from __future__ import annotations

import re

_SENTENCE_BOUNDARY = re.compile(r"[。！？.!?\n]")


def chunk_text(text: str, limit: int = 20000) -> list[str]:
    if len(text) <= limit:
        return [text]

    chunks: list[str] = []
    paragraphs = text.split("\n\n")
    current = ""

    for para in paragraphs:
        if len(current) + len(para) + 2 <= limit:
            current = f"{current}\n\n{para}" if current else para
        else:
            if current:
                chunks.append(current)
            if len(para) > limit:
                sub_chunks = _chunk_long_paragraph(para, limit)
                if sub_chunks:
                    if sub_chunks[-1]:
                        current = sub_chunks.pop()
                    else:
                        sub_chunks.pop()
                        current = ""
                    chunks.extend(sub_chunks)
                else:
                    current = ""
            else:
                current = para

    if current:
        chunks.append(current)
    return chunks or [text[:limit]]


def _chunk_long_paragraph(text: str, limit: int) -> list[str]:
    chunks: list[str] = []
    while len(text) > limit:
        split_at = _find_split_point(text, limit)
        chunk = text[:split_at].rstrip()
        if chunk:
            chunks.append(chunk)
        text = text[split_at:].lstrip()
    if text:
        chunks.append(text)
    return chunks


def _find_split_point(text: str, limit: int) -> int:
    candidates = [m.start() for m in _SENTENCE_BOUNDARY.finditer(text, limit // 2, limit)]
    if candidates:
        return candidates[-1] + 1
    newline = text.rfind("\n", limit // 2, limit)
    if newline != -1:
        return newline + 1
    space = text.rfind(" ", limit // 2, limit)
    if space != -1:
        return space + 1
    return limit