#!/usr/bin/python

import os
import sys
import time
import struct
import serial

from binascii import crc32


def _write(dst, data):
    for i in range(len(data)):
        dst.write(data[i])
        time.sleep(0.1)
    if len(data) == 4:
        print("Wrote 0x{:02x}{:02x}{:02x}{:02x}".format(ord(data[0]), ord(data[1]), ord(data[2]), ord(data[3])))
    else:
        print("Wrote {!r}".format(data))


def _read(dst):
    res = ''
    while True:
        x = dst.read(1)
        if not x:
            break
        res += x
    print ("Read {!r}".format(res))
    return res


def _execute(dst, cmd):
    _write(dst, '\r')
    prompt = _read(dst)
    if prompt.endswith('Username: '):
        _write(dst, 'ct\r')
        prompt = _read(dst)
    if prompt.endswith('Password: '):
        _write(dst, 'ct\r')
        prompt = _read(dst)
    if not prompt.endswith('> '):
        sys.stderr.write('Device does not seem to be ready for a file transfer (got {!r})\n'.format(prompt))
        return False
    _write(dst, cmd + '\r')
    response = _read(dst)
    return response

def send_file(filename, device='/dev/ttyUSB0', initiate=True):
    s = os.stat(filename)
    size = s.st_size
    src = open(filename, 'rb')

    dst = serial.Serial(device, 921600, timeout=0.1)

    if initiate:
        response = _execute(dst, 'filetransfer')
        if 'OK' not in response:
            sys.stderr.write('Device did not accept the filetransfer command (got {!r})\n'.format(response))
            return False

    # 1. Write size of file (4 bytes)
    _write(dst, struct.pack('<I', size))
    _read(dst)
    # 2. Write file contents while calculating CRC-32
    crc = 0
    counter = 0
    while True:
        data = src.read(4096)
        if not data:
            break
        dst.write(data)
        print("Wrote {!s} bytes".format(len(data)))
        # read ACK (a counter of number of 4k chunks received)
        while True:
            ack = dst.read(4)
            if len(ack) == 4:
                break
            print('ERROR: Did not receive an ACK, got {!r}'.format(ack))
            dst.write('\r')
        new_counter = struct.unpack('<I', ack)[0]
        if new_counter != counter + 1:
            print('ERROR: Did not receive the expected counter as ACK (got {!r}/{!r}, not {!r})'.format(new_counter, ack, counter))
            flush = dst.read(100)
            print('FLUSH data: {!r}'.format(flush))
            return False
        counter += 1

        crc = crc32(data, crc) & 0xffffffff

    _read(dst)

    # 3. Write CRC-32 (4 bytes)
    _write(dst, struct.pack('<I', crc))
    _read(dst)

    src.close()
    dst.close()
    return True


if len(sys.argv) != 2:
    sys.stderr.write('Syntax: {!s} filename\n'.format(sys.argv[0]))
    sys.exit(1)

if send_file(sys.argv[1]):
    sys.exit(0)

sys.exit(1)