (utilization - borrowKink)));
        }
    }

    /**
     * @dev Note: Does not accrue interest first
     * @return The utilization rate of the base asset
     */
    function getUtilization() override public view returns (uint) {
        uint totalSupply_ = presentValueSupply(baseSupplyIndex, totalSupplyBase);
        uint totalBorrow_ = presentValueBorrow(baseBorrowIndex, totalBorrowBase);
        if (totalSupply_ == 0) {
            return 0;
        } else {
            return totalBorrow_ * FACTOR_SCALE / totalSupply_;
        }
    }

    /**
     * @notice Get the current price from a feed
     * @param priceFeed The address of a price feed
     * @return The price, scaled by `PRICE_SCALE`
     */
    function getPrice(address priceFeed) override public view returns (uint256) {
        (, int price, , , ) = IPriceFeed(priceFeed).latestRoundData();
        if (price <= 0) revert BadPrice();
        return uint256(price);
    }

    /**
     * @notice Gets the total balance of protocol collateral reserves for an asset
     * @dev Note: Reverts if collateral reserves are somehow negative, which should not be possible
     * @param asset The collateral asset
     */
    function getCollateralReserves(address asset) override public view returns (uint) {
        return IERC20NonStandard(asset).balanceOf(address(this)) - totalsCollateral[asset].totalSupplyAsset;
    }

    /**
     * @notice Gets the total amount of protocol reserves of the base asset
     */
    function getReserves() override public view returns (int) {
        (uint64 baseSupplyIndex_, uint64 baseBorrowIndex_) = accruedInterestIndices(getNowInternal() - lastAccrualTime);
        uint balance = IERC20NonStandard(baseToken).balanceOf(address(this));
        uint totalSupply_ = presentValueSupply(baseSupplyIndex_, totalSupplyBase);
        uint totalBorrow_ = presentValueBorrow(baseBorrowIndex_, totalBorrowBase);
        return signed256(balance) - signed256(totalSupply_) + signed256(totalBorrow_);
    }

    /**
     * @notice Check whether an account has enough collateral to borrow
     * @param account The address to check
     * @return Whether the account is minimally collateralized enough to borrow
     */
    function isBorrowCollateralized(address account) override public view returns (bool) {
        int104 principal = userBasic[account].principal;

        if (principal >= 0) {
            return true;
        }

        uint16 assetsIn = userBasic[account].assetsIn;
        uint8 _reserved = userBasic[account]._reserved;
        int liquidity = signedMulPrice(
            presentValue(principal),
            getPrice(baseTokenPriceFeed),
            uint64(baseScale)
        );

        for (uint8 i = 0; i < numAssets; ) {
            if (isInAsset(assetsIn, i, _reserved)) {
                if (liquidity >= 0) {
                    return true;
                }

                AssetInfo memory asset = getAssetInfo(i);
                uint newAmount = mulPrice(
                    userCollateral[account][asset.asset].balance,
                    getPrice(asset.priceFeed),
                    asset.scale
                );
                liquidity += signed256(mulFactor(
                    newAmount,
                    asset.borrowCollateralFactor
                ));
            }
            unchecked { i++; }
        }

        return liquidity >= 0;
    }

    /**
     * @notice Check whether an account has enough collateral to not be liquidated
     * @param account The address to check
     * @return Whether the account is minimally collateralized enough to not be liquidated
     */
    function isLiquidatable(address account) override public view returns (bool) {
        int104 principal = userBasic[account].principal;

        if (principal >= 0) {
            return false;
        }

        uint16 assetsIn = userBasic[account].assetsIn;
        uint8 _reserved = userBasic[account]._reserved;
        int liquidity = signedMulPrice(
            presentValue(principal),
            getPrice(baseTokenPriceFeed),
            uint64(baseScale)
        );

        for (uint8 i = 0; i < numAssets; ) {
            if (isInAsset(assetsIn, i, _reserved)) {
                if (liquidity >= 0) {
                    return false;
                }

                AssetInfo memory asset = getAssetInfo(i);
                uint newAmount = mulPrice(
                    userCollateral[account][asset.asset].balance,
                    getPrice(asset.priceFeed),
                    asset.scale
                );
                liquidity += signed256(mulFactor(
                    newAmount,
                    asset.liquidateCollateralFactor
                ));
            }
            unchecked { i++; }
        }

        return liquidity < 0;
    }

    /**
     * @dev The change in principal broken into repay and supply amounts
     */
    function repayAndSupplyAmount(int104 oldPrincipal, int104 newPrincipal) internal pure returns (uint104, uint104) {
        // If the new principal is less than the old principal, then no amount has been repaid or supplied
        if (newPrincipal < oldPrincipal) return (0, 0);

        if (newPrincipal <= 0) {
            return (uint104(newPrincipal - oldPrincipal), 0);
        } else if (oldPrincipal >= 0) {
            return (0, uint104(newPrincipal - oldPrincipal));
        } else {
            return (uint104(-oldPrincipal), uint104(newPrincipal));
        }
    }

    /**
     * @dev The change in principal broken into withdraw and borrow amounts
     */
    function withdrawAndBorrowAmount(int104 oldPrincipal, int104 newPrincipal) internal pure returns (uint104, uint104) {
        // If the new principal is greater than the old principal, then no amount has been withdrawn or borrowed
        if (newPrincipal > oldPrincipal) return (0, 0);

        if (newPrincipal >= 0) {
            return (uint104(oldPrincipal - newPrincipal), 0);
        } else if (oldPrincipal <= 0) {
            return (0, uint104(oldPrincipal - newPrincipal));
        } else {
            return (uint104(oldPrincipal), uint104(-newPrincipal));
        }
    }

    /**
     * @notice Pauses different actions within Comet
     * @param supplyPaused Boolean for pausing supply actions
     * @param transferPaused Boolean for pausing transfer actions
     * @param withdrawPaused Boolean for pausing withdraw actions
     * @param absorbPaused Boolean for pausing absorb actions
     * @param buyPaused Boolean for pausing buy actions
     */
    function pause(
        bool supplyPaused,
        bool transferPaused,
        bool withdrawPaused,
        bool absorbPaused,
        bool buyPaused
    ) override external {
        if (msg.sender != governor && msg.sender != pauseGuardian) revert Unauthorized();

        pauseFlags =
            uint8(0) |
            (toUInt8(supplyPaused) << PAUSE_SUPPLY_OFFSET) |
            (toUInt8(transferPaused) << PAUSE_TRANSFER_OFFSET) |
            (toUInt8(withdrawPaused) << PAUSE_WITHDRAW_OFFSET) |
            (toUInt8(absorbPaused) << PAUSE_ABSORB_OFFSET) |
            (toUInt8(buyPaused) << PAUSE_BUY_OFFSET);

        emit PauseAction(supplyPaused, transferPaused, withdrawPaused, absorbPaused, buyPaused);
    }

    /**
     * @return Whether or not supply actions are paused
     */
    function isSupplyPaused() override public view returns (bool) {
        return toBool(pauseFlags & (uint8(1) << PAUSE_SUPPLY_OFFSET));
    }

    /**
     * @return Whether or not transfer actions are paused
     */
    function isTransferPaused() override public view returns (bool) {
        return toBool(pauseFlags & (uint8(1) << PAUSE_TRANSFER_OFFSET));
    }

    /**
     * @return Whether or not withdraw actions are paused
     */
    function isWithdrawPaused() override public view returns (bool) {
        return toBool(pauseFlags & (uint8(1) << PAUSE_WITHDRAW_OFFSET));
    }

    /**
     * @return Whether or not absorb actions are paused
     */
    function isAbsorbPaused() override public view returns (bool) {
        return toBool(pauseFlags & (uint8(1) << PAUSE_ABSORB_OFFSET));
    }

    /**
     * @return Whether or not buy actions are paused
     */
    function isBuyPaused() override public view returns (bool) {
        return toBool(pauseFlags & (uint8(1) << PAUSE_BUY_OFFSET));
    }

    /**
     * @dev Multiply a number by a factor
     */
    function mulFactor(uint n, uint factor) internal pure returns (uint) {
        return n * factor / FACTOR_SCALE;
    }

    /**
     * @dev Divide a number by an amount of base
     */
    function divBaseWei(uint n, uint baseWei) internal view returns (uint) {
        return n * baseScale / baseWei;
    }

    /**
     * @dev Multiply a `fromScale` quantity by a price, returning a common price quantity
     */
    function mulPrice(uint n, uint price, uint64 fromScale) internal pure returns (uint) {
        return n * price / fromScale;
    }

    /**
     * @dev Multiply a signed `fromScale` quantity by a price, returning a common price quantity
     */
    function signedMulPrice(int n, uint price, uint64 fromScale) internal pure returns (int) {
        return n * signed256(price) / int256(uint256(fromScale));
    }

    /**
     * @dev Divide a common price quantity by a price, returning a `toScale` quantity
     */
    function divPrice(uint n, uint price, uint64 toScale) internal pure returns (uint) {
        return n * toScale / price;
    }

    /**
     * @dev Whether user has a non-zero balance of an asset, given assetsIn flags
     * @dev _reserved is used to check bits 16-23 of assetsIn
     */
    function isInAsset(uint16 assetsIn, uint8 assetOffset, uint8 _reserved) internal pure returns (bool) {
        if (assetOffset < 16) {
            // check bit in assetsIn (for bits 0-15)
            return (assetsIn & (uint16(1) << assetOffset)) != 0;
        } else if (assetOffset < 24) {
            // check bit in reserved (for bits 16-23)
            return (_reserved & (uint8(1) << (assetOffset - 16))) != 0;
        }
        return false; // if assetOffset >= 24 (should not happen)
    }

    /**
     * @dev Update assetsIn bit vector if user has entered or exited an asset
     */
    function updateAssetsIn(
        address account,
        AssetInfo memory assetInfo,
        uint128 initialUserBalance,
        uint128 finalUserBalance
    ) internal {
        if (initialUserBalance == 0 && finalUserBalance != 0) {
            // set bit for asset
            if (assetInfo.offset < 16) {
                // set bit in assetsIn for bits 0-15
                userBasic[account].assetsIn |= (uint16(1) << assetInfo.offset);
            } else if (assetInfo.offset < 24) {
                // set bit in _reserved for bits 16-23
                userBasic[account]._reserved |= (uint8(1) << (assetInfo.offset - 16));
            }
        } else if (initialUserBalance != 0 && finalUserBalance == 0) {
            // clear bit for asset
            if (assetInfo.offset < 16) {
                // clear bit in assetsIn for bits 0-15
                userBasic[account].assetsIn &= ~(uint16(1) << assetInfo.offset);
            } else if (assetInfo.offset < 24) {
                // clear bit in _reserved for bits 16-23
                userBasic[account]._reserved &= ~(uint8(1) << (assetInfo.offset - 16));
            }
        }
    }

    /**
     * @dev Write updated principal to store and tracking participation
     */
    function updateBasePrincipal(address account, UserBasic memory basic, int104 principalNew) internal {
        int104 principal = basic.principal;
        basic.principal = principalNew;

        if (principal >= 0) {
            uint indexDelta = uint256(trackingSupplyIndex - basic.baseTrackingIndex);
            basic.baseTrackingAccrued += safe64(uint104(principal) * indexDelta / trackingIndexScale / accrualDescaleFactor);
        } else {
            uint indexDelta = uint256(trackingBorrowIndex - basic.baseTrackingIndex);
            basic.baseTrackingAccrued += safe64(uint104(-principal) * indexDelta / trackingIndexScale / accrualDescaleFactor);
        }

        if (principalNew >= 0) {
            basic.baseTrackingIndex = trackingSupplyIndex;
        } else {
            basic.baseTrackingIndex = trackingBorrowIndex;
        }

        userBasic[account] = basic;
    }

    /**
     * @dev Safe ERC20 transfer in and returns the final amount transferred (taking into account any fees)
     * @dev Note: Safely handles non-standard ERC-20 tokens that do not return a value. See here: https://medium.com/coinmonks/missing-return-value-bug-at-least-130-tokens-affected-d67bf08521ca
     */
    function doTransferIn(address asset, address from, uint amount) internal returns (uint) {
        uint256 preTransferBalance = IERC20NonStandard(asset).balanceOf(address(this));
        IERC20NonStandard(asset).transferFrom(from, address(this), amount);
        bool success;
        assembly ("memory-safe") {
            switch returndatasize()
                case 0 {                       // This is a non-standard ERC-20
                    success := not(0)          // set success to true
                }
                case 32 {                      // This is a compliant ERC-20
                    returndatacopy(0, 0, 32)
                    success := mload(0)        // Set `success = returndata` of override external call
                }
                default {                      // This is an excessively non-compliant ERC-20, revert.
                    revert(0, 0)
                }
        }
        if (!success) revert TransferInFailed();
        return IERC20NonStandard(asset).balanceOf(address(this)) - preTransferBalance;
    }

    /**
     * @dev Safe ERC20 transfer out
     * @dev Note: Safely handles non-standard ERC-20 tokens that do not return a value. See here: https://medium.com/coinmonks/missing-return-value-bug-at-least-130-tokens-affected-d67bf08521ca
     */
    function doTransferOut(address asset, address to, uint amount) internal {
        IERC20NonStandard(asset).transfer(to, amount);
        bool success;
        assembly ("memory-safe") {
            switch returndatasize()
                case 0 {                       // This is a non-standard ERC-20
                    success := not(0)          // set success to true
                }
                case 32 {                      // This is a compliant ERC-20
                    returndatacopy(0, 0, 32)
                    success := mload(0)        // Set `success = returndata` of override external call
                }
                default {                      // This is an excessively non-compliant ERC-20, revert.
                    revert(0, 0)
                }
        }
        if (!success) revert TransferOutFailed();
    }

    /**
     * @notice Supply an amount of asset to the protocol
     * @param asset The asset to supply
     * @param amount The quantity to supply
     */
    function supply(address asset, uint amount) override external {
        return supplyInternal(msg.sender, msg.sender, msg.sender, asset, amount);
    }

    /**
     * @notice Supply an amount of asset to dst
     * @param dst The address which will hold the balance
     * @param asset The asset to supply
     * @param amount The quantity to supply
     */
    function supplyTo(address dst, address asset, uint amount) override external {
        return supplyInternal(msg.sender, msg.sender, dst, asset, amount);
    }

    /**
     * @notice Supply an amount of asset from `from` to dst, if allowed
     * @param from The supplier address
     * @param dst The address which will hold the balance
     * @param asset The asset to supply
     * @param amount The quantity to supply
     */
    function supplyFrom(address from, address dst, address asset, uint amount) override external {
        return supplyInternal(msg.sender, from, dst, asset, amount);
    }

    /**
     * @dev Supply either collateral or base asset, depending on the asset, if operator is allowed
     * @dev Note: Specifying an `amount` of uint256.max will repay all of `dst`'s accrued base borrow balance
     */
    function supplyInternal(address operator, address from, address dst, address asset, uint amount) internal nonReentrant {
        if (isSupplyPaused()) revert Paused();
        if (!hasPermission(from, operator)) revert Unauthorized();

        if (asset == baseToken) {
            if (amount == type(uint256).max) {
                amount = borrowBalanceOf(dst);
            }
            return supplyBase(from, dst, amount);
        } else {
            return supplyCollateral(from, dst, asset, safe128(amount));
        }
    }

    /**
     * @dev Supply an amount of base asset from `from` to dst
     */
    function supplyBase(address from, address dst, uint256 amount) internal {
        amount = doTransferIn(baseToken, from, amount);

        accrueInternal();

        UserBasic memory dstUser = userBasic[dst];
        int104 dstPrincipal = dstUser.principal;
        int256 dstBalance = presentValue(dstPrincipal) + signed256(amount);
        int104 dstPrincipalNew = principalValue(dstBalance);

        (uint104 repayAmount, uint104 supplyAmount) = repayAndSupplyAmount(dstPrincipal, dstPrincipalNew);

        totalSupplyBase += supplyAmount;
        totalBorrowBase -= repayAmount;

        updateBasePrincipal(dst, dstUser, dstPrincipalNew);

        emit Supply(from, dst, amount);

        if (supplyAmount > 0) {
            emit Transfer(address(0), dst, presentValueSupply(baseSupplyIndex, supplyAmount));
        }
    }

    /**
     * @dev Supply an amount of collateral asset from `from` to dst
     */
    function supplyCollateral(address from, address dst, address asset, uint128 amount) internal {
        amount = safe128(doTransferIn(asset, from, amount));

        AssetInfo memory assetInfo = getAssetInfoByAddress(asset);
        TotalsCollateral memory totals = totalsCollateral[asset];
        totals.totalSupplyAsset += amount;
        if (totals.totalSupplyAsset > assetInfo.supplyCap) revert SupplyCapExceeded();

        uint128 dstCollateral = userCollateral[dst][asset].balance;
        uint128 dstCollateralNew = dstCollateral + amount;

        totalsCollateral[asset] = totals;
        userCollateral[dst][asset].balance = dstCollateralNew;

        updateAssetsIn(dst, assetInfo, dstCollateral, dstCollateralNew);

        emit SupplyCollateral(from, dst, asset, amount);
    }

    /**
     * @notice ERC20 transfer an amount of base token to dst
     * @param dst The recipient address
     * @param amount The quantity to transfer
     * @return true
     */
    function transfer(address dst, uint amount) override external returns (bool) {
        transferInternal(msg.sender, msg.sender, dst, baseToken, amount);
        return true;
    }

    /**
     * @notice ERC20 transfer an amount of base token from src to dst, if allowed
     * @param src The sender address
     * @param dst The recipient address
     * @param amount The quantity to transfer
     * @return true
     */
    function transferFrom(address src, address dst, uint amount) override external returns (bool) {
        transferInternal(msg.sender, src, dst, baseToken, amount);
        return true;
    }

    /**
     * @notice Transfer an amount of asset to dst
     * @param dst The recipient address
     * @param asset The asset to transfer
     * @param amount The quantity to transfer
     */
    function transferAsset(address dst, address asset, uint amount) override external {
        return transferInternal(msg.sender, msg.sender, dst, asset, amount);
    }

    /**
     * @notice Transfer an amount of asset from src to dst, if allowed
     * @param src The sender address
     * @param dst The recipient address
     * @param asset The asset to transfer
     * @param amount The quantity to transfer
     */
    function transferAssetFrom(address src, address dst, address asset, uint amount) override external {
        return transferInternal(msg.sender, src, dst, asset, amount);
    }

    /**
     * @dev Transfer either collateral or base asset, depending on the asset, if operator is allowed
     * @dev Note: Specifying an `amount` of uint256.max will transfer all of `src`'s accrued base balance
     */
    function transferInternal(address operator, address src, address dst, address asset, uint amount) internal nonReentrant {
        if (isTransferPaused()) revert Paused();
        if (!hasPermission(src, operator)) revert Unauthorized();
        if (src == dst) revert NoSelfTransfer();

        if (asset == baseToken) {
            if (amount == type(uint256).max) {
                amount = balanceOf(src);
            }
            return transferBase(src, dst, amount);
        } else {
            return transferCollateral(src, dst, asset, safe128(amount));
        }
    }

    /**
     * @dev Transfer an amount of base asset from src to dst, borrowing if possible/necessary
     */
    function transferBase(address src, address dst, uint256 amount) internal {
        accrueInternal();

        UserBasic memory srcUser = userBasic[src];
        UserBasic memory dstUser = userBasic[dst];

        int104 srcPrincipal = srcUser.principal;
        int104 dstPrincipal = dstUser.principal;
        int256 srcBalance = presentValue(srcPrincipal) - signed256(amount);
        int256 dstBalance = presentValue(dstPrincipal) + signed256(amount);
        int104 srcPrincipalNew = principalValue(srcBalance);
        int104 dstPrincipalNew = principalValue(dstBalance);

        (uint104 withdrawAmount, uint104 borrowAmount) = withdrawAndBorrowAmount(srcPrincipal, srcPrincipalNew);
        (uint104 repayAmount, uint104 supplyAmount) = repayAndSupplyAmount(dstPrincipal, dstPrincipalNew);

        // Note: Instead of `total += addAmount - subAmount` to avoid underflow errors.
        totalSupplyBase = totalSupplyBase + supplyAmount - withdrawAmount;
        totalBorrowBase = totalBorrowBase + borrowAmount - repayAmount;

        updateBasePrincipal(src, srcUser, srcPrincipalNew);
        updateBasePrincipal(dst, dstUser, dstPrincipalNew);

        if (srcBalance < 0) {
            if (uint256(-srcBalance) < baseBorrowMin) revert BorrowTooSmall();
            if (!isBorrowCollateralized(src)) revert NotCollateralized();
        }

        if (withdrawAmount > 0) {
            emit Transfer(src, address(0), presentValueSupply(baseSupplyIndex, withdrawAmount));
        }

        if (supplyAmount > 0) {
            emit Transfer(address(0), dst, presentValueSupply(baseSupplyIndex, supplyAmount));
        }
    }

    /**
     * @dev Transfer an amount of collateral asset from src to dst
     */
    function transferCollateral(address src, address dst, address asset, uint128 amount) internal {
        uint128 srcCollateral = userCollateral[src][asset].balance;
        uint128 dstCollateral = userCollateral[dst][asset].balance;
        uint128 srcCollateralNew = srcCollateral - amount;
        uint128 dstCollateralNew = dstCollateral + amount;

        userCollateral[src][asset].balance = srcCollateralNew;
        userCollateral[dst][asset].balance = dstCollateralNew;

        AssetInfo memory assetInfo = getAssetInfoByAddress(asset);
        updateAssetsIn(src, assetInfo, srcCollateral, srcCollateralNew);
        updateAssetsIn(dst, assetInfo, dstCollateral, dstCollateralNew);

        // Note: no accrue interest, BorrowCF < LiquidationCF covers small changes
        if (!isBorrowCollateralized(src)) revert NotCollateralized();

        emit TransferCollateral(src, dst, asset, amount);
    }

    /**
     * @notice Withdraw an amount of asset from the protocol
     * @param asset The asset to withdraw
     * @param amount The quantity to withdraw
     */
    function withdraw(address asset, uint amount) override external {
        return withdrawInternal(msg.sender, msg.sender, msg.sender, asset, amount);
    }

    /**
     * @notice Withdraw an amount of asset to `to`
     * @param to The recipient address
     * @param asset The asset to withdraw
     * @param amount The quantity to withdraw
     */
    function withdrawTo(address to, address asset, uint amount) override external {
        return withdrawInternal(msg.sender, msg.sender, to, asset, amount);
    }

    /**
     * @notice Withdraw an amount of asset from src to `to`, if allowed
     * @param src The sender address
     * @param to The recipient address
     * @param asset The asset to withdraw
     * @param amount The quantity to withdraw
     */
    function withdrawFrom(address src, address to, address asset, uint amount) override external {
        return withdrawInternal(msg.sender, src, to, asset, amount);
    }

    /**
     * @dev Withdraw either collateral or base asset, depending on the asset, if operator is allowed
     * @dev Note: Specifying an `amount` of uint256.max will withdraw all of `src`'s accrued base balance
     */
    function withdrawInternal(address operator, address src, address to, address asset, uint amount) internal nonReentrant {
        if (isWithdrawPaused()) revert Paused();
        if (!hasPermission(src, operator)) revert Unauthorized();

        if (asset == baseToken) {
            if (amount == type(uint256).max) {
                amount = balanceOf(src);
            }
            return withdrawBase(src, to, amount);
        } else {
            return withdrawCollateral(src, to, asset, safe128(amount));
        }
    }

    /**
     * @dev Withdraw an amount of base asset from src to `to`, borrowing if possible/necessary
     */
    function withdrawBase(address src, address to, uint256 amount) internal {
        accrueInternal();

        UserBasic memory srcUser = userBasic[src];
        int104 srcPrincipal = srcUser.principal;
        int256 srcBalance = presentValue(srcPrincipal) - signed256(amount);
        int104 srcPrincipalNew = principalValue(srcBalance);

        (uint104 withdrawAmount, uint104 borrowAmount) = withdrawAndBorrowAmount(srcPrincipal, srcPrincipalNew);

        totalSupplyBase -= withdrawAmount;
        totalBorrowBase += borrowAmount;

        updateBasePrincipal(src, srcUser, srcPrincipalNew);

        if (srcBalance < 0) {
            if (uint256(-srcBalance) < baseBorrowMin) revert BorrowTooSmall();
            if (!isBorrowCollateralized(src)) revert NotCollateralized();
        }

        doTransferOut(baseToken, to, amount);

        emit Withdraw(src, to, amount);

        if (withdrawAmount > 0) {
            emit Transfer(src, address(0), presentValueSupply(baseSupplyIndex, withdrawAmount));
        }
    }

    /**
     * @dev Withdraw an amount of collateral asset from src to `to`
     */
    function withdrawCollateral(address src, address to, address asset, uint128 amount) internal {
        uint128 srcCollateral = userCollateral[src][asset].balance;
        uint128 srcCollateralNew = srcCollateral - amount;

        totalsCollateral[asset].totalSupplyAsset -= amount;
        userCollateral[src][asset].balance = srcCollateralNew;

        AssetInfo memory assetInfo = getAssetInfoByAddress(asset);
        updateAssetsIn(src, assetInfo, srcCollateral, srcCollateralNew);

        // Note: no accrue interest, BorrowCF < LiquidationCF covers small changes
        if (!isBorrowCollateralized(src)) revert NotCollateralized();

        doTransferOut(asset, to, amount);

        emit WithdrawCollateral(src, to, asset, amount);
    }

    /**
     * @notice Absorb a list of underwater accounts onto the protocol balance sheet
     * @param absorber The recipient of the incentive paid to the caller of absorb
     * @param accounts The list of underwater accounts to absorb
     */
    function absorb(address absorber, address[] calldata accounts) override external {
        if (isAbsorbPaused()) revert Paused();

        uint startGas = gasleft();
        accrueInternal();
        for (uint i = 0; i < accounts.length; ) {
            absorbInternal(absorber, accounts[i]);
            unchecked { i++; }
        }
        uint gasUsed = startGas - gasleft();

        // Note: liquidator points are an imperfect tool for governance,
        //  to be used while evaluating strategies for incentivizing absorption.
        // Using gas price instead of base fee would more accurately reflect spend,
        //  but is also subject to abuse if refunds were to be given automatically.
        LiquidatorPoints memory points = liquidatorPoints[absorber];
        points.numAbsorbs++;
        points.numAbsorbed += safe64(accounts.length);
        points.approxSpend += safe128(gasUsed * block.basefee);
        liquidatorPoints[absorber] = points;
    }

    /**
     * @dev Transfer user's collateral and debt to the protocol itself.
     */
    function absorbInternal(address absorber, address account) internal {
        if (!isLiquidatable(account)) revert NotLiquidatable();

        UserBasic memory accountUser = userBasic[account];
        int104 oldPrincipal = accountUser.principal;
        int256 oldBalance = presentValue(oldPrincipal);
        uint16 assetsIn = accountUser.assetsIn;
        uint8 _reserved = accountUser._reserved;

        uint256 basePrice = getPrice(baseTokenPriceFeed);
        uint256 deltaValue = 0;

        for (uint8 i = 0; i < numAssets; ) {
            if (isInAsset(assetsIn, i, _reserved)) {
                AssetInfo memory assetInfo = getAssetInfo(i);
                address asset = assetInfo.asset;
                uint128 seizeAmount = userCollateral[account][asset].balance;
                userCollateral[account][asset].balance = 0;
                totalsCollateral[asset].totalSupplyAsset -= seizeAmount;

                uint256 value = mulPrice(seizeAmount, getPrice(assetInfo.priceFeed), assetInfo.scale);
                deltaValue += mulFactor(value, assetInfo.liquidationFactor);

                emit AbsorbCollateral(absorber, account, asset, seizeAmount, value);
            }
            unchecked { i++; }
        }

        uint256 deltaBalance = divPrice(deltaValue, basePrice, uint64(baseScale));
        int256 newBalance = oldBalance + signed256(deltaBalance);
        // New balance will not be negative, all excess debt absorbed by reserves
        if (newBalance < 0) {
            newBalance = 0;
        }

        int104 newPrincipal = principalValue(newBalance);
        updateBasePrincipal(account, accountUser, newPrincipal);

        // reset assetsIn
        userBasic[account].assetsIn = 0;
        userBasic[account]._reserved = 0;

        (uint104 repayAmount, uint104 supplyAmount) = repayAndSupplyAmount(oldPrincipal, newPrincipal);

        // Reserves are decreased by increasing total supply and decreasing borrows
        //  the amount of debt repaid by reserves is `newBalance - oldBalance`
        totalSupplyBase += supplyAmount;
        totalBorrowBase -= repayAmount;

        uint256 basePaidOut = unsigned256(newBalance - oldBalance);
        uint256 valueOfBasePaidOut = mulPrice(basePaidOut, basePrice, uint64(baseScale));
        emit AbsorbDebt(absorber, account, basePaidOut, valueOfBasePaidOut);

        if (newPrincipal > 0) {
            emit Transfer(address(0), account, presentValueSupply(baseSupplyIndex, unsigned104(newPrincipal)));
        }
    }

    /**
     * @notice Buy collateral from the protocol using base tokens, increasing protocol reserves
       A minimum collateral amount should be specified to indicate the maximum slippage acceptable for the buyer.
     * @param asset The asset to buy
     * @param minAmount The minimum amount of collateral tokens that should be received by the buyer
     * @param baseAmount The amount of base tokens used to buy the collateral
     * @param recipient The recipient address
     */
    function buyCollateral(address asset, uint minAmount, uint baseAmount, address recipient) override external nonReentrant {
        if (isBuyPaused()) revert Paused();

        int reserves = getReserves();
        if (reserves >= 0 && uint(reserves) >= targetReserves) revert NotForSale();

        // Note: Re-entrancy can skip the reserves check above on a second buyCollateral call.
        baseAmount = doTransferIn(baseToken, msg.sender, baseAmount);

        uint collateralAmount = quoteCollateral(asset, baseAmount);
        if (collateralAmount < minAmount) revert TooMuchSlippage();
        if (collateralAmount > getCollateralReserves(asset)) revert InsufficientReserves();

        // Note: Pre-transfer hook can re-enter buyCollateral with a stale collateral ERC20 balance.
        //  Assets should not be listed which allow re-entry from pre-transfer now, as too much collateral could be bought.
        //  This is also a problem if quoteCollateral derives its discount from the collateral ERC20 balance.
        doTransferOut(asset, recipient, safe128(collateralAmount));

        emit BuyCollateral(msg.sender, asset, baseAmount, collateralAmount);
    }

    /**
     * @notice Gets the quote for a collateral asset in exchange for an amount of base asset
     * @param asset The collateral asset to get the quote for
     * @param baseAmount The amount of the base asset to get the quote for
     * @return The quote in terms of the collateral asset
     */
    function quoteCollateral(address asset, uint baseAmount) override public view returns (uint) {
        AssetInfo memory assetInfo = getAssetInfoByAddress(asset);
        uint256 assetPrice = getPrice(assetInfo.priceFeed);
        // Store front discount is derived from the collateral asset's liquidationFactor and storeFrontPriceFactor
        // discount = storeFrontPriceFactor * (1e18 - liquidationFactor)
        uint256 discountFactor = mulFactor(storeFrontPriceFactor, FACTOR_SCALE - assetInfo.liquidationFactor);
        uint256 assetPriceDiscounted = mulFactor(assetPrice, FACTOR_SCALE - discountFactor);
        uint256 basePrice = getPrice(baseTokenPriceFeed);
        // # of collateral assets
        // = (TotalValueOfBaseAmount / DiscountedPriceOfCollateralAsset) * assetScale
        // = ((basePrice * baseAmount / baseScale) / assetPriceDiscounted) * assetScale
        return basePrice * baseAmount * assetInfo.scale / assetPriceDiscounted / baseScale;
    }

    /**
     * @notice Withdraws base token reserves if called by the governor
     * @param to An address of the receiver of withdrawn reserves
     * @param amount The amount of reserves to be withdrawn from the protocol
     */
    function withdrawReserves(address to, uint amount) override external {
        if (msg.sender != governor) revert Unauthorized();

        int reserves = getReserves();
        if (reserves < 0 || amount > unsigned256(reserves)) revert InsufficientReserves();

        doTransferOut(baseToken, to, amount);

        emit WithdrawReserves(to, amount);
    }

    /**
     * @notice Sets Comet's ERC20 allowance of an asset for a manager
     * @dev Only callable by governor
     * @dev Note: Setting the `asset` as Comet's address will allow the manager
     * to withdraw from Comet's Comet balance
     * @dev Note: For USDT, if there is non-zero prior allowance, it must be reset to 0 first before setting a new value in proposal
     * @param asset The asset that the manager will gain approval of
     * @param manager The account which will be allowed or disallowed
     * @param amount The amount of an asset to approve
     */
    function approveThis(address manager, address asset, uint amount) override external {
        if (msg.sender != governor) revert Unauthorized();

        IERC20NonStandard(asset).approve(manager, amount);
    }

    /**
     * @notice Get the total number of tokens in circulation
     * @dev Note: uses updated interest indices to calculate
     * @return The supply of tokens
     **/
    function totalSupply() override external view returns (uint256) {
        (uint64 baseSupplyIndex_, ) = accruedInterestIndices(getNowInternal() - lastAccrualTime);
        return presentValueSupply(baseSupplyIndex_, totalSupplyBase);
    }

    /**
     * @notice Get the total amount of debt
     * @dev Note: uses updated interest indices to calculate
     * @return The amount of debt
     **/
    function totalBorrow() override external view returns (uint256) {
        (, uint64 baseBorrowIndex_) = accruedInterestIndices(getNowInternal() - lastAccrualTime);
        return presentValueBorrow(baseBorrowIndex_, totalBorrowBase);
    }

    /**
     * @notice Query the current positive base balance of an account or zero
     * @dev Note: uses updated interest indices to calculate
     * @param account The account whose balance to query
     * @return The present day base balance magnitude of the account, if positive
     */
    function balanceOf(address account) override public view returns (uint256) {
        (uint64 baseSupplyIndex_, ) = accruedInterestIndices(getNowInternal() - lastAccrualTime);
        int104 principal = userBasic[account].principal;
        return principal > 0 ? presentValueSupply(baseSupplyIndex_, unsigned104(principal)) : 0;
    }

    /**
     * @notice Query the current negative base balance of an account or zero
     * @dev Note: uses updated interest indices to calculate
     * @param account The account whose balance to query
     * @return The present day base balance magnitude of the account, if negative
     */
    function borrowBalanceOf(address account) override public view returns (uint256) {
        (, uint64 baseBorrowIndex_) = accruedInterestIndices(getNowInternal() - lastAccrualTime);
        int104 principal = userBasic[account].principal;
        return principal < 0 ? presentValueBorrow(baseBorrowIndex_, unsigned104(-principal)) : 0;
    }

    /**
     * @notice Fallback to calling the extension delegate for everything else
     */
    fallback() external payable {
        address delegate = extensionDelegate;
        assembly {
            calldatacopy(0, 0, calldatasize())
            let result := delegatecall(gas(), delegate, 0, calldatasize(), 0, 0)
            returndatacopy(0, 0, returndatasize())
            switch result
            case 0 { revert(0, returndatasize()) }
            default { return(0, returndatasize()) }
        }
    }
}