"""The only module that touches the network.

Two things matter here. First, a single 2s per-host reachability probe
short-circuits every later request, so an offline run fails in seconds instead
of timing out once per package across ~900 lookups. Second, failures are
returned, never raised: the gate must degrade to a cached answer rather than
crash a pre-commit hook the user is forbidden from bypassing.
"""

from __future__ import annotations

import json
import socket
from typing import Any
from urllib.error import HTTPError, URLError
from urllib.parse import urlsplit
from urllib.request import Request, urlopen

from dep_freshness._tables import (
    HTTP_ATTEMPTS,
    HTTP_TIMEOUT,
    PROBE_TIMEOUT,
    USER_AGENT,
)


class Offline(Exception):
    """The host is unreachable; callers should fall back to the cache."""


_reachable: dict[str, bool] = {}
_forced_offline = False


def force_offline(value: bool = True) -> None:
    """Make every request raise `Offline` without touching the network."""
    global _forced_offline
    _forced_offline = value


def reset_probes() -> None:
    """Forget cached reachability verdicts (tests, and `--refresh`)."""
    _reachable.clear()


def host_reachable(url: str) -> bool:
    """One cheap TCP probe per host, memoised for the run."""
    if _forced_offline:
        return False
    parts = urlsplit(url)
    host = parts.hostname or ""
    if host in _reachable:
        return _reachable[host]
    port = parts.port or (443 if parts.scheme == "https" else 80)
    try:
        with socket.create_connection((host, port), timeout=PROBE_TIMEOUT):
            _reachable[host] = True
    except OSError:
        _reachable[host] = False
    return _reachable[host]


def get_text(url: str, accept: str | None = None) -> str | None:
    """Fetch a body as text, or raise `Offline` / return None on 404.

    Same contract as `get_json`; Maven metadata is XML, not JSON.
    """
    if not host_reachable(url):
        raise Offline(url)
    headers = {"User-Agent": USER_AGENT}
    if accept:
        headers["Accept"] = accept
    request = Request(url, headers=headers)
    # A slow registry is retried with a longer timeout each time; an HTTP
    # status is an answer and is never retried.
    for attempt in range(1, HTTP_ATTEMPTS + 1):
        try:
            with urlopen(request, timeout=HTTP_TIMEOUT * attempt) as response:
                return response.read().decode("utf-8")
        except HTTPError as exc:
            if exc.code == 404:
                return None
            raise Offline(f"{url}: HTTP {exc.code}") from exc
        except (URLError, TimeoutError, OSError, ValueError) as exc:
            if attempt == HTTP_ATTEMPTS:
                raise Offline(f"{url}: {exc}") from exc
    return None  # the loop always returns or raises; this satisfies the type


def get_json(url: str, accept: str | None = None) -> Any:
    """Fetch and decode JSON, or raise `Offline` / return None on 404.

    `Offline` means "ask the cache"; None means "the registry answered and
    this package genuinely is not there", which is a real finding rather than
    a degraded run and must not be papered over with a stale cache entry.
    """
    body = get_text(url, accept)
    if body is None:
        return None
    try:
        return json.loads(body)
    except ValueError as exc:
        raise Offline(f"{url}: {exc}") from exc