[telegram] Return error on trying to use Polling, WebHook together

Feature:

  Polling and WebHook are mutually exclusive. Therefore, return an
  error whenever the user tries to start polling, and the instance has
  an open webhook, or user tries to open a webhook, and the instance
  is already polling.

README.md

@@ -150,6 +150,7 @@ Emits `message` when a message arrives.
 
 ### telegramBot.startPolling([options]) ⇒ <code>Promise</code>
 Start polling.
+Rejects returned promise if a WebHook is being used by this instance.
 
 **Kind**: instance method of <code>[TelegramBot](#TelegramBot)</code>  
 
@@ -190,6 +191,7 @@ Return true if polling. Otherwise, false.
 ### telegramBot.openWebHook() ⇒ <code>Promise</code>
 Open webhook.
 Multiple invocations do nothing if webhook is already open.
+Rejects returned promise if Polling is being used by this instance.
 
 **Kind**: instance method of <code>[TelegramBot](#TelegramBot)</code>  
 <a name="TelegramBot+closeWebHook"></a>

src/telegram.js

@@ -237,11 +237,15 @@ class TelegramBot extends EventEmitter {
 
   /**
    * Start polling.
+   * Rejects returned promise if a WebHook is being used by this instance.
    * @param  {Object} [options]
    * @param  {Boolean} [options.restart=true] Consecutive calls to this method causes polling to be restarted
    * @return {Promise}
    */
   startPolling(options = {}) {
+    if (this.hasOpenWebHook()) {
+      return Promise.reject(new Error('Polling and WebHook are mutually exclusive'));
+    }
     options.restart = typeof options.restart === 'undefined' ? true : options.restart;
     if (!this._polling) {
       this._polling = new TelegramBotPolling(this._request.bind(this), this.options.polling, this.processUpdate.bind(this));
@@ -284,9 +288,13 @@ class TelegramBot extends EventEmitter {
   /**
    * Open webhook.
    * Multiple invocations do nothing if webhook is already open.
+   * Rejects returned promise if Polling is being used by this instance.
    * @return {Promise}
    */
   openWebHook() {
+    if (this.isPolling()) {
+      return Promise.reject(new Error('WebHook and Polling are mutually exclusive'));
+    }
     if (!this._webHook) {
       this._webHook = new TelegramBotWebHook(this.token, this.options.webHook, this.processUpdate.bind(this));
     }

test/telegram.js

@@ -185,6 +185,12 @@ describe('TelegramBot', function telegramSuite() {
         return utils.isPollingMockServer(pollingPort);
       });
     });
+    it('returns error if using webhook', function test() {
+      return botWebHook.startPolling().catch((err) => {
+        // TODO: check for error in a better way
+        assert.ok(err.message.indexOf('mutually exclusive') !== -1);
+      });
+    });
   });
 
   describe('#isPolling', function isPollingSuite() {
@@ -219,6 +225,12 @@ describe('TelegramBot', function telegramSuite() {
         return utils.hasOpenWebHook(webHookPort);
       });
     });
+    it('returns error if using polling', function test() {
+      return botPolling.openWebHook().catch((err) => {
+        // TODO: check for error in a better way
+        assert.ok(err.message.indexOf('mutually exclusive') !== -1);
+      });
+    });
   });
 
   describe('#hasOpenWebHook', function hasOpenWebHookSuite() {