src/telegram: Add TelegramBot#removeTextListener()

Feature:

  This is the opposite action to `TelegramBot#onText()`.
  It allows removing any previously-registered listeners.

  It is similar to `TelegramBot#removeReplyListener()`.

doc/api.md

@@ -49,6 +49,7 @@ TelegramBot
     * [.getFileLink(fileId)](#TelegramBot+getFileLink) ⇒ <code>Promise</code>
     * [.downloadFile(fileId, downloadDir)](#TelegramBot+downloadFile) ⇒ <code>Promise</code>
     * [.onText(regexp, callback)](#TelegramBot+onText)
+    * [.removeTextListener(regexp)](#TelegramBot+removeTextListener) ⇒ <code>Object</code>
     * [.onReplyToMessage(chatId, messageId, callback)](#TelegramBot+onReplyToMessage) ⇒ <code>Number</code>
     * [.removeReplyListener(replyListenerId)](#TelegramBot+removeReplyListener) ⇒ <code>Object</code>
     * [.getChat(chatId)](#TelegramBot+getChat) ⇒ <code>Promise</code>
@@ -597,6 +598,20 @@ Register a RegExp to test against an incomming text message.
 | regexp | <code>RegExp</code> | RegExp to be executed with `exec`. |
 | callback | <code>function</code> | Callback will be called with 2 parameters, the `msg` and the result of executing `regexp.exec` on message text. |
 
+<a name="TelegramBot+removeTextListener"></a>
+
+### telegramBot.removeTextListener(regexp) ⇒ <code>Object</code>
+Remove a listener registered with `onText()`.
+
+**Kind**: instance method of <code>[TelegramBot](#TelegramBot)</code>  
+**Returns**: <code>Object</code> - deletedListener The removed reply listener if
+  found. This object has `regexp` and `callback`
+  properties. If not found, returns `null`.  
+
+| Param | Type | Description |
+| --- | --- | --- |
+| regexp | <code>RegExp</code> | RegExp used previously in `onText()` |
+
 <a name="TelegramBot+onReplyToMessage"></a>
 
 ### telegramBot.onReplyToMessage(chatId, messageId, callback) ⇒ <code>Number</code>

src/telegram.js

@@ -1006,6 +1006,23 @@ class TelegramBot extends EventEmitter {
     this._textRegexpCallbacks.push({ regexp, callback });
   }
 
+  /**
+   * Remove a listener registered with `onText()`.
+   * @param  {RegExp} regexp RegExp used previously in `onText()`
+   * @return {Object} deletedListener The removed reply listener if
+   *   found. This object has `regexp` and `callback`
+   *   properties. If not found, returns `null`.
+   */
+  removeTextListener(regexp) {
+    const index = this._textRegexpCallbacks.findIndex((textListener) => {
+      return textListener.regexp === regexp;
+    });
+    if (index === -1) {
+      return null;
+    }
+    return this._textRegexpCallbacks.splice(index, 1)[0];
+  }
+
   /**
    * Register a reply to wait for a message response.
    * @param  {Number|String}   chatId       The chat id where the message cames from.

test/telegram.js

@@ -987,6 +987,28 @@ describe('TelegramBot', function telegramSuite() {
     });
   });
 
+  describe('#removeTextListener', function removeTextListenerSuite() {
+    const regexp = /\/onText/;
+    const regexp2 = /\/onText/;
+    const callback = function noop() {};
+    after(function after() {
+      bot.removeTextListener(regexp);
+      bot.removeTextListener(regexp2);
+    });
+    it('removes the right text-listener', function test() {
+      bot.onText(regexp, callback);
+      bot.onText(regexp2, callback);
+      const textListener = bot.removeTextListener(regexp);
+      assert.equal(regexp, textListener.regexp);
+      assert.equal(callback, textListener.callback);
+      assert.notEqual(regexp2, textListener.regexp);
+      assert.equal(null, bot.removeTextListener(regexp));
+    });
+    it('returns `null` if missing', function test() {
+      assert.equal(null, bot.removeTextListener(/404/));
+    });
+  });
+
   describe.skip('#onReplyToMessage', function onReplyToMessageSuite() {});
 
   describe('#removeReplyListener', function removeReplyListenerSuite() {