Post to MQTT

Co-authored-by: Copilot <copilot@github.com>

app/helpers/MqttClient.rb

@@ -0,0 +1,77 @@
+begin
+  require "mqtt"
+rescue LoadError
+  # Fallback to mosquitto_pub when the mqtt gem is not available.
+end
+
+module MqttClient
+  class << self
+    def publish(topic, payload, retain: false, qos: 0)
+      return false if topic.nil? || topic.empty?
+
+      if defined?(MQTT)
+        publish_with_ruby_mqtt(topic, payload, retain, qos)
+      else
+        publish_with_mosquitto_pub(topic, payload, retain, qos)
+      end
+    rescue StandardError => e
+      warn("[MqttClient] publish failed: #{e.class}: #{e.message}")
+      false
+    end
+
+    private
+
+    def publish_with_ruby_mqtt(topic, payload, retain, qos)
+      options = {
+        host: mqtt_host,
+        port: mqtt_port,
+        keep_alive: 30
+      }
+
+      options[:username] = mqtt_username if mqtt_username
+      options[:password] = mqtt_password if mqtt_password
+
+      MQTT::Client.connect(options) do |client|
+        client.publish(topic, payload.to_s, retain, qos)
+      end
+
+      true
+    end
+
+    def publish_with_mosquitto_pub(topic, payload, retain, qos)
+      command = [
+        "mosquitto_pub",
+        "-h", mqtt_host,
+        "-p", mqtt_port.to_s,
+        "-q", qos.to_s,
+        "-t", topic,
+        "-m", payload.to_s
+      ]
+
+      command << "-r" if retain
+
+      ok = system(*command)
+      warn("[MqttClient] mosquitto_pub failed") unless ok
+      ok
+    end
+
+    def mqtt_host
+      ENV.fetch("MQTT_HOST", "localhost")
+    end
+
+    def mqtt_port
+      Integer(ENV.fetch("MQTT_PORT", "1883"))
+    rescue ArgumentError
+      1883
+    end
+
+    def mqtt_username
+      v = ENV["MQTT_USERNAME"]
+      v.nil? || v.strip.empty? ? nil : v
+    end
+
+    def mqtt_password
+      ENV["MQTT_PASSWORD"]
+    end
+  end
+end