package keeper import ( sdk "github.com/cosmos/cosmos-sdk/types" sdkerrors "github.com/cosmos/cosmos-sdk/types/errors" "github.com/kava-labs/kava/x/hard/types" ) var ( scalingFactor = 1e18 secondsPerYear = 31536000 ) // ApplyInterestRateUpdates translates the current interest rate models from the params to the store, // with each money market accruing interest. func (k Keeper) ApplyInterestRateUpdates(ctx sdk.Context) { denomSet := map[string]bool{} params := k.GetParams(ctx) for _, mm := range params.MoneyMarkets { // Set any new money markets in the store moneyMarket, found := k.GetMoneyMarket(ctx, mm.Denom) if !found { moneyMarket = mm k.SetMoneyMarket(ctx, mm.Denom, moneyMarket) } // Accrue interest according to the current money markets in the store err := k.AccrueInterest(ctx, mm.Denom) if err != nil { panic(err) } // Update the interest rate in the store if the params have changed if !moneyMarket.Equal(mm) { k.SetMoneyMarket(ctx, mm.Denom, mm) } denomSet[mm.Denom] = true } // Edge case: money markets removed from params that still exist in the store k.IterateMoneyMarkets(ctx, func(denom string, i types.MoneyMarket) bool { if !denomSet[denom] { // Accrue interest according to current store money market err := k.AccrueInterest(ctx, denom) if err != nil { panic(err) } // Delete the money market from the store k.DeleteMoneyMarket(ctx, denom) } return false }) } // AccrueInterest applies accrued interest to total borrows and reserves by calculating // interest from the last checkpoint time and writing the updated values to the store. func (k Keeper) AccrueInterest(ctx sdk.Context, denom string) error { previousAccrualTime, found := k.GetPreviousAccrualTime(ctx, denom) if !found { k.SetPreviousAccrualTime(ctx, denom, ctx.BlockTime()) return nil } timeElapsed := ctx.BlockTime().Unix() - previousAccrualTime.Unix() if timeElapsed == 0 { return nil } // Get current protocol state and hold in memory as 'prior' cashPrior := k.supplyKeeper.GetModuleAccount(ctx, types.ModuleName).GetCoins().AmountOf(denom) borrowedPrior := sdk.NewCoin(denom, sdk.ZeroInt()) borrowedCoinsPrior, foundBorrowedCoinsPrior := k.GetBorrowedCoins(ctx) if foundBorrowedCoinsPrior { borrowedPrior = sdk.NewCoin(denom, borrowedCoinsPrior.AmountOf(denom)) } reservesPrior, foundReservesPrior := k.GetTotalReserves(ctx, denom) if !foundReservesPrior { newReservesPrior := sdk.NewCoin(denom, sdk.ZeroInt()) k.SetTotalReserves(ctx, denom, newReservesPrior) reservesPrior = newReservesPrior } borrowInterestFactorPrior, foundBorrowInterestFactorPrior := k.GetBorrowInterestFactor(ctx, denom) if !foundBorrowInterestFactorPrior { newBorrowInterestFactorPrior := sdk.MustNewDecFromStr("1.0") k.SetBorrowInterestFactor(ctx, denom, newBorrowInterestFactorPrior) borrowInterestFactorPrior = newBorrowInterestFactorPrior } supplyInterestFactorPrior, foundSupplyInterestFactorPrior := k.GetSupplyInterestFactor(ctx, denom) if !foundSupplyInterestFactorPrior { newSupplyInterestFactorPrior := sdk.MustNewDecFromStr("1.0") k.SetSupplyInterestFactor(ctx, denom, newSupplyInterestFactorPrior) supplyInterestFactorPrior = newSupplyInterestFactorPrior } // Fetch money market from the store mm, found := k.GetMoneyMarket(ctx, denom) if !found { return sdkerrors.Wrapf(types.ErrMoneyMarketNotFound, "%s", denom) } // GetBorrowRate calculates the current interest rate based on utilization (the fraction of supply that has been borrowed) borrowRateApy, err := CalculateBorrowRate(mm.InterestRateModel, sdk.NewDecFromInt(cashPrior), sdk.NewDecFromInt(borrowedPrior.Amount), sdk.NewDecFromInt(reservesPrior.Amount)) if err != nil { return err } // Convert from APY to SPY, expressed as (1 + borrow rate) borrowRateSpy, err := APYToSPY(sdk.OneDec().Add(borrowRateApy)) if err != nil { return err } // Calculate borrow interest factor and update borrowInterestFactor := CalculateBorrowInterestFactor(borrowRateSpy, sdk.NewInt(timeElapsed)) interestBorrowAccumulated := (borrowInterestFactor.Mul(sdk.NewDecFromInt(borrowedPrior.Amount)).TruncateInt()).Sub(borrowedPrior.Amount) totalBorrowInterestAccumulated := sdk.NewCoins(sdk.NewCoin(denom, interestBorrowAccumulated)) reservesNew := interestBorrowAccumulated.ToDec().Mul(mm.ReserveFactor).TruncateInt() borrowInterestFactorNew := borrowInterestFactorPrior.Mul(borrowInterestFactor) k.SetBorrowInterestFactor(ctx, denom, borrowInterestFactorNew) // Calculate supply interest factor and update supplyInterestNew := interestBorrowAccumulated.Sub(reservesNew) supplyInterestFactor := CalculateSupplyInterestFactor(supplyInterestNew.ToDec(), cashPrior.ToDec(), borrowedPrior.Amount.ToDec(), reservesPrior.Amount.ToDec()) supplyInterestFactorNew := supplyInterestFactorPrior.Mul(supplyInterestFactor) k.SetSupplyInterestFactor(ctx, denom, supplyInterestFactorNew) // Update accural keys in store k.IncrementBorrowedCoins(ctx, totalBorrowInterestAccumulated) k.IncrementSuppliedCoins(ctx, sdk.NewCoins(sdk.NewCoin(denom, supplyInterestNew))) k.SetTotalReserves(ctx, denom, reservesPrior.Add(sdk.NewCoin(mm.Denom, reservesNew))) k.SetSupplyInterestFactor(ctx, denom, supplyInterestFactorNew) k.SetPreviousAccrualTime(ctx, denom, ctx.BlockTime()) return nil } // CalculateBorrowRate calculates the borrow rate, which is the current APY expressed as a decimal // based on the current utilization. func CalculateBorrowRate(model types.InterestRateModel, cash, borrows, reserves sdk.Dec) (sdk.Dec, error) { utilRatio := CalculateUtilizationRatio(cash, borrows, reserves) // Calculate normal borrow rate (under kink) if utilRatio.LTE(model.Kink) { return utilRatio.Mul(model.BaseMultiplier).Add(model.BaseRateAPY), nil } // Calculate jump borrow rate (over kink) normalRate := model.Kink.Mul(model.BaseMultiplier).Add(model.BaseRateAPY) excessUtil := utilRatio.Sub(model.Kink) return excessUtil.Mul(model.JumpMultiplier).Add(normalRate), nil } // CalculateUtilizationRatio calculates an asset's current utilization rate func CalculateUtilizationRatio(cash, borrows, reserves sdk.Dec) sdk.Dec { // Utilization rate is 0 when there are no borrows if borrows.Equal(sdk.ZeroDec()) { return sdk.ZeroDec() } totalSupply := cash.Add(borrows).Sub(reserves) if totalSupply.IsNegative() { return sdk.OneDec() } return sdk.MinDec(sdk.OneDec(), borrows.Quo(totalSupply)) } // CalculateBorrowInterestFactor calculates the simple interest scaling factor, // which is equal to: (per-second interest rate * number of seconds elapsed) // Will return 1.000x, multiply by principal to get new principal with added interest func CalculateBorrowInterestFactor(perSecondInterestRate sdk.Dec, secondsElapsed sdk.Int) sdk.Dec { scalingFactorUint := sdk.NewUint(uint64(scalingFactor)) scalingFactorInt := sdk.NewInt(int64(scalingFactor)) // Convert per-second interest rate to a uint scaled by 1e18 interestMantissa := sdk.NewUint(perSecondInterestRate.MulInt(scalingFactorInt).RoundInt().Uint64()) // Convert seconds elapsed to uint (*not scaled*) secondsElapsedUint := sdk.NewUint(secondsElapsed.Uint64()) // Calculate the interest factor as a uint scaled by 1e18 interestFactorMantissa := sdk.RelativePow(interestMantissa, secondsElapsedUint, scalingFactorUint) // Convert interest factor to an unscaled sdk.Dec return sdk.NewDecFromBigInt(interestFactorMantissa.BigInt()).QuoInt(scalingFactorInt) } // CalculateSupplyInterestFactor calculates the supply interest factor, which is the percentage of borrow interest // that flows to each unit of supply, i.e. at 50% utilization and 0% reserve factor, a 5% borrow interest will // correspond to a 2.5% supply interest. func CalculateSupplyInterestFactor(newInterest, cash, borrows, reserves sdk.Dec) sdk.Dec { totalSupply := cash.Add(borrows).Sub(reserves) if totalSupply.IsZero() { return sdk.OneDec() } return (newInterest.Quo(totalSupply)).Add(sdk.OneDec()) } // SyncBorrowInterest updates the user's owed interest on newly borrowed coins to the latest global state func (k Keeper) SyncBorrowInterest(ctx sdk.Context, addr sdk.AccAddress) { totalNewInterest := sdk.Coins{} // Update user's borrow interest factor list for each asset in the 'coins' array. // We use a list of BorrowInterestFactors here because Amino doesn't support marshaling maps. borrow, found := k.GetBorrow(ctx, addr) if !found { return } for _, coin := range borrow.Amount { // Locate the borrow interest factor item by coin denom in the user's list of borrow indexes foundAtIndex := -1 for i := range borrow.Index { if borrow.Index[i].Denom == coin.Denom { foundAtIndex = i break } } interestFactorValue, _ := k.GetBorrowInterestFactor(ctx, coin.Denom) if foundAtIndex == -1 { // First time user has borrowed this denom borrow.Index = append(borrow.Index, types.NewBorrowInterestFactor(coin.Denom, interestFactorValue)) } else { // User has an existing borrow index for this denom // Calculate interest owed by user since asset's last borrow index update storedAmount := sdk.NewDecFromInt(borrow.Amount.AmountOf(coin.Denom)) userLastInterestFactor := borrow.Index[foundAtIndex].Value interest := (storedAmount.Quo(userLastInterestFactor).Mul(interestFactorValue)).Sub(storedAmount) totalNewInterest = totalNewInterest.Add(sdk.NewCoin(coin.Denom, interest.TruncateInt())) // We're synced up, so update user's borrow index value to match the current global borrow index value borrow.Index[foundAtIndex].Value = interestFactorValue } } // Add all pending interest to user's borrow borrow.Amount = borrow.Amount.Add(totalNewInterest...) // Update user's borrow in the store k.SetBorrow(ctx, borrow) } // SyncSupplyInterest updates the user's earned interest on supplied coins based on the latest global state func (k Keeper) SyncSupplyInterest(ctx sdk.Context, addr sdk.AccAddress) { totalNewInterest := sdk.Coins{} // Update user's supply index list for each asset in the 'coins' array. // We use a list of SupplyInterestFactors here because Amino doesn't support marshaling maps. deposit, found := k.GetDeposit(ctx, addr) if !found { return } for _, coin := range deposit.Amount { // Locate the deposit index item by coin denom in the user's list of deposit indexes foundAtIndex := -1 for i := range deposit.Index { if deposit.Index[i].Denom == coin.Denom { foundAtIndex = i break } } interestFactorValue, _ := k.GetSupplyInterestFactor(ctx, coin.Denom) if foundAtIndex == -1 { // First time user has supplied this denom deposit.Index = append(deposit.Index, types.NewSupplyInterestFactor(coin.Denom, interestFactorValue)) } else { // User has an existing supply index for this denom // Calculate interest earned by user since asset's last deposit index update storedAmount := sdk.NewDecFromInt(deposit.Amount.AmountOf(coin.Denom)) userLastInterestFactor := deposit.Index[foundAtIndex].Value interest := (storedAmount.Mul(interestFactorValue).Quo(userLastInterestFactor)).Sub(storedAmount) if interest.TruncateInt().GT(sdk.ZeroInt()) { totalNewInterest = totalNewInterest.Add(sdk.NewCoin(coin.Denom, interest.TruncateInt())) } // We're synced up, so update user's deposit index value to match the current global deposit index value deposit.Index[foundAtIndex].Value = interestFactorValue } } // Add all pending interest to user's deposit deposit.Amount = deposit.Amount.Add(totalNewInterest...) // Update user's deposit in the store k.SetDeposit(ctx, deposit) } // APYToSPY converts the input annual interest rate. For example, 10% apy would be passed as 1.10. // SPY = Per second compounded interest rate is how cosmos mathematically represents APY. func APYToSPY(apy sdk.Dec) (sdk.Dec, error) { // Note: any APY 179 or greater will cause an out-of-bounds error root, err := apy.ApproxRoot(uint64(secondsPerYear)) if err != nil { return sdk.ZeroDec(), err } return root, nil } // minInt64 returns the smaller of x or y func minDec(x, y sdk.Dec) sdk.Dec { if x.GT(y) { return y } return x }