Add Button component

src/homeassistant/button.rs

@@ -0,0 +1,40 @@
+//! Tools for publishing a [Home Assistant button](https://www.home-assistant.io/integrations/button.mqtt/).
+use core::ops::Deref;
+
+use serde::Serialize;
+
+use crate::{homeassistant::Component, Error, Topic};
+
+/// The type of button.
+#[derive(Serialize)]
+#[serde(rename_all = "snake_case")]
+#[allow(missing_docs)]
+pub enum ButtonClass {
+    Identify,
+    Restart,
+    Update,
+}
+
+/// A button that can be pressed.
+#[derive(Serialize)]
+pub struct Button {
+    /// The type of button.
+    pub device_class: Option<ButtonClass>,
+}
+
+impl Component for Button {
+    type State = ();
+
+    fn platform() -> &'static str {
+        "button"
+    }
+
+    async fn publish_state<T: Deref<Target = str>>(
+        &self,
+        _topic: &Topic<T>,
+        _state: Self::State,
+    ) -> Result<(), Error> {
+        // Buttons don't have a state
+        Err(Error::Invalid)
+    }
+}

src/homeassistant/light.rs

@@ -324,9 +324,6 @@ impl Serialize for LightState<'_> {
 
 /// A light entity
 pub struct Light<'a, const C: usize, const E: usize> {
-    /// A command topic that Home Assistant can use to control the light.
-    /// It will be sent a [`LightState`] payload.
-    pub command_topic: Option<Topic<&'a str>>,
     /// The color modes supported by the light.
     pub supported_color_modes: [SupportedColorMode; C],
     /// Any effects that can be used.
@@ -338,7 +335,7 @@ impl<const C: usize, const E: usize> Serialize for Light<'_, C, E> {
     where
         S: Serializer,
     {
-        let mut len = 3;
+        let mut len = 2;
 
         if C > 0 {
             len += 1;
@@ -350,7 +347,6 @@ impl<const C: usize, const E: usize> Serialize for Light<'_, C, E> {
 
         let mut serializer = serializer.serialize_struct("Light", len)?;
 
-        serializer.serialize_field("cmd_t", &self.command_topic)?;
         serializer.serialize_field("schema", "json")?;
 
         if C > 0 {

src/homeassistant/mod.rs

@@ -20,7 +20,8 @@
 //!     unique_id: Some("motion"),
 //!     name: "Motion",
 //!     availability: AvailabilityTopics::All([DEVICE_AVAILABILITY_TOPIC]),
-//!     state_topic: MOTION_STATE_TOPIC,
+//!     state_topic: Some(MOTION_STATE_TOPIC),
+//!     command_topic: None,
 //!     component: BinarySensor {
 //!         device_class: Some(BinarySensorClass::Motion),
 //!     },
@@ -49,6 +50,7 @@ use crate::{
 };
 
 pub mod binary_sensor;
+pub mod button;
 pub mod light;
 pub mod sensor;
 mod ser;
@@ -206,7 +208,9 @@ pub struct Entity<'a, const A: usize, C: Component> {
     /// determine this entity's availability.
     pub availability: AvailabilityTopics<'a, A>,
     /// The state topic that this entity's state is published to.
-    pub state_topic: Topic<&'a str>,
+    pub state_topic: Option<Topic<&'a str>>,
+    /// The command topic that this entity receives commands from.
+    pub command_topic: Option<Topic<&'a str>>,
     /// The specific entity.
     pub component: C,
 }
@@ -233,8 +237,16 @@ impl<const A: usize, C: Component> Entity<'_, A, C> {
     }
 
     /// Publishes this entity's state to the broker.
+    ///
+    /// # Errors
+    ///
+    /// - [`Error::Invalid`] if the entity doesn't have a state topic.
     pub async fn publish_state(&self, state: C::State) -> Result<(), Error> {
-        self.component.publish_state(&self.state_topic, state).await
+        if let Some(topic) = self.state_topic {
+            self.component.publish_state(&topic, state).await
+        } else {
+            Err(Error::Invalid)
+        }
     }
 }
 

src/homeassistant/ser.rs

@@ -88,7 +88,13 @@ impl<const A: usize, C: Component, S: Serializer> Serializer for DiscoverySerial
         name: &'static str,
         mut len: usize,
     ) -> Result<Self::SerializeStruct, Self::Error> {
-        len += 6;
+        len += 5;
+        if self.discovery.state_topic.is_some() {
+            len += 1;
+        }
+        if self.discovery.command_topic.is_some() {
+            len += 1;
+        }
         if self.discovery.unique_id.is_some() {
             len += 1;
         }
@@ -104,7 +110,18 @@ impl<const A: usize, C: Component, S: Serializer> Serializer for DiscoverySerial
         serializer.serialize_field("obj_id", self.discovery.object_id)?;
 
         serializer.serialize_field("name", self.discovery.name)?;
-        serializer.serialize_field("stat_t", &self.discovery.state_topic)?;
+
+        if let Some(t) = self.discovery.state_topic {
+            serializer.serialize_field("stat_t", &t)?;
+        } else {
+            serializer.skip_field("stat_t")?;
+        }
+
+        if let Some(t) = self.discovery.command_topic {
+            serializer.serialize_field("cmd_t", &t)?;
+        } else {
+            serializer.skip_field("cmd_t")?;
+        }
 
         match &self.discovery.availability {
             AvailabilityTopics::None => {

src/lib.rs

@@ -68,6 +68,8 @@ pub enum Error {
     TooLarge,
     /// A packet or payload could not be decoded or encoded.
     PacketError,
+    /// An invalid or unsupported operation was attempted.
+    Invalid,
 }
 
 #[allow(clippy::large_enum_variant)]