Add support for selectors in services.yaml (#43162)

* Add support for selectors in services.yaml

* Add base schema validation

homeassistant/helpers/selector.py

@@ -0,0 +1,57 @@
+"""Selectors for Home Assistant."""
+from typing import Any, Callable, Dict, cast
+
+import voluptuous as vol
+
+from homeassistant.util import decorator
+
+SELECTORS = decorator.Registry()
+
+
+def validate_selector(config: Any) -> Dict:
+    """Validate a selector."""
+    if not isinstance(config, dict):
+        raise vol.Invalid("Expected a dictionary")
+
+    if len(config) != 1:
+        raise vol.Invalid(f"Only one type can be specified. Found {', '.join(config)}")
+
+    selector_type = list(config)[0]
+
+    seslector_class = SELECTORS.get(selector_type)
+
+    if seslector_class is None:
+        raise vol.Invalid(f"Unknown selector type {selector_type} found")
+
+    return cast(Dict, seslector_class.CONFIG_SCHEMA(config[selector_type]))
+
+
+class Selector:
+    """Base class for selectors."""
+
+    CONFIG_SCHEMA: Callable
+
+
+@SELECTORS.register("entity")
+class EntitySelector(Selector):
+    """Selector of a single entity."""
+
+    CONFIG_SCHEMA = vol.Schema(
+        {
+            vol.Optional("integration"): str,
+            vol.Optional("domain"): str,
+        }
+    )
+
+
+@SELECTORS.register("device")
+class DeviceSelector(Selector):
+    """Selector of a single device."""
+
+    CONFIG_SCHEMA = vol.Schema(
+        {
+            vol.Optional("integration"): str,
+            vol.Optional("manufacturer"): str,
+            vol.Optional("model"): str,
+        }
+    )