# Silent-until-asked serial probe for crbug.com/559872992 testing.
# Board: Adafruit Feather nRF52840 Sense (CircuitPython).
#
# Never transmits unsolicited. Commands (newline-terminated):
#   PING -> PONG
#   LED  -> toggles red LED, replies OK
#   ID   -> identification string
#   *    -> ERR

import sys

import board
import digitalio
import supervisor

led = digitalio.DigitalInOut(board.RED_LED)
led.direction = digitalio.Direction.OUTPUT
led.value = False

buf = ""

while True:
    if supervisor.runtime.serial_bytes_available:
        ch = sys.stdin.read(1)
        if ch in ("\n", "\r"):
            line = buf.strip().upper()
            buf = ""
            if not line:
                continue
            if line == "PING":
                print("PONG")
            elif line == "LED":
                led.value = not led.value
                print("OK")
            elif line == "ID":
                print("serial-repo probe, crbug.com/559872992")
            else:
                print("ERR")
        else:
            buf += ch