feat: Begins breaking out topic listener and publisher as it's own dependency.

Sources/TopicDependencies/TopicPublisher.swift

@@ -0,0 +1,114 @@
+import Dependencies
+import DependenciesMacros
+import MQTTNIO
+import NIO
+
+/// A dependency that is responsible for publishing values to an MQTT broker.
+///
+/// - Note: This dependency only conforms to `TestDependencyKey` because it
+/// requires an active `MQTTClient` to generate the live dependency.
+@DependencyClient
+public struct TopicPublisher: Sendable {
+
+  private var _publish: @Sendable (PublishRequest) async throws -> Void
+
+  /// Create a new topic publisher.
+  ///
+  /// - Parameters:
+  ///   -  publish: Handle the publish request.
+  public init(
+    publish: @Sendable @escaping (PublishRequest) async throws -> Void
+  ) {
+    self._publish = publish
+  }
+
+  /// Publish a new value to the given topic.
+  ///
+  /// - Parameters:
+  ///   - topicName: The topic to publish the new value to.
+  ///   - payload: The value to publish.
+  ///   - qos: The MQTTQoS.
+  ///   - retain: The retain flag.
+  public func publish(
+    to topicName: String,
+    payload: ByteBuffer,
+    qos: MQTTQoS,
+    retain: Bool = false
+  ) async throws {
+    try await _publish(.init(
+      topicName: topicName,
+      payload: payload,
+      qos: qos,
+      retain: retain
+    ))
+  }
+
+  /// Create the live topic publisher with the given `MQTTClient`.
+  ///
+  /// - Parameters:
+  ///   - client: The mqtt broker client to use.
+  public static func live(client: MQTTClient) -> Self {
+    .init(
+      publish: { request in
+        assert(client.isActive(), "Client not connected.")
+        client.logger.trace("Begin publishing to topic: \(request.topicName)")
+        defer { client.logger.trace("Done publishing to topic: \(request.topicName)") }
+        try await client.publish(
+          to: request.topicName,
+          payload: request.payload,
+          qos: request.qos,
+          retain: request.retain
+        )
+      }
+    )
+  }
+
+  /// Represents the parameters required to publish a new value to the
+  /// MQTT broker.
+  public struct PublishRequest: Equatable, Sendable {
+
+    /// The topic to publish the new value to.
+    public let topicName: String
+
+    /// The value to publish.
+    public let payload: ByteBuffer
+
+    /// The qos of the request.
+    public let qos: MQTTQoS
+
+    /// The retain flag for the request.
+    public let retain: Bool
+
+    /// Create a new publish request.
+    ///
+    /// - Parameters:
+    ///   - topicName: The topic to publish to.
+    ///   - payload: The value to publish.
+    ///   - qos: The qos of the request.
+    ///   - retain: The retain flag of the request.
+    public init(
+      topicName: String,
+      payload: ByteBuffer,
+      qos: MQTTQoS,
+      retain: Bool
+    ) {
+      self.topicName = topicName
+      self.payload = payload
+      self.qos = qos
+      self.retain = retain
+    }
+  }
+}
+
+extension TopicPublisher: TestDependencyKey {
+  public static var testValue: TopicPublisher { Self() }
+}
+
+public extension DependencyValues {
+
+  /// A dependency that is responsible for publishing values to an MQTT broker.
+  var topicPublisher: TopicPublisher {
+    get { self[TopicPublisher.self] }
+    set { self[TopicPublisher.self] = newValue }
+  }
+}