#!/usr/bin/env python3

# Copyright:
#   Yclept Nemo 
#       2016
#       pscjtwjdjtAhnbjm/dpn
# License:
#   GPLv3

import itertools
import argparse
import PyPDF2


def grouper(iterable, n, fillvalue=None):
    "Collect data into fixed-length chunks or blocks"
    # grouper('ABCDEFG', 3, 'x') --> ABC DEF Gxx"
    args = [iter(iterable)] * n
    return itertools.zip_longest(*args, fillvalue=fillvalue)

def pdf_page_size(page):
    return  ( page.mediaBox.lowerRight[0] - page.mediaBox.lowerLeft[0]
            , page.mediaBox.upperRight[1] - page.mediaBox.lowerRight[1]
            )

parser = argparse.ArgumentParser(description='Impose PDF files')
parser.add_argument("source", help="PDF, source path", type=argparse.FileType("rb"))
parser.add_argument("output", help="PDF, output path", type=argparse.FileType("wb"))
parser.add_argument("-s", "--spacer", help="PDF, spacer path", type=argparse.FileType("rb"))

args = parser.parse_args()

source = PyPDF2.PdfFileReader(args.source)
output = PyPDF2.PdfFileWriter()

spacer_page = None
spacer_size = [0,0]

if args.spacer is not None:
    spacer = PyPDF2.PdfFileReader(args.spacer)
    if spacer.getNumPages():
        spacer_page = spacer.getPage(0)
        spacer_size = pdf_page_size(spacer_page)

if source.getNumPages():
    output.addPage(source.getPage(0))

for i in grouper(range(1, source.getNumPages()), 2):
    pages = [None if j is None else source.getPage(j) for j in i]
    sizes = [(0,0) if j is None else pdf_page_size(j) for j in pages]
    out_size = [ sum(j[0] for j in sizes)
               , max(j[1] for j in sizes)
               ]
    if pages[1] is not None and spacer_page is not None:
        out_size[0] += spacer_size[0]
    out_page = output.addBlankPage(*out_size)
    out_page.mergePage(pages[0])
    if pages[1] is not None:
        offset = sizes[0][0]
        if spacer_page is not None:
            out_page.mergeTranslatedPage(spacer_page, offset, 0, True)
            offset += spacer_size[0]
        out_page.mergeTranslatedPage(pages[1], offset, 0, True)

output.addMetadata(source.getDocumentInfo())

output.write(args.output)

args.output.close()