import logging

import requests


log = logging.getLogger(__name__)


class UnpaywallResolver:
    def __init__(self, email: str, timeout=(10, 30)):
        self.email = (email or "").strip()
        self.timeout = timeout
        self.base_url = "https://api.unpaywall.org/v2"

    def resolve(self, paper):
        if not paper.doi:
            return paper

        if not self.email:
            log.warning(
                "Unpaywall email missing; OA lookup skipped: %s",
                paper.title,
            )
            return paper

        doi = paper.doi.strip()

        try:
            response = requests.get(
                f"{self.base_url}/{doi}",
                params={"email": self.email},
                timeout=self.timeout,
            )
            response.raise_for_status()

        except requests.exceptions.HTTPError as exc:
            status = (
                exc.response.status_code
                if exc.response is not None
                else None
            )

            # DOI not present in Unpaywall is not fatal.
            if status == 404:
                paper.oa_status = "not_found"
                return paper

            raise

        data = response.json()

        paper.oa_status = str(
            data.get("oa_status") or ""
        )

        best = data.get("best_oa_location") or {}

        pdf_url = best.get("url_for_pdf") or ""

        # Some OA records do not expose url_for_pdf but do expose a landing URL.
        # We intentionally do NOT treat url as a PDF here.
        paper.pdf_url = str(pdf_url).strip()

        return paper