#!/usr/bin/env python2

import sys
import mmap

ext4Magic = '\x53\xEF'
ext4MagicOffset = 1080

if len(sys.argv) < 2:
    print("No I/O supplied")
    exit(1)

def copyExt4Image(origin, offset, size, dest):
    with open(origin, 'r') as input:
        with open(dest, 'w') as output:
            input.seek(offset - ext4MagicOffset)
            output.write(input.read(size + ext4MagicOffset))

def findMagics(input):
    magics = [0]
    with open(input, 'r+b') as f:
        mm = mmap.mmap(f.fileno(), 0)
        while magics[-1] != -1:
            magics.append(mm.find(ext4Magic, magics[-1] + ext4MagicOffset))
    return magics

systemimg = sys.argv[1]
offsets = findMagics(systemimg)
if len(offsets[1:]) != 0:
    for num, offset in enumerate(offsets[1:], start=1):
        print('ext4 magic number found at byte %d' % offset)
        name = "{}_part{}.img".format(systemimg, num)
        print('Creating {}...'.format(name))
        copyExt4Image(systemimg, offset, offsets[num + 1] - offset, name)
else:
    print("Not ext4 images found")