feat: early interface with Python

src/home_assistant/event/specific/state_changed.rs

@@ -0,0 +1,34 @@
+use std::str::FromStr;
+
+use pyo3::exceptions::PyValueError;
+use pyo3::prelude::*;
+
+use crate::home_assistant::{entity_id::EntityId, state::State};
+
+#[derive(Debug, Clone)]
+pub struct Type;
+
+impl<'py> FromPyObject<'py> for Type {
+    fn extract_bound(ob: &Bound<'py, PyAny>) -> PyResult<Self> {
+        let s = ob.extract::<&str>()?;
+
+        if s == "state_changed" {
+            Ok(Type)
+        } else {
+            Err(PyValueError::new_err(format!(
+                "expected a string of value 'state_changed', but got {s}"
+            )))
+        }
+    }
+}
+
+#[derive(Debug, FromPyObject)]
+#[pyo3(from_item_all)]
+pub struct Data {
+    pub entity_id: EntityId,
+    pub old_state: Option<State>,
+    pub new_state: Option<State>,
+}
+
+/// A state changed event is fired when on state write the state is changed.
+pub type Event = super::super::event::Event<Type, Data>;