"""Metrics registry and helpers for Prometheus and JSON fallbacks."""
from __future__ import annotations

import logging
import time
from typing import Any, Dict, Tuple

try:
    from prometheus_client import CollectorRegistry, Counter, Histogram, generate_latest, CONTENT_TYPE_LATEST
except Exception:
    CollectorRegistry = None  # type: ignore
    Counter = None  # type: ignore
    Histogram = None  # type: ignore
    generate_latest = None  # type: ignore
    CONTENT_TYPE_LATEST = "text/plain; version=0.0.4; charset=utf-8"

_start_time = time.time()
_total_submissions = 0

_prom_registry = CollectorRegistry() if CollectorRegistry is not None else None
_prom_total_submissions = (
    Counter("contact_total_submissions", "Total contact submissions", registry=_prom_registry)
    if Counter is not None
    else None
)
_prom_request_counter = None
_prom_request_latency = None

if Counter is not None and _prom_registry is not None:
    try:
        _prom_request_counter = Counter(
            "http_requests_total",
            "Total HTTP requests",
            ["method", "endpoint"],
            registry=_prom_registry,
        )
    except Exception:
        _prom_request_counter = None

if Histogram is not None and _prom_registry is not None:
    try:
        _prom_request_latency = Histogram(
            "http_request_duration_seconds",
            "Request duration",
            ["method", "endpoint"],
            registry=_prom_registry,
        )
    except Exception:
        _prom_request_latency = None


def record_submission() -> None:
    """Register a completed contact submission."""
    global _total_submissions
    _total_submissions += 1
    if _prom_total_submissions is not None:
        try:
            _prom_total_submissions.inc()
        except Exception:
            logging.debug("Failed to increment Prometheus submission counter", exc_info=True)


def observe_request(method: str, endpoint: str, start_time: float | None, status: int | None = None) -> None:
    """Update request counters and latency histograms."""
    if _prom_request_counter is not None:
        try:
            _prom_request_counter.labels(method=method, endpoint=endpoint).inc()
        except Exception:
            logging.debug("Failed to increment request counter", exc_info=True)

    if _prom_request_latency is not None and start_time:
        try:
            _prom_request_latency.labels(method=method, endpoint=endpoint).observe(time.time() - start_time)
        except Exception:
            logging.debug("Failed to observe request latency", exc_info=True)


def export_metrics() -> Tuple[Any, int, Dict[str, str]]:
    """Return a Flask-style response tuple for the metrics endpoint."""
    uptime = int(time.time() - _start_time)
    if generate_latest is not None and _prom_registry is not None:
        payload = generate_latest(_prom_registry)
        headers = {"Content-Type": CONTENT_TYPE_LATEST}
        return payload, 200, headers
    body = {"uptime_seconds": uptime, "total_submissions": _total_submissions}
    return body, 200, {"Content-Type": "application/json"}