"""PDF 下载 — 从 arXiv 下载论文 PDF。"""

from __future__ import annotations

import logging
import os
import shutil
from pathlib import Path

import requests

from app.config import settings
from app.utils import PAPERS_DIR, TMP_DIR

logger = logging.getLogger(__name__)


# ── 自定义异常 ──────────────────────────────────────────────────────────


class PdfDownloadError(Exception):
    pass


# ── 路径工具 ────────────────────────────────────────────────────────────


def paper_dir(arxiv_id: str) -> Path:
    return PAPERS_DIR / arxiv_id


def tmp_dir(arxiv_id: str) -> Path:
    return TMP_DIR / arxiv_id


# ── PDF 下载 ────────────────────────────────────────────────────────────

# 复用 TCP 连接的 session
_http_session: requests.Session | None = None


def _get_session() -> requests.Session:
    global _http_session
    if _http_session is None:
        _http_session = requests.Session()
        _http_session.headers.update({"User-Agent": "hf-daily-papers/1.0"})
        # 代理：优先 $PROXY_SERVER，其次 settings.http_proxy
        proxy = os.environ.get("PROXY_SERVER")
        if proxy:
            _http_session.proxies = {"http": proxy, "https": proxy}
            logger.info("PDF download using proxy from $PROXY_SERVER: %s", proxy)
    return _http_session


def close_http_session() -> None:
    """关闭全局 HTTP Session，供应用 shutdown 时调用。"""
    global _http_session
    if _http_session is not None:
        _http_session.close()
        _http_session = None


async def download_pdf(arxiv_id: str, pdf_url: str) -> Path:
    """下载 PDF 到 data/tmp/{arxiv_id}/paper.pdf。"""
    if not pdf_url:
        raise PdfDownloadError(f"no pdf_url for {arxiv_id}")

    dest_dir = tmp_dir(arxiv_id)
    dest_dir.mkdir(parents=True, exist_ok=True)
    dest = dest_dir / "paper.pdf"

    try:
        session = _get_session()
        resp = session.get(
            pdf_url, timeout=settings.PDF_DOWNLOAD_TIMEOUT, allow_redirects=True
        )
        resp.raise_for_status()
        dest.write_bytes(resp.content)
    except Exception as exc:
        # 清理残留的部分文件
        if dest.exists():
            try:
                dest.unlink()
            except OSError:
                pass
        raise PdfDownloadError(f"failed to download PDF for {arxiv_id}: {exc}") from exc

    logger.info("Downloaded PDF: %s (%d bytes)", arxiv_id, dest.stat().st_size)
    return dest


# ── 临时文件清理 ────────────────────────────────────────────────────────


def cleanup_tmp(arxiv_id: str) -> None:
    """清理 data/tmp/{arxiv_id}/ 目录。"""
    td = tmp_dir(arxiv_id)
    if td.exists():
        try:
            shutil.rmtree(td)
            logger.debug("Cleaned tmp: %s", arxiv_id)
        except Exception:
            logger.warning("Failed to clean tmp for %s", arxiv_id, exc_info=True)