#!/usr/bin/env python3
#
# Copyright (c) 2019-2020 Tilman Sauerbeck (tilman at code-monkey de)
#
# Permission is hereby granted, free of charge, to any person obtaining
# a copy of this software and associated documentation files (the
# "Software"), to deal in the Software without restriction, including
# without limitation the rights to use, copy, modify, merge, publish,
# distribute, sublicense, and/or sell copies of the Software, and to
# permit persons to whom the Software is furnished to do so, subject to
# the following conditions:
#
# The above copyright notice and this permission notice shall be
# included in all copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
# EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
# MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
# NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
# LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
# OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
# WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

import argparse
import serial
import struct
import sys

crc32_table = [
    0x00000000, 0x77073096, 0xee0e612c, 0x990951ba, 0x076dc419, 0x706af48f,
    0xe963a535, 0x9e6495a3, 0x0edb8832, 0x79dcb8a4, 0xe0d5e91e, 0x97d2d988,
    0x09b64c2b, 0x7eb17cbd, 0xe7b82d07, 0x90bf1d91, 0x1db71064, 0x6ab020f2,
    0xf3b97148, 0x84be41de, 0x1adad47d, 0x6ddde4eb, 0xf4d4b551, 0x83d385c7,
    0x136c9856, 0x646ba8c0, 0xfd62f97a, 0x8a65c9ec, 0x14015c4f, 0x63066cd9,
    0xfa0f3d63, 0x8d080df5, 0x3b6e20c8, 0x4c69105e, 0xd56041e4, 0xa2677172,
    0x3c03e4d1, 0x4b04d447, 0xd20d85fd, 0xa50ab56b, 0x35b5a8fa, 0x42b2986c,
    0xdbbbc9d6, 0xacbcf940, 0x32d86ce3, 0x45df5c75, 0xdcd60dcf, 0xabd13d59,
    0x26d930ac, 0x51de003a, 0xc8d75180, 0xbfd06116, 0x21b4f4b5, 0x56b3c423,
    0xcfba9599, 0xb8bda50f, 0x2802b89e, 0x5f058808, 0xc60cd9b2, 0xb10be924,
    0x2f6f7c87, 0x58684c11, 0xc1611dab, 0xb6662d3d, 0x76dc4190, 0x01db7106,
    0x98d220bc, 0xefd5102a, 0x71b18589, 0x06b6b51f, 0x9fbfe4a5, 0xe8b8d433,
    0x7807c9a2, 0x0f00f934, 0x9609a88e, 0xe10e9818, 0x7f6a0dbb, 0x086d3d2d,
    0x91646c97, 0xe6635c01, 0x6b6b51f4, 0x1c6c6162, 0x856530d8, 0xf262004e,
    0x6c0695ed, 0x1b01a57b, 0x8208f4c1, 0xf50fc457, 0x65b0d9c6, 0x12b7e950,
    0x8bbeb8ea, 0xfcb9887c, 0x62dd1ddf, 0x15da2d49, 0x8cd37cf3, 0xfbd44c65,
    0x4db26158, 0x3ab551ce, 0xa3bc0074, 0xd4bb30e2, 0x4adfa541, 0x3dd895d7,
    0xa4d1c46d, 0xd3d6f4fb, 0x4369e96a, 0x346ed9fc, 0xad678846, 0xda60b8d0,
    0x44042d73, 0x33031de5, 0xaa0a4c5f, 0xdd0d7cc9, 0x5005713c, 0x270241aa,
    0xbe0b1010, 0xc90c2086, 0x5768b525, 0x206f85b3, 0xb966d409, 0xce61e49f,
    0x5edef90e, 0x29d9c998, 0xb0d09822, 0xc7d7a8b4, 0x59b33d17, 0x2eb40d81,
    0xb7bd5c3b, 0xc0ba6cad, 0xedb88320, 0x9abfb3b6, 0x03b6e20c, 0x74b1d29a,
    0xead54739, 0x9dd277af, 0x04db2615, 0x73dc1683, 0xe3630b12, 0x94643b84,
    0x0d6d6a3e, 0x7a6a5aa8, 0xe40ecf0b, 0x9309ff9d, 0x0a00ae27, 0x7d079eb1,
    0xf00f9344, 0x8708a3d2, 0x1e01f268, 0x6906c2fe, 0xf762575d, 0x806567cb,
    0x196c3671, 0x6e6b06e7, 0xfed41b76, 0x89d32be0, 0x10da7a5a, 0x67dd4acc,
    0xf9b9df6f, 0x8ebeeff9, 0x17b7be43, 0x60b08ed5, 0xd6d6a3e8, 0xa1d1937e,
    0x38d8c2c4, 0x4fdff252, 0xd1bb67f1, 0xa6bc5767, 0x3fb506dd, 0x48b2364b,
    0xd80d2bda, 0xaf0a1b4c, 0x36034af6, 0x41047a60, 0xdf60efc3, 0xa867df55,
    0x316e8eef, 0x4669be79, 0xcb61b38c, 0xbc66831a, 0x256fd2a0, 0x5268e236,
    0xcc0c7795, 0xbb0b4703, 0x220216b9, 0x5505262f, 0xc5ba3bbe, 0xb2bd0b28,
    0x2bb45a92, 0x5cb36a04, 0xc2d7ffa7, 0xb5d0cf31, 0x2cd99e8b, 0x5bdeae1d,
    0x9b64c2b0, 0xec63f226, 0x756aa39c, 0x026d930a, 0x9c0906a9, 0xeb0e363f,
    0x72076785, 0x05005713, 0x95bf4a82, 0xe2b87a14, 0x7bb12bae, 0x0cb61b38,
    0x92d28e9b, 0xe5d5be0d, 0x7cdcefb7, 0x0bdbdf21, 0x86d3d2d4, 0xf1d4e242,
    0x68ddb3f8, 0x1fda836e, 0x81be16cd, 0xf6b9265b, 0x6fb077e1, 0x18b74777,
    0x88085ae6, 0xff0f6a70, 0x66063bca, 0x11010b5c, 0x8f659eff, 0xf862ae69,
    0x616bffd3, 0x166ccf45, 0xa00ae278, 0xd70dd2ee, 0x4e048354, 0x3903b3c2,
    0xa7672661, 0xd06016f7, 0x4969474d, 0x3e6e77db, 0xaed16a4a, 0xd9d65adc,
    0x40df0b66, 0x37d83bf0, 0xa9bcae53, 0xdebb9ec5, 0x47b2cf7f, 0x30b5ffe9,
    0xbdbdf21c, 0xcabac28a, 0x53b39330, 0x24b4a3a6, 0xbad03605, 0xcdd70693,
    0x54de5729, 0x23d967bf, 0xb3667a2e, 0xc4614ab8, 0x5d681b02, 0x2a6f2b94,
    0xb40bbe37, 0xc30c8ea1, 0x5a05df1b, 0x2d02ef8d
]

def crc32(buf):
    c = 0xffffffff

    for b in buf:
        c = crc32_table[(c & 0xff) ^ b] ^ (c >> 8)

    return c ^ 0xffffffff

class DummySerial():
    def __init__(self):
        pass

    def read(self, count):
        return b'\0' * count

    def write(self, buf):
        pass

    def flush(self):
        pass

class BootloaderError(Exception):
    def __init__(self, msg):
        super(BootloaderError, self).__init__(msg)

class UnknownCommand(BootloaderError):
    def __init__(self, command):
        msg = 'Command {} not recognized by target'.format(command)

        super(UnknownCommand, self).__init__(msg)

class InvalidArgument(BootloaderError):
    def __init__(self, command):
        msg = 'Target rejected arguments for command {}'.format(command)

        super(InvalidArgument, self).__init__(msg)

class ChecksumMismatch(BootloaderError):
    def __init__(self, command):
        msg = 'Target reported bad checksum for command {}'.format(command)

        super(ChecksumMismatch, self).__init__(msg)

class PermissionDenied(BootloaderError):
    def __init__(self, command):
        msg = 'Target reported permission denied for command {}'.format(command)

        super(PermissionDenied, self).__init__(msg)

class Command:
    def __init__(self, num, name):
        self._num = num
        self._name = name

    def __int__(self):
        return self._num

    def __str__(self):
        return self._name

class EraseCommand(Command):
    def __init__(self):
        super(EraseCommand, self).__init__(0x49e89a20, 'ERASE')

class ProgramCommand(Command):
    def __init__(self):
        super(ProgramCommand, self).__init__(0x37f7dc8d, 'PROGRAM')

class VerifyCommand(Command):
    def __init__(self):
        super(VerifyCommand, self).__init__(0x4a213efb, 'VERIFY')

class LoadChunkCommand(Command):
    def __init__(self):
        super(LoadChunkCommand, self).__init__(0x1b329768, 'LOAD_CHUNK')

class StartAppCommand(Command):
    def __init__(self):
        super(StartAppCommand, self).__init__(0xd27df1bf, 'START_APP')

class Application:
    SECTOR_SIZE = 1024
    MAX_NUM_CHUNKS = 256

    def __init__(self, args):
        self._last_command = None
        self._log_level = args.log_level

        if args.dry_run:
            self._serial = DummySerial()
        else:
            self._serial = serial.Serial(args.device, 115200)

        self._do_write = args.write
        self._do_verify = args.verify
        self._do_start = args.start

        self._filename = args.filename
        self._offset = args.offset

    def run(self):
        chunks = []

        if self._filename:
            with open(self._filename, 'rb') as f:
                while True:
                    chunk = f.read(Application.SECTOR_SIZE)

                    if len(chunk) == 0:
                        break

                    chunks.append(chunk)

            if len(chunks) > Application.MAX_NUM_CHUNKS:
                sys.stderr.write('File too large.\n')
                return 3

            # The bootloader only accepts chunks whose size is word-aligned:
            num_extra = len(chunks[-1]) & 3

            if num_extra != 0:
                num_pad = 4 - extra
                chunks[-1] += b'\xff' * num_pad

        # Defaulting to zero seems too dangerous:
        if self._offset is None:
            sector0 = None
        else:
            sector0 = self._offset // Application.SECTOR_SIZE

        try:
            return self._run(sector0, chunks)
        except BootloaderError as e:
            print(e)
            return 10

    def _run(self, sector0, chunks):
        if self._do_write:
            for i in range(len(chunks)):
                sector = sector0 + i

                # The bootloader will refuse to erase the second sector
                # as it contains the precious flash configuration field.
                if sector != 1:
                    self._erase(sector)

            # Write first sector last, to prevent the bootloader from
            # jumping to partially programmed code.
            for i, chunk in reversed(list(enumerate(chunks))):
                sector = sector0 + i

                if sector != 1:
                    self._load_chunk(chunk)
                    self._program(sector)

        num_verify_errors = 0

        if self._do_verify:
            for i, chunk in enumerate(chunks):
                sector = sector0 + i

                self._load_chunk(chunk)

                if not self._verify(sector):
                    self._log(0, 'Failed to verify sector {} contents.\n'.format(sector))

                    num_verify_errors += 1

        if self._do_start and num_verify_errors == 0:
            self._start_app()

        if num_verify_errors == 0:
            return 0
        else:
            return 9

    def _erase(self, sector):
        self._log(0, 'Erasing sector {}... '.format(sector))

        self._prepare_command(EraseCommand())
        self._serial.write(struct.pack('<L', sector))
        self._serial.flush()

        self._read_and_handle_error()

        self._log(0, 'OK\n')

    def _program(self, sector):
        self._log(0, 'Programming sector {}... '.format(sector))

        self._prepare_command(ProgramCommand())
        self._serial.write(struct.pack('<L', sector))
        self._serial.flush()

        self._read_and_handle_error()

        self._log(0, 'OK\n')

    def _load_chunk(self, chunk):
        self._log(3, 'Loading chunk of {} bytes... '.format(len(chunk)))

        self._prepare_command(LoadChunkCommand())
        self._serial.write(struct.pack('<L', len(chunk)))
        self._serial.flush()
        self._read_and_handle_error()

        self._serial.write(chunk)
        self._serial.write(struct.pack('<L', crc32(chunk)))
        self._serial.flush()
        self._read_and_handle_error()

        self._log(3, 'OK\n')

    def _verify(self, sector):
        self._log(0, 'Verifying sector {}... '.format(sector))

        self._prepare_command(VerifyCommand())
        self._serial.write(struct.pack('<L', sector))
        self._serial.flush()
        self._read_and_handle_error()

        response = self._serial.read(8)
        num_mismatches, first_mismatch = struct.unpack('<LL', response)

        if num_mismatches == 0:
            self._log(0, 'OK\n')

            return True

        self._log(0, 'FAILED\n')
        self._log(0, 'Found {} mismatches. first one at 0x{:x}.\n'.format(num_mismatches, first_mismatch))

        return False

    def _start_app(self):
        self._log(0, 'Starting application... ')

        self._prepare_command(StartAppCommand())
        self._serial.flush()
        self._read_and_handle_error()

        self._log(0, 'OK\n')

    def _prepare_command(self, command):
        self._last_command = command

        self._serial.write(struct.pack('<L', int(command)))

    def _read_and_handle_error(self):
        error_response = self._serial.read(1)
        e, = struct.unpack('<B', error_response)

        if e == 0:
            return

        if e == 1:
            raise UnknownCommand(self._last_command)
        elif e == 2:
            raise InvalidArgument(self._last_command)
        elif e == 3:
            raise ChecksumMismatch(self._last_command)
        elif e == 4:
            raise PermissionDenied(self._last_command)
        else:
            msg = 'Target reported some other error for {}'.format(self._last_command)

            raise BootloaderError(msg)

    def _log(self, required_log_level, s):
        if self._log_level >= required_log_level:
            sys.stdout.write(s)
            sys.stdout.flush()

def offset(s):
    o = int(s, 0)

    if (o & (Application.SECTOR_SIZE - 1)) != 0:
        msg = 'offset needs to be multiple of {}'.format(Application.SECTOR_SIZE)

        raise argparse.ArgumentTypeError(msg)

    return o

if __name__ == '__main__':
    parser = argparse.ArgumentParser(description='Flash GPS watch firmware')

    parser.add_argument('-d', '--device', type=str, required=True)
    parser.add_argument('-o', '--offset', type=offset, default=None)
    parser.add_argument('-n', '--dry-run', action='store_true')
    parser.add_argument('-l', '--log-level', type=int, default=0)
    parser.add_argument('-w', '--write', action='store_true')
    parser.add_argument('-v', '--verify', action='store_true')
    parser.add_argument('-s', '--start', action='store_true')
    parser.add_argument('filename', type=str, nargs='?', default=None)

    args = parser.parse_args()

    if not args.write and not args.verify and not args.start:
        parser.error('one or more of the following arguments are required: ' +
                     '-w/--write, -v/--verify, -s/--start')

    if args.filename is None:
        if args.write:
            parser.error('argument -w/--write: expected one argument')
        elif args.verify:
            parser.error('argument -v/--verify: expected one argument')

    if args.offset is None:
        if args.write or args.verify:
            parser.error('the following arguments are required: -o/--offset')

    sys.exit(Application(args).run())