"""Shared GitHub REST session with rate-limit and transient-network retries."""
from __future__ import annotations

import logging
import time

import requests

log = logging.getLogger(__name__)

GITHUB_API = "https://api.github.com"
_RATE_FLOOR = 200
_MAX_NETWORK_RETRIES = 8
_RETRY_BASE_SEC = 2.0
_TRANSIENT_HTTP = {502, 503, 504, 520, 521, 522, 429}
_TRANSIENT_EXC = (
    requests.exceptions.ConnectionError,
    requests.exceptions.Timeout,
    requests.exceptions.ChunkedEncodingError,
)


class GitHubSession:
    """requests.Session wrapper: rate limits, 202 polling, network retries."""

    def __init__(self, token: str) -> None:
        self._s = requests.Session()
        headers = {
            "Accept": "application/vnd.github+json",
            "X-GitHub-Api-Version": "2022-11-28",
        }
        if token:
            headers["Authorization"] = f"Bearer {token}"
        self._s.headers.update(headers)

    def get(self, url: str, **kwargs) -> requests.Response:
        kwargs.setdefault("timeout", (15, 90))
        attempt = 0
        while True:
            attempt += 1
            try:
                resp = self._s.get(url, **kwargs)
            except _TRANSIENT_EXC as exc:
                if attempt >= _MAX_NETWORK_RETRIES:
                    raise
                sleep_sec = min(120.0, _RETRY_BASE_SEC * (2 ** (attempt - 1)))
                log.warning(
                    "Network error on GET (attempt %d/%d), sleeping %.0fs: %s",
                    attempt, _MAX_NETWORK_RETRIES, sleep_sec, exc,
                )
                time.sleep(sleep_sec)
                continue

            remaining = int(resp.headers.get("X-RateLimit-Remaining", 9999))
            reset_at = int(resp.headers.get("X-RateLimit-Reset", 0))

            if resp.status_code == 403 and remaining == 0:
                sleep_sec = max(reset_at - int(time.time()), 0) + 5
                log.warning("Rate limit hit; sleeping %ds", sleep_sec)
                time.sleep(sleep_sec)
                continue
            if resp.status_code == 202:
                time.sleep(3)
                continue
            if resp.status_code in _TRANSIENT_HTTP and attempt < _MAX_NETWORK_RETRIES:
                retry_after = int(resp.headers.get("Retry-After", 0))
                sleep_sec = retry_after or min(120.0, _RETRY_BASE_SEC * (2 ** (attempt - 1)))
                log.warning(
                    "HTTP %d on GET (attempt %d/%d), sleeping %.0fs",
                    resp.status_code, attempt, _MAX_NETWORK_RETRIES, sleep_sec,
                )
                time.sleep(sleep_sec)
                continue
            if remaining < _RATE_FLOOR:
                sleep_sec = max(reset_at - int(time.time()), 0) + 2
                log.info("Rate budget low (%d remaining); sleeping %ds", remaining, sleep_sec)
                time.sleep(sleep_sec)
            return resp