Start work on adding reaction support

src/client/actions/MessageReactionAdd.js

@@ -0,0 +1,38 @@
+const Action = require('./Action');
+const Constants = require('../../util/Constants');
+
+/*
+{ user_id: 'id',
+     message_id: 'id',
+     emoji: { name: '<27>', id: null },
+     channel_id: 'id' } }
+*/
+
+class MessageReactionAdd extends Action {
+  handle(data) {
+    const user = this.client.users.get(data.user_id);
+    if (!user) return false;
+
+    const channel = this.client.channels.get(data.channel_id);
+    if (!channel || channel.type === 'voice') return false;
+
+    const message = channel.messages.get(data.message_id);
+    if (!message) return false;
+
+    if (!data.emoji) return false;
+
+    const reaction = message._addReaction(data.emoji, user);
+
+    if (reaction) {
+      this.client.emit(Constants.Events.MESSAGE_REACTION_ADD, reaction, user);
+    }
+
+    return {
+      message,
+      reaction,
+      user,
+    };
+  }
+}
+
+module.exports = MessageReactionAdd;