ReserveLogic.sol

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

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 {IAToken} from '../../../interfaces/IAToken.sol';
import {IStableDebtToken} from '../../../interfaces/IStableDebtToken.sol';
import {IVariableDebtToken} from '../../../interfaces/IVariableDebtToken.sol';
import {IReserveInterestRateStrategy} from '../../../interfaces/IReserveInterestRateStrategy.sol';
import {ReserveConfiguration} from '../configuration/ReserveConfiguration.sol';
import {MathUtils} from '../math/MathUtils.sol';
import {WadRayMath} from '../math/WadRayMath.sol';
import {PercentageMath} from '../math/PercentageMath.sol';
import {Errors} from '../helpers/Errors.sol';
import {DataTypes} from '../types/DataTypes.sol';

/**
 * @title ReserveLogic library
 * @author Aave
 * @notice Implements the logic to update the reserves state
 */
library ReserveLogic {
  using SafeMath for uint256;
  using WadRayMath for uint256;
  using PercentageMath for uint256;
  using SafeERC20 for IERC20;

  /**
   * @dev Emitted when the state of a reserve is updated
   * @param asset The address of the underlying asset of the reserve
   * @param liquidityRate The new liquidity rate
   * @param stableBorrowRate The new stable borrow rate
   * @param variableBorrowRate The new variable borrow rate
   * @param liquidityIndex The new liquidity index
   * @param variableBorrowIndex The new variable borrow index
   **/
  event ReserveDataUpdated(
    address indexed asset,
    uint256 liquidityRate,
    uint256 stableBorrowRate,
    uint256 variableBorrowRate,
    uint256 liquidityIndex,
    uint256 variableBorrowIndex
  );

  using ReserveLogic for DataTypes.ReserveData;
  using ReserveConfiguration for DataTypes.ReserveConfigurationMap;

  /**
   * @dev Returns the ongoing normalized income for the reserve
   * A value of 1e27 means there is no income. As time passes, the income is accrued
   * A value of 2*1e27 means for each unit of asset one unit of income has been accrued
   * @param reserve The reserve object
   * @return the normalized income. expressed in ray
   **/
  function getNormalizedIncome(DataTypes.ReserveData storage reserve)
    internal
    view
    returns (uint256)
  {
    uint40 timestamp = reserve.lastUpdateTimestamp;

    //solium-disable-next-line
    if (timestamp == uint40(block.timestamp)) {
      //if the index was updated in the same block, no need to perform any calculation
      return reserve.liquidityIndex;
    }

    uint256 cumulated =
      MathUtils.calculateLinearInterest(reserve.currentLiquidityRate, timestamp).rayMul(
        reserve.liquidityIndex
      );

    return cumulated;
  }

  /**
   * @dev Returns the ongoing normalized variable debt for the reserve
   * A value of 1e27 means there is no debt. As time passes, the income is accrued
   * A value of 2*1e27 means that for each unit of debt, one unit worth of interest has been accumulated
   * @param reserve The reserve object
   * @return The normalized variable debt. expressed in ray
   **/
  function getNormalizedDebt(DataTypes.ReserveData storage reserve)
    internal
    view
    returns (uint256)
  {
    uint40 timestamp = reserve.lastUpdateTimestamp;

    //solium-disable-next-line
    if (timestamp == uint40(block.timestamp)) {
      //if the index was updated in the same block, no need to perform any calculation
      return reserve.variableBorrowIndex;
    }

    uint256 cumulated =
      MathUtils.calculateCompoundedInterest(reserve.currentVariableBorrowRate, timestamp).rayMul(
        reserve.variableBorrowIndex
      );

    return cumulated;
  }

  /**
   * @dev Updates the liquidity cumulative index and the variable borrow index.
   * @param reserve the reserve object
   **/
  function updateState(DataTypes.ReserveData storage reserve) internal {
    uint256 scaledVariableDebt =
      IVariableDebtToken(reserve.variableDebtTokenAddress).scaledTotalSupply();
    uint256 previousVariableBorrowIndex = reserve.variableBorrowIndex;
    uint256 previousLiquidityIndex = reserve.liquidityIndex;
    uint40 lastUpdatedTimestamp = reserve.lastUpdateTimestamp;

    (uint256 newLiquidityIndex, uint256 newVariableBorrowIndex) =
      _updateIndexes(
        reserve,
        scaledVariableDebt,
        previousLiquidityIndex,
        previousVariableBorrowIndex,
        lastUpdatedTimestamp
      );

    _mintToTreasury(
      reserve,
      scaledVariableDebt,
      previousVariableBorrowIndex,
      newLiquidityIndex,
      newVariableBorrowIndex,
      lastUpdatedTimestamp
    );
  }

  /**
   * @dev Accumulates a predefined amount of asset to the reserve as a fixed, instantaneous income. Used for example to accumulate
   * the flashloan fee to the reserve, and spread it between all the depositors
   * @param reserve The reserve object
   * @param totalLiquidity The total liquidity available in the reserve
   * @param amount The amount to accomulate
   **/
  function cumulateToLiquidityIndex(
    DataTypes.ReserveData storage reserve,
    uint256 totalLiquidity,
    uint256 amount
  ) internal {
    uint256 amountToLiquidityRatio = amount.wadToRay().rayDiv(totalLiquidity.wadToRay());

    uint256 result = amountToLiquidityRatio.add(WadRayMath.ray());

    result = result.rayMul(reserve.liquidityIndex);
    require(result <= type(uint128).max, Errors.RL_LIQUIDITY_INDEX_OVERFLOW);

    reserve.liquidityIndex = uint128(result);
  }

  /**
   * @dev Initializes a reserve
   * @param reserve The reserve object
   * @param aTokenAddress The address of the overlying atoken contract
   * @param interestRateStrategyAddress The address of the interest rate strategy contract
   **/
  function init(
    DataTypes.ReserveData storage reserve,
    address aTokenAddress,
    address stableDebtTokenAddress,
    address variableDebtTokenAddress,
    address interestRateStrategyAddress
  ) external {
    require(reserve.aTokenAddress == address(0), Errors.RL_RESERVE_ALREADY_INITIALIZED);

    reserve.liquidityIndex = uint128(WadRayMath.ray());
    reserve.variableBorrowIndex = uint128(WadRayMath.ray());
    reserve.aTokenAddress = aTokenAddress;
    reserve.stableDebtTokenAddress = stableDebtTokenAddress;
    reserve.variableDebtTokenAddress = variableDebtTokenAddress;
    reserve.interestRateStrategyAddress = interestRateStrategyAddress;
  }

  struct UpdateInterestRatesLocalVars {
    address stableDebtTokenAddress;
    uint256 availableLiquidity;
    uint256 totalStableDebt;
    uint256 newLiquidityRate;
    uint256 newStableRate;
    uint256 newVariableRate;
    uint256 avgStableRate;
    uint256 totalVariableDebt;
  }

  /**
   * @dev Updates the reserve current stable borrow rate, the current variable borrow rate and the current liquidity rate
   * @param reserve The address of the reserve to be updated
   * @param liquidityAdded The amount of liquidity added to the protocol (deposit or repay) in the previous action
   * @param liquidityTaken The amount of liquidity taken from the protocol (redeem or borrow)
   **/
  function updateInterestRates(
    DataTypes.ReserveData storage reserve,
    address reserveAddress,
    address aTokenAddress,
    uint256 liquidityAdded,
    uint256 liquidityTaken
  ) internal {
    UpdateInterestRatesLocalVars memory vars;

    vars.stableDebtTokenAddress = reserve.stableDebtTokenAddress;

    (vars.totalStableDebt, vars.avgStableRate) = IStableDebtToken(vars.stableDebtTokenAddress)
      .getTotalSupplyAndAvgRate();

    //calculates the total variable debt locally using the scaled total supply instead
    //of totalSupply(), as it's noticeably cheaper. Also, the index has been
    //updated by the previous updateState() call
    vars.totalVariableDebt = IVariableDebtToken(reserve.variableDebtTokenAddress)
      .scaledTotalSupply()
      .rayMul(reserve.variableBorrowIndex);

    vars.availableLiquidity = IERC20(reserveAddress).balanceOf(aTokenAddress);

    (
      vars.newLiquidityRate,
      vars.newStableRate,
      vars.newVariableRate
    ) = IReserveInterestRateStrategy(reserve.interestRateStrategyAddress).calculateInterestRates(
      reserveAddress,
      vars.availableLiquidity.add(liquidityAdded).sub(liquidityTaken),
      vars.totalStableDebt,
      vars.totalVariableDebt,
      vars.avgStableRate,
      reserve.configuration.getReserveFactor()
    );
    require(vars.newLiquidityRate <= type(uint128).max, Errors.RL_LIQUIDITY_RATE_OVERFLOW);
    require(vars.newStableRate <= type(uint128).max, Errors.RL_STABLE_BORROW_RATE_OVERFLOW);
    require(vars.newVariableRate <= type(uint128).max, Errors.RL_VARIABLE_BORROW_RATE_OVERFLOW);

    reserve.currentLiquidityRate = uint128(vars.newLiquidityRate);
    reserve.currentStableBorrowRate = uint128(vars.newStableRate);
    reserve.currentVariableBorrowRate = uint128(vars.newVariableRate);

    emit ReserveDataUpdated(
      reserveAddress,
      vars.newLiquidityRate,
      vars.newStableRate,
      vars.newVariableRate,
      reserve.liquidityIndex,
      reserve.variableBorrowIndex
    );
  }

  struct MintToTreasuryLocalVars {
    uint256 currentStableDebt;
    uint256 principalStableDebt;
    uint256 previousStableDebt;
    uint256 currentVariableDebt;
    uint256 previousVariableDebt;
    uint256 avgStableRate;
    uint256 cumulatedStableInterest;
    uint256 totalDebtAccrued;
    uint256 amountToMint;
    uint256 reserveFactor;
    uint40 stableSupplyUpdatedTimestamp;
  }

  /**
   * @dev Mints part of the repaid interest to the reserve treasury as a function of the reserveFactor for the
   * specific asset.
   * @param reserve The reserve reserve to be updated
   * @param scaledVariableDebt The current scaled total variable debt
   * @param previousVariableBorrowIndex The variable borrow index before the last accumulation of the interest
   * @param newLiquidityIndex The new liquidity index
   * @param newVariableBorrowIndex The variable borrow index after the last accumulation of the interest
   **/
  function _mintToTreasury(
    DataTypes.ReserveData storage reserve,
    uint256 scaledVariableDebt,
    uint256 previousVariableBorrowIndex,
    uint256 newLiquidityIndex,
    uint256 newVariableBorrowIndex,
    uint40 timestamp
  ) internal {
    MintToTreasuryLocalVars memory vars;

    vars.reserveFactor = reserve.configuration.getReserveFactor();

    if (vars.reserveFactor == 0) {
      return;
    }

    //fetching the principal, total stable debt and the avg stable rate
    (
      vars.principalStableDebt,
      vars.currentStableDebt,
      vars.avgStableRate,
      vars.stableSupplyUpdatedTimestamp
    ) = IStableDebtToken(reserve.stableDebtTokenAddress).getSupplyData();

    //calculate the last principal variable debt
    vars.previousVariableDebt = scaledVariableDebt.rayMul(previousVariableBorrowIndex);

    //calculate the new total supply after accumulation of the index
    vars.currentVariableDebt = scaledVariableDebt.rayMul(newVariableBorrowIndex);

    //calculate the stable debt until the last timestamp update
    vars.cumulatedStableInterest = MathUtils.calculateCompoundedInterest(
      vars.avgStableRate,
      vars.stableSupplyUpdatedTimestamp,
      timestamp
    );

    vars.previousStableDebt = vars.principalStableDebt.rayMul(vars.cumulatedStableInterest);

    //debt accrued is the sum of the current debt minus the sum of the debt at the last update
    vars.totalDebtAccrued = vars
      .currentVariableDebt
      .add(vars.currentStableDebt)
      .sub(vars.previousVariableDebt)
      .sub(vars.previousStableDebt);

    vars.amountToMint = vars.totalDebtAccrued.percentMul(vars.reserveFactor);

    if (vars.amountToMint != 0) {
      IAToken(reserve.aTokenAddress).mintToTreasury(vars.amountToMint, newLiquidityIndex);
    }
  }

  /**
   * @dev Updates the reserve indexes and the timestamp of the update
   * @param reserve The reserve reserve to be updated
   * @param scaledVariableDebt The scaled variable debt
   * @param liquidityIndex The last stored liquidity index
   * @param variableBorrowIndex The last stored variable borrow index
   **/
  function _updateIndexes(
    DataTypes.ReserveData storage reserve,
    uint256 scaledVariableDebt,
    uint256 liquidityIndex,
    uint256 variableBorrowIndex,
    uint40 timestamp
  ) internal returns (uint256, uint256) {
    uint256 currentLiquidityRate = reserve.currentLiquidityRate;

    uint256 newLiquidityIndex = liquidityIndex;
    uint256 newVariableBorrowIndex = variableBorrowIndex;

    //only cumulating if there is any income being produced
    if (currentLiquidityRate > 0) {
      uint256 cumulatedLiquidityInterest =
        MathUtils.calculateLinearInterest(currentLiquidityRate, timestamp);
      newLiquidityIndex = cumulatedLiquidityInterest.rayMul(liquidityIndex);
      require(newLiquidityIndex <= type(uint128).max, Errors.RL_LIQUIDITY_INDEX_OVERFLOW);

      reserve.liquidityIndex = uint128(newLiquidityIndex);

      //as the liquidity rate might come only from stable rate loans, we need to ensure
      //that there is actual variable debt before accumulating
      if (scaledVariableDebt != 0) {
        uint256 cumulatedVariableBorrowInterest =
          MathUtils.calculateCompoundedInterest(reserve.currentVariableBorrowRate, timestamp);
        newVariableBorrowIndex = cumulatedVariableBorrowInterest.rayMul(variableBorrowIndex);
        require(
          newVariableBorrowIndex <= type(uint128).max,
          Errors.RL_VARIABLE_BORROW_INDEX_OVERFLOW
        );
        reserve.variableBorrowIndex = uint128(newVariableBorrowIndex);
      }
    }

    //solium-disable-next-line
    reserve.lastUpdateTimestamp = uint40(block.timestamp);
    return (newLiquidityIndex, newVariableBorrowIndex);
  }
}