Introduce internal API call queueing mechanism to send messages sequentially (no more random order)

src/functions/api.js

@@ -1,6 +1,17 @@
 // API methods
 import fetch from './fetch';
 
+/**
+ * Simple replacement for Bluebird's Promise.mapSeries() implementation
+ * @param {Array} tasks to run serially
+ * @param {Function} task function to execute
+ * @return {Promise}
+ */
+function sequence(tasks, fn) {
+  return tasks.reduce((promise, task) => promise.then(() => fn(task)), Promise.resolve());
+}
+
+
 /**
  * API class, has a function for each method of the Telegram API which take
  * an object argument, and send request to the API server
@@ -8,6 +19,7 @@ import fetch from './fetch';
  * Methods: getMe, sendMessage, forwardMessage, sendPhoto, sendAudio,
  * sendDocument, sendSticker, sendVideo, sendLocation, sendChatAction,
  * getUserProfilePhotos, getUpdates
+ *
  */
 export default class API {
   /**
@@ -16,6 +28,29 @@ export default class API {
    */
   constructor(token) {
     this.token = token;
+    this._queue = [];
+    this._inUseQueue = [];
+  }
+
+  /**
+   * Run Telegram API calls serially using internal queueing mechanism
+   * @private
+   */
+  _runQueue() {
+    // implementation taken from https://github.com/yagop/node-telegram-bot-api/issues/192#issuecomment-249488807
+    if (this._inUseQueue.length || !this._queue.length) return;
+
+    this._inUseQueue = this._queue;
+    this._queue = [];
+
+    sequence(this._inUseQueue, request => { //eslint-disable-line
+      return this.request(request.method, request.data)
+        .then(request.resolve)
+        .catch(request.reject);
+    }).then(() => {
+      this._inUseQueue = [];
+      this._runQueue();
+    });
   }
 }
 
@@ -30,6 +65,18 @@ const methods = ['getMe', 'sendMessage', 'forwardMessage', 'sendPhoto',
 
 methods.forEach(method => {
   API.prototype[method] = function (data) { //eslint-disable-line
-    return this.request(method, data);
+    // implementation taken from https://github.com/yagop/node-telegram-bot-api/issues/192#issuecomment-249488807
+    let resolve;
+    let reject;
+
+    const promise = new Promise((_resolve, _reject) => {
+      resolve = _resolve;
+      reject = _reject;
+    });
+
+    this._queue.push({ method, data, resolve, reject });
+    process.nextTick(this._runQueue.bind(this));
+
+    return promise;
   };
 });