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