Issue 4394 - Create a filter class for element hiding emulation filters

lib/common.js

Index: lib/common.js
===================================================================
new file mode 100644
--- /dev/null
+++ b/lib/common.js
@@ -0,0 +1,50 @@
+/*
+ * This file is part of Adblock Plus <https://adblockplus.org/>,
+ * Copyright (C) 2006-2016 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/>.
+ */
+
+/**
+ * Converts filter text into regular expression string
+ * @param {String} text as in Filter()
+ * @return {String} regular expression representation of filter text
+ */
+function filterToRegExp(text)
+{
+  return text
+    // remove multiple wildcards
+    .replace(/\*+/g, "*")
+    // remove anchors following separator placeholder
+    .replace(/\^\|$/, "^")
+    // escape special symbols
+    .replace(/\W/g, "\\$&")
+    // replace wildcards by .*
+    .replace(/\\\*/g, ".*")
+    // process separator placeholders (all ANSI characters but alphanumeric
+    // characters and _%.-)
+    .replace(/\\\^/g, "(?:[\\x00-\\x24\\x26-\\x2C\\x2F\\x3A-\\x40\\x5B-\\x5E\\x60\\x7B-\\x7F]|$)")
+    // process extended anchor at expression start
+    .replace(/^\\\|\\\|/, "^[\\w\\-]+:\\/+(?!\\/)(?:[^\\/]+\\.)?")
+    // process anchor at expression start
+    .replace(/^\\\|/, "^")
+    // process anchor at expression end
+    .replace(/\\\|$/, "$")
+    // remove leading wildcards
+    .replace(/^(\.\*)/, "")
+    // remove trailing wildcards
+    .replace(/(\.\*)$/, "");
+}
+
+if (typeof exports != "undefined")
+  exports.filterToRegExp = filterToRegExp;