"""A tiny, safe Markdown subset → HTML, for admin feedback replies.

Everything is HTML-escaped FIRST, then a small whitelist of structures is
introduced: bold (**…**), bullet lists (- / *), headings (#/##/###),
paragraphs, and line breaks. No links, no attributes, no inline styles, no raw
HTML passthrough — so the output is safe to render and to email. Authored only
by admins, but sanitized on principle regardless.
"""

from __future__ import annotations

import html
import re

_BULLET_RE = re.compile(r"^\s*[-*]\s+")
_HEADING_RE = re.compile(r"^\s*(#{1,3})\s+")
_BOLD_RE = re.compile(r"\*\*(.+?)\*\*")
_HEADING_TAG = {1: "h3", 2: "h4", 3: "h5"}


def _inline(s: str) -> str:
    """Escape, then apply the only inline transform we allow: **bold**."""
    s = html.escape(s, quote=False)
    return _BOLD_RE.sub(r"<strong>\1</strong>", s)


def render_reply_html(text: str) -> str:
    """Render the supported Markdown subset to sanitized HTML (or '' if empty)."""
    text = (text or "").replace("\r\n", "\n").replace("\r", "\n").strip()
    if not text:
        return ""
    out: list[str] = []
    for block in re.split(r"\n\s*\n", text):
        lines = [ln for ln in block.split("\n")]
        nonempty = [ln for ln in lines if ln.strip()]
        if not nonempty:
            continue
        if all(_BULLET_RE.match(ln) for ln in nonempty):
            items = "".join("<li>" + _inline(_BULLET_RE.sub("", ln)) + "</li>" for ln in nonempty)
            out.append("<ul>" + items + "</ul>")
        elif len(nonempty) == 1 and _HEADING_RE.match(nonempty[0]):
            level = len(_HEADING_RE.match(nonempty[0]).group(1))
            content = _HEADING_RE.sub("", nonempty[0])
            tag = _HEADING_TAG[level]
            out.append(f"<{tag}>" + _inline(content) + f"</{tag}>")
        else:
            out.append("<p>" + "<br>".join(_inline(ln) for ln in nonempty) + "</p>")
    return "".join(out)