#!/usr/bin/env python3
# -*- coding: utf-8 -*-

# To use python v2.7 change the first line to:
#!/usr/bin/env python

# Copyright (C) 2015 Bernhard Ehlers
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 2 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.

"""
iou_import imports startup/private configuration into IOU NVRAM file.

usage: iou_import [-h] [-c size] NVRAM startup-config [private-config]

positional arguments:
  NVRAM                 NVRAM file
  startup-config        startup configuration
  private-config        private configuration

optional arguments:
  -h, --help            show this help message and exit
  -c size, --create size
                        create NVRAM file, size in kByte
"""

import struct


# calculate padding
def padding(length, start_address):
    pad = -length % 4                   # padding to alignment of 4
    # extra padding if pad != 0 and big start_address
    if pad != 0 and (start_address & 0x80000000) != 0:
        pad += 4
    return pad


# update checksum
def checksum(data, start, end):
    chk = 0
    # calculate checksum of first two words
    for word in struct.unpack_from('>2H', data, start):
        chk += word

    # add remaining words, ignoring old checksum at offset 4
    struct_format = '>{:d}H'.format((end - start - 6) // 2)
    for word in struct.unpack_from(struct_format, data, start+6):
        chk += word

    # handle 16 bit overflow
    while chk >> 16:
        chk = (chk & 0xffff) + (chk >> 16)
    chk = chk ^ 0xffff

    # save checksum
    struct.pack_into('>H', data, start+4, chk)


# import IOU NVRAM
# NVRAM format: https://github.com/ehlers/IOUtools/blob/master/NVRAM.md
def nvram_import(nvram, startup, private, size):
    DEFAULT_IOS  = 0x0F04               # IOS 15.4
    base_address = 0x10000000

    # check size parameter
    if size is not None and (size < 8 or size > 1024):
        raise ValueError('invalid size')

    # create new nvram if nvram is empty or has wrong size
    if nvram is None or (size is not None and len(nvram) != size*1024):
        nvram = bytearray([0] * (size*1024))
    else:
        nvram = bytearray(nvram)

    # check nvram size
    nvram_len = len(nvram)
    if nvram_len < 8*1024 or nvram_len > 1024*1024 or nvram_len % 1024 != 0:
        raise ValueError('invalid NVRAM length')
    nvram_len = nvram_len // 2

    # get size of current config
    config_len = 0
    try:
        (magic, _, _, ios, start_addr, _, length, _, _, _, _, _) = \
            struct.unpack_from('>HHHHIIIIIHHI', nvram, offset=0)
        if magic == 0xABCD:
            base_address = start_addr - 36
            config_len = 36 + length + padding(length, base_address)
            (magic, _, _, _, length) = \
                struct.unpack_from('>HHIII', nvram, offset=config_len)
            if magic == 0xFEDC:
                config_len += 16 + length
        else:
            ios = None
    except struct.error:
        raise ValueError('unknown nvram format')
    if config_len > nvram_len:
        raise ValueError('unknown nvram format')

    # calculate max. config size
    max_config = nvram_len - 2*1024             # reserve 2k for files
    idx = max_config
    empty_sector = bytearray([0] * 1024)
    while True:
        idx -= 1024
        if idx < config_len:
            break
        # if valid file header:
        (magic, _, flags, length, _) = \
            struct.unpack_from('>HHHH24s', nvram, offset=idx)
        if magic == 0xDCBA and flags < 8 and length <= 992:
            max_config = idx
        elif nvram[idx:idx+1024] != empty_sector:
            break

    # import startup config
    new_nvram = bytearray()
    if ios is None:
        # Target IOS version is unknown. As some IOU don't work nicely with
        # the padding of a different version, the startup config is padded
        # with '\n' to the alignment of 4.
        ios = DEFAULT_IOS
        startup += b'\n' * (-len(startup) % 4)
    new_nvram.extend(struct.pack('>HHHHIIIIIHHI',
        0xABCD,                             # magic
        1,                                  # raw data
        0,                                  # checksum, not yet calculated
        ios,                                # IOS version
        base_address + 36,                  # start address
        base_address + 36 + len(startup),   # end address
        len(startup),                       # length
        0, 0, 0, 0, 0))
    new_nvram.extend(startup)
    new_nvram.extend([0] * padding(len(new_nvram), base_address))

    # import private config
    if private is None:
        private = b''
    offset = len(new_nvram)
    new_nvram.extend(struct.pack('>HHIII',
        0xFEDC,                             # magic
        1,                                  # raw data
        base_address + offset + 16,         # start address
        base_address + offset + 16 + len(private),  # end address
        len(private) ))                     # length
    new_nvram.extend(private)

    # add rest
    if len(new_nvram) > max_config:
        raise ValueError('NVRAM size too small')
    new_nvram.extend([0] * (max_config - len(new_nvram)))
    new_nvram.extend(nvram[max_config:])

    checksum(new_nvram, 0, nvram_len)

    return new_nvram


if __name__ == '__main__':
    # Main program
    import argparse
    import sys

    def check_size(string):
        try:
            value = int(string)
        except ValueError:
            raise argparse.ArgumentTypeError('invalid int value: ' + string)
        if value < 8 or value > 1024:
            raise argparse.ArgumentTypeError('size must be 8..1024')
        return value

    parser = argparse.ArgumentParser(description='%(prog)s imports startup/private configuration into IOU NVRAM file.')
    parser.add_argument('-c', '--create', metavar='size', type=check_size,
                        help='create NVRAM file, size in kByte')
    parser.add_argument('nvram', metavar='NVRAM',
                        help='NVRAM file')
    parser.add_argument('startup', metavar='startup-config',
                        help='startup configuration')
    parser.add_argument('private', metavar='private-config', nargs='?',
                        help='private configuration')
    args = parser.parse_args()

    try:
        if args.create is None:
            fd = open(args.nvram, 'rb')
            nvram = fd.read()
            fd.close()
        else:
            nvram = None
        fd = open(args.startup, 'rb')
        startup = fd.read()
        fd.close()
        if args.private is None:
            private = None
        else:
            fd = open(args.private, 'rb')
            private = fd.read()
            fd.close()
    except (IOError, OSError) as err:
        sys.stderr.write("Error reading file: {}\n".format(err))
        sys.exit(1)

    try:
        nvram = nvram_import(nvram, startup, private, args.create)
    except ValueError as err:
        sys.stderr.write("nvram_import: {}\n".format(err))
        sys.exit(3)

    try:
        fd = open(args.nvram, 'wb')
        fd.write(nvram)
        fd.close()
    except (IOError, OSError) as err:
        sys.stderr.write("Error writing file: {}\n".format(err))
        sys.exit(1)