Add MOS gate control via select entity

Adds a Select entity with four options (Normal / Charge Disabled /
Discharge Disabled / Both Disabled) that sends the 0xE1 write command
to the BMS and immediately refreshes sensor state.  Current option is
derived from the mos_charge_enabled / mos_discharge_enabled bits
already parsed on every poll.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

custom_components/xiaoxiang_bms/select.py

@@ -0,0 +1,73 @@
+"""Select entity for Xiaoxiang Smart BMS MOS gate control."""
+from __future__ import annotations
+
+from homeassistant.components.select import SelectEntity
+from homeassistant.config_entries import ConfigEntry
+from homeassistant.core import HomeAssistant
+from homeassistant.helpers.entity_platform import AddEntitiesCallback
+from homeassistant.helpers.update_coordinator import CoordinatorEntity
+
+from .const import (
+    DOMAIN,
+    MOS_BOTH_OFF,
+    MOS_CHARGE_OFF,
+    MOS_DISCHARGE_OFF,
+    MOS_NORMAL,
+)
+from .coordinator import BmsCoordinator
+
+# Maps the human-readable option to the XX byte value in the write command
+_OPTION_TO_VALUE: dict[str, int] = {
+    "Normal":           MOS_NORMAL,
+    "Charge Disabled":  MOS_CHARGE_OFF,
+    "Discharge Disabled": MOS_DISCHARGE_OFF,
+    "Both Disabled":    MOS_BOTH_OFF,
+}
+_OPTIONS = list(_OPTION_TO_VALUE)
+
+
+async def async_setup_entry(
+    hass: HomeAssistant,
+    entry: ConfigEntry,
+    async_add_entities: AddEntitiesCallback,
+) -> None:
+    coordinator: BmsCoordinator = hass.data[DOMAIN][entry.entry_id]
+    async_add_entities([BmsMosSelect(coordinator)])
+
+
+class BmsMosSelect(CoordinatorEntity[BmsCoordinator], SelectEntity):
+    """Dropdown to control the BMS charge/discharge MOSFET gates.
+
+    Current state is derived from the MOS status bits returned by the BMS
+    on every poll.  Selecting an option sends the write command (0xE1)
+    immediately and triggers a coordinator refresh so sensors update.
+    """
+
+    _attr_has_entity_name = True
+    _attr_name = "MOS Control"
+    _attr_options = _OPTIONS
+    _attr_icon = "mdi:electric-switch"
+
+    def __init__(self, coordinator: BmsCoordinator) -> None:
+        super().__init__(coordinator)
+        self._attr_unique_id = f"{coordinator.address}_mos_control"
+        self._attr_device_info = coordinator.device_info
+
+    @property
+    def current_option(self) -> str | None:
+        data = self.coordinator.data
+        if not data:
+            return None
+        charge    = data.get("mos_charge_enabled", True)
+        discharge = data.get("mos_discharge_enabled", True)
+        if charge and discharge:
+            return "Normal"
+        if not charge and discharge:
+            return "Charge Disabled"
+        if charge and not discharge:
+            return "Discharge Disabled"
+        return "Both Disabled"
+
+    async def async_select_option(self, option: str) -> None:
+        value = _OPTION_TO_VALUE[option]
+        await self.coordinator.async_write_mos(value)