Issue 7285 - Abstract caching logic

lib/caching.js

Index: lib/caching.js
===================================================================
new file mode 100644
--- /dev/null
+++ b/lib/caching.js
@@ -0,0 +1,81 @@
+/*
+ * This file is part of Adblock Plus <https://adblockplus.org/>,
+ * Copyright (C) 2006-present eyeo GmbH
+ *
+ * Adblock Plus is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 3 as
+ * published by the Free Software Foundation.
+ *
+ * Adblock Plus is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with Adblock Plus.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+"use strict";
+
+/**
+ * A <code>Cache</code> object represents a cache of arbitrary data.
+ */
+class Cache
+{
+  /**
+   * Creates a cache.
+   * @param {number} capacity The maximum number of entries that can exist in
+   *   the cache.
+   */
+  constructor(capacity)
+  {
+    if (isNaN(capacity))
+      throw new Error("capacity must be a number.");
+
+    this._capacity = capacity;
+    this._storage = new Map();
+  }
+
+  /**
+   * Reads an entry from the cache.
+   * @param {?*} key The key for the entry.
+   * @returns {?*} The value of the entry, or <code>undefined</code> if the
+   *   entry doesn't exist in the cache.
+   */
+  read(key)

[hub, 2019/02/14 20:43:00]

I think I would still have names these methods `get` and `set`.

[Manish Jethani, 2019/02/16 12:17:17]

Done.

+  {
+    return this._storage.get(key);
+  }
+
+  /**
+   * Saves an entry into the cache. If the cache has reached the specified
+   * maximum number of entries, all the old entries are cleared first.
+   * @param {?*} key The key for the entry.
+   * @param {?*} value The value of the entry.
+   */
+  save(key, value)
+  {
+    // To prevent logical errors, neither key nor value is allowed to be
+    // undefined.
+    if (typeof key == "undefined")
+      throw new Error("key must not be undefined.");
+
+    if (typeof value == "undefined")
+      throw new Error("value must not be undefined.");
+
+    if (this._storage.size >= this._capacity)
+      this._storage.clear();
+
+    this._storage.set(key, value);
+  }
+
+  /**
+   * Clears the cache.
+   */
+  clear()
+  {
+    this._storage.clear();
+  }
+}
+
+exports.Cache = Cache;