import io
from pathlib import Path
from typing import List

import httpx


async def prepare_images_from_file(
    file_url: str, filename: str, max_pages: int = 5, dpi: int = 180
) -> List[bytes]:
    """presigned URL → bytes. PDF이면 앞쪽 max_pages 페이지만 이미지로 변환하여 bytes 리스트 반환"""
    async with httpx.AsyncClient() as client:
        resp = await client.get(file_url, timeout=None)
        resp.raise_for_status()
        file_bytes = resp.content

    ext = Path(filename).suffix.lower()
    if ext in [".pdf", ".tif", ".tiff"]:
        try:
            from pdf2image import convert_from_bytes
        except ImportError as e:
            raise RuntimeError(
                "pdf2image가 필요합니다. `pip install pdf2image poppler-utils`"
            ) from e

        pil_images = convert_from_bytes(file_bytes, dpi=dpi)
        images = []
        for i, im in enumerate(pil_images[:max_pages]):
            buf = io.BytesIO()
            im.save(buf, format="PNG")
            images.append(buf.getvalue())
        return images
    else:
        # 단일 이미지
        return [file_bytes]