fix-pdftitle.py

#!/usr/bin/env python
# file: fix-pdftitle.py
# vim:fileencoding=utf-8:ft=python
#
# Copyright © 2017-2018 R.F. Smith <rsmith@xs4all.nl>.
# SPDX-License-Identifier: MIT
# Created: 2017-04-11T16:17:26+02:00
# Last modified: 2022-08-18T14:36:43+0200
"""
Fix PDF file titles.

Decrypt PDF safety data sheets and fix the title to match the filename.
This is done to make sure that the reader app on a tablet displays a sensible title.
"""

from collections import defaultdict
from datetime import datetime
import argparse
import logging
import os
import shutil
import subprocess as sp
import sys
import tempfile

__version__ = "2022.08.18"


def main():
    args = setup()
    tdir = tempfile.mkdtemp()
    for path in args.files:
        logging.debug(f"processing “{path}”")
        info = pdfinfo(path)
        if len(info) == 0:
            logging.error(f"skipping “{path}”; could not retrieve info dict")
            continue
        fn = os.path.basename(path)
        if info["Encrypted"].startswith("yes"):
            logging.info(f"“{path}” is encrypted")
            rv = decrypt(path, fn, tdir)
            if rv != 0:
                logging.error(f"could not decrypt “{path}”; qpdf returned {rv}")
                continue
            logging.debug(f"“{path}” decrypted")
        else:
            logging.debug(f"“{path}” is not encrypted")
        newtitle = fn.replace("_", " ")[:-4]
        if info["Title"] != newtitle:
            set_title(path, fn, tdir, newtitle)
        else:
            logging.debug(f"the title of “{path}” does not need to be changed")
    shutil.rmtree(tdir)


def setup():
    parser = argparse.ArgumentParser(description=__doc__)
    parser.add_argument(
        "--log",
        default="info",
        choices=["debug", "info", "warning", "error"],
        help="logging level (defaults to “info”)",
    )
    parser.add_argument("-v", "--version", action="version", version=__version__)
    parser.add_argument(
        "files", metavar="file", nargs="+", help="one or more files to process"
    )
    args = parser.parse_args(sys.argv[1:])
    logging.basicConfig(
        level=getattr(logging, args.log.upper(), None),
        format="%(levelname)s: %(message)s",
    )
    if args.log == "debug":
        logging.debug("using verbose logging")
    # Look for required programs.
    try:
        for prog in (["pdfinfo"], ["gs", "-v"], ["qpdf"]):
            sp.run(prog, stdout=sp.DEVNULL, stderr=sp.DEVNULL)
            logging.debug(f"found “{prog}”")
    except FileNotFoundError:
        logging.error("required program “{prog}” not found")
        sys.exit(1)
    return args


def pdfinfo(path):
    """
    Retrieves the contents of the ‘info’ dictionary from a PDF file using
    the ``pdfinfo`` program.

    Arguments:
        path (str): The path to the PDF file to use.

    Returns:
        A collections.defaultdict containing the info dictionary. Using a
        non-existing key will return an empty string.
    """
    args = ["pdfinfo", path]
    cp = sp.run(args, stdout=sp.PIPE, stderr=sp.DEVNULL, text=True)
    if cp.returncode != 0:
        return defaultdict(lambda: "")
    pairs = [
        (k, v.strip())
        for k, v in [ln.split(":", 1) for ln in cp.stdout.splitlines() if ln]
    ]
    return defaultdict(lambda: "", pairs)


def decrypt(path, fn, tempdir):
    """
    Decrypt a PDF file using ``qpdf``.

    Arguments:
        path (str): Path to the file to decrypt.
        fn (str): Only the name of the file to decrypt.
        tempdir (str): Location of temporary directory to use.

    Returns:
        The return value of the ``qpdf`` call; 0 when succesfull.
    """
    tmppath = tempdir + os.sep + fn
    args = ["qpdf", "--decrypt", path, tmppath]
    rv = sp.run(args, stdout=sp.DEVNULL, stderr=sp.DEVNULL)
    if rv.returncode == 0:
        os.remove(path)
        shutil.copyfile(tmppath, path)
    os.remove(tmppath)
    return rv.returncode


def set_title(path, fn, tempdir, newtitle):
    """
    Change the title of a PDF file.

    Arguments:
        path (str): Path to the file to change.
        fn (str): Only the name of the file to change.
        tempdir (str): Location of temporary directory to use.
        newtitle (str): New title to set.
    """
    orig = os.getcwd()
    os.chdir(tempdir)
    with open("pdfmarks", "w") as marksfile:
        marks = f"[ /Title ({newtitle})\n  /ModDate ({datetime.now():%Y%m%d%H%M%z})\n  /DOCINFO pdfmark"
        marksfile.write(marks)
        logging.debug(marks)
    args = [
        "gs",
        "-q",
        "-dBATCH",
        "-dNOPAUSE",
        "-sDEVICE=pdfwrite",
        "-sOutputFile=withmarks.pdf",
        orig + os.sep + path,
        "pdfmarks",
    ]
    logging.debug(args)
    rv = sp.run(args, stdout=sp.DEVNULL, stderr=sp.PIPE)
    os.remove("pdfmarks")
    os.chdir(orig)
    if rv.returncode != 0:
        os.remove(tempdir + os.sep + "withmarks.pdf")
        logging.debug(rv.stderr)
        logging.error(
            f"could not change title of “{path}”; ghostscript returned {rv.returncode}"
        )
    else:
        try:
            os.remove(path)
            shutil.copy(tempdir + os.sep + "withmarks.pdf", path)
            logging.info(f"title of “{path}” changed")
        except OSError as e:
            logging.error(f"could not rename withmarks.pdf to “{path}”: {e}")


if __name__ == "__main__":
    main()