Plugin that edits a PDF in the library

[HebrewReader]

Hi,

I have an idea for a plugin but I'm not sure I know which type of plugin this should be.

The problem:
I have many pdf books which have no cover.

I would like to add a cover image to the pdf file itself. The cover could be taken from Calibre's metadata for that book.

Would it be possible to write some plugin that would do all this? I was not able to find a way for a plugin to alter the book file itself.

[kovidgoyal]

Sure you make an interface plugin. Then when you click it the plugin can iterate over all the selected books, find the PDF files and do whatever it likes with them.

[HebrewReader]

Great, thanks.

[HebrewReader]

Another question:

I have working python code for inserting a cover page from an image to a pdf.
However it uses 3rd-party libraries, namely pypdf and reportlab.
I know I can add them to my plugin, but if Calibre's existing code could handle this already, I'd rather make my plugin leaner and use it instead.

So can someone here guide me on if and how to use Calibre's pdf modules?

Here's my existing code for reference:

import pypdf
from reportlab.pdfgen import canvas
from reportlab.lib.utils import ImageReader

def generate_cover_pdf_stream(
        cover_url: str,
        main_pdf_reader: pypdf.PdfReader) -> io.BytesIO:
    cover_pdf_stream = io.BytesIO()
    sample_page = main_pdf_reader.pages[0]
    cover_image = ImageReader(cover_url)
    image_canvas = canvas.Canvas(cover_pdf_stream,
                                 pagesize=(sample_page.mediabox.width, sample_page.mediabox.height),
                                 cropBox=sample_page.cropbox,
                                 artBox=sample_page.artbox,
                                 trimBox=sample_page.trimbox)
    image_canvas.drawImage(cover_image,
                           x=float(sample_page.trimbox.left),
                           y=float(sample_page.trimbox.bottom),
                           width=float(sample_page.trimbox.width),
                           height=float(sample_page.trimbox.height))
    image_canvas.showPage()
    image_canvas.save()
    return cover_pdf_stream


def add_cover(filename_or_stream: str | IO | Path,
              cover_url: str,
              out_filename_or_stream: Path | str | IO):
    reader = pypdf.PdfReader(filename_or_stream)
    merger = pypdf.PdfMerger()

    cover_pdf_stream = generate_cover_pdf_stream(cover_url, reader)
    merger.append(cover_pdf_stream)
    merger.append(reader.stream)

    merger.write(out_filename_or_stream)

Thanks!

[kovidgoyal]

The podofo module in calibre has the ability to insert a page from one PDF file into another. So you create your image page using the functions in pdf/image_writer.py and then do the insert by creating two podofo PDFDoc objects and using the insert_existing_page method. See the add_cover function in pdf/html_writer.py for an example.

[RelUnrelated]

Originally Posted by HebrewReader

Another question:

I have working python code for inserting a cover page from an image to a pdf.
However it uses 3rd-party libraries, namely pypdf and reportlab.

I've got a shell script that I use in Linux to add the cover image as a page to the front of a PDF. Page numbering is a secondary issue that I've run into, but I'm learning more about PDF structure as I dive into it. I'll have to take a look at the podofo options to see what might work best.