Added MQTTStore.

Sources/ClientLive/Helpers.swift

@@ -68,7 +68,12 @@ extension Sensor: FetchableTopic where Reading: BufferInitalizable {
 
 extension MQTTNIO.MQTTClient {
   
-  func mqttSubscription(topic: String, qos: MQTTQoS = .atLeastOnce, retainAsPublished: Bool = true, retainHandling: MQTTSubscribeInfoV5.RetainHandling = .sendAlways)  -> MQTTSubscribeInfoV5 {
+  func mqttSubscription(
+    topic: String,
+    qos: MQTTQoS = .atLeastOnce,
+    retainAsPublished: Bool = true,
+    retainHandling: MQTTSubscribeInfoV5.RetainHandling = .sendAlways
+  )  -> MQTTSubscribeInfoV5 {
     .init(topicFilter: topic, qos: qos, retainAsPublished: retainAsPublished, retainHandling: retainHandling)
   }
   
@@ -103,7 +108,6 @@ extension MQTTNIO.MQTTClient {
   }
   
   func fetch(setPoint: KeyPath<Topics.SetPoints, String>, setPoints: Topics.SetPoints) -> EventLoopFuture<Double> {
-//    logger.debug("Fetching data for set point: \(setPoint.topic)")
     return fetch(mqttSubscription(topic: setPoints[keyPath: setPoint]))
   }
   

Sources/MQTTStore/MQTTStore.swift

@@ -0,0 +1,95 @@
+import Logging
+import Foundation
+import MQTTNIO
+import NIO
+
+// TODO: This works and allows tests to complete, but should potentially be simplified.
+
+typealias PublishTopicHandler<State> = (inout State, Result<MQTTPublishInfo, Error>) -> Void
+
+struct ServerDetails {
+    let identifier: String
+    let hostname: String
+    let port: Int
+    let version: MQTTClient.Version
+    let cleanSession: Bool
+    let useTLS: Bool
+    let useWebSocket: Bool
+    let webSocketUrl: String
+    let username: String?
+    let password: String?
+}
+
+class MQTTStore<State> {
+  typealias Subscription = (topic: String, onPublish: PublishTopicHandler<State>)
+  
+  var state: State
+  var subscriptions: [Subscription]
+  var client: MQTTClient?
+  var serverDetails: ServerDetails
+  var eventLoopGroup: EventLoopGroup
+  var logger: Logger?
+  
+  init(
+    state: State,
+    subscriptions: [Subscription],
+    serverDetails: ServerDetails,
+    eventLoopGroup: EventLoopGroup,
+    logger: Logger? = nil
+  ) {
+    self.state = state
+    self.subscriptions = subscriptions
+    self.serverDetails = serverDetails
+    self.eventLoopGroup = eventLoopGroup
+    self.logger = logger
+    self.createClient()
+  }
+  
+  private func createClient() {
+    let client = MQTTClient(
+      host: serverDetails.hostname,
+      identifier: serverDetails.identifier,
+      eventLoopGroupProvider: .shared(eventLoopGroup),
+      logger: logger,
+      configuration: .init(
+        version: serverDetails.version,
+        userName: serverDetails.username,
+        password: serverDetails.password,
+        useSSL: serverDetails.useTLS,
+        useWebSockets: serverDetails.useWebSocket,
+        webSocketURLPath: serverDetails.webSocketUrl
+      )
+    )
+    for subscription in subscriptions {
+      client.addPublishListener(
+        named: subscription.topic,
+        { result in subscription.onPublish(&self.state, result) }
+      )
+    }
+    self.client = client
+  }
+  
+  func createSubscriptions() -> EventLoopFuture<Void> {
+    let subscriptionInfo = subscriptions.map { MQTTSubscribeInfo.init(topicFilter: $0.0, qos: .atLeastOnce) }
+    return client?.subscribe(to: subscriptionInfo).map { _ in } ?? eventLoopGroup.next().makeSucceededVoidFuture()
+  }
+  
+  func connect(cleanSession: Bool) -> EventLoopFuture<Bool> {
+    client?.connect(cleanSession: cleanSession) ?? eventLoopGroup.next().makeSucceededFuture(false)
+  }
+  
+  func connectAndSubscribe(cleanSession: Bool) -> EventLoopFuture<Void> {
+    connect(cleanSession: cleanSession)
+      .flatMap{ _ in self.createSubscriptions() }
+  }
+  
+  func destroy() -> EventLoopFuture<Void> {
+    guard let client = client else {
+      return eventLoopGroup.next().makeSucceededVoidFuture()
+    }
+    return client.disconnect().map { _ in
+      try? self.client?.syncShutdownGracefully()
+      self.client = nil
+    }
+  }
+}