#!/usr/bin/env python
#
# Interactive shell for communication with LG devices in download mode (LAF).
#
# Copyright (C) 2015 Peter Wu <peter@lekensteyn.nl>
# Licensed under the MIT license <http://opensource.org/licenses/MIT>.

from __future__ import print_function
from contextlib import closing
import argparse, logging, re, struct, sys

# Enhanced prompt with history
try: import readline
except ImportError: pass
# Try USB interface
try: import usb.core
except ImportError: pass

_logger = logging.getLogger("LGLAF.py")

# Python 2/3 compat
try: input = raw_input
except: pass
if '\0' == b'\0': int_as_byte = chr
else: int_as_byte = lambda x: bytes([x])

_ESCAPE_PATTERN = re.compile(b'''\\\\(
x[0-9a-fA-F]{2} |
[0-7]{1,3} |
.)''', re.VERBOSE)
_ESCAPE_MAP = {
    b'n': b'\n',
    b'r': b'\r',
    b't': b'\t',
}
_ESCAPED_CHARS = b'"\\\''
def text_unescape(text):
    """Converts a string with escape sequences to bytes."""
    text_bin = text.encode("utf8")
    def sub_char(m):
        what = m.group(1)
        if what[0:1] == b'x' and len(what) == 3:
            return int_as_byte(int(what[1:], 16))
        elif what[0:1] in b'01234567':
            return int_as_byte(int(what, 8))
        elif what in _ESCAPE_MAP:
            return _ESCAPE_MAP[what]
        elif what in _ESCAPED_CHARS:
            return what
        else:
            raise RuntimeError('Unknown escape sequence \\%s' %
                    what.decode('utf8'))
    return re.sub(_ESCAPE_PATTERN, sub_char, text_bin)

def parse_number_or_escape(text):
    try:
        return int(text, 0) if text else 0
    except ValueError:
        return text_unescape(text)

### Protocol-related stuff

def crc16(data):
    """CRC-16-CCITT computation with LSB-first and inversion."""
    crc = 0xffff
    for byte in data:
        crc ^= byte
        for bits in range(8):
            if crc & 1:
                crc = (crc >> 1) ^ 0x8408
            else:
                crc >>= 1
    return crc ^ 0xffff

def invert_dword(dword_bin):
    dword = struct.unpack("I", dword_bin)[0]
    return struct.pack("I", dword ^ 0xffffffff)

def make_request(cmd, args=[], body=b''):
    if not isinstance(cmd, bytes):
        cmd = cmd.encode('ascii')
    assert isinstance(body, bytes)

    # Header: command, args, ... body size, header crc16, inverted command
    header = bytearray(0x20)
    def set_header(offset, val):
        if isinstance(val, int):
            val = struct.pack('<I', val)
        assert len(val) == 4
        header[offset:offset+4] = val

    set_header(0, cmd)
    assert len(args) <= 4
    for i, arg in enumerate(args):
        set_header(4 * (i + 1), arg)

    # 0x14: body length
    set_header(0x14, len(body))
    # 0x1c: Inverted command
    set_header(0x1c, invert_dword(cmd))
    # Header finished (with CRC placeholder), append body...
    header += body
    # finish with CRC for header and body
    set_header(0x18, crc16(header))
    return bytes(header)

def validate_message(payload, ignore_crc=False):
    if len(payload) < 0x20:
        raise RuntimeError("Invalid header length: %d" % len(payload))
    if not ignore_crc:
        crc = struct.unpack_from('<I', payload, 0x18)[0]
        payload_before_crc = bytearray(payload)
        payload_before_crc[0x18:0x18+4] = b'\0\0\0\0'
        crc_exp = crc16(payload_before_crc)
        if crc_exp != crc:
            raise RuntimeError("Expected CRC %04x, found %04x" % (crc_exp, crc))
    tail_exp = invert_dword(payload[0:4])
    tail = payload[0x1c:0x1c+4]
    if tail_exp != tail:
        raise RuntimeError("Expected trailer %r, found %r" % (tail_exp, tail))

def make_exec_request(shell_command):
    # Allow use of shell constructs such as piping. Needs more work not to eat
    # all repetitive spaces, it should also escape some things...
    body = b'sh -c "$@" -- eval 2>&1 '
    body += shell_command.encode('ascii') + b'\0'
    return make_request(b'EXEC', body=body)


### USB or serial port communication

class Communication(object):
    def read(self, n):
        raise NotImplementedError
    def write(self, data):
        raise NotImplementedError
    def close(self):
        raise NotImplementedError
    def reset(self):
        """Tries to consume all outstanding incoming data."""
        raise NotImplementedError
    def call(self, payload):
        """Sends a command and returns its response."""
        validate_message(payload)
        self.write(payload)
        header = self.read(0x20)
        validate_message(header, ignore_crc=True)
        cmd = header[0:4]
        size = struct.unpack_from('<I', header, 0x14)[0]
        # could validate CRC and inverted command here...
        data = self.read(size) if size else b''
        if cmd == b'FAIL':
            errCode = struct.unpack_from('<I', header, 4)
            raise RuntimeError('Command failed with error code %#x' % errCode)
        if cmd != payload[0:4]:
            raise RuntimeError("Unexpected response: %r" % header)
        return header, data

class FileCommunication(Communication):
    def __init__(self, file_path):
        if sys.version_info[0] >= 3:
            self.f = open(file_path, 'r+b', buffering=0)
        else:
            self.f = open(file_path, 'r+b')
    def read(self, n):
        return self.f.read(n)
    def write(self, data):
        self.f.write(data)
    def close(self):
        self.f.close()
    def reset(self):
        # TODO non-blocking read
        _logger.warn("Reset is not implemented yet")

class USBCommunication(Communication):
    EP_IN = 0x85
    EP_OUT = 3
    # Read timeout. Set to 0 to disable timeouts
    READ_TIMEOUT_MS = 0
    def __init__(self):
        self.read_buffer = b''
        self.usbdev = usb.core.find(idVendor=0x1004, idProduct=0x633e)
        if self.usbdev is None:
            raise RuntimeError("USB device not found")
    def read(self, n):
        while len(self.read_buffer) < n:
            buff = self._read_chunk(self.READ_TIMEOUT_MS)
            self.read_buffer += buff
            if not buff:
                raise EOFError
        data, self.read_buffer = self.read_buffer[0:n], self.read_buffer[n:]
        return data
    def _read_chunk(self, timeout):
        # device seems to use 16 KiB buffers.
        return self.usbdev.read(self.EP_IN, 2**14, timeout=timeout)
    def write(self, data):
        # Reset read buffer for response
        if self.read_buffer:
            _logger.warn('non-empty read buffer %r', self.read_buffer)
            self.read_buffer = b''
        self.usbdev.write(self.EP_OUT, data)
    def close(self):
        usb.util.dispose_resources(self.usbdev)
    def reset(self):
        # TODO: do some handshake and only if the response is unexpected, drain
        # the queue and try again
        self.read_buffer = b''
        try:
            while True:
                junk = bytes(self._read_chunk(timeout=100))
                _logger.debug("Ignoring: %r", junk)
        except usb.core.USBError as e:
            # Ignore ETIMEDOUT (110)
            if e.errno != 110:
                raise


### Interactive loop

def get_commands(command):
    if command:
        yield command
        return
    # Happened on Win32/Py3.4.4 when: echo ls | lglaf.py --serial com4
    if sys.stdin is None:
        raise RuntimeError('No console input available!')
    if sys.stdin.isatty():
        print("LGLAF.py by Peter Wu (https://lekensteyn.nl/lglaf)\n"
                "Type a shell command to execute or \"exit\" to leave.",
                file=sys.stderr)
        prompt = '# '
    else:
        prompt = ''
    try:
        while True:
            line = input(prompt)
            if line == "exit":
                break
            if line:
                yield line
    except EOFError:
        if prompt:
            print("", file=sys.stderr)

def command_to_payload(command):
    # Handle '!' as special commands, treat others as shell command
    if command[0] != '!':
        return make_exec_request(command)
    command = command[1:]
    # !command [arg1[,arg2[,arg3[,arg4]]]] [body]
    # args are treated as integers (decimal or hex)
    # body is treated as string (escape sequences are supported)
    command, args, body = (command.split(' ', 2) + ['', ''])[0:3]
    command = text_unescape(command)
    args = list(map(parse_number_or_escape, args.split(',') + [0, 0, 0]))[0:4]
    body = text_unescape(body)
    return make_request(command, args, body)

parser = argparse.ArgumentParser(description='LG LAF Download Mode utility')
parser.add_argument("-c", "--command", help='Shell command to execute')
parser.add_argument("--serial", metavar="PATH", dest="serial_path",
        help="Path to serial device (e.g. COM4).")
parser.add_argument("--debug", action='store_true', help="Enable debug messages")

def main():
    args = parser.parse_args()
    logging.basicConfig(format='%(name)s: %(levelname)s: %(message)s',
            level=logging.DEBUG if args.debug else logging.INFO)

    # Binary stdout (output data from device as-is)
    try: stdout_bin = sys.stdout.buffer
    except: stdout_bin = sys.stdout

    if args.serial_path:
        comm = FileCommunication(args.serial_path)
    else:
        if 'usb.core' not in sys.modules:
            raise RuntimeError("Please install PyUSB for USB support")
        comm = USBCommunication()

    with closing(comm):
        comm.reset()
        for command in get_commands(args.command):
            try:
                payload = command_to_payload(command)
                header, response = comm.call(payload)
                # For debugging, print header
                if command[0] == '!':
                    _logger.debug('Header: %s',
                            ' '.join(str(header[i:i+4]).replace("\\x00", "\\0")
                        for i in range(0, len(header), 4)))
                stdout_bin.write(response)
            except Exception as e:
                _logger.warn(e)
                if args.debug:
                    import traceback; traceback.print_exc()

if __name__ == '__main__':
    main()