"""Tests for restart-free DSMR subscription management (apply_dsmr_subscription).

These verify that toggling DSMR ingest / changing its topic / changing its sample
interval via the config UI is reflected in the live MQTT subscription without an
app restart.  A fake MQTT manager is injected so no real broker is touched.
"""

from __future__ import annotations

from unittest.mock import MagicMock

import pytest

from app.services import dsmr_ingest


class _FakeMqtt:
    def __init__(self) -> None:
        self.subscribe_calls: list[tuple[str, object]] = []
        self.unsubscribe_calls: list[str] = []

    def subscribe(self, topic: str, handler) -> None:
        self.subscribe_calls.append((topic, handler))

    def unsubscribe(self, topic: str) -> None:
        self.unsubscribe_calls.append(topic)


def _settings(*, enabled: bool = True, topic: str = "dsmr/json", interval: int = 10):
    s = MagicMock()
    s.dsmr_ingest_enabled = enabled
    s.dsmr_mqtt_topic = topic
    s.dsmr_sample_interval_s = interval
    return s


@pytest.fixture()
def fake_mqtt(monkeypatch):
    fake = _FakeMqtt()
    # apply_dsmr_subscription does `from app.integrations.mqtt import mqtt_manager`
    # at call time, so patching the module attribute is picked up.
    monkeypatch.setattr("app.integrations.mqtt.mqtt_manager", fake)
    # Reset (and auto-restore) the module-level "currently subscribed topic".
    monkeypatch.setattr(dsmr_ingest, "_current_dsmr_topic", None)
    return fake


def test_enabled_subscribes_to_topic(fake_mqtt):
    dsmr_ingest.apply_dsmr_subscription(_settings(enabled=True, topic="dsmr/json"))

    assert len(fake_mqtt.subscribe_calls) == 1
    assert fake_mqtt.subscribe_calls[0][0] == "dsmr/json"
    assert fake_mqtt.unsubscribe_calls == []
    assert dsmr_ingest._current_dsmr_topic == "dsmr/json"


def test_disabled_after_enabled_unsubscribes(fake_mqtt):
    dsmr_ingest.apply_dsmr_subscription(_settings(enabled=True, topic="dsmr/json"))
    dsmr_ingest.apply_dsmr_subscription(_settings(enabled=False))

    assert fake_mqtt.unsubscribe_calls == ["dsmr/json"]
    assert dsmr_ingest._current_dsmr_topic is None


def test_topic_change_unsubscribes_old_subscribes_new(fake_mqtt):
    dsmr_ingest.apply_dsmr_subscription(_settings(topic="dsmr/json"))
    dsmr_ingest.apply_dsmr_subscription(_settings(topic="meter/dsmr"))

    assert fake_mqtt.unsubscribe_calls == ["dsmr/json"]
    assert [t for t, _ in fake_mqtt.subscribe_calls] == ["dsmr/json", "meter/dsmr"]
    assert dsmr_ingest._current_dsmr_topic == "meter/dsmr"


def test_reapply_same_topic_resubscribes_fresh_handler(fake_mqtt):
    # A changed sample interval must take effect — the handler is re-bound to a
    # fresh settings snapshot, so re-applying the same topic re-subscribes.
    dsmr_ingest.apply_dsmr_subscription(_settings(topic="dsmr/json", interval=10))
    dsmr_ingest.apply_dsmr_subscription(_settings(topic="dsmr/json", interval=20))

    assert len(fake_mqtt.subscribe_calls) == 2
    assert fake_mqtt.unsubscribe_calls == []  # same topic, no churn
    handler1 = fake_mqtt.subscribe_calls[0][1]
    handler2 = fake_mqtt.subscribe_calls[1][1]
    assert handler1 is not handler2  # fresh closure carrying the new settings


def test_disabled_when_never_enabled_is_noop(fake_mqtt):
    dsmr_ingest.apply_dsmr_subscription(_settings(enabled=False))

    assert fake_mqtt.subscribe_calls == []
    assert fake_mqtt.unsubscribe_calls == []
    assert dsmr_ingest._current_dsmr_topic is None