import argparse
import logging
import os
import serial


kCrc16Polynomial = 0x1021
kCrc16Preset = 0xFFFF

kDefaultSerialPort = None
kDefaultBaudrate = 115200
kDefaultChunkSize = 0x20

logger = logging.getLogger(__name__)


def crc16(data):
    crc = kCrc16Preset
    for c in data:
        crc ^= c << 8
        for j in range(8):
            mix = crc & 0x8000
            crc <<= 1
            if mix:
                crc ^= kCrc16Polynomial
            crc &= 0xFFFF
    return crc


def getserial(port=None, baudrate=None, **kwargs):
    if port is not None:
        return serial.Serial(port, baudrate)

    # return first /dev/ttyACMx found
    for i in range(10):
        try:
            return serial.Serial(f"/dev/ttyACM{i}", baudrate)
        except serial.SerialException:
            pass
    raise RuntimeError("No serial device available.")


def ftpserve(file, device, chunksize=0x20):
    with open(file, "rb") as f:
        data = f.read()
    device.reset_input_buffer()
    logger.info(f"Serving file {file}")
    for i in range(0, len(data), chunksize):
        device.write(data[i : i + chunksize])
        r = device.read()
        if r != b"\x42":
            raise RuntimeError(f"wrong response {r}")
        logger.info(f"ack for chunk @{i}")
    logger.info(f"Done serving file {file}")
    crc = crc16(data)
    logger.info(f"File length: {len(data):04x}, crc16: {crc:04x}")


def parse_args():
    parser = argparse.ArgumentParser(description="Serve a file to ftpget.")
    parser.add_argument("file", help="file to serve")
    parser.add_argument("--port", help="path to the serial port")
    parser.add_argument("--baudrate", default=kDefaultBaudrate)
    parser.add_argument("--chunksize", default=kDefaultChunkSize)
    return parser.parse_args()


def main():
    logging.basicConfig(level=logging.INFO)
    args = parse_args()
    device = getserial(**vars(args))
    ftpserve(args.file, device, args.chunksize)


if __name__ == "__main__":
    try:
        main()
    except KeyboardInterrupt:
        pass