Issue 6665 - Abstract element hiding container logic into its own module

lib/elemHide.js

Index: lib/elemHide.js
===================================================================
--- a/lib/elemHide.js
+++ b/lib/elemHide.js
@@ -20,177 +20,195 @@
 /**
  * @fileOverview Element hiding implementation.
  */
 
 const {ElemHideExceptions} = require("./elemHideExceptions");
 const {FilterNotifier} = require("./filterNotifier");
 
 /**
- * Lookup table, active flag, by filter by domain.
- * (Only contains filters that aren't unconditionally matched for all domains.)
- * @type {Map.<string,Map.<Filter,boolean>>}
- */
-let filtersByDomain = new Map();
-
-/**
- * Lookup table, filter by selector. (Only used for selectors that are
- * unconditionally matched for all domains.)
- * @type {Map.<string,Filter>}
- */
-let filterBySelector = new Map();
-
-/**
- * This array caches the keys of filterBySelector table (selectors
- * which unconditionally apply on all domains). It will be null if the
- * cache needs to be rebuilt.
- * @type {?string[]}
- */
-let unconditionalSelectors = null;
-
-/**
  * Map to be used instead when a filter has a blank domains property.
  * @type {Map.<string,boolean>}
  * @const
  */
 let defaultDomains = new Map([["", true]]);
 
 /**
- * Set containing known element hiding filters
- * @type {Set.<ElemHideFilter>}
+ * Template for element hiding and element hiding emulation filter containers
+ * @class
  */
-let knownFilters = new Set();
-
-/**
- * Adds a filter to the lookup table of filters by domain.
- * @param {Filter} filter
- */
-function addToFiltersByDomain(filter)
+function ElemHideTemplate()
 {
-  let domains = filter.domains || defaultDomains;
-  for (let [domain, isIncluded] of domains)
-  {
-    // There's no need to note that a filter is generically disabled.
-    if (!isIncluded && domain == "")
-      continue;
+  this._filtersByDomain = new Map();
+  this._filterBySelector = new Map();
+  this._unconditionalSelectors = null;
+  this._knownFilters = new Set();
 
-    let filters = filtersByDomain.get(domain);
-    if (!filters)
-      filtersByDomain.set(domain, filters = new Map());
-    filters.set(filter, isIncluded);
-  }
+  ElemHideExceptions.on("added", this._onExceptionAdded.bind(this));
 }
 
-/**
- * Returns a list of selectors that apply on each website unconditionally.
- * @returns {string[]}
- */
-function getUnconditionalSelectors()
-{
-  if (!unconditionalSelectors)
-    unconditionalSelectors = [...filterBySelector.keys()];
+ElemHideTemplate.prototype = {
+  /**
+   * Lookup table, active flag, by filter by domain.
+   * (Only contains filters that aren't unconditionally matched for all
+   * domains.)
+   * @type {Map.<string,Map.<Filter,boolean>>}
+   */
+  _filtersByDomain: null,
+
+  /**
+   * Lookup table, filter by selector. (Only used for selectors that are
+   * unconditionally matched for all domains.)
+   * @type {Map.<string,Filter>}
+   */
+  _filterBySelector: null,
 
-  return unconditionalSelectors;
-}
+  /**
+   * This array caches the keys of _filterBySelector table (selectors
+   * which unconditionally apply on all domains). It will be null if the
+   * cache needs to be rebuilt.
+   * @type {?string[]}
+   */
+  _unconditionalSelectors: null,
 
-ElemHideExceptions.on("added", ({selector}) =>
-{
-  // If this is the first exception for a previously unconditionally applied
-  // element hiding selector we need to take care to update the lookups.
-  let unconditionalFilterForSelector = filterBySelector.get(selector);
-  if (unconditionalFilterForSelector)
+  /**
+   * Set containing known element hiding filters
+   * @type {Set.<ElemHideFilter>}
+   */
+  _knownFilters: null,
+
+  /**
+   * Adds a filter to the lookup table of filters by domain.
+   * @param {Filter} filter
+   */
+  _addToFiltersByDomain(filter)
   {
-    addToFiltersByDomain(unconditionalFilterForSelector);
-    filterBySelector.delete(selector);
-    unconditionalSelectors = null;
-  }
+    let domains = filter.domains || defaultDomains;
+    for (let [domain, isIncluded] of domains)
+    {
+      // There's no need to note that a filter is generically disabled.
+      if (!isIncluded && domain == "")
+        continue;
 
-  FilterNotifier.emit("elemhideupdate");
-});
+      let filters = this._filtersByDomain.get(domain);
+      if (!filters)
+        this._filtersByDomain.set(domain, filters = new Map());
+      filters.set(filter, isIncluded);
+    }
+  },
+
+  /**
+   * Returns a list of selectors that apply on each website unconditionally.
+   * @returns {string[]}
+   */
+  _getUnconditionalSelectors()
+  {
+    if (!this._unconditionalSelectors)
+      this._unconditionalSelectors = [...this._filterBySelector.keys()];
 
-ElemHideExceptions.on("removed", () =>
-{
-  FilterNotifier.emit("elemhideupdate");
-});
+    return this._unconditionalSelectors;
+  },
+
+  /**
+   * Handles the event when a new element hiding exception has been added
+   * @param {ElemHideException} exception
+   */
+  _onExceptionAdded(exception)
+  {
+    let {selector} = exception;
 
-/**
- * Container for element hiding filters
- * @class
- */
-exports.ElemHide = {
+    // If this is the first exception for a previously unconditionally applied
+    // element hiding selector we need to take care to update the lookups.
+    let unconditionalFilterForSelector = this._filterBySelector.get(selector);
+    if (unconditionalFilterForSelector)
+    {
+      this._addToFiltersByDomain(unconditionalFilterForSelector);
+      this._filterBySelector.delete(selector);
+      this._unconditionalSelectors = null;
+    }
+  },
+
   /**
    * Removes all known filters
    */
   clear()
   {
-    for (let collection of [filtersByDomain, filterBySelector,
-                            knownFilters])
+    for (let collection of [this._filtersByDomain, this._filterBySelector,
+                            this._knownFilters])
     {
       collection.clear();
     }
-    unconditionalSelectors = null;
+    this._unconditionalSelectors = null;
     FilterNotifier.emit("elemhideupdate");
   },
 
   /**
    * Add a new element hiding filter
    * @param {ElemHideFilter} filter
    */
   add(filter)
   {
-    if (knownFilters.has(filter))
+    if (this._knownFilters.has(filter))
       return;
 
     if (!(filter.domains || ElemHideExceptions.hasExceptions(filter.selector)))
     {
       // The new filter's selector is unconditionally applied to all domains
-      filterBySelector.set(filter.selector, filter);
-      unconditionalSelectors = null;
+      this._filterBySelector.set(filter.selector, filter);
+      this._unconditionalSelectors = null;
     }
     else
     {
       // The new filter's selector only applies to some domains
-      addToFiltersByDomain(filter);
+      this._addToFiltersByDomain(filter);
     }
 
-    knownFilters.add(filter);
+    this._knownFilters.add(filter);
     FilterNotifier.emit("elemhideupdate");
   },
 
   /**
    * Removes an element hiding filter
    * @param {ElemHideFilter} filter
    */
   remove(filter)
   {
-    if (!knownFilters.has(filter))
+    if (!this._knownFilters.has(filter))
       return;
 
     // Unconditially applied element hiding filters
-    if (filterBySelector.get(filter.selector) == filter)
+    if (this._filterBySelector.get(filter.selector) == filter)
     {
-      filterBySelector.delete(filter.selector);
-      unconditionalSelectors = null;
+      this._filterBySelector.delete(filter.selector);
+      this._unconditionalSelectors = null;
     }
     // Conditionally applied element hiding filters
     else
     {
       let domains = filter.domains || defaultDomains;
       for (let domain of domains.keys())
       {
-        let filters = filtersByDomain.get(domain);
+        let filters = this._filtersByDomain.get(domain);
         if (filters)
           filters.delete(filter);
       }
     }
 
-    knownFilters.delete(filter);
+    this._knownFilters.delete(filter);
     FilterNotifier.emit("elemhideupdate");
-  },
+  }
+};
+
+exports.ElemHideTemplate = ElemHideTemplate;
 
+/**
+ * Container for element hiding filters
+ * @class
+ */
+exports.ElemHide = Object.assign(new ElemHideTemplate(), {
   /**
    * Determines from the current filter list which selectors should be applied
    * on a particular host name.
    * @param {string} domain
    * @param {boolean} [specificOnly] true if generic filters should not apply.
    * @returns {string[]} List of selectors.
    */
   getSelectorsForDomain(domain, specificOnly = false)
@@ -202,17 +220,17 @@
 
     // This code is a performance hot-spot, which is why we've made certain
     // micro-optimisations. Please be careful before making changes.
     while (true)
     {
       if (specificOnly && currentDomain == "")
         break;
 
-      let filters = filtersByDomain.get(currentDomain);
+      let filters = this._filtersByDomain.get(currentDomain);
       if (filters)
       {
         for (let [filter, isIncluded] of filters)
         {
           if (!isIncluded)
           {
             excluded.add(filter);
           }
@@ -227,13 +245,13 @@
       if (currentDomain == "")
         break;
 
       let nextDot = currentDomain.indexOf(".");
       currentDomain = nextDot == -1 ? "" : currentDomain.substr(nextDot + 1);
     }
 
     if (!specificOnly)
-      selectors = getUnconditionalSelectors().concat(selectors);
+      selectors = this._getUnconditionalSelectors().concat(selectors);
 
     return selectors;
   }
-};
+});