Fixed acknowledging of channels (#1411)

* Fixed acknowledging of channels

* using channel#lastMessageID and resolve when it's not present

src/client/rest/RESTMethods.js

@@ -159,7 +159,9 @@ class RESTMethods {
   }
 
   ackTextChannel(channel) {
-    return this.rest.makeRequest('post', Endpoints.Channel(channel).ack, true, { token: this._ackToken }).then(res => {
+    return this.rest.makeRequest('post', Endpoints.Channel(channel).Message(channel.lastMessageID).ack, true, {
+      token: this._ackToken,
+    }).then(res => {
       if (res.token) this._ackToken = res.token;
       return channel;
     });

src/structures/interfaces/TextBasedChannel.js

@@ -385,7 +385,8 @@ class TextBasedChannel {
    * @returns {Promise<TextChannel|GroupDMChannel|DMChannel>}
    */
   acknowledge() {
-    return this.client.rest.methods.ackTextMessage(this);
+    if (!this.lastMessageID) return Promise.resolve(this);
+    return this.client.rest.methods.ackTextChannel(this);
   }
 
   _cacheMessage(message) {
@@ -480,6 +481,7 @@ exports.applyToClass = (structure, full = false, ignore = []) => {
   if (full) {
     props.push(
       '_cacheMessage',
+      'acknowledge',
       'fetchMessages',
       'fetchMessage',
       'search',

src/util/Constants.js

@@ -155,7 +155,6 @@ const Endpoints = exports.Endpoints = {
       permissions: `${base}/permissions`,
       webhooks: `${base}/webhooks`,
       search: `${base}/messages/search`,
-      ack: `${base}/ack`,
       pins: `${base}/pins`,
       Pin: messageID => `${base}/pins/${messageID}`,
       Recipient: recipientID => `${base}/recipients/${recipientID}`,