import time
from machine import Pin
from neopixel import NeoPixel

LED_AANTAL = 16
FLASH_TIME = 0.25
PIN_NR_21 = 21
PIN_NR_25 = 25
DENDER_VALUE = 0.3

pin = Pin(PIN_NR_21, Pin.OUT)   # set GPIO0 to output to drive NeoPixels
np = NeoPixel(pin, LED_AANTAL)   # create NeoPixel driver on GPIO0 for 8 pixels
druk_mode = Pin(PIN_NR_25, Pin.IN, Pin.PULL_DOWN)   # switch direction

def led_neopixel_stuur(led_strip, start, stop, step):

    for i in range(start, stop, step):
        global direction
        global druk_mode_now
        global druk_mode_prev
        global start_flash
        
        led_strip[i] = (255, 0, 0)  # red, full intensity
        led_strip.write()
        time.sleep(FLASH_TIME)
        led_strip[i] = (0, 0, 0)    # reset pixel
        led_strip.write()
        druk_mode_now = druk_mode.value()
        if druk_mode_now != druk_mode_prev:
            druk_mode_prev = druk_mode_now
            if druk_mode_now:
                direction = not direction
                start_flash = i     # keep position when interupted
                break
            else:
                if direction:
                    start_flash = LED_AANTAL
                else:
                    start_flash = 0

            time.sleep(DENDER_VALUE)

druk_mode_now = 0
druk_mode_prev = 0
direction = 0
start_flash = 0

while True:
    if direction:
        led_neopixel_stuur(np, start_flash-1, -1, -1)
    else:
        led_neopixel_stuur(np, start_flash, LED_AANTAL, 1)