''' Digital rate limiter filter implementation '''

class RateLimiter:
    ''' Implementation of a digital rate limiter filter. '''
    def __init__(self, rateDown, rateUp, dt):
        ''' Builds a biquad filter from the given parameters. '''
        self.InitFilter(0)
        self.rateUp = rateUp
        self.rateDown = rateDown
        self.dt = dt

        if self.rateDown > self.rateUp:
            print('Warning : rate limiter with id ' + str(id(self)) + ' : lower limit is higher than upper limit !')

    def InitFilter(self, v):
        ''' Initializes the filter with the value v. '''
        self.xn_0 = v
        self.yn_1 = v

    def Filter(self, xn_0):
        ''' Computes the next value of the filter. '''
        self.xn_0 = xn_0
        if ((self.xn_0 - self.yn_1)/self.dt) > self.rateUp:
            self.yn_1 = self.yn_1 + self.rateUp * self.dt       # next output value is set at max up rate
        elif ((self.xn_0 - self.yn_1)/self.dt) < self.rateDown:
            self.yn_1 = self.yn_1 + self.rateDown * self.dt     # next output value is set at max down rate
        else:
            self.yn_1 = self.xn_0
        return self.yn_1