correct lendRate calculation

src/erc-20-pool-factory.ts

@@ -14,7 +14,6 @@ import {
 } from "./utils/constants"
 import { addressToBytes, wadToDecimal } from "./utils/convert"
 import { getTokenDecimals, getTokenName, getTokenSymbol, getTokenTotalSupply } from "./utils/token-erc20"
-import { wmul } from "./utils/math"
 import { getRatesAndFees } from "./utils/pool"
 import { loadOrCreateFactory } from "./utils/pool-factory"
 
@@ -86,7 +85,7 @@ export function handlePoolCreated(event: PoolCreatedEvent): void {
   pool.t0debt = ZERO_BD
   pool.inflator = ONE_BD
   pool.borrowRate = wadToDecimal(interestRateResults.value0)
-  pool.lendRate = wadToDecimal(wmul(interestRateResults.value0, ratesAndFees.lenderInterestMargin))
+  pool.lendRate = ZERO_BD
   pool.borrowFeeRate = wadToDecimal(ratesAndFees.borrowFeeRate)
   pool.depositFeeRate = wadToDecimal(ratesAndFees.depositFeeRate)
   pool.pledgedCollateral = ZERO_BD

src/erc-20-pool.ts

@@ -70,13 +70,12 @@ import { getBucketId, getBucketInfo, loadOrCreateBucket } from "./utils/bucket"
 import { getLendId, loadOrCreateLend } from "./utils/lend"
 import { getBorrowerInfo, getLoanId, loadOrCreateLoan } from "./utils/loan"
 import { getLiquidationAuctionId, getAuctionInfoERC20Pool, loadOrCreateLiquidationAuction, updateLiquidationAuction, getAuctionStatus, loadOrCreateBucketTake } from "./utils/liquidation"
-import { getBurnInfo, updatePool, addLiquidationToPool, addReserveAuctionToPool, getLenderInfo, getRatesAndFees } from "./utils/pool"
+import { getBurnInfo, updatePool, addLiquidationToPool, addReserveAuctionToPool, getLenderInfo, getRatesAndFees, calculateLendRate } from "./utils/pool"
 import { lpbValueInQuote } from "./utils/common"
 import { loadOrCreateReserveAuction, reserveAuctionKickerReward } from "./utils/reserve-auction"
 import { incrementTokenTxCount } from "./utils/token-erc20"
 import { approveTransferors, loadOrCreateTransferors, revokeTransferors } from "./utils/lp-transferors"
 import { loadOrCreateAllowances, increaseAllowances, decreaseAllowances, revokeAllowances } from "./utils/lp-allowances"
-import { wmul } from "./utils/math"
 
 export function handleAddCollateral(event: AddCollateralEvent): void {
   const addCollateral = new AddCollateral(
@@ -991,14 +990,15 @@ export function handleResetInterestRate(event: ResetInterestRateEvent): void {
   const poolAddress = addressToBytes(event.address)
   const pool = Pool.load(poolAddress)!
   const ratesAndFees = getRatesAndFees(poolAddress)
+  updatePool(pool)
 
   resetInterestRate.pool = pool.id
   resetInterestRate.oldBorrowRate = pool.borrowRate
   resetInterestRate.oldLendRate = pool.lendRate
   resetInterestRate.oldBorrowFeeRate = pool.borrowFeeRate
   resetInterestRate.oldDepositFeeRate = pool.depositFeeRate
   resetInterestRate.newBorrowRate = wadToDecimal(event.params.newRate)
-  resetInterestRate.newLendRate = wadToDecimal(wmul(event.params.newRate, ratesAndFees.lenderInterestMargin))
+  resetInterestRate.newLendRate = pool.lendRate
   resetInterestRate.newBorrowFeeRate = wadToDecimal(ratesAndFees.borrowFeeRate)
   resetInterestRate.newDepositFeeRate = wadToDecimal(ratesAndFees.depositFeeRate)
 
@@ -1007,7 +1007,6 @@ export function handleResetInterestRate(event: ResetInterestRateEvent): void {
   resetInterestRate.transactionHash = event.transaction.hash
 
   // update pool state
-  updatePool(pool)
   pool.borrowRate = resetInterestRate.newBorrowRate
   pool.lendRate = resetInterestRate.newLendRate
   pool.borrowFeeRate = wadToDecimal(ratesAndFees.borrowFeeRate)
@@ -1236,14 +1235,15 @@ export function handleUpdateInterestRate(event: UpdateInterestRateEvent): void {
   const poolAddress = addressToBytes(event.address)
   const pool = Pool.load(poolAddress)!
   const ratesAndFees = getRatesAndFees(poolAddress)
+  updatePool(pool)
 
   updateInterestRate.pool = pool.id
   updateInterestRate.oldBorrowRate = pool.borrowRate
   updateInterestRate.oldLendRate = pool.lendRate
   updateInterestRate.oldBorrowFeeRate = pool.borrowFeeRate
   updateInterestRate.oldDepositFeeRate = pool.depositFeeRate
   updateInterestRate.newBorrowRate = wadToDecimal(event.params.newRate)
-  updateInterestRate.newLendRate = wadToDecimal(wmul(event.params.newRate, ratesAndFees.lenderInterestMargin))
+  updateInterestRate.newLendRate = pool.lendRate
   updateInterestRate.newBorrowFeeRate = wadToDecimal(ratesAndFees.borrowFeeRate)
   updateInterestRate.newDepositFeeRate = wadToDecimal(ratesAndFees.depositFeeRate)
 
@@ -1252,7 +1252,6 @@ export function handleUpdateInterestRate(event: UpdateInterestRateEvent): void {
   updateInterestRate.transactionHash = event.transaction.hash
 
   // update pool state
-  updatePool(pool)
   pool.borrowRate = updateInterestRate.newBorrowRate
   pool.lendRate = updateInterestRate.newLendRate
   pool.borrowFeeRate = wadToDecimal(ratesAndFees.borrowFeeRate)

src/utils/pool.ts

@@ -4,10 +4,10 @@ import { LiquidationAuction, Pool, ReserveAuction, Token } from "../../generated
 import { ERC20Pool } from '../../generated/templates/ERC20Pool/ERC20Pool'
 import { PoolInfoUtils } from '../../generated/templates/ERC20Pool/PoolInfoUtils'
 
-import { poolInfoUtilsAddressTable, ONE_BI, TEN_BI, ONE_WAD_BI } from "./constants"
+import { poolInfoUtilsAddressTable, TEN_BI } from "./constants"
 import { decimalToWad, wadToDecimal } from './convert'
 import { getTokenBalance } from './token-erc20'
-import { wdiv, wmul } from './math'
+import { wmul, wdiv } from './math'
 
 export function getPoolAddress(poolId: Bytes): Address {
   return Address.fromBytes(poolId)
@@ -61,6 +61,10 @@ export function getRatesAndFees(poolId: Bytes): RatesAndFees {
   return new RatesAndFees(lim, bfr, dfr);
 }
 
+export function calculateLendRate(borrowRate: BigInt, lenderInterestMargin: BigInt, utilization: BigInt): BigDecimal {
+  return wadToDecimal(wmul(wmul(borrowRate,lenderInterestMargin), utilization))
+}
+
 export class LoansInfo {
     poolSize: BigInt
     loansCount: BigInt
@@ -226,8 +230,10 @@ export function updatePool(pool: Pool): void {
 
     // update lend rate and borrow fee, which change irrespective of borrow rate
     const ratesAndFees = getRatesAndFees(poolAddress)
-    const borrowRate = decimalToWad(pool.borrowRate)
-    pool.lendRate = wadToDecimal(wmul(borrowRate, ratesAndFees.lenderInterestMargin))
+    pool.lendRate = calculateLendRate(
+      decimalToWad(pool.borrowRate), 
+      ratesAndFees.lenderInterestMargin, 
+      poolUtilizationInfo.actualUtilization)
     pool.borrowFeeRate = wadToDecimal(ratesAndFees.borrowFeeRate)
 }