import time

temp_file = '/sys/bus/iio/devices/iio:device0/in_temp160_temp_input'
fanpwm_file = '/sys/class/hwmon/hwmon0/pwm1'

temp_min = 35.0
temp_max = 75.0
temp_hist_up = 1.0
temp_hist_down = 5.0
temp_prev = 0.0

print("FAN Control start ...\n")

# equation of a straight line: a*x + b*y + c = 0
# A = [temp_min; pwm_min], B = [temp_max, pwm_max]
# A = [temp_min; 0],       B = [temp_max, 255]
# u = B - A = (temp_max - temp_min; pwm_max - pwm_min)
# u = (temp_max - temp_min; 255 - 0)
# n = (255, -(temp_max - temp_min))
# p: 255*x -(temp_max - temp_min)*y + c = 0
# c: A is on the p
# c = -255*temp_min - (temp_max - temp_min)*0
c = -255 * temp_min

f_temp = open(temp_file, 'r')

while True:
  f_temp = open(temp_file, 'r')
  temp = float(f_temp.readline())
  f_temp.close()

  if ((temp - temp_prev) >= temp_hist_up) or ((temp_prev - temp) >= temp_hist_down):

    pwm = (-c - (255 * temp)) / -(temp_max - temp_min)
    pwmi = int(pwm)

    if pwmi < 0:
      pwmi = 0

    if pwmi > 255:
      pwmi = 255

    #print(str(temp), str(temp_prev), str(pwm), str(pwmi))

    f_pwm = open(fanpwm_file, 'w')
    f_pwm.write(str(pwmi))
    f_pwm.close()

    temp_prev = temp


  time.sleep(1)