"""一次性修复: 把误标为全文 PDF 的 Elsevier "摘要预览页"(1 页)纠正回未下载状态。

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), 而全文 XML 却能正常拿到。旧抓取
  逻辑只校验魔数 + 体积, 误将预览页落库并置 has_fulltext_pdf=True。

本命令重新核对本地 PDF 的页数, 对 <= 1 页者:
  - has_fulltext_pdf 置回 False
  - 若该论文有 XML 全文(has_fulltext_xml=True), 保留 has_fulltext=True;
    否则(此前只有这张假预览页冒充全文)一并把 has_fulltext 回退为 False,
    让它能重新进入下载链路去找真正的全文。
  - 追加 fail_reason 'elsevier_pdf_preview_only' (供 Elsevier 补抓队列排除, 避免无限重试)
  - 可选: 删除本地预览 PDF 文件 (--delete-file)

文件读取依赖本地存在 PDF (在跑抓取的服务器上执行)。建议先 --dry-run 看统计。

用法:
  python manage.py fix_preview_pdf --dry-run
  python manage.py fix_preview_pdf --delete-file
"""
import os

from django.core.management.base import BaseCommand

from apps.resm.models import Paper
from apps.resm.tasks import _pdf_page_count


class Command(BaseCommand):
    help = "纠正被误标为全文的 Elsevier 摘要预览 PDF(1 页)"

    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="同时删除本地预览 PDF 文件")

    def handle(self, *args, **opts):
        dry = opts["dry_run"]
        limit = opts["limit"]
        del_file = opts["delete_file"]

        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}")

        checked = fixed = only_pdf = missing = unreadable = 0
        for paper in qs.iterator():
            if limit and checked >= limit:
                break
            checked += 1

            path = paper.init_paper_path("pdf")
            if not os.path.exists(path):
                missing += 1
                continue
            try:
                with open(path, "rb") as f:
                    content = f.read()
            except OSError:
                unreadable += 1
                continue

            pages = _pdf_page_count(content)
            if pages is None:
                unreadable += 1
                continue
            if pages > 1:
                continue  # 真全文, 跳过

            fixed += 1
            only_pdf_case = not paper.has_fulltext_xml
            if only_pdf_case:
                only_pdf += 1
            self.stdout.write(
                f"[preview {pages}p]{' (only-pdf)' if only_pdf_case else ''} "
                f"{paper.doi}  {path}")
            if dry:
                continue

            paper.has_fulltext_pdf = False
            update_fields = ["has_fulltext_pdf", "update_time"]
            # 没有 XML 全文时, 之前的 has_fulltext 只是被这张假预览页置上的, 一并回退
            if not paper.has_fulltext_xml:
                paper.has_fulltext = False
                update_fields.insert(0, "has_fulltext")
            paper.save(update_fields=update_fields)
            if "elsevier_pdf_preview_only" not in (paper.fail_reason or ""):
                paper.save_fail_reason("elsevier_pdf_preview_only")
            if del_file:
                try:
                    os.remove(path)
                except OSError:
                    pass

        self.stdout.write(self.style.SUCCESS(
            f"检查={checked} 预览页修复={fixed} (其中无XML全文/一并回退has_fulltext={only_pdf}) "
            f"文件缺失={missing} 无法解析={unreadable}"
            + ("  (dry-run, 未写库)" if dry else "")
        ))