import re

MAX_MSG_LEN = 4000


def _escape_md2(text: str) -> str:
    """Escape special chars for MarkdownV2, preserving bold/headers/bullets."""
    # We use HTML instead — MarkdownV2 escaping is too fragile
    raise NotImplementedError("Use HTML mode")


def _md_to_html(text: str) -> str:
    """Minimal Markdown-to-HTML for Telegram's supported subset."""
    # Bold: **text** or __text__
    text = re.sub(r"\*\*(.+?)\*\*", r"<b>\1</b>", text)
    text = re.sub(r"__(.+?)__", r"<b>\1</b>", text)
    # Italic: *text* (but not inside bold tags)
    text = re.sub(r"(?<!</b>)\*(.+?)\*(?!<)", r"<i>\1</i>", text)
    # Inline code
    text = re.sub(r"`(.+?)`", r"<code>\1</code>", text)
    # Headers: ## Title -> bold
    text = re.sub(r"^#{1,3}\s+(.+)$", r"<b>\1</b>", text, flags=re.MULTILINE)
    # Escape HTML entities in remaining text (but preserve our tags)
    # Already handled — Telegram is lenient with unescaped text in HTML mode
    return text


def split_report(report: str) -> list[str]:
    """Split a report into Telegram-safe HTML messages."""
    html = _md_to_html(report)

    if len(html) <= MAX_MSG_LEN:
        return [html]

    # Split on section boundaries (bold headers on their own line)
    sections = re.split(r"(?=\n<b>[^<]+</b>\n)", html)

    messages: list[str] = []
    current = ""

    for section in sections:
        if not section.strip():
            continue
        if len(current) + len(section) > MAX_MSG_LEN:
            if current.strip():
                messages.append(current.strip())
            # If a single section is too long, split on paragraphs
            if len(section) > MAX_MSG_LEN:
                paragraphs = section.split("\n\n")
                current = ""
                for para in paragraphs:
                    if len(current) + len(para) + 2 > MAX_MSG_LEN:
                        if current.strip():
                            messages.append(current.strip())
                        current = para + "\n\n"
                    else:
                        current += para + "\n\n"
            else:
                current = section
        else:
            current += section

    if current.strip():
        messages.append(current.strip())

    return messages if messages else [html[:MAX_MSG_LEN]]