package keeper import ( "fmt" "math" sdk "github.com/cosmos/cosmos-sdk/types" "github.com/kava-labs/kava/x/cdp/types" ) var ( scalingFactor = 1e18 secondsPerYear = 31536000 ) // AccumulateInterest calculates the new interest that has accrued for the input collateral type based on the total amount of principal // that has been created with that collateral type and the amount of time that has passed since interest was last accumulated func (k Keeper) AccumulateInterest(ctx sdk.Context, ctype string) error { previousAccrualTime, found := k.GetPreviousAccrualTime(ctx, ctype) if !found { k.SetPreviousAccrualTime(ctx, ctype, ctx.BlockTime()) return nil } timeElapsed := int64(math.RoundToEven( ctx.BlockTime().Sub(previousAccrualTime).Seconds(), )) if timeElapsed == 0 { return nil } totalPrincipalPrior := k.GetTotalPrincipal(ctx, ctype, types.DefaultStableDenom) if totalPrincipalPrior.IsZero() || totalPrincipalPrior.IsNegative() { k.SetPreviousAccrualTime(ctx, ctype, ctx.BlockTime()) return nil } interestFactorPrior, foundInterestFactorPrior := k.GetInterestFactor(ctx, ctype) if !foundInterestFactorPrior { k.SetInterestFactor(ctx, ctype, sdk.OneDec()) // set previous accrual time exit early because interest accumulated will be zero k.SetPreviousAccrualTime(ctx, ctype, ctx.BlockTime()) return nil } borrowRateSpy := k.getFeeRate(ctx, ctype) if borrowRateSpy.Equal(sdk.OneDec()) { k.SetPreviousAccrualTime(ctx, ctype, ctx.BlockTime()) return nil } interestFactor := CalculateInterestFactor(borrowRateSpy, sdk.NewInt(timeElapsed)) interestAccumulated := (interestFactor.Mul(totalPrincipalPrior.ToDec())).RoundInt().Sub(totalPrincipalPrior) if interestAccumulated.IsZero() { // in the case accumulated interest rounds to zero, exit early without updating accrual time return nil } err := k.MintDebtCoins(ctx, types.ModuleName, k.GetDebtDenom(ctx), sdk.NewCoin(types.DefaultStableDenom, interestAccumulated)) if err != nil { return err } dp, found := k.GetDebtParam(ctx, types.DefaultStableDenom) if !found { panic(fmt.Sprintf("Debt parameters for %s not found", types.DefaultStableDenom)) } newFeesSurplus := interestAccumulated // mint surplus coins to the liquidator module account. if newFeesSurplus.IsPositive() { err := k.supplyKeeper.MintCoins(ctx, types.LiquidatorMacc, sdk.NewCoins(sdk.NewCoin(dp.Denom, newFeesSurplus))) if err != nil { return err } } interestFactorNew := interestFactorPrior.Mul(interestFactor) totalPrincipalNew := totalPrincipalPrior.Add(interestAccumulated) k.SetTotalPrincipal(ctx, ctype, types.DefaultStableDenom, totalPrincipalNew) k.SetInterestFactor(ctx, ctype, interestFactorNew) k.SetPreviousAccrualTime(ctx, ctype, ctx.BlockTime()) return nil } // CalculateInterestFactor 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 CalculateInterestFactor(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) } // SynchronizeInterest updates the input cdp object to reflect the current accumulated interest, updates the cdp state in the store, // and returns the updated cdp object func (k Keeper) SynchronizeInterest(ctx sdk.Context, cdp types.CDP) types.CDP { globalInterestFactor, found := k.GetInterestFactor(ctx, cdp.Type) if !found { k.SetInterestFactor(ctx, cdp.Type, sdk.OneDec()) cdp.InterestFactor = sdk.OneDec() cdp.FeesUpdated = ctx.BlockTime() k.SetCDP(ctx, cdp) return cdp } accumulatedInterest := k.CalculateNewInterest(ctx, cdp) if accumulatedInterest.IsZero() { // accumulated interest is zero if apy is zero or are if the total fees for all cdps round to zero prevAccrualTime, found := k.GetPreviousAccrualTime(ctx, cdp.Type) if !found { return cdp } if cdp.FeesUpdated.Equal(prevAccrualTime) { // if all fees are rounding to zero, don't update FeesUpdated return cdp } // if apy is zero, we need to update FeesUpdated cdp.FeesUpdated = ctx.BlockTime() k.SetCDP(ctx, cdp) } cdp.AccumulatedFees = cdp.AccumulatedFees.Add(accumulatedInterest) cdp.FeesUpdated = ctx.BlockTime() cdp.InterestFactor = globalInterestFactor collateralToDebtRatio := k.CalculateCollateralToDebtRatio(ctx, cdp.Collateral, cdp.Type, cdp.GetTotalPrincipal()) k.UpdateCdpAndCollateralRatioIndex(ctx, cdp, collateralToDebtRatio) return cdp } // CalculateNewInterest returns the amount of interest that has accrued to the cdp since its interest was last synchronized func (k Keeper) CalculateNewInterest(ctx sdk.Context, cdp types.CDP) sdk.Coin { globalInterestFactor, found := k.GetInterestFactor(ctx, cdp.Type) if !found { return sdk.NewCoin(cdp.AccumulatedFees.Denom, sdk.ZeroInt()) } cdpInterestFactor := globalInterestFactor.Quo(cdp.InterestFactor) if cdpInterestFactor.Equal(sdk.OneDec()) { return sdk.NewCoin(cdp.AccumulatedFees.Denom, sdk.ZeroInt()) } accumulatedInterest := cdp.GetTotalPrincipal().Amount.ToDec().Mul(cdpInterestFactor).RoundInt().Sub(cdp.GetTotalPrincipal().Amount) return sdk.NewCoin(cdp.AccumulatedFees.Denom, accumulatedInterest) } // SynchronizeInterestForRiskyCDPs synchronizes the interest for the slice of cdps with the lowest collateral:debt ratio func (k Keeper) SynchronizeInterestForRiskyCDPs(ctx sdk.Context, slice sdk.Int, targetRatio sdk.Dec, collateralType string) error { cdps := k.GetSliceOfCDPsByRatioAndType(ctx, slice, targetRatio, collateralType) for _, cdp := range cdps { k.SynchronizeInterest(ctx, cdp) } return nil }