aave-protocol-v2/contracts/protocol/lendingpool/LendingPool.sol

// SPDX-License-Identifier: agpl-3.0
pragma solidity 0.6.12;
pragma experimental ABIEncoderV2;

import {SafeMath} from '../../dependencies/openzeppelin/contracts/SafeMath.sol';
import {IERC20} from '../../dependencies/openzeppelin/contracts/IERC20.sol';
import {SafeERC20} from '../../dependencies/openzeppelin/contracts/SafeERC20.sol';
import {Address} from '../../dependencies/openzeppelin/contracts/Address.sol';
import {ILendingPoolAddressesProvider} from '../../interfaces/ILendingPoolAddressesProvider.sol';
import {IAToken} from '../../interfaces/IAToken.sol';
import {IVariableDebtToken} from '../../interfaces/IVariableDebtToken.sol';
import {IFlashLoanReceiver} from '../../flashloan/interfaces/IFlashLoanReceiver.sol';
import {IPriceOracleGetter} from '../../interfaces/IPriceOracleGetter.sol';
import {IStableDebtToken} from '../../interfaces/IStableDebtToken.sol';
import {ILendingPool} from '../../interfaces/ILendingPool.sol';
import {VersionedInitializable} from '../libraries/aave-upgradeability/VersionedInitializable.sol';
import {Helpers} from '../libraries/helpers/Helpers.sol';
import {Errors} from '../libraries/helpers/Errors.sol';
import {WadRayMath} from '../libraries/math/WadRayMath.sol';
import {PercentageMath} from '../libraries/math/PercentageMath.sol';
import {ReserveLogic} from '../libraries/logic/ReserveLogic.sol';
import {GenericLogic} from '../libraries/logic/GenericLogic.sol';
import {ValidationLogic} from '../libraries/logic/ValidationLogic.sol';
import {ReserveConfiguration} from '../libraries/configuration/ReserveConfiguration.sol';
import {UserConfiguration} from '../libraries/configuration/UserConfiguration.sol';
import {DataTypes} from '../libraries/types/DataTypes.sol';
import {LendingPoolStorage} from './LendingPoolStorage.sol';

/**
 * @title LendingPool contract
 * @dev Main point of interaction with an Aave protocol's market
 * - Users can:
 *   # Deposit
 *   # Withdraw
 *   # Borrow
 *   # Repay
 *   # Swap their loans between variable and stable rate
 *   # Enable/disable their deposits as collateral rebalance stable rate borrow positions
 *   # Liquidate positions
 *   # Execute Flash Loans
 * - To be covered by a proxy contract, owned by the LendingPoolAddressesProvider of the specific market
 * - All admin functions are callable by the LendingPoolConfigurator contract defined also in the
 *   LendingPoolAddressesProvider
 * @author Aave
 **/
contract LendingPool is VersionedInitializable, ILendingPool, LendingPoolStorage {
  using SafeMath for uint256;
  using WadRayMath for uint256;
  using PercentageMath for uint256;
  using SafeERC20 for IERC20;

  //main configuration parameters
  uint256 public constant MAX_STABLE_RATE_BORROW_SIZE_PERCENT = 2500;
  uint256 public constant FLASHLOAN_PREMIUM_TOTAL = 9;
  uint256 public constant MAX_NUMBER_RESERVES = 128;
  uint256 public constant LENDINGPOOL_REVISION = 0x2;

  modifier whenNotPaused() {
    _whenNotPaused();
    _;
  }

  modifier onlyLendingPoolConfigurator() {
    _onlyLendingPoolConfigurator();
    _;
  }

  function _whenNotPaused() internal view {
    require(!_paused, Errors.LP_IS_PAUSED);
  }

  function _onlyLendingPoolConfigurator() internal view {
    require(
      _addressesProvider.getLendingPoolConfigurator() == msg.sender,
      Errors.LP_CALLER_NOT_LENDING_POOL_CONFIGURATOR
    );
  }

  function getRevision() internal pure override returns (uint256) {
    return LENDINGPOOL_REVISION;
  }

  /**
   * @dev Function is invoked by the proxy contract when the LendingPool contract is added to the
   * LendingPoolAddressesProvider of the market.
   * - Caching the address of the LendingPoolAddressesProvider in order to reduce gas consumption
   *   on subsequent operations
   * @param provider The address of the LendingPoolAddressesProvider
   **/
  function initialize(ILendingPoolAddressesProvider provider) public initializer {
    _addressesProvider = provider;
  }

  /**
   * @dev Deposits an `amount` of underlying asset into the reserve, receiving in return overlying aTokens.
   * - E.g. User deposits 100 USDC and gets in return 100 aUSDC
   * @param asset The address of the underlying asset to deposit
   * @param amount The amount to be deposited
   * @param onBehalfOf The address that will receive the aTokens, same as msg.sender if the user
   *   wants to receive them on his own wallet, or a different address if the beneficiary of aTokens
   *   is a different wallet
   * @param referralCode Code used to register the integrator originating the operation, for potential rewards.
   *   0 if the action is executed directly by the user, without any middle-man
   **/
  function deposit(
    address asset,
    uint256 amount,
    address onBehalfOf,
    uint16 referralCode
  ) external override whenNotPaused {
    DataTypes.ReserveData storage reserve = _reserves[asset];

    ValidationLogic.validateDeposit(reserve, amount);

    address aToken = reserve.aTokenAddress;

    reserve.updateState();
    reserve.updateInterestRates(asset, aToken, amount, 0);

    IERC20(asset).safeTransferFrom(msg.sender, aToken, amount);

    bool isFirstDeposit = IAToken(aToken).mint(onBehalfOf, amount, reserve.liquidityIndex);

    if (isFirstDeposit) {
      _usersConfig[onBehalfOf].setUsingAsCollateral(reserve.id, true);
      emit ReserveUsedAsCollateralEnabled(asset, onBehalfOf);
    }

    emit Deposit(asset, msg.sender, onBehalfOf, amount, referralCode);
  }

  /**
   * @dev Withdraws an `amount` of underlying asset from the reserve, burning the equivalent aTokens owned
   * E.g. User has 100 aUSDC, calls withdraw() and receives 100 USDC, burning the 100 aUSDC
   * @param asset The address of the underlying asset to withdraw
   * @param amount The underlying amount to be withdrawn
   *   - Send the value type(uint256).max in order to withdraw the whole aToken balance
   * @param to Address that will receive the underlying, same as msg.sender if the user
   *   wants to receive it on his own wallet, or a different address if the beneficiary is a
   *   different wallet
   * @return The final amount withdrawn
   **/
  function withdraw(
    address asset,
    uint256 amount,
    address to
  ) external override whenNotPaused  returns (uint256) {
    DataTypes.ReserveData storage reserve = _reserves[asset];

    address aToken = reserve.aTokenAddress;

    uint256 userBalance = IAToken(aToken).balanceOf(msg.sender);

    uint256 amountToWithdraw = amount;

    if (amount == type(uint256).max) {
      amountToWithdraw = userBalance;
    }

    ValidationLogic.validateWithdraw(
      asset,
      amountToWithdraw,
      userBalance,
      _reserves,
      _usersConfig[msg.sender],
      _reservesList,
      _reservesCount,
      _addressesProvider.getPriceOracle()
    );

    reserve.updateState();

    reserve.updateInterestRates(asset, aToken, 0, amountToWithdraw);

    if (amountToWithdraw == userBalance) {
      _usersConfig[msg.sender].setUsingAsCollateral(reserve.id, false);
      emit ReserveUsedAsCollateralDisabled(asset, msg.sender);
    }

    IAToken(aToken).burn(msg.sender, to, amountToWithdraw, reserve.liquidityIndex);

    emit Withdraw(asset, msg.sender, to, amountToWithdraw);

    return amountToWithdraw;
  }

  /**
   * @dev Allows users to borrow a specific `amount` of the reserve underlying asset, provided that the borrower
   * already deposited enough collateral, or he was given enough allowance by a credit delegator on the
   * corresponding debt token (StableDebtToken or VariableDebtToken)
   * - E.g. User borrows 100 USDC passing as `onBehalfOf` his own address, receiving the 100 USDC in his wallet
   *   and 100 stable/variable debt tokens, depending on the `interestRateMode`
   * @param asset The address of the underlying asset to borrow
   * @param amount The amount to be borrowed
   * @param interestRateMode The interest rate mode at which the user wants to borrow: 1 for Stable, 2 for Variable
   * @param referralCode Code used to register the integrator originating the operation, for potential rewards.
   *   0 if the action is executed directly by the user, without any middle-man
   * @param onBehalfOf Address of the user who will receive the debt. Should be the address of the borrower itself
   * calling the function if he wants to borrow against his own collateral, or the address of the credit delegator
   * if he has been given credit delegation allowance
   **/
  function borrow(
    address asset,
    uint256 amount,
    uint256 interestRateMode,
    uint16 referralCode,
    address onBehalfOf
  ) external override whenNotPaused {
    DataTypes.ReserveData storage reserve = _reserves[asset];

    _executeBorrow(
      ExecuteBorrowParams(
        asset,
        msg.sender,
        onBehalfOf,
        amount,
        interestRateMode,
        reserve.aTokenAddress,
        referralCode,
        true
      )
    );
  }

  /**
   * @notice Repays a borrowed `amount` on a specific reserve, burning the equivalent debt tokens owned
   * - E.g. User repays 100 USDC, burning 100 variable/stable debt tokens of the `onBehalfOf` address
   * @param asset The address of the borrowed underlying asset previously borrowed
   * @param amount The amount to repay
   * - Send the value type(uint256).max in order to repay the whole debt for `asset` on the specific `debtMode`
   * @param rateMode The interest rate mode at of the debt the user wants to repay: 1 for Stable, 2 for Variable
   * @param onBehalfOf Address of the user who will get his debt reduced/removed. Should be the address of the
   * user calling the function if he wants to reduce/remove his own debt, or the address of any other
   * other borrower whose debt should be removed
   * @return The final amount repaid
   **/
  function repay(
    address asset,
    uint256 amount,
    uint256 rateMode,
    address onBehalfOf
  ) external override whenNotPaused returns (uint256) {
    DataTypes.ReserveData storage reserve = _reserves[asset];

    (uint256 stableDebt, uint256 variableDebt) = Helpers.getUserCurrentDebt(onBehalfOf, reserve);

    DataTypes.InterestRateMode interestRateMode = DataTypes.InterestRateMode(rateMode);

    ValidationLogic.validateRepay(
      reserve,
      amount,
      interestRateMode,
      onBehalfOf,
      stableDebt,
      variableDebt
    );

    uint256 paybackAmount =
      interestRateMode == DataTypes.InterestRateMode.STABLE ? stableDebt : variableDebt;

    if (amount < paybackAmount) {
      paybackAmount = amount;
    }

    reserve.updateState();

    if (interestRateMode == DataTypes.InterestRateMode.STABLE) {
      IStableDebtToken(reserve.stableDebtTokenAddress).burn(onBehalfOf, paybackAmount);
    } else {
      IVariableDebtToken(reserve.variableDebtTokenAddress).burn(
        onBehalfOf,
        paybackAmount,
        reserve.variableBorrowIndex
      );
    }

    address aToken = reserve.aTokenAddress;
    reserve.updateInterestRates(asset, aToken, paybackAmount, 0);

    if (stableDebt.add(variableDebt).sub(paybackAmount) == 0) {
      _usersConfig[onBehalfOf].setBorrowing(reserve.id, false);
    }

    IERC20(asset).safeTransferFrom(msg.sender, aToken, paybackAmount);

    emit Repay(asset, onBehalfOf, msg.sender, paybackAmount);

    return paybackAmount;
  }

  /**
   * @dev Allows a borrower to swap his debt between stable and variable mode, or viceversa
   * @param asset The address of the underlying asset borrowed
   * @param rateMode The rate mode that the user wants to swap to
   **/
  function swapBorrowRateMode(address asset, uint256 rateMode) external override whenNotPaused {
    DataTypes.ReserveData storage reserve = _reserves[asset];

    (uint256 stableDebt, uint256 variableDebt) = Helpers.getUserCurrentDebt(msg.sender, reserve);

    DataTypes.InterestRateMode interestRateMode = DataTypes.InterestRateMode(rateMode);

    ValidationLogic.validateSwapRateMode(
      reserve,
      _usersConfig[msg.sender],
      stableDebt,
      variableDebt,
      interestRateMode
    );

    reserve.updateState();

    if (interestRateMode == DataTypes.InterestRateMode.STABLE) {
      IStableDebtToken(reserve.stableDebtTokenAddress).burn(msg.sender, stableDebt);
      IVariableDebtToken(reserve.variableDebtTokenAddress).mint(
        msg.sender,
        msg.sender,
        stableDebt,
        reserve.variableBorrowIndex
      );
    } else {
      IVariableDebtToken(reserve.variableDebtTokenAddress).burn(
        msg.sender,
        variableDebt,
        reserve.variableBorrowIndex
      );
      IStableDebtToken(reserve.stableDebtTokenAddress).mint(
        msg.sender,
        msg.sender,
        variableDebt,
        reserve.currentStableBorrowRate
      );
    }

    reserve.updateInterestRates(asset, reserve.aTokenAddress, 0, 0);

    emit Swap(asset, msg.sender, rateMode);
  }

  /**
   * @dev Rebalances the stable interest rate of a user to the current stable rate defined on the reserve.
   * - Users can be rebalanced if the following conditions are satisfied:
   *     1. Usage ratio is above 95%
   *     2. the current deposit APY is below REBALANCE_UP_THRESHOLD * maxVariableBorrowRate, which means that too much has been
   *        borrowed at a stable rate and depositors are not earning enough
   * @param asset The address of the underlying asset borrowed
   * @param user The address of the user to be rebalanced
   **/
  function rebalanceStableBorrowRate(address asset, address user) external override whenNotPaused {
    DataTypes.ReserveData storage reserve = _reserves[asset];

    IERC20 stableDebtToken = IERC20(reserve.stableDebtTokenAddress);
    IERC20 variableDebtToken = IERC20(reserve.variableDebtTokenAddress);
    address aTokenAddress = reserve.aTokenAddress;

    uint256 stableDebt = IERC20(stableDebtToken).balanceOf(user);

    ValidationLogic.validateRebalanceStableBorrowRate(
      reserve,
      asset,
      stableDebtToken,
      variableDebtToken,
      aTokenAddress
    );

    reserve.updateState();

    IStableDebtToken(address(stableDebtToken)).burn(user, stableDebt);
    IStableDebtToken(address(stableDebtToken)).mint(
      user,
      user,
      stableDebt,
      reserve.currentStableBorrowRate
    );

    reserve.updateInterestRates(asset, aTokenAddress, 0, 0);

    emit RebalanceStableBorrowRate(asset, user);
  }

  /**
   * @dev Allows depositors to enable/disable a specific deposited asset as collateral
   * @param asset The address of the underlying asset deposited
   * @param useAsCollateral `true` if the user wants to use the deposit as collateral, `false` otherwise
   **/
  function setUserUseReserveAsCollateral(address asset, bool useAsCollateral)
    external
    override
    whenNotPaused
  {
    DataTypes.ReserveData storage reserve = _reserves[asset];

    ValidationLogic.validateSetUseReserveAsCollateral(
      reserve,
      asset,
      useAsCollateral,
      _reserves,
      _usersConfig[msg.sender],
      _reservesList,
      _reservesCount,
      _addressesProvider.getPriceOracle()
    );

    _usersConfig[msg.sender].setUsingAsCollateral(reserve.id, useAsCollateral);

    if (useAsCollateral) {
      emit ReserveUsedAsCollateralEnabled(asset, msg.sender);
    } else {
      emit ReserveUsedAsCollateralDisabled(asset, msg.sender);
    }
  }

  /**
   * @dev Function to liquidate a non-healthy position collateral-wise, with Health Factor below 1
   * - The caller (liquidator) covers `debtToCover` amount of debt of the user getting liquidated, and receives
   *   a proportionally amount of the `collateralAsset` plus a bonus to cover market risk
   * @param collateralAsset The address of the underlying asset used as collateral, to receive as result of the liquidation
   * @param debtAsset The address of the underlying borrowed asset to be repaid with the liquidation
   * @param user The address of the borrower getting liquidated
   * @param debtToCover The debt amount of borrowed `asset` the liquidator wants to cover
   * @param receiveAToken `true` if the liquidators wants to receive the collateral aTokens, `false` if he wants
   * to receive the underlying collateral asset directly
   **/
  function liquidationCall(
    address collateralAsset,
    address debtAsset,
    address user,
    uint256 debtToCover,
    bool receiveAToken
  ) external override whenNotPaused {
    address collateralManager = _addressesProvider.getLendingPoolCollateralManager();

    //solium-disable-next-line
    (bool success, bytes memory result) =
      collateralManager.delegatecall(
        abi.encodeWithSignature(
          'liquidationCall(address,address,address,uint256,bool)',
          collateralAsset,
          debtAsset,
          user,
          debtToCover,
          receiveAToken
        )
      );
    require(success, Errors.LP_LIQUIDATION_CALL_FAILED);

    (uint256 returnCode, string memory returnMessage) = abi.decode(result, (uint256, string));

    require(returnCode == 0, string(abi.encodePacked(returnMessage)));
  }

  struct FlashLoanLocalVars {
    IFlashLoanReceiver receiver;
    address oracle;
    uint256 i;
    address currentAsset;
    address currentATokenAddress;
    uint256 currentAmount;
    uint256 currentPremium;
    uint256 currentAmountPlusPremium;
    address debtToken;
  }

  /**
   * @dev Allows smartcontracts to access the liquidity of the pool within one transaction,
   * as long as the amount taken plus a fee is returned.
   * IMPORTANT There are security concerns for developers of flashloan receiver contracts that must be kept into consideration.
   * For further details please visit https://developers.aave.com
   * @param receiverAddress The address of the contract receiving the funds, implementing the IFlashLoanReceiver interface
   * @param assets The addresses of the assets being flash-borrowed
   * @param amounts The amounts amounts being flash-borrowed
   * @param modes Types of the debt to open if the flash loan is not returned:
   *   0 -> Don't open any debt, just revert if funds can't be transferred from the receiver
   *   1 -> Open debt at stable rate for the value of the amount flash-borrowed to the `onBehalfOf` address
   *   2 -> Open debt at variable rate for the value of the amount flash-borrowed to the `onBehalfOf` address
   * @param onBehalfOf The address  that will receive the debt in the case of using on `modes` 1 or 2
   * @param params Variadic packed params to pass to the receiver as extra information
   * @param referralCode Code used to register the integrator originating the operation, for potential rewards.
   *   0 if the action is executed directly by the user, without any middle-man
   **/
  function flashLoan(
    address receiverAddress,
    address[] calldata assets,
    uint256[] calldata amounts,
    uint256[] calldata modes,
    address onBehalfOf,
    bytes calldata params,
    uint16 referralCode
  ) external override whenNotPaused {
    FlashLoanLocalVars memory vars;

    ValidationLogic.validateFlashloan(assets, amounts);

    address[] memory aTokenAddresses = new address[](assets.length);
    uint256[] memory premiums = new uint256[](assets.length);

    vars.receiver = IFlashLoanReceiver(receiverAddress);

    for (vars.i = 0; vars.i < assets.length; vars.i++) {
      aTokenAddresses[vars.i] = _reserves[assets[vars.i]].aTokenAddress;

      premiums[vars.i] = amounts[vars.i].mul(FLASHLOAN_PREMIUM_TOTAL).div(10000);

      IAToken(aTokenAddresses[vars.i]).transferUnderlyingTo(receiverAddress, amounts[vars.i]);
    }

    require(
      vars.receiver.executeOperation(assets, amounts, premiums, msg.sender, params),
      Errors.LP_INVALID_FLASH_LOAN_EXECUTOR_RETURN
    );

    for (vars.i = 0; vars.i < assets.length; vars.i++) {
      vars.currentAsset = assets[vars.i];
      vars.currentAmount = amounts[vars.i];
      vars.currentPremium = premiums[vars.i];
      vars.currentATokenAddress = aTokenAddresses[vars.i];
      vars.currentAmountPlusPremium = vars.currentAmount.add(vars.currentPremium);

      if (DataTypes.InterestRateMode(modes[vars.i]) == DataTypes.InterestRateMode.NONE) {
        _reserves[vars.currentAsset].updateState();
        _reserves[vars.currentAsset].cumulateToLiquidityIndex(
          IERC20(vars.currentATokenAddress).totalSupply(),
          vars.currentPremium
        );
        _reserves[vars.currentAsset].updateInterestRates(
          vars.currentAsset,
          vars.currentATokenAddress,
          vars.currentAmountPlusPremium,
          0
        );

        IERC20(vars.currentAsset).safeTransferFrom(
          receiverAddress,
          vars.currentATokenAddress,
          vars.currentAmountPlusPremium
        );
      } else {
        // If the user chose to not return the funds, the system checks if there is enough collateral and
        // eventually opens a debt position
        _executeBorrow(
          ExecuteBorrowParams(
            vars.currentAsset,
            msg.sender,
            onBehalfOf,
            vars.currentAmount,
            modes[vars.i],
            vars.currentATokenAddress,
            referralCode,
            false
          )
        );
      }
      emit FlashLoan(
        receiverAddress,
        msg.sender,
        vars.currentAsset,
        vars.currentAmount,
        vars.currentPremium,
        referralCode
      );
    }
  }

  /**
   * @dev Returns the state and configuration of the reserve
   * @param asset The address of the underlying asset of the reserve
   * @return The state of the reserve
   **/
  function getReserveData(address asset)
    external
    view
    override
    returns (DataTypes.ReserveData memory)
  {
    return _reserves[asset];
  }

  /**
   * @dev Returns the user account data across all the reserves
   * @param user The address of the user
   * @return totalCollateralETH the total collateral in ETH of the user
   * @return totalDebtETH the total debt in ETH of the user
   * @return availableBorrowsETH the borrowing power left of the user
   * @return currentLiquidationThreshold the liquidation threshold of the user
   * @return ltv the loan to value of the user
   * @return healthFactor the current health factor of the user
   **/
  function getUserAccountData(address user)
    external
    view
    override
    returns (
      uint256 totalCollateralETH,
      uint256 totalDebtETH,
      uint256 availableBorrowsETH,
      uint256 currentLiquidationThreshold,
      uint256 ltv,
      uint256 healthFactor
    )
  {
    (
      totalCollateralETH,
      totalDebtETH,
      ltv,
      currentLiquidationThreshold,
      healthFactor
    ) = GenericLogic.calculateUserAccountData(
      user,
      _reserves,
      _usersConfig[user],
      _reservesList,
      _reservesCount,
      _addressesProvider.getPriceOracle()
    );

    availableBorrowsETH = GenericLogic.calculateAvailableBorrowsETH(
      totalCollateralETH,
      totalDebtETH,
      ltv
    );
  }

  /**
   * @dev Returns the configuration of the reserve
   * @param asset The address of the underlying asset of the reserve
   * @return The configuration of the reserve
   **/
  function getConfiguration(address asset)
    external
    view
    override
    returns (DataTypes.ReserveConfigurationMap memory)
  {
    return _reserves[asset].configuration;
  }

  /**
   * @dev Returns the configuration of the user across all the reserves
   * @param user The user address
   * @return The configuration of the user
   **/
  function getUserConfiguration(address user)
    external
    view
    override
    returns (DataTypes.UserConfigurationMap memory)
  {
    return _usersConfig[user];
  }

  /**
   * @dev Returns the normalized income per unit of asset
   * @param asset The address of the underlying asset of the reserve
   * @return The reserve's normalized income
   */
  function getReserveNormalizedIncome(address asset)
    external
    view
    virtual
    override
    returns (uint256)
  {
    return _reserves[asset].getNormalizedIncome();
  }

  /**
   * @dev Returns the normalized variable debt per unit of asset
   * @param asset The address of the underlying asset of the reserve
   * @return The reserve normalized variable debt
   */
  function getReserveNormalizedVariableDebt(address asset)
    external
    view
    override
    returns (uint256)
  {
    return _reserves[asset].getNormalizedDebt();
  }

  /**
   * @dev Returns if the LendingPool is paused
   */
  function paused() external view override returns (bool) {
    return _paused;
  }

  /**
   * @dev Returns the list of the initialized reserves
   **/
  function getReservesList() external view override returns (address[] memory) {
    address[] memory _activeReserves = new address[](_reservesCount);

    for (uint256 i = 0; i < _reservesCount; i++) {
      _activeReserves[i] = _reservesList[i];
    }
    return _activeReserves;
  }

  /**
   * @dev Returns the cached LendingPoolAddressesProvider connected to this contract
   **/
  function getAddressesProvider() external view override returns (ILendingPoolAddressesProvider) {
    return _addressesProvider;
  }

  /**
   * @dev Validates and finalizes an aToken transfer
   * - Only callable by the overlying aToken of the `asset`
   * @param asset The address of the underlying asset of the aToken
   * @param from The user from which the aTokens are transferred
   * @param to The user receiving the aTokens
   * @param amount The amount being transferred/withdrawn
   * @param balanceFromBefore The aToken balance of the `from` user before the transfer
   * @param balanceToBefore The aToken balance of the `to` user before the transfer
   */
  function finalizeTransfer(
    address asset,
    address from,
    address to,
    uint256 amount,
    uint256 balanceFromBefore,
    uint256 balanceToBefore
  ) external override whenNotPaused {
    require(msg.sender == _reserves[asset].aTokenAddress, Errors.LP_CALLER_MUST_BE_AN_ATOKEN);

    ValidationLogic.validateTransfer(
      from,
      _reserves,
      _usersConfig[from],
      _reservesList,
      _reservesCount,
      _addressesProvider.getPriceOracle()
    );

    uint256 reserveId = _reserves[asset].id;

    if (from != to) {
      if (balanceFromBefore.sub(amount) == 0) {
        DataTypes.UserConfigurationMap storage fromConfig = _usersConfig[from];
        fromConfig.setUsingAsCollateral(reserveId, false);
        emit ReserveUsedAsCollateralDisabled(asset, from);
      }

      if (balanceToBefore == 0 && amount != 0) {
        DataTypes.UserConfigurationMap storage toConfig = _usersConfig[to];
        toConfig.setUsingAsCollateral(reserveId, true);
        emit ReserveUsedAsCollateralEnabled(asset, to);
      }
    }
  }

  /**
   * @dev Initializes a reserve, activating it, assigning an aToken and debt tokens and an
   * interest rate strategy
   * - Only callable by the LendingPoolConfigurator contract
   * @param asset The address of the underlying asset of the reserve
   * @param aTokenAddress The address of the aToken that will be assigned to the reserve
   * @param stableDebtAddress The address of the StableDebtToken that will be assigned to the reserve
   * @param aTokenAddress The address of the VariableDebtToken that will be assigned to the reserve
   * @param interestRateStrategyAddress The address of the interest rate strategy contract
   **/
  function initReserve(
    address asset,
    address aTokenAddress,
    address stableDebtAddress,
    address variableDebtAddress,
    address interestRateStrategyAddress
  ) external override onlyLendingPoolConfigurator {
    require(Address.isContract(asset), Errors.LP_NOT_CONTRACT);
    _reserves[asset].init(
      aTokenAddress,
      stableDebtAddress,
      variableDebtAddress,
      interestRateStrategyAddress
    );
    _addReserveToList(asset);
  }

  /**
   * @dev Updates the address of the interest rate strategy contract
   * - Only callable by the LendingPoolConfigurator contract
   * @param asset The address of the underlying asset of the reserve
   * @param rateStrategyAddress The address of the interest rate strategy contract
   **/
  function setReserveInterestRateStrategyAddress(address asset, address rateStrategyAddress)
    external
    override
    onlyLendingPoolConfigurator
  {
    _reserves[asset].interestRateStrategyAddress = rateStrategyAddress;
  }

  /**
   * @dev Sets the configuration bitmap of the reserve as a whole
   * - Only callable by the LendingPoolConfigurator contract
   * @param asset The address of the underlying asset of the reserve
   * @param configuration The new configuration bitmap
   **/
  function setConfiguration(address asset, uint256 configuration)
    external
    override
    onlyLendingPoolConfigurator
  {
    _reserves[asset].configuration.data = configuration;
  }

  /**
   * @dev Set the _pause state of a reserve
   * - Only callable by the LendingPoolConfigurator contract
   * @param val `true` to pause the reserve, `false` to un-pause it
   */
  function setPause(bool val) external override onlyLendingPoolConfigurator {
    _paused = val;
    if (_paused) {
      emit Paused();
    } else {
      emit Unpaused();
    }
  }

  struct ExecuteBorrowParams {
    address asset;
    address user;
    address onBehalfOf;
    uint256 amount;
    uint256 interestRateMode;
    address aTokenAddress;
    uint16 referralCode;
    bool releaseUnderlying;
  }

  function _executeBorrow(ExecuteBorrowParams memory vars) internal {
    DataTypes.ReserveData storage reserve = _reserves[vars.asset];
    DataTypes.UserConfigurationMap storage userConfig = _usersConfig[vars.onBehalfOf];

    address oracle = _addressesProvider.getPriceOracle();

    uint256 amountInETH =
      IPriceOracleGetter(oracle).getAssetPrice(vars.asset).mul(vars.amount).div(
        10**reserve.configuration.getDecimals()
      );

    ValidationLogic.validateBorrow(
      vars.asset,
      reserve,
      vars.onBehalfOf,
      vars.amount,
      amountInETH,
      vars.interestRateMode,
      MAX_STABLE_RATE_BORROW_SIZE_PERCENT,
      _reserves,
      userConfig,
      _reservesList,
      _reservesCount,
      oracle
    );

    reserve.updateState();

    uint256 currentStableRate = 0;

    bool isFirstBorrowing = false;
    if (DataTypes.InterestRateMode(vars.interestRateMode) == DataTypes.InterestRateMode.STABLE) {
      currentStableRate = reserve.currentStableBorrowRate;

      isFirstBorrowing = IStableDebtToken(reserve.stableDebtTokenAddress).mint(
        vars.user,
        vars.onBehalfOf,
        vars.amount,
        currentStableRate
      );
    } else {
      isFirstBorrowing = IVariableDebtToken(reserve.variableDebtTokenAddress).mint(
        vars.user,
        vars.onBehalfOf,
        vars.amount,
        reserve.variableBorrowIndex
      );
    }

    if (isFirstBorrowing) {
      userConfig.setBorrowing(reserve.id, true);
    }

    reserve.updateInterestRates(
      vars.asset,
      vars.aTokenAddress,
      0,
      vars.releaseUnderlying ? vars.amount : 0
    );

    if (vars.releaseUnderlying) {
      IAToken(vars.aTokenAddress).transferUnderlyingTo(vars.user, vars.amount);
    }

    emit Borrow(
      vars.asset,
      vars.user,
      vars.onBehalfOf,
      vars.amount,
      vars.interestRateMode,
      DataTypes.InterestRateMode(vars.interestRateMode) == DataTypes.InterestRateMode.STABLE
        ? currentStableRate
        : reserve.currentVariableBorrowRate,
      vars.referralCode
    );
  }

  function _addReserveToList(address asset) internal {
    uint256 reservesCount = _reservesCount;

    require(reservesCount < MAX_NUMBER_RESERVES, Errors.LP_NO_MORE_RESERVES_ALLOWED);

    bool reserveAlreadyAdded = _reserves[asset].id != 0 || _reservesList[0] == asset;

    if (!reserveAlreadyAdded) {
      _reserves[asset].id = uint8(reservesCount);
      _reservesList[reservesCount] = asset;

      _reservesCount = reservesCount + 1;
    }
  }
}