Add GroupDMChannel support

src/structures/GroupDMChannel.js

@@ -0,0 +1,133 @@
+const Channel = require('./Channel');
+const TextBasedChannel = require('./interface/TextBasedChannel');
+const Collection = require('../util/Collection');
+
+/*
+{ type: 3,
+  recipients:
+   [ { username: 'Charlie',
+       id: '123',
+       discriminator: '6631',
+       avatar: '123' },
+     { username: 'Ben',
+       id: '123',
+       discriminator: '2055',
+       avatar: '123' },
+     { username: 'Adam',
+       id: '123',
+       discriminator: '2406',
+       avatar: '123' } ],
+  owner_id: '123',
+  name: null,
+  last_message_id: '123',
+  id: '123',
+  icon: null }
+*/
+
+
+function arraysEqual(a, b) {
+  if (a === b) return true;
+  if (a.length !== b.length) return false;
+
+  for (const itemInd in a) {
+    const item = a[itemInd];
+    const ind = b.indexOf(item);
+    if (ind) {
+      b.splice(ind, 1);
+    }
+  }
+
+  return b.length === 0;
+}
+
+/**
+ * Represents a Group DM on Discord
+ * @extends {Channel}
+ * @implements {TextBasedChannel}
+ */
+class GroupDMChannel extends Channel {
+
+  constructor(client, data) {
+    super(client, data);
+
+    this.messages = new Collection();
+  }
+
+  equals(other) {
+    const base = (
+      this.id === other.id &&
+      this.name === other.name &&
+      this.icon === other.icon &&
+      this.owner.id === other.owner_id
+    );
+
+    if (base) {
+      const thisIDs = this.recipients.array().map(r => r.id);
+      const otherIDs = other.recipients.map(r => r.id);
+      return arraysEqual(thisIDs, otherIDs);
+    }
+
+    return base;
+  }
+
+  setup(data) {
+    super.setup(data);
+
+    if (!this.recipients) {
+      /**
+       * A collection of the recipients of this DM, mapped by their ID.
+       * @type {Collection<String, User>}
+       */
+      this.recipients = new Collection();
+    }
+
+    if (data.recipients) {
+      for (const recipient of data.recipients) {
+        const user = this.client.dataManager.newUser(recipient);
+        this.recipients.set(user.id, user);
+      }
+    }
+    /**
+     * The name of this Group DM, can be null if one isn't set.
+     * @type {String}
+     */
+    this.name = data.name;
+    /**
+     * The ID of this Group DM Channel.
+     * @type {String}
+     */
+    this.id = data.id;
+    /**
+     * A hash of the Group DM icon.
+     * @type {String}
+     */
+    this.icon = data.icon;
+    /**
+     * The ID of the last message in the channel, if one was sent.
+     * @type {?String}
+     */
+    this.lastMessageID = data.last_message_id;
+    /**
+     * The owner of this Group DM.
+     * @type {User}
+     */
+    this.owner = this.client.users.get(data.owner_id);
+  }
+
+  sendMessage() {
+    return;
+  }
+
+  sendTTSMessage() {
+    return;
+  }
+
+  _cacheMessage() {
+    return;
+  }
+
+}
+
+TextBasedChannel.applyToClass(GroupDMChannel, true);
+
+module.exports = GroupDMChannel;