from pyb import millis

from math import pi, isnan



class PID:

    _kp = _ki = _kd = _integrator = _imax = 0

    _last_error = _last_derivative = _last_t = 0

    _RC = 1/(2 * pi * 20)

    def __init__(self, p=0, i=0, d=0, imax=0):

        self._kp = float(p)

        self._ki = float(i)

        self._kd = float(d)

        self._imax = abs(imax)

        self._last_derivative = float('nan')



    def get_pid(self, error, scaler):

        tnow = millis()

        dt = tnow - self._last_t

        output = 0

        if self._last_t == 0 or dt > 1000:

            dt = 0

            self.reset_I()

        self._last_t = tnow

        delta_time = float(dt) / float(1000)

        output += error * self._kp

        if abs(self._kd) > 0 and dt > 0:

            if isnan(self._last_derivative):

                derivative = 0

                self._last_derivative = 0

            else:

                derivative = (error - self._last_error) / delta_time

            derivative = self._last_derivative + \

                                     ((delta_time / (self._RC + delta_time)) * \

                                        (derivative - self._last_derivative))

            self._last_error = error

            self._last_derivative = derivative

            output += self._kd * derivative

        output *= scaler

        if abs(self._ki) > 0 and dt > 0:

            self._integrator += (error * self._ki) * scaler * delta_time

            if self._integrator < -self._imax: self._integrator = -self._imax

            elif self._integrator > self._imax: self._integrator = self._imax

            output += self._integrator

        return output

    def reset_I(self):

        self._integrator = 0

        self._last_derivative = float('nan')