"""Exports the domain's counters; the only module that names prometheus_client.

`rag/metrics.py` defines what is counted and why. This decides how it leaves
the process, and is imported lazily so the service runs — and the suite passes
— with no metrics stack installed.

Counter names carry a `duocthu_` prefix and a `_total` suffix because that is
what Prometheus expects of a counter; the dashboard queries them by name.
"""
from __future__ import annotations

from typing import Any

from rag.metrics import (
    ABSTENTION,
    ANSWER_EXTRACTIVE,
    GENERATION_REJECTED,
    GENERATION_SERVED,
    RETRIEVAL_ROUTE,
)

_LABELS: dict[str, tuple[str, ...]] = {
    ABSTENTION: ("reason",),
    GENERATION_REJECTED: ("reason",),
    RETRIEVAL_ROUTE: ("route",),
    GENERATION_SERVED: (),
    ANSWER_EXTRACTIVE: (),
}

_HELP = {
    ABSTENTION: "Answers refused, by the reason retrieval gave.",
    GENERATION_REJECTED: (
        "Generations discarded before reaching the caller. `reason=\"ungrounded_number\"` "
        "counts answers that stated a figure absent from the cited source."
    ),
    GENERATION_SERVED: "Generations that passed grounding verification and were served.",
    ANSWER_EXTRACTIVE: "Answers served as verbatim source text.",
    RETRIEVAL_ROUTE: "Retrievals by route: section filter, or similarity fallback.",
}


class PrometheusMetrics:
    """Domain `Metrics` backed by a Prometheus registry."""

    def __init__(self, registry: Any | None = None) -> None:
        from prometheus_client import CollectorRegistry, Counter

        self._registry = registry or CollectorRegistry()
        self._counters = {
            name: Counter(name, _HELP[name], labels, registry=self._registry)
            for name, labels in _LABELS.items()
        }

    @property
    def registry(self) -> Any:
        return self._registry

    def increment(self, name: str, **labels: str) -> None:
        counter = self._counters.get(name)
        if counter is None:
            return
        # An unexpected label would raise at scrape time, far from its cause.
        # Metrics must not be able to break a clinical answer, so a mismatch
        # drops the sample rather than the request.
        expected = set(_LABELS[name])
        if set(labels) != expected:
            return
        (counter.labels(**labels) if labels else counter).inc()

    def render(self) -> tuple[bytes, str]:
        from prometheus_client import CONTENT_TYPE_LATEST, generate_latest

        return generate_latest(self._registry), CONTENT_TYPE_LATEST