"""Markdown (.md / .markdown) -> PDF.

Rendered with the `markdown` library (tables, fenced code, nl2br) and
typeset by WeasyPrint with app.BASE_CSS injected at the top of <head> so
the fallback layer sits under any user CSS. The first ATX H1 becomes the
export name and PDF /Title (it stays in the rendered document for visual
fidelity); without an H1 the file stem is used.

Empty input renders 0 pages and fails in finalize with
"no renderable content: ..." — unpinned, acceptable.
"""
from __future__ import annotations

import re
from pathlib import Path

from . import common

_FIRST_H1_RE = re.compile(r"^\s*#\s+(.+?)\s*#*\s*$", re.MULTILINE)


def _extract_h1(md_text: str) -> str | None:
    m = _FIRST_H1_RE.search(md_text)
    if not m:
        return None
    title = re.sub(r"[#*`_]", "", m.group(1))
    title = " ".join(title.split())
    return title or None


def convert(path: Path, job_id: str, progress_cb=None, output_dir=None,
            source_name=None) -> str:
    """Render a Markdown file to a typeset PDF."""
    import app  # lazy: BASE_CSS lives with the EPUB pipeline
    import markdown

    text = common.decode_text(path.read_bytes())
    title = _extract_h1(text)
    body_html = markdown.markdown(
        text, extensions=["tables", "fenced_code", "nl2br"]
    )
    html_doc = (
        f"<!DOCTYPE html><html><head><style>\n{app.BASE_CSS}\n</style>"
        f"</head><body>{body_html}</body></html>"
    )

    def _build():
        return html_doc, path.name

    return common.convert_single(
        path, job_id, build_html=_build, title=title, css="",
        progress_cb=progress_cb, output_dir=output_dir,
        name_src=source_name or path.name,
    )