#!/usr/bin/python3

default_block_size = 512

def slice_file(source_filename, dest_filename, slice_from, slice_to, block):
    f_in = open(source_filename, 'rb')
    f_out = open(dest_filename, 'wb')
    read_count = 0
    eof = False
    import random
    random.seed()
    while not eof:
        read = f_in.read(block)
        if(len(read) < block): eof = True
        if(read_count < slice_from or read_count >= slice_to):
            f_out.write(read)
        else:
            for i in range(block):
                f_out.write(bytes(chr(random.randint(0,127)), encoding = 'utf-8'))
        read_count += block
    f_in.close()
    f_out.close()


if __name__ == '__main__':
    import sys
    if(len(sys.argv) < 3):
        print('missing arguments:')
        print(sys.argv[0] + ' source_filename dest_filename [slicing_starts_from slicing_length [block_size]]')
        quit()
    source_filename = sys.argv[1]
    dest_filename = sys.argv[2]
    if(len(sys.argv) < 4):
        slice_from = int(input('slicing starts from: '))
        slice_to = slice_from + int(input('slicing length: '))
    else:
        slice_from = int(sys.argv[3])
        slice_to = int(sys.argv[3]) + int(sys.argv[4])
    if(len(sys.argv) >= 6):
        block = int(sys.argv[6])
    else: block = default_block_size
    slice_file(source_filename, dest_filename, slice_from, slice_to, block)