"""Proxy requests to the gpu-fan host agent."""

from __future__ import annotations

import json
import logging
import urllib.error
import urllib.request
from typing import Any

log = logging.getLogger(__name__)


class AgentProxyError(Exception):
    """Raised when the gpu-fan agent request fails."""


def check_agent_health(agent_url: str, agent_api_key: str) -> dict[str, Any]:
    """Return health info for the gpu-fan agent."""
    try:
        forward_request(agent_url, "GET", "status", agent_api_key=agent_api_key)
        return {"ok": True, "agent_url": agent_url}
    except AgentProxyError as exc:
        return {"ok": False, "agent_url": agent_url, "error": str(exc)}


def resolve_agent_url(configured_url: str, agent_api_key: str) -> str:
    """Pick first reachable agent URL (18090 preferred, 8090 legacy fallback)."""
    candidates: list[str] = []
    if configured_url:
        candidates.append(configured_url.rstrip("/"))
    for url in ("http://127.0.0.1:18090", "http://127.0.0.1:8090"):
        if url not in candidates:
            candidates.append(url)
    for url in candidates:
        if check_agent_health(url, agent_api_key).get("ok"):
            log.info("GPU fan agent reachable at %s", url)
            return url
    return candidates[0] if candidates else "http://127.0.0.1:18090"


def forward_request(
    agent_url: str,
    method: str,
    path: str,
    *,
    body: bytes | None = None,
    agent_api_key: str,
    content_type: str = "application/json",
) -> tuple[int, dict[str, str], bytes]:
    """Forward a request to the gpu-fan agent API."""
    path = path.lstrip("/")
    url = f"{agent_url.rstrip('/')}/api/{path}"
    headers = {"Accept": "application/json"}
    if agent_api_key:
        headers["X-API-Key"] = agent_api_key
    if body is not None:
        headers["Content-Type"] = content_type

    req = urllib.request.Request(url, data=body, headers=headers, method=method.upper())
    try:
        with urllib.request.urlopen(req, timeout=10) as resp:
            return resp.status, dict(resp.headers), resp.read()
    except urllib.error.HTTPError as exc:
        payload = exc.read()
        detail = payload.decode("utf-8", errors="replace")
        try:
            parsed = json.loads(detail)
            if isinstance(parsed, dict) and "detail" in parsed:
                detail = str(parsed["detail"])
        except json.JSONDecodeError:
            pass
        raise AgentProxyError(detail or f"Agent HTTP {exc.code}") from exc
    except urllib.error.URLError as exc:
        raise AgentProxyError(f"Agent unreachable at {agent_url}: {exc.reason}") from exc