"""企微 markdown 按字节上限拆分为多条消息（按区块，不截断正文）。"""

from __future__ import annotations

import re

_SECTION_START = re.compile(r"^[📰💡🎯🌍📈🔥🐙🌱🤖📦📄]")


def _utf8_len(text: str) -> int:
    return len(text.encode("utf-8"))


def _split_lines_by_budget(text: str, limit: int) -> list[str]:
    lines = text.splitlines()
    chunks: list[str] = []
    buf: list[str] = []
    for line in lines:
        candidate = "\n".join(buf + [line]) if buf else line
        if _utf8_len(candidate) <= limit:
            buf.append(line)
            continue
        if buf:
            chunks.append("\n".join(buf))
            buf = []
        if _utf8_len(line) <= limit:
            buf = [line]
        else:
            encoded = line.encode("utf-8")
            start = 0
            while start < len(encoded):
                piece = encoded[start : start + limit].decode("utf-8", errors="ignore")
                chunks.append(piece)
                start += len(piece.encode("utf-8"))
    if buf:
        chunks.append("\n".join(buf))
    return chunks


def _split_sections(text: str) -> list[str]:
    sections: list[str] = []
    current: list[str] = []
    for line in text.splitlines():
        if _SECTION_START.match(line) and current:
            sections.append("\n".join(current))
            current = [line]
        else:
            current.append(line)
    if current:
        sections.append("\n".join(current))
    return sections


def split_wecom_messages(text: str, limit: int = 4096) -> list[str]:
    """超长时拆成多条；每条不超过 limit 字节，按区块边界优先。"""
    text = text.strip()
    if not text or _utf8_len(text) <= limit:
        return [text] if text else []

    footer_reserve = 40
    pack_limit = max(512, limit - footer_reserve)

    sections: list[str] = []
    for sec in _split_sections(text):
        if _utf8_len(sec) <= pack_limit:
            sections.append(sec)
        else:
            sections.extend(_split_lines_by_budget(sec, pack_limit))

    packed: list[str] = []
    buf: list[str] = []
    for sec in sections:
        candidate = "\n\n".join(buf + [sec]) if buf else sec
        if _utf8_len(candidate) <= pack_limit:
            buf.append(sec)
        else:
            if buf:
                packed.append("\n\n".join(buf))
            buf = [sec]
    if buf:
        packed.append("\n\n".join(buf))

    total = len(packed)
    if total <= 1:
        return packed

    result: list[str] = []
    for i, chunk in enumerate(packed, 1):
        suffix = f"\n\n> 📄 {i}/{total}"
        body = chunk
        while body and _utf8_len(body + suffix) > limit:
            body = body.rsplit("\n", 1)[0] if "\n" in body else body[:-1]
        result.append(body + suffix)
    return result