"""OpenTelemetry metrics with Prometheus export.

Provides ``init_metrics()`` to lazily initialise the MeterProvider and all
business metric instruments.  Safe to call from both the API and Celery
workers — the provider is created at most once per process.
"""
from __future__ import annotations

from opentelemetry.metrics import (
    Counter,
    Histogram,
    Meter,
    UpDownCounter,
    get_meter,
    set_meter_provider,
)
from opentelemetry.sdk.metrics import MeterProvider
from opentelemetry.sdk.resources import SERVICE_NAME, Resource
from opentelemetry.exporter.prometheus import PrometheusMetricReader
from prometheus_client import make_asgi_app

_reader: PrometheusMetricReader | None = None
_meter: Meter | None = None

# ---------------------------------------------------------------------------
# Scrape metrics
# ---------------------------------------------------------------------------
scrape_listings_found: Counter
scrape_listings_processed: Counter
scrape_listings_failed: Counter
scrape_duration_seconds: Histogram
scrape_pages_fetched: Counter
scrape_subqueries_total: Counter

# ---------------------------------------------------------------------------
# Throttle / circuit-breaker metrics
# ---------------------------------------------------------------------------
throttle_events_total: Counter
# circuit_breaker_state is registered as an ObservableGauge in circuit_breaker.py

# ---------------------------------------------------------------------------
# API / cache metrics
# ---------------------------------------------------------------------------
geojson_cache_operations: Counter

# ---------------------------------------------------------------------------
# OCR metrics
# ---------------------------------------------------------------------------
ocr_attempts: Counter
ocr_successes: Counter

# ---------------------------------------------------------------------------
# Celery task metrics
# ---------------------------------------------------------------------------
celery_tasks_total: Counter
celery_task_duration_seconds: Histogram
celery_tasks_active: UpDownCounter


def init_metrics(service_name: str = "realestate-crawler") -> PrometheusMetricReader:
    """Initialise the OTel MeterProvider and define all instruments.

    Returns the ``PrometheusMetricReader`` so the API can mount the ASGI app.
    Calling this more than once is a no-op (returns the existing reader).
    """
    global _reader, _meter
    global scrape_listings_found, scrape_listings_processed, scrape_listings_failed
    global scrape_duration_seconds, scrape_pages_fetched, scrape_subqueries_total
    global throttle_events_total
    global geojson_cache_operations
    global ocr_attempts, ocr_successes
    global celery_tasks_total, celery_task_duration_seconds, celery_tasks_active

    if _reader is not None:
        return _reader

    _reader = PrometheusMetricReader()
    provider = MeterProvider(
        metric_readers=[_reader],
        resource=Resource.create({SERVICE_NAME: service_name}),
    )
    set_meter_provider(provider)
    _meter = get_meter(__name__)

    # -- Scrape --
    scrape_listings_found = _meter.create_counter(
        "scrape_listings_found_total",
        description="Total listings discovered during scrape runs",
    )
    scrape_listings_processed = _meter.create_counter(
        "scrape_listings_processed_total",
        description="Total listings successfully processed",
    )
    scrape_listings_failed = _meter.create_counter(
        "scrape_listings_failed_total",
        description="Total listings that failed processing",
    )
    scrape_duration_seconds = _meter.create_histogram(
        "scrape_duration_seconds",
        description="Duration of a full scrape run in seconds",
    )
    scrape_pages_fetched = _meter.create_counter(
        "scrape_pages_fetched_total",
        description="Total API pages fetched during scraping",
    )
    scrape_subqueries_total = _meter.create_counter(
        "scrape_subqueries_total",
        description="Total subqueries executed after query splitting",
    )

    # -- Throttle --
    throttle_events_total = _meter.create_counter(
        "throttle_events_total",
        description="Total throttling events by type",
    )

    # -- Cache --
    geojson_cache_operations = _meter.create_counter(
        "geojson_cache_operations_total",
        description="GeoJSON cache operations (hit/miss)",
    )

    # -- OCR --
    ocr_attempts = _meter.create_counter(
        "ocr_attempts_total",
        description="Total OCR detection attempts",
    )
    ocr_successes = _meter.create_counter(
        "ocr_successes_total",
        description="Total OCR detections that found square meters",
    )

    # -- Celery --
    celery_tasks_total = _meter.create_counter(
        "celery_tasks_total",
        description="Total Celery tasks by name and status",
    )
    celery_task_duration_seconds = _meter.create_histogram(
        "celery_task_duration_seconds",
        description="Duration of Celery tasks in seconds",
    )
    celery_tasks_active = _meter.create_up_down_counter(
        "celery_tasks_active",
        description="Currently active Celery tasks",
    )

    return _reader


def get_metrics_asgi_app():  # type: ignore[no-untyped-def]
    """Return the Prometheus ASGI app for mounting at /metrics."""
    return make_asgi_app()