Issue 6538, 6781 - Implement support for snippet filters

lib/snippets.js

Index: lib/snippets.js
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new file mode 100644
--- /dev/null
+++ b/lib/snippets.js
@@ -0,0 +1,77 @@
+/*
+ * 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";
+
+/**
+ * @fileOverview Snippets implementation.
+ */
+
+const {Filter} = require("./filterClasses");
+
+let filters = new Set();
+
+/**
+ * Container for snippet filters
+ * @class
+ */
+let Snippets = {
+  /**
+   * Removes all known filters
+   */
+  clear()
+  {
+    filters.clear();
+  },
+
+  /**
+   * Add a new snippet filter
+   * @param {SnippetFilter} filter
+   */
+  add(filter)
+  {
+    filters.add(filter.text);
+  },
+
+  /**
+   * Removes a snippet filter
+   * @param {SnippetFilter} filter
+   */
+  remove(filter)
+  {
+    filters.delete(filter.text);
+  },
+
+  /**
+   * Returns a list of all scripts active on a particular domain
+   * @param {string} domain
+   * @return {string[]}
+   */
+  getScriptsForDomain(domain)
+  {
+    let result = [];
+    for (let text of filters)
+    {
+      let filter = Filter.fromText(text);

[hub, 2018/07/05 08:40:14]

My concern here is that we parse the filters each time with call this method,
which is about every document.

Is there a reason why `filters` isn't just a Set of (Snippet)Filter objects?
This would avoid the need `Filter.fromText()`

[Manish Jethani, 2018/07/06 13:32:15]

This is an exact copy of lib/elemHideEmulation.js with some renaming. The plan
is to merge the two along with lib/elemHide.js and as part of that this be taken
care of.

See:

https://codereview.adblockplus.org/29783618/
https://codereview.adblockplus.org/29784555/

If you think it's a good idea to do those first then maybe we should do that. I
think maybe it's OK to leave this like it is for now, for the initial
implementation.
I'm not sure why it was done this way in lib/elemHideEmulation.js

+      if (filter.isActiveOnDomain(domain))
+        result.push(filter.script);
+    }
+    return result;
+  }
+};
+
+exports.Snippets = Snippets;