"""NATS offload client — sends inference requests to remote nodes with
circuit breaker, retries, and deadline enforcement."""
import asyncio
import json
import logging
import os
import time
from typing import Any, Dict, Literal, Optional, Set

logger = logging.getLogger("offload_client")

CB_FAILS = int(os.getenv("ROUTER_OFFLOAD_CB_FAILS", "3"))
CB_WINDOW_S = int(os.getenv("ROUTER_OFFLOAD_CB_WINDOW_S", "60"))
CB_OPEN_S = int(os.getenv("ROUTER_OFFLOAD_CB_OPEN_S", "120"))
MAX_RETRIES = int(os.getenv("ROUTER_OFFLOAD_RETRIES", "1"))
MAX_CONCURRENCY = int(os.getenv("ROUTER_OFFLOAD_MAX_CONCURRENCY_REMOTE", "8"))

_semaphore: Optional[asyncio.Semaphore] = None
_breakers: Dict[str, Dict[str, Any]] = {}


def _get_semaphore() -> asyncio.Semaphore:
    global _semaphore
    if _semaphore is None:
        _semaphore = asyncio.Semaphore(MAX_CONCURRENCY)
    return _semaphore


def _breaker_key(node_id: str, req_type: str) -> str:
    return f"{node_id}:{req_type}"


def is_node_available(node_id: str, req_type: str) -> bool:
    key = _breaker_key(node_id, req_type)
    state = _breakers.get(key)
    if not state:
        return True
    open_until = state.get("open_until", 0)
    if open_until > time.time():
        return False
    if open_until > 0 and open_until <= time.time():
        return True
    now = time.time()
    window_start = now - CB_WINDOW_S
    recent = [t for t in state.get("failures", []) if t > window_start]
    state["failures"] = recent
    return len(recent) < CB_FAILS


def record_failure(node_id: str, req_type: str):
    key = _breaker_key(node_id, req_type)
    state = _breakers.setdefault(key, {"failures": [], "open_until": 0})
    state["failures"].append(time.time())
    window_start = time.time() - CB_WINDOW_S
    recent = [t for t in state["failures"] if t > window_start]
    state["failures"] = recent
    if len(recent) >= CB_FAILS:
        state["open_until"] = time.time() + CB_OPEN_S
        logger.warning(f"Circuit OPEN: {key} ({len(recent)} failures in {CB_WINDOW_S}s, open for {CB_OPEN_S}s)")


def record_success(node_id: str, req_type: str):
    key = _breaker_key(node_id, req_type)
    state = _breakers.get(key)
    if state:
        state["failures"] = []
        state["open_until"] = 0


def get_unavailable_nodes(req_type: str) -> Set[str]:
    result = set()
    for key, state in _breakers.items():
        if not key.endswith(f":{req_type}"):
            continue
        nid = key.rsplit(":", 1)[0]
        if not is_node_available(nid, req_type):
            result.add(nid)
    return result


async def offload_infer(
    nats_client,
    node_id: str,
    required_type: Literal["llm", "vision", "stt", "tts", "ocr", "image"],
    job_payload: Dict[str, Any],
    timeout_ms: int = 25000,
) -> Optional[Dict[str, Any]]:
    """Send inference job to remote node via NATS request/reply.

    Returns parsed JobResponse dict or None on total failure.
    Retries on transient errors (timeout, busy). Does NOT retry on provider errors.
    """
    subject = f"node.{node_id.lower()}.{required_type}.request"
    payload_bytes = json.dumps(job_payload).encode()
    sem = _get_semaphore()

    for attempt in range(1 + MAX_RETRIES):
        timeout_s = timeout_ms / 1000.0
        if timeout_s <= 0:
            logger.warning(f"[offload] deadline exhausted before attempt {attempt}")
            return None

        t0 = time.time()
        try:
            async with sem:
                logger.info(
                    f"[offload.start] node={node_id} subj={subject} "
                    f"timeout={timeout_ms}ms attempt={attempt}"
                )
                msg = await nats_client.request(subject, payload_bytes, timeout=timeout_s)
                resp = json.loads(msg.data)

            latency = int((time.time() - t0) * 1000)
            status = resp.get("status", "error")

            if status == "ok":
                record_success(node_id, required_type)
                logger.info(
                    f"[offload.done] node={node_id} status=ok latency={latency}ms "
                    f"provider={resp.get('provider')} model={resp.get('model')} "
                    f"cached={resp.get('cached', False)}"
                )
                return resp

            if status in ("timeout", "busy") and attempt < MAX_RETRIES:
                elapsed = int((time.time() - t0) * 1000)
                timeout_ms -= elapsed
                logger.warning(f"[offload.retry] node={node_id} status={status} → retry {attempt+1}")
                continue

            record_failure(node_id, required_type)
            logger.warning(
                f"[offload.fail] node={node_id} status={status} "
                f"error={resp.get('error', {}).get('code', '?')}"
            )
            return resp

        except asyncio.TimeoutError:
            record_failure(node_id, required_type)
            elapsed = int((time.time() - t0) * 1000)
            timeout_ms -= elapsed
            if attempt < MAX_RETRIES:
                logger.warning(f"[offload.timeout] node={node_id} {elapsed}ms → retry {attempt+1}")
                continue
            logger.warning(f"[offload.timeout] node={node_id} all retries exhausted")
            return None

        except Exception as e:
            record_failure(node_id, required_type)
            logger.warning(f"[offload.error] node={node_id} {e}")
            return None

    return None