TezFin/contracts/InterestRateModel.py at main · StableTechnologies/TezFin · GitHub

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import smartpy as sp

IRMErrors = sp.io.import_script_from_url(
    "file:contracts/errors/InterestRateModelErrors.py")
EC = IRMErrors.ErrorCodes

IRMInterface = sp.io.import_script_from_url(
    "file:contracts/interfaces/InterestRateModelInterface.py")


class InterestRateModel(IRMInterface.InterestRateModelInterface):
    def __init__(self,
                baseRatePerBlock_,
                multiplierPerBlock_,
                jumpMultiplierPerBlock_,
                kink_,
                scale_,
                **extra_storage):
        self.init(
            scale=scale_,  # must match order of reserveFactorMantissa
            # The multiplier of utilization rate that gives the slope of the interest rate
            multiplierPerBlock=multiplierPerBlock_,
            # The base interest rate which is the y-intercept when utilization rate is 0
            baseRatePerBlock=baseRatePerBlock_,
            # The multiplier per block after hitting the kink point
            jumpMultiplierPerBlock=jumpMultiplierPerBlock_,
            # The utilization point at which the jump multiplier is applied
            kink=kink_,
            **extra_storage
        )

    """
        Calculates the current borrow interest rate per block

        params: TBorrowRateParams

        return: The borrow rate per block (as a percentage)
    """
    @sp.entry_point
    def getBorrowRate(self, params):
        sp.set_type(params, IRMInterface.TBorrowRateParams)
        utRate = self.utilizationRate(sp.record(
            cash=params.cash, borrows=params.borrows, reserves=params.reserves))
        result = self.calculateBorrowRate(utRate)
        sp.transfer(result, sp.mutez(0), params.cb)

    """
        Calculates the current supply interest rate per block

        params: TSupplyRateParams

        return: The supply rate per block (as a percentage)
    """
    @sp.entry_point
    def getSupplyRate(self, params):
        sp.set_type(params, IRMInterface.TSupplyRateParams)
        oneMinusReserveFactor = sp.as_nat(
            self.data.scale - params.reserveFactorMantissa)
        utRate = self.utilizationRate(sp.record(
            cash=params.cash, borrows=params.borrows, reserves=params.reserves))
        borrowRate = self.calculateBorrowRate(utRate)
        rateToPool = borrowRate * oneMinusReserveFactor // self.data.scale
        result = utRate * rateToPool // self.data.scale
        sp.transfer(result, sp.mutez(0), params.cb)

    @sp.private_lambda(with_storage="read-only")
    def utilizationRate(self, params):
        sp.set_type(params, IRMInterface.TUtilizationParams)
        ur = sp.local('ur', sp.nat(0))
        sp.if params.borrows > sp.nat(0):
            divisor = sp.compute(sp.as_nat(params.cash + params.borrows - params.reserves))
            sp.verify(divisor > 0, EC.IRM_INSUFFICIENT_CASH)
            ur.value = params.borrows * self.data.scale // divisor
        sp.result(ur.value)

    @sp.private_lambda(with_storage="read-only")
    def calculateBorrowRate(self, utRate):
        sp.if utRate <= self.data.kink:
            sp.result(sp.compute(utRate * self.data.multiplierPerBlock // self.data.scale + self.data.baseRatePerBlock))
        sp.else:
            # Calculate the rate at the kink point
            normalRate = sp.compute(
                self.data.kink * self.data.multiplierPerBlock // self.data.scale + self.data.baseRatePerBlock
            )
            # Calculate excess utilization beyond kink
            excessUtil = sp.as_nat(utRate - self.data.kink)
            # Apply jump multiplier to excess utilization
            rate = sp.compute(
                excessUtil * self.data.jumpMultiplierPerBlock // self.data.scale + normalRate
            )
            sp.result(rate)