"""一次性修复: 纠正被误标为全文 PDF 的历史记录(Elsevier 摘要预览页 / 损坏文件)。

背景:
  Elsevier Article API 对未授权 / in-press 文章, application/pdf 端点会返回仅含
  摘要的 1 页预览 PDF(魔数仍是 %PDF、体积也不小); 另有部分历史记录把 HTML 错误页 /
  被截断的垃圾当 PDF 存了。旧抓取逻辑只校验魔数 + 体积, 都会误标 has_fulltext_pdf=True。

本命令核对本地 PDF, 分两类处理:
  - 预览页(1 页):   has_fulltext_pdf 置回 False; 文件**仅在 --delete-file 时**删除。
  - 损坏文件(非 PDF / pypdf 解析失败): has_fulltext_pdf 置回 False; 文件**总是删除**
    (dry-run 除外), 因为它根本不是有效全文, 留着无用且会污染下游解析。
  两类在缺少 XML 全文(has_fulltext_xml=False)时, 一并把 has_fulltext 回退 False,
  让其重新进入下载链路去找真正的全文; 并追加 fail_reason 标记供抓取任务排除。

性能:
  读文件 + pypdf 解析是 CPU/IO 密集, 用 ProcessPoolExecutor 并行(--workers, 默认 CPU 核数);
  数据库写入留在主进程串行(坏文件仅占少数, 非瓶颈, 也避免子进程共享 DB 连接)。

安全前提:
  "损坏"只在铁证下判定 —— 文件不以 %PDF 开头, 或已装 pypdf 且解析直接失败。
  若未装 pypdf 且魔数正常但页数判不出, 归为 unknown, **不处理、绝不删除**。
  强烈建议先 `pip install pypdf` 再跑, 否则只能处理魔数明显不符的坏文件。

用法:
  python manage.py fix_preview_pdf --dry-run
  python manage.py fix_preview_pdf                      # 纠正标记 + 删坏文件, 保留预览页文件
  python manage.py fix_preview_pdf --delete-file        # 并删除预览页文件
  python manage.py fix_preview_pdf --workers 16         # 指定并发进程数
"""
import os
from concurrent.futures import ProcessPoolExecutor

from django.conf import settings
from django.core.management.base import BaseCommand
from django.utils import timezone

from apps.resm.models import Paper
from apps.resm.pdf_utils import classify_pdf_file


def _pdf_path(doi, pub_date):
    """按 doi + publication_date 推算 PDF 落盘路径(不创建目录, 只读用)。"""
    safe = doi.replace("/", "_")
    if pub_date is None:
        d = os.path.join(settings.BASE_DIR, "media/papers", "unknown")
    else:
        d = os.path.join(settings.BASE_DIR, "media/papers",
                         str(pub_date.year), str(pub_date.month), str(pub_date.day))
    return os.path.join(d, f"{safe}.pdf")


def _batched(iterable, size):
    batch = []
    for item in iterable:
        batch.append(item)
        if len(batch) >= size:
            yield batch
            batch = []
    if batch:
        yield batch


class Command(BaseCommand):
    help = "纠正被误标为全文的 Elsevier 预览页 / 损坏 PDF(多进程并发)"

    def add_arguments(self, parser):
        parser.add_argument("--dry-run", action="store_true",
                            help="只统计, 不写库 / 不删文件")
        parser.add_argument("--limit", type=int, default=0,
                            help="最多处理多少条 (0=不限)")
        parser.add_argument("--delete-file", action="store_true",
                            help="同时删除预览页文件(坏文件无论该开关都会删)")
        parser.add_argument("--workers", type=int, default=0,
                            help="并发进程数 (0=CPU 核数)")
        parser.add_argument("--batch", type=int, default=2000,
                            help="每批处理多少条(控制内存与进度粒度)")

    def handle(self, *args, **opts):
        dry = opts["dry_run"]
        limit = opts["limit"]
        del_preview = opts["delete_file"]
        batch = max(1, opts["batch"])
        workers = opts["workers"] or (os.cpu_count() or 4)

        qs = Paper.objects.filter(
            has_fulltext_pdf=True, doi__startswith="10.1016"
        ).order_by("id")
        total = qs.count()
        self.stdout.write(
            f"候选(has_fulltext_pdf=True 且 DOI 以 10.1016 开头): {total}; "
            f"workers={workers} batch={batch}"
            + ("  (dry-run)" if dry else ""))

        rows_iter = qs.values(
            "id", "doi", "publication_date", "has_fulltext_xml", "fail_reason"
        ).iterator(chunk_size=batch)

        checked = preview = broken = only_pdf = deleted = 0
        missing = unknown = 0

        with ProcessPoolExecutor(max_workers=workers) as ex:
            stop = False
            for chunk in _batched(rows_iter, batch):
                if stop:
                    break
                paths = [_pdf_path(r["doi"], r["publication_date"]) for r in chunk]
                results = ex.map(classify_pdf_file, paths, chunksize=32)
                for r, (_path, kind, pages) in zip(chunk, results):
                    if limit and checked >= limit:
                        stop = True
                        break
                    checked += 1

                    if kind == "missing":
                        missing += 1
                        continue
                    if kind in ("ok", "unknown", "unreadable"):
                        if kind != "ok":
                            unknown += 1
                        continue

                    # kind in ('preview', 'broken'): 纠正标记
                    do_delete = (kind == "broken") or del_preview
                    only_pdf_case = not r["has_fulltext_xml"]
                    if kind == "preview":
                        preview += 1
                        tag = f"preview {pages}p"
                        reason = "elsevier_pdf_preview_only"
                    else:
                        broken += 1
                        tag = "broken"
                        reason = "pdf_broken"
                    if only_pdf_case:
                        only_pdf += 1
                    self.stdout.write(
                        f"[{tag}]{' (only-pdf)' if only_pdf_case else ''}"
                        f"{' +rm' if do_delete else ''} {r['doi']}  {_path}")
                    if dry:
                        continue

                    fr = r["fail_reason"]
                    if reason not in (fr or ""):
                        fr = f"{fr};{reason}" if fr else f";{reason}"
                    upd = {"has_fulltext_pdf": False, "fail_reason": fr,
                           "update_time": timezone.now()}
                    if only_pdf_case:
                        upd["has_fulltext"] = False
                    Paper.objects.filter(id=r["id"]).update(**upd)
                    if do_delete:
                        try:
                            os.remove(_path)
                            deleted += 1
                        except OSError:
                            pass

                self.stdout.write(
                    f"  进度 checked={checked}/{total} preview={preview} "
                    f"broken={broken} deleted={deleted} missing={missing} "
                    f"unknown={unknown}")

        self.stdout.write(self.style.SUCCESS(
            f"完成 检查={checked} 预览页={preview} 坏文件={broken} "
            f"(无XML全文一并回退has_fulltext={only_pdf}) 删除文件={deleted} "
            f"文件缺失={missing} 未知/跳过={unknown}"
            + ("  (dry-run, 未写库)" if dry else "")
        ))