from machine import Pin, Timer

led_pins = [19, 18, 5, 17]
pins = [Pin(i, Pin.OUT) for i in led_pins]
register = [1, 0, 0, 0]
register1 = [0, 0, 0, 1]
direction = 1 # +1 = right, -1 = left


def shift_right(reg, new_bit):  # 1000 -> 0100
    for i in range(len(reg) - 1, 0, -1):
        reg[i] = reg[i - 1]
    reg[0] = new_bit
    return reg


def shift_left(reg, new_bit):  # 0100 -> 1000
    for i in range(0, len(reg) - 1):
        reg[i] = reg[i + 1]
    reg[len(reg) - 1] = new_bit
    return reg

def register_to_led():
    for i, led in enumerate(pins):
        led.value(register[i])


def clk_signal(t):
    global register, direction
    register_to_led()


    if direction == 1:
        shift_right(register, 0)
        if register == register1:
            direction = -1
    elif direction == -1:
        shift_left(register, 0)
        if register == [1, 0, 0, 0]:
            direction = 1

Timer(0).init(period=100, mode=Timer.PERIODIC, callback=clk_signal)