#!/usr/bin/env python3
# SPDX-License-Identifier: GPL-2.0-only
# Copyright (C) Akira Yokosawa, 2024
#
# Ported to Python by (c) Mauro Carvalho Chehab, 2025
#
# For "make pdfdocs", reports of build errors of translations.pdf started
# arriving early 2024 [1, 2].  It turned out that Fedora and openSUSE
# tumbleweed have started deploying variable-font [3] format of "Noto CJK"
# fonts [4, 5].  For PDF, a LaTeX package named xeCJK is used for CJK
# (Chinese, Japanese, Korean) pages.  xeCJK requires XeLaTeX/XeTeX, which
# does not (and likely never will) understand variable fonts for historical
# reasons.
#
# The build error happens even when both of variable- and non-variable-format
# fonts are found on the build system.  To make matters worse, Fedora enlists
# variable "Noto CJK" fonts in the requirements of langpacks-ja, -ko, -zh_CN,
# -zh_TW, etc.  Hence developers who have interest in CJK pages are more
# likely to encounter the build errors.
#
# This script is invoked from the error path of "make pdfdocs" and emits
# suggestions if variable-font files of "Noto CJK" fonts are in the list of
# fonts accessible from XeTeX.
#
# References:
# [1]: https://lore.kernel.org/r/8734tqsrt7.fsf@meer.lwn.net/
# [2]: https://lore.kernel.org/r/1708585803.600323099@f111.i.mail.ru/
# [3]: https://en.wikipedia.org/wiki/Variable_font
# [4]: https://fedoraproject.org/wiki/Changes/Noto_CJK_Variable_Fonts
# [5]: https://build.opensuse.org/request/show/1157217
#
#===========================================================================
# Workarounds for building translations.pdf
#===========================================================================
#
# * Denylist "variable font" Noto CJK fonts.
#   - Create $HOME/deny-vf/fontconfig/fonts.conf from template below, with
#     tweaks if necessary.  Remove leading "# ".
#   - Path of fontconfig/fonts.conf can be overridden by setting an env
#     variable FONTS_CONF_DENY_VF.
#
#     * Template:
# -----------------------------------------------------------------
# <?xml version="1.0"?>
# <!DOCTYPE fontconfig SYSTEM "urn:fontconfig:fonts.dtd">
# <fontconfig>
# <!--
#   Ignore variable-font glob (not to break xetex)
# -->
#     <selectfont>
#         <rejectfont>
#             <!--
#                 for Fedora
#             -->
#             <glob>/usr/share/fonts/google-noto-*-cjk-vf-fonts</glob>
#             <!--
#                 for openSUSE tumbleweed
#             -->
#             <glob>/usr/share/fonts/truetype/Noto*CJK*-VF.otf</glob>
#         </rejectfont>
#     </selectfont>
# </fontconfig>
# -----------------------------------------------------------------
#
#     The denylisting is activated for "make pdfdocs".
#
# * For skipping CJK pages in PDF
#   - Uninstall texlive-xecjk.
#     Denylisting is not needed in this case.
#
# * For printing CJK pages in PDF
#   - Need non-variable "Noto CJK" fonts.
#     * Fedora
#       - google-noto-sans-cjk-fonts
#       - google-noto-serif-cjk-fonts
#     * openSUSE tumbleweed
#       - Non-variable "Noto CJK" fonts are not available as distro packages
#         as of April, 2024.  Fetch a set of font files from upstream Noto
#         CJK Font released at:
#           https://github.com/notofonts/noto-cjk/tree/main/Sans#super-otc
#         and at:
#           https://github.com/notofonts/noto-cjk/tree/main/Serif#super-otc
#         , then uncompress and deploy them.
#       - Remember to update fontconfig cache by running fc-cache.
#
# !!! Caution !!!
#     Uninstalling "variable font" packages can be dangerous.
#     They might be depended upon by other packages important for your work.
#     Denylisting should be less invasive, as it is effective only while
#     XeLaTeX runs in "make pdfdocs".

import os
import re
import subprocess
import sys
import textwrap

class LatexFontChecker:
    """
    Detect problems with CJK variable fonts that affect PDF builds for
    translations.
    """

    def __init__(self):
        deny_vf = os.environ.get('FONTS_CONF_DENY_VF', "~/deny-vf")

        self.environ = os.environ.copy()
        self.environ['XDG_CONFIG_HOME'] = os.path.expanduser(deny_vf)

        self.re_cjk = re.compile(r"([^:]+):\s*Noto\s+(Sans|Sans Mono|Serif) CJK")

    def get_noto_cjk_vf_fonts(self):
        """Get Noto CJK fonts"""

        cjk_fonts = set()
        cmd = ["fc-list", ":", "file", "family", "variable"]
        try:
            result = subprocess.run(cmd,stdout=subprocess.PIPE,
                                    stderr=subprocess.PIPE,
                                    universal_newlines=True,
                                    env=self.environ,
                                    check=True)

        except subprocess.CalledProcessError as exc:
            sys.exit(f"Error running fc-list: {repr(exc)}")

        for line in result.stdout.splitlines():
            if 'variable=True' not in line:
                continue

            match = self.re_cjk.search(line)
            if match:
                cjk_fonts.add(match.group(1))

        return sorted(cjk_fonts)

    def check(self):
        """Check for problems with CJK fonts"""

        fonts = textwrap.indent("\n".join(self.get_noto_cjk_vf_fonts()), "    ")
        if not fonts:
            return None

        rel_file = os.path.relpath(__file__, os.getcwd())

        msg = "=" * 77 + "\n"
        msg += 'XeTeX is confused by "variable font" files listed below:\n'
        msg += fonts + "\n"
        msg += textwrap.dedent(f"""
                For CJK pages in PDF, they need to be hidden from XeTeX by denylisting.
                Or, CJK pages can be skipped by uninstalling texlive-xecjk.

                For more info on denylisting, other options, and variable font, see header
                comments of {rel_file}.
            """)
        msg += "=" * 77

        return msg

if __name__ == "__main__":
    msg = LatexFontChecker().check()
    if msg:
        print(msg)

    sys.exit(1)