"""
Rozlozi naskenovanou brozuru do PDF se strankami razenymi od 1.

Predpoklady:
  - Kazda PDF stranka obsahuje dve stranky brozury vedle sebe (leva + prava).
  - Sken probíhal duplexne od stredoveho listu smerem ven.
  - Stredove stranky se odvodi automaticky z poctu PDF stranek.

Pouziti:
  python rozloz_brozuru.py <vstup.pdf> [vystup.pdf]
"""

import sys
import copy
from pypdf import PdfReader, PdfWriter
from pypdf.generic import RectangleObject


def rozloz(input_path, output_path):
    reader = PdfReader(input_path)
    n_pdf = len(reader.pages)

    center_left  = n_pdf           # napr. 12 nebo 40
    center_right = n_pdf + 1       # napr. 13 nebo 41
    total_pages  = n_pdf * 2       # celkovy pocet stran brozury

    print(f"PDF stranek : {n_pdf}")
    print(f"Stran brozury: {total_pages}  (stred: {center_left}+{center_right})")

    # Mapovani: brozurova strana -> (pdf_idx 0-based, 'L'/'P')
    page_map = {}
    n_sheets = n_pdf // 2

    for k in range(n_sheets):
        front_pdf = 2 * k
        back_pdf  = 2 * k + 1

        page_map[center_left  - 2 * k]     = (front_pdf, 'L')
        page_map[center_right + 2 * k]     = (front_pdf, 'P')
        page_map[center_right + 2 * k + 1] = (back_pdf,  'L')
        page_map[center_left  - 2 * k - 1] = (back_pdf,  'P')

    writer = PdfWriter()

    for bp in range(1, total_pages + 1):
        pdf_idx, lr = page_map[bp]
        src = reader.pages[pdf_idx]

        width  = float(src.mediabox.width)
        height = float(src.mediabox.height)
        half_w = width / 2

        new_page = copy.copy(src)
        if lr == 'L':
            box = RectangleObject([0,      0, half_w, height])
        else:
            box = RectangleObject([half_w, 0, width,  height])
        new_page.mediabox = box
        new_page.cropbox  = box

        writer.add_page(new_page)

    with open(output_path, "wb") as f:
        writer.write(f)

    print(f"Hotovo: {output_path}  ({total_pages} stranek)")


if __name__ == "__main__":
    if len(sys.argv) < 2:
        print("Pouziti: python rozloz_brozuru.py <vstup.pdf> [vystup.pdf]")
        sys.exit(1)

    inp = sys.argv[1]
    out = sys.argv[2] if len(sys.argv) > 2 else inp.replace(".pdf", "_serazena.pdf")
    rozloz(inp, out)