"""Semantic Scholar API client.

Provides:
- fetch_references: retrieve references for a paper as Citation dataclasses.
- fetch_recommendations: retrieve recommended paper IDs.

Requests are rate-limited to 1 per second via tenacity wait_fixed.
"""

from __future__ import annotations

import logging
from typing import Any

import httpx
from tenacity import retry, stop_after_attempt, wait_fixed

from codex.models import Citation

logger = logging.getLogger(__name__)

_BASE_GRAPH = "https://api.semanticscholar.org/graph/v1"
_BASE_RECS = "https://api.semanticscholar.org/recommendations/v1"


@retry(
    stop=stop_after_attempt(5),
    wait=wait_fixed(1),
    before_sleep=lambda rs: logger.warning(
        "SemanticScholar retry %d after %s",
        rs.attempt_number,
        rs.outcome.exception(),  # type: ignore[union-attr]
    ),
)
def _get(url: str, params: dict[str, Any] | None = None) -> httpx.Response:
    response = httpx.get(url, params=params, timeout=30)
    response.raise_for_status()
    return response


def fetch_references(paper_id: str) -> list[Citation]:
    """Fetch references for a paper from Semantic Scholar.

    Parameters
    ----------
    paper_id:
        Semantic Scholar paper ID (or ``arXiv:…`` / ``DOI:…`` prefixed ID).

    Returns
    -------
    list[Citation]
        One Citation per reference, with optional context snippet.
    """
    url = f"{_BASE_GRAPH}/paper/{paper_id}/references"
    params: dict[str, Any] = {"fields": "externalIds,contexts"}
    try:
        response = _get(url, params=params)
    except httpx.HTTPStatusError as exc:
        if exc.response.status_code == 404:
            return []
        raise

    data = response.json()
    raw_refs: list[dict[str, Any]] = data.get("data", [])
    citations: list[Citation] = []
    for entry in raw_refs:
        cited_paper: dict[str, Any] = entry.get("citedPaper", {})
        external_ids: dict[str, str] = cited_paper.get("externalIds") or {}
        contexts: list[str] = entry.get("contexts", [])
        context: str | None = contexts[0] if contexts else None

        cited_id: str = (
            external_ids.get("DOI") or external_ids.get("ArXiv") or cited_paper.get("paperId") or ""
        )
        if cited_id:
            citations.append(Citation(citing_id=paper_id, cited_id=cited_id, context=context))
    return citations


def fetch_recommendations(paper_id: str, limit: int = 20) -> list[str]:
    """Fetch recommended paper IDs from Semantic Scholar.

    Parameters
    ----------
    paper_id:
        Semantic Scholar paper ID.
    limit:
        Maximum number of recommendations to return.

    Returns
    -------
    list[str]
        List of recommended paper IDs.
    """
    url = f"{_BASE_RECS}/papers/forpaper/{paper_id}"
    params: dict[str, Any] = {"limit": limit}
    try:
        response = _get(url, params=params)
    except httpx.HTTPStatusError as exc:
        if exc.response.status_code == 404:
            return []
        raise

    data = response.json()
    recommended: list[dict[str, Any]] = data.get("recommendedPapers", [])
    return [p["paperId"] for p in recommended if p.get("paperId")]