#!/usr/bin/env python3
"""Download the papers' PDFs into pdf/<slug>.pdf from arXiv.

PDFs are not shipped with the vault (most arXiv papers carry arXiv's default
license, which does not allow redistribution), so each reader fetches their
own copies from the source. Every paper note with an `arxiv:` id is fetched
from arxiv.org, 3 s apart (arXiv's rate limit); existing files are skipped.
Notes without an arXiv id are listed at the end with their venue, to get by
hand (OpenReview ones: _scripts/fetch_openreview_pdf.py, own credentials).

    python3 _scripts/fetch_pdfs.py                  # everything missing
    python3 _scripts/fetch_pdfs.py --dry-run        # list, download nothing
    python3 _scripts/fetch_pdfs.py --only kirkpatrick2017-ewc wu2019-bic
"""
import argparse
import glob
import os
import re
import time
import urllib.request

VAULT = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))
PDF = os.path.join(VAULT, "pdf")


def field(fm: str, key: str) -> str:
    m = re.search(rf"^{key}:\s*(.*)$", fm, re.M)
    return m.group(1).strip().strip("\"'") if m else ""


def load_papers() -> list[dict]:
    papers = []
    for path in sorted(glob.glob(os.path.join(VAULT, "papers", "*.md"))):
        m = re.match(r"---\n(.*?)\n---", open(path, encoding="utf-8").read(), re.S)
        fm = m.group(1) if m else ""
        papers.append({"slug": os.path.splitext(os.path.basename(path))[0],
                       "arxiv": field(fm, "arxiv"), "title": field(fm, "title"),
                       "venue": field(fm, "venue"), "year": field(fm, "year")})
    return papers


def download(aid: str, dest: str) -> None:
    req = urllib.request.Request(f"https://arxiv.org/pdf/{aid}",
                                 headers={"User-Agent": "cl-vault-fetch-pdfs/1.0"})
    with urllib.request.urlopen(req, timeout=60) as r:
        data = r.read()
    if not data.startswith(b"%PDF"):
        raise ValueError("response is not a PDF")
    tmp = dest + ".part"
    with open(tmp, "wb") as f:
        f.write(data)
    os.replace(tmp, dest)


def main() -> None:
    ap = argparse.ArgumentParser()
    ap.add_argument("--only", nargs="+", metavar="SLUG", help="fetch only these papers")
    ap.add_argument("--dry-run", action="store_true", help="list what would be fetched")
    args = ap.parse_args()

    papers = load_papers()
    if args.only:
        papers = [p for p in papers if p["slug"] in set(args.only)]
    os.makedirs(PDF, exist_ok=True)
    todo = [p for p in papers if p["arxiv"]
            and not os.path.exists(os.path.join(PDF, p["slug"] + ".pdf"))]
    manual = [p for p in papers if not p["arxiv"]
              and not os.path.exists(os.path.join(PDF, p["slug"] + ".pdf"))]

    print(f"{len(papers)} papers · {len(todo)} to fetch from arXiv · {len(manual)} without arXiv id")
    ok = failed = 0
    for i, p in enumerate(todo, 1):
        dest = os.path.join(PDF, p["slug"] + ".pdf")
        if args.dry_run:
            print(f"  would fetch {p['arxiv']:>12}  ->  pdf/{p['slug']}.pdf")
            continue
        try:
            download(p["arxiv"], dest)
            ok += 1
            print(f"  [{i}/{len(todo)}] {p['slug']}")
        except Exception as e:
            failed += 1
            print(f"  [{i}/{len(todo)}] FAILED {p['slug']} ({p['arxiv']}): {e}")
        time.sleep(3)
    if not args.dry_run:
        print(f"fetched {ok}, failed {failed}")

    if manual:
        print("\nNo arXiv id, get by hand:")
        for p in manual:
            print(f"  {p['slug']}: {p['title']} ({p['venue']}, {p['year']})")


if __name__ == "__main__":
    main()