Initial commit

src/util/LimitedCollection.js

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+'use strict';
+
+const { Collection } = require('@discordjs/collection');
+const { TypeError } = require('../errors/DJSError.js');
+
+/**
+ * Options for defining the behavior of a LimitedCollection
+ * @typedef {Object} LimitedCollectionOptions
+ * @property {?number} [maxSize=Infinity] The maximum size of the Collection
+ * @property {?Function} [keepOverLimit=null] A function, which is passed the value and key of an entry, ran to decide
+ * to keep an entry past the maximum size
+ */
+
+/**
+ * A Collection which holds a max amount of entries.
+ * @extends {Collection}
+ * @param {LimitedCollectionOptions} [options={}] Options for constructing the Collection.
+ * @param {Iterable} [iterable=null] Optional entries passed to the Map constructor.
+ */
+class LimitedCollection extends Collection {
+  constructor(options = {}, iterable) {
+    if (typeof options !== 'object' || options === null) {
+      throw new TypeError('INVALID_TYPE', 'options', 'object', true);
+    }
+    const { maxSize = Infinity, keepOverLimit = null } = options;
+
+    if (typeof maxSize !== 'number') {
+      throw new TypeError('INVALID_TYPE', 'maxSize', 'number');
+    }
+    if (keepOverLimit !== null && typeof keepOverLimit !== 'function') {
+      throw new TypeError('INVALID_TYPE', 'keepOverLimit', 'function');
+    }
+
+    super(iterable);
+
+    /**
+     * The max size of the Collection.
+     * @type {number}
+     */
+    this.maxSize = maxSize;
+
+    /**
+     * A function called to check if an entry should be kept when the Collection is at max size.
+     * @type {?Function}
+     */
+    this.keepOverLimit = keepOverLimit;
+  }
+
+  set(key, value) {
+    if (this.maxSize === 0) return this;
+    if (this.size >= this.maxSize && !this.has(key)) {
+      for (const [k, v] of this.entries()) {
+        const keep = this.keepOverLimit?.(v, k, this) ?? false;
+        if (!keep) {
+          this.delete(k);
+          break;
+        }
+      }
+    }
+    return super.set(key, value);
+  }
+
+  static get [Symbol.species]() {
+    return Collection;
+  }
+}
+
+module.exports = LimitedCollection;