Add message reaction collectors & abstract collectors (#1335)

* message reaction collectors

* docs cleanup

* abstraction

* remove pointless method

* rename reaction collector creator method

* docs and stuff

* fix docs & build

* backwards compatibility, fix docs

* fix docs

* remove deprecated comments

* betterer docs again

* Fix documentation

* Fix Alias to not break depreciated code

src/structures/ReactionCollector.js

@@ -0,0 +1,64 @@
+const Collector = require('./interfaces/Collector');
+const Collection = require('../util/Collection');
+
+/**
+ * @typedef {CollectorOptions} ReactionCollectorOptions
+ * @property {number} max The maximum total amount of reactions to collect.
+ * @property {number} maxEmojis The maximum number of emojis to collect.
+ * @property {number} maxUsers The maximum number of users to react.
+ */
+
+/**
+ * Collects reactions on messages.
+ * @implements {Collector}
+ */
+class ReactionCollector extends Collector {
+
+  /**
+   * @param {Message} message The message upon which to collect reactions.
+   * @param {CollectorFilter} filter The filter to apply to this collector.
+   * @param {ReactionCollectorOptions} [options={}] The options to apply to this collector.
+   */
+  constructor(message, filter, options = {}) {
+    super(message.client, filter, options);
+
+    /**
+     * @type {Message} message The message.
+     */
+    this.message = message;
+
+    /**
+     * @type {Collection} users Users which have reacted.
+     */
+    this.users = new Collection();
+
+    /**
+     * @type {number} total Total number of reactions collected.
+     */
+    this.total = 0;
+
+    this.client.on('messageReactionAdd', this.listener);
+  }
+
+  handle(reaction) {
+    if (reaction.message.id !== this.message.id) return null;
+    return {
+      key: reaction.emoji.id || reaction.emoji.name,
+      value: reaction,
+    };
+  }
+
+  postCheck(reaction, user) {
+    this.users.set(user.id, user);
+    if (this.options.max && ++this.total >= this.options.max) return 'limit';
+    if (this.options.maxEmojis && this.collected.size >= this.options.maxEmojis) return 'emojiLimit';
+    if (this.options.maxUsers && this.users.size >= this.options.maxUsers) return 'userLimit';
+    return null;
+  }
+
+  cleanup() {
+    this.client.removeListener('messageReactionAdd', this.listener);
+  }
+}
+
+module.exports = ReactionCollector;