"""Minimal e621 API client for server-side matching and metadata refresh.

The SPA talks to e621 directly for browsing; this client exists for work the
browser cannot do reliably: long batch scans, and requests tied to a library
item rather than an open page. It uses the requesting user's stored
credentials and a global throttle (e621 asks for at most two requests per
second).
"""

import threading
import time

import requests
from django.conf import settings

REQUEST_INTERVAL = 0.5  # seconds between requests, per process


class E621Error(Exception):
    """A non-404 failure while talking to e621."""


class E621NotFound(E621Error):
    """The requested post does not exist (HTTP 404)."""


_throttle_lock = threading.Lock()
_last_request_at = 0.0


def credentials_configured(user):
    return bool(user is not None and getattr(user, "e621_configured", False))


def _wait_for_slot():
    global _last_request_at
    with _throttle_lock:
        delay = _last_request_at + REQUEST_INTERVAL - time.monotonic()
        if delay > 0:
            time.sleep(delay)
        _last_request_at = time.monotonic()


def get(user, path, params=None, timeout=30, require_auth=True):
    """GET an e621 API path using the user's credentials.

    Reads that e621 serves anonymously (searches, pools, tags) can pass
    require_auth=False; matching endpoints keep requiring credentials.

    Raises E621NotFound for 404s and E621Error for everything else that isn't
    a 2xx, so callers never see requests exceptions.
    """
    configured = credentials_configured(user)
    if require_auth and not configured:
        raise E621Error("Configure your e621 credentials in Account first.")
    base = (getattr(user, "e621_base_url", "") or "https://e621.net").rstrip("/")
    _wait_for_slot()
    try:
        response = requests.get(
            f"{base}{path}",
            params=params,
            auth=(user.e621_username, user.e621_api_key) if configured else None,
            headers={"User-Agent": settings.USER_AGENT},
            timeout=timeout,
        )
    except requests.RequestException as exc:
        raise E621Error(f"Could not reach e621: {exc}") from exc
    if response.status_code == 404:
        raise E621NotFound(f"e621 returned 404 for {path}")
    if response.status_code >= 400:
        raise E621Error(f"e621 replied {response.status_code} for {path}")
    try:
        return response.json()
    except ValueError as exc:
        raise E621Error("e621 returned an unexpected response.") from exc


def find_post_by_md5(user, md5):
    """The e621 post with this exact MD5, or None."""
    payload = get(user, "/posts.json", params={"tags": f"md5:{md5}", "limit": 1})
    posts = payload.get("posts") if isinstance(payload, dict) else None
    if not posts:
        return None
    return posts[0]


def fetch_post(user, post_id):
    """One post by id. Raises E621NotFound when the post is gone."""
    payload = get(user, f"/posts/{int(post_id)}.json")
    post = payload.get("post") if isinstance(payload, dict) else None
    if not isinstance(post, dict):
        raise E621Error("e621 returned an unexpected post payload.")
    return post