Prototype reader for Greencard (TAS) card dumps.

greencard_reader.py

#!/usr/bin/env python
# -*- mode: python; indent-tabs-mode: nil; tab-width: 2 -*-
"""
greencard_reader.py
Prototype reader for Greencard (TAS) card dumps.
See https://github.com/micolous/metrodroid/wiki/Greencard for format details.

Copyright 2017 Michael Farrell <[email protected]>

Note: This loads the entire file into memory blindly.  Do not use on large file
sizes, as the memory usage of this file is extremely inefficient.

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 3 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/>.
"""

from __future__ import print_function
from argparse import ArgumentParser, FileType
from struct import unpack
from datetime import datetime, timedelta
from pytz import utc, timezone

EPOCH = utc.localize(datetime(1970,1,1,0,0))
HOBART_TZ = timezone('Australia/Hobart')

def parse_greencard(input_data):
  if len(input_data) != 4096:
    raise Exception, 'mfc data must be exactly 4096 bytes'

  # TODO: read the other headers

  # Read trips
  off = 0x800
  while off < 0xcf0:
    if off % 0x100 >= 0xf0:
      # This is a key, skip it
      off += 0x10
      continue
      
    record_type = unpack('>L', input_data[off:off+0x4])[0]
    
    if record_type & 0xffff00 != 0x011000:
      # We wanted a record header.
      off += 0x10
      continue
      
    is_credit = (record_type & 0xff000000) == 0x31000000

    # Get the timestamp for the transaction
    ts = unpack('>L', input_data[off+0xc:off+0x10])[0]
    ts = (EPOCH + timedelta(seconds=ts)).astimezone(HOBART_TZ)
    
    txn_no, unknown_14, route = unpack('>LL2x6s', input_data[off+0x10:off+0x20])
    route = route.strip('\0')
    
    if is_credit:
      new_balance = unpack('>L', input_data[off+0x26:off+0x2a])[0]
      amount = 0.
    else:
      amount, new_balance = unpack('>H4xL', input_data[off+0x22:off+0x2c])
    
    print('@0x%03x : %s' % (off, ts.isoformat()))
    print('record type = %08x (%s)' % (record_type, 'credit' if is_credit else 'trip'))
    print('    txn num = %i' % txn_no)
    print(' unknown 14 = %i' % unknown_14)
    print('  bus route = Route %s' % route)
    print('      value = $%0.2f (new balance $%0.2f)' % (amount/100., new_balance/100.))
    print()      
    
    off += 0x50

  

def main():
  parser = ArgumentParser()
  parser.add_argument('input', type=FileType('rb'), nargs=1)
  options = parser.parse_args()
  parse_greencard(options.input[0].read())

if __name__ == '__main__':
  main()