"""Prometheus metrics for Fabric routing layer.

Exposed via /fabric_metrics (separate from main /metrics to avoid conflicts).
Falls back to no-op counters if prometheus_client is not installed.
"""
import logging
import time
from typing import Optional

logger = logging.getLogger("fabric_metrics")

try:
    from prometheus_client import Counter, Gauge, Histogram, CollectorRegistry, generate_latest
    PROM_AVAILABLE = True
    REGISTRY = CollectorRegistry()

    caps_refresh = Counter(
        "fabric_caps_refresh_total", "Capabilities refresh attempts",
        ["status"], registry=REGISTRY,
    )
    caps_stale = Counter(
        "fabric_caps_stale_total", "Stale capabilities used",
        registry=REGISTRY,
    )
    model_select = Counter(
        "fabric_model_select_total", "Model selection decisions",
        ["chosen_node", "chosen_runtime", "type"], registry=REGISTRY,
    )
    offload_total = Counter(
        "fabric_offload_total", "Offload attempts",
        ["status", "node", "type"], registry=REGISTRY,
    )
    breaker_state = Gauge(
        "fabric_breaker_state", "Circuit breaker state (1=open)",
        ["node", "type"], registry=REGISTRY,
    )
    score_hist = Histogram(
        "fabric_score_ms", "Model selection score distribution",
        buckets=[100, 250, 500, 1000, 2000, 5000, 10000],
        registry=REGISTRY,
    )

except ImportError:
    PROM_AVAILABLE = False
    REGISTRY = None
    logger.info("prometheus_client not installed, fabric metrics disabled")


def inc_caps_refresh(status: str):
    if PROM_AVAILABLE:
        caps_refresh.labels(status=status).inc()


def inc_caps_stale():
    if PROM_AVAILABLE:
        caps_stale.inc()


def inc_model_select(node: str, runtime: str, req_type: str):
    if PROM_AVAILABLE:
        model_select.labels(chosen_node=node, chosen_runtime=runtime, type=req_type).inc()


def inc_offload(status: str, node: str, req_type: str):
    if PROM_AVAILABLE:
        offload_total.labels(status=status, node=node, type=req_type).inc()


def set_breaker(node: str, req_type: str, is_open: bool):
    if PROM_AVAILABLE:
        breaker_state.labels(node=node, type=req_type).set(1 if is_open else 0)


def observe_score(score: int):
    if PROM_AVAILABLE:
        score_hist.observe(score)


def get_metrics_text() -> Optional[bytes]:
    if PROM_AVAILABLE and REGISTRY:
        return generate_latest(REGISTRY)
    return None