Add diagnostics support for Nut (#65893)

.coveragerc

@@ -759,6 +759,7 @@ omit =
     homeassistant/components/nuki/const.py
     homeassistant/components/nuki/binary_sensor.py
     homeassistant/components/nuki/lock.py
+    homeassistant/components/nut/diagnostics.py
     homeassistant/components/nx584/alarm_control_panel.py
     homeassistant/components/nzbget/coordinator.py
     homeassistant/components/obihai/*

homeassistant/components/nut/diagnostics.py

@@ -0,0 +1,68 @@
+"""Diagnostics support for Nut."""
+from __future__ import annotations
+
+from typing import Any
+
+import attr
+
+from homeassistant.components.diagnostics import async_redact_data
+from homeassistant.config_entries import ConfigEntry
+from homeassistant.const import CONF_PASSWORD, CONF_USERNAME
+from homeassistant.core import HomeAssistant
+from homeassistant.helpers import device_registry as dr, entity_registry as er
+
+from . import PyNUTData
+from .const import DOMAIN, PYNUT_DATA, PYNUT_UNIQUE_ID
+
+TO_REDACT = {CONF_PASSWORD, CONF_USERNAME}
+
+
+async def async_get_config_entry_diagnostics(
+    hass: HomeAssistant, entry: ConfigEntry
+) -> dict[str, dict[str, Any]]:
+    """Return diagnostics for a config entry."""
+    data = {"entry": async_redact_data(entry.as_dict(), TO_REDACT)}
+    hass_data = hass.data[DOMAIN][entry.entry_id]
+
+    # Get information from Nut library
+    nut_data: PyNUTData = hass_data[PYNUT_DATA]
+    data["nut_data"] = {"ups_list": nut_data.ups_list, "status": nut_data.status}
+
+    # Gather information how this Nut device is represented in Home Assistant
+    device_registry = dr.async_get(hass)
+    entity_registry = er.async_get(hass)
+    hass_device = device_registry.async_get_device(
+        identifiers={(DOMAIN, hass_data[PYNUT_UNIQUE_ID])}
+    )
+    if not hass_device:
+        return data
+
+    data["device"] = {
+        **attr.asdict(hass_device),
+        "entities": {},
+    }
+
+    hass_entities = er.async_entries_for_device(
+        entity_registry,
+        device_id=hass_device.id,
+        include_disabled_entities=True,
+    )
+
+    for entity_entry in hass_entities:
+        state = hass.states.get(entity_entry.entity_id)
+        state_dict = None
+        if state:
+            state_dict = dict(state.as_dict())
+            # The entity_id is already provided at root level.
+            state_dict.pop("entity_id", None)
+            # The context doesn't provide useful information in this case.
+            state_dict.pop("context", None)
+
+        data["device"]["entities"][entity_entry.entity_id] = {
+            **attr.asdict(
+                entity_entry, filter=lambda attr, value: attr.name != "entity_id"
+            ),
+            "state": state_dict,
+        }
+
+    return data