Make receiving messages event driven

README.md

@@ -49,14 +49,28 @@ mqtt.connect
 Publish message to topic.
 
 ```ruby
+while !mqtt.connected do
+  ESP32::System.delay(100)
+end
 mqtt.publish("topic", 'message')
 ```
 
-Subscribe to topic and get message.
+Subscribe to one or more topics to receive messages. Received messages are event driven. For each message, the main mruby task pauses temporarily, allowing the block given for the receiving topic to run.
 
 ```ruby
-mqtt.subscribe("topic")
-topic, message = mqtt.get
+mqtt.subscribe("topic1") do |message|
+  puts "Received from topic1: #{message}"
+end
+
+mqtt.on_message_from("topic2") do |message|
+  puts "New message from topic2: #{message}"
+end
+mqtt.subscribe("topic2")
+
+loop do
+  # Do whatever in your main loop.
+  ESP32::System.delay(1000)
+end
 ```
 
 Disconnect.

mrblib/mrb_esp32_mqtt.rb

@@ -1,7 +1,58 @@
 module ESP32
   module MQTT
     class Client
-      attr_accessor :ca, :cert, :key
+      attr_accessor :ca, :cert, :key, :connected
+
+      def initialize(host, port)
+        self._initialize(host, port)
+
+        @connected = false
+        @connect_callbacks = []
+        @message_callbacks = {}
+
+        self.set_connected_handler do
+          @connected = true
+          @connect_callbacks.each { |cb| cb.call }
+          @connect_callbacks = []
+        end
+
+        self.set_disconnected_handler do
+          @connected = false
+        end
+
+        self.set_unsubscribed_handler do |topic|
+          @message_callbacks[topic] = nil
+        end
+
+        # C calls this block with every received message.
+        self.set_data_handler do |topic, message|
+          @message_callbacks[topic].call(message) if @message_callbacks[topic]
+        end
+      end
+
+      def subscribe(topic, &block)
+        @message_callbacks[topic] = block if block
+
+        # Take semaphore
+
+        if @connected
+          self._subscribe(topic)
+        else
+          self.on_connect do
+            self._subscribe(topic)
+          end
+        end
+
+        # Release semaphore
+      end
+
+      def on_connect(&block)
+        @connect_callbacks << block
+      end
+
+      def on_message_from(topic, &block)
+        @message_callbacks[topic] = block
+      end
     end
   end
 end