#!/bin/python3

from PyPDF2 import PdfFileReader, PdfFileWriter
from PyPDF2.pdf import PageObject
import argparse

parser = argparse.ArgumentParser()
parser.add_argument('first', help='First file (first page becomes first page)')
parser.add_argument('second', help='Second file (first page becomes second page)')
parser.add_argument('output', nargs='?', help='Output file name (optional)')
args = parser.parse_args()

if args.output:
    output_file = args.output
else:
    output_file = args.first[:-4] + '_merged.pdf'

reader = PdfFileReader(open(args.first,'rb'))

sup_reader = PdfFileReader(open(args.second,'rb'))

writer = PdfFileWriter()

for pageNo in range(reader.getNumPages() + sup_reader.getNumPages()):
    if (pageNo < reader.getNumPages()):
        writer.addPage(reader.getPage(pageNo))
    if (pageNo < sup_reader.getNumPages()):
        writer.addPage(sup_reader.getPage(pageNo))

with open(output_file, 'wb') as f:
    writer.write(f)