import RPi.GPIO as GPIO
import time, os, threading

GPIO_PIR = 23
GPIO_TRIGGER = 18
GPIO_ECHO = 24

THRESHOLD = 60 # cm
TIMEOUT = 180 # sec

############################
GPIO.setwarnings(False)
GPIO.setmode(GPIO.BCM)
GPIO.setup(GPIO_PIR, GPIO.IN)
GPIO.setup(GPIO_TRIGGER, GPIO.OUT)
GPIO.setup(GPIO_ECHO, GPIO.IN)

LAST_MOVE = 0

def distance(sample_size=5, sample_wait=0.01):
    # https://raw.githubusercontent.com/alaudet/hcsr04sensor/master/hcsr04sensor/sensor.py
    speed_of_sound = 331.3
    sample = []
    for distance_reading in range(sample_size):
        GPIO.output(GPIO_TRIGGER, GPIO.LOW)
        time.sleep(sample_wait)
        GPIO.output(GPIO_TRIGGER, True)
        time.sleep(0.00001)
        GPIO.output(GPIO_TRIGGER, False)
        echo_status_counter = 1
        sonar_signal_on, sonar_signal_off = time.time(), time.time()
        while GPIO.input(GPIO_ECHO) == 0:
            if echo_status_counter < 1000:
                sonar_signal_off = time.time()
                echo_status_counter += 1
            #else:
            #    raise SystemError('Echo pulse was not received')
        while GPIO.input(GPIO_ECHO) == 1:
            sonar_signal_on = time.time()
        time_passed = sonar_signal_on - sonar_signal_off
        distance_cm = time_passed * ((speed_of_sound * 100) / 2)
        sample.append(distance_cm)
    sorted_sample = sorted(sample)
    return sorted_sample[sample_size // 2]

def standby():
    d = distance()
    if d >= THRESHOLD:
        os.system("echo 1 > /sys/class/backlight/rpi_backlight/bl_power") # off
    else:
        os.system("echo 0 > /sys/class/backlight/rpi_backlight/bl_power") # on
        threading.Timer(TIMEOUT, standby).start()
        LAST_MOVE = time.time()

def has_moved(channel):
    d = distance()
    if d <= THRESHOLD:
        os.system("echo 0 > /sys/class/backlight/rpi_backlight/bl_power") # on
        if time.time() - LAST_MOVE >= 1:
            threading.Timer(TIMEOUT, standby).start()

try:
    #while True:
    GPIO.add_event_detect(GPIO_PIR , GPIO.RISING, callback=has_moved)
    while True:
        time.sleep(1)
except KeyboardInterrupt:
    print "Beende..."
GPIO.cleanup()