src/telegram: Add metadata argument in `message` event (and friends)

References:

  * FR: https://github.com/yagop/node-telegram-bot-api/issues/409
  * PR: https://github.com/yagop/node-telegram-bot-api/pull/413

CHANGELOG.md

@@ -7,7 +7,9 @@ This project adheres to [Semantic Versioning](http://semver.org/).
 
 Added:
 
-* Add support for Node.js v9
+1. Add `metadata` argument in `message` event (and
+   friends e.g. `text`, `audio`, etc.) (#409) (by @jlsjonas, @GochoMugo)
+1. Add support for Node.js v9 (by @GochoMugo)
 
 Changed:
 

doc/usage.md

@@ -8,17 +8,19 @@
 <a name="events"></a>
 ## Events
 
-*TelegramBot* is an event-emitter that emits the following events:
+*TelegramBot* is an [EventEmitter](https://nodejs.org/api/events.html#events_class_eventemitter)
+that emits the following events:
 
 1. `message`: Received a new incoming [Message][message] of any kind
   1. Depending on the properties of the [Message][message], one of these
-     events will **ALSO** be emitted: `text`, `audio`, `document`, `photo`,
+     events may **ALSO** be emitted: `text`, `audio`, `document`, `photo`,
      `sticker`, `video`, `voice`, `contact`, `location`,
      `new_chat_members`, `left_chat_member`, `new_chat_title`,
      `new_chat_photo`, `delete_chat_photo`, `group_chat_created`,
      `game`, `pinned_message`, `migrate_from_chat_id`, `migrate_to_chat_id`,
      `channel_chat_created`, `supergroup_chat_created`,
      `successful_payment`, `invoice`, `video_note`
+  1. **Arguments**: `message` ([Message][message]), `metadata` (`{ type?:string }`)
   1. `new_chat_participant`, `left_chat_participant` are **deprecated**
 1. `callback_query`: Received a new incoming [Callback Query][callback-query]
 1. `inline_query`: Received a new incoming [Inline Query][inline-query]

src/telegram.js

@@ -531,14 +531,15 @@ class TelegramBot extends EventEmitter {
 
     if (message) {
       debug('Process Update message %j', message);
-      this.emit('message', message);
-      const processMessageType = messageType => {
-        if (message[messageType]) {
-          debug('Emitting %s: %j', messageType, message);
-          this.emit(messageType, message);
-        }
-      };
-      TelegramBot.messageTypes.forEach(processMessageType);
+      const metadata = {};
+      metadata.type = TelegramBot.messageTypes.find((messageType) => {
+        return message[messageType];
+      });
+      this.emit('message', message, metadata);
+      if (metadata.type) {
+        debug('Emitting %s: %j', metadata.type, message);
+        this.emit(metadata.type, message, metadata);
+      }
       if (message.text) {
         debug('Text message');
         this._textRegexpCallbacks.some(reg => {