formatting.py

"""Convert markdown to Telegram-safe HTML."""

from __future__ import annotations

import html
import re


def md_to_telegram_html(text: str) -> str:
    """Convert common markdown to Telegram HTML.

    Handles: **bold**, *italic*, `inline code`, ```code blocks```,
    [text](url), and # headings.  Everything else is HTML-escaped.
    """
    # Extract code blocks first to protect their content
    code_blocks: list[str] = []

    def _save_code_block(m: re.Match) -> str:
        lang = m.group(1) or ""
        code = html.escape(m.group(2))
        code_blocks.append(f"<pre>{code}</pre>")
        return f"\x00CODEBLOCK{len(code_blocks) - 1}\x00"

    text = re.sub(r"```(\w*)\n?(.*?)```", _save_code_block, text, flags=re.DOTALL)

    # Extract inline code
    inline_codes: list[str] = []

    def _save_inline_code(m: re.Match) -> str:
        code = html.escape(m.group(1))
        inline_codes.append(f"<code>{code}</code>")
        return f"\x00INLINE{len(inline_codes) - 1}\x00"

    text = re.sub(r"`([^`]+)`", _save_inline_code, text)

    # HTML-escape the rest
    text = html.escape(text)

    # Links: [text](url)
    text = re.sub(
        r"\[([^\]]+)\]\(([^)]+)\)",
        r'<a href="\2">\1</a>',
        text,
    )

    # Bold: **text**
    text = re.sub(r"\*\*(.+?)\*\*", r"<b>\1</b>", text)

    # Italic: *text* (but not inside words like file*name)
    text = re.sub(r"(?<!\w)\*(.+?)\*(?!\w)", r"<i>\1</i>", text)

    # Headings: # Title → bold
    text = re.sub(r"^#{1,6}\s+(.+)$", r"<b>\1</b>", text, flags=re.MULTILINE)

    # Restore code blocks and inline code
    for i, block in enumerate(code_blocks):
        text = text.replace(f"\x00CODEBLOCK{i}\x00", block)
    for i, code in enumerate(inline_codes):
        text = text.replace(f"\x00INLINE{i}\x00", code)

    return text