Issue 235 - Improved performance of ElemHide.getSelectorsForDomain()

lib/elemHide.js

Index: lib/elemHide.js
===================================================================
--- a/lib/elemHide.js
+++ b/lib/elemHide.js
@@ -59,6 +59,18 @@
 let styleURL = null;
 
 /**
+ * Lookup table, blocking filters by domain which they are applied to
+ * @type Object
+ */
+let filtersByDomain = Object.create(null);
+
+/**
+ * Indicates whether stylesheets can be used for element hiding
+ * @type Boolean
+ */
+let canUseStylesheets = ("nsIStyleSheetService" in Ci);
+
+/**
  * Element hiding component
  * @class
  */
@@ -105,6 +117,7 @@
     keyByFilter = Object.create(null);
     knownExceptions = Object.create(null);
     exceptions = Object.create(null);
+    filtersByDomain = Object.create(null);
     ElemHide.isDirty = false;
     ElemHide.unapply();
   },
@@ -131,6 +144,28 @@
       if (filter.text in keyByFilter)
         return;
 
+      if (!canUseStylesheets)
+      {
+        let domains = filter.domains;
+        if (domains === null)
+        {
+          domains = Object.create(null);
+          domains[""] = true;
+        }
+
+        for (let domain in domains)
+        {
+          if (!(domain in filtersByDomain))
+          {
+            filtersByDomain[domain] = Object.create(null);
+            filtersByDomain[domain].$length = 0;
+          }
+
+          filtersByDomain[domain][filter.text] = domains[domain];
+          filtersByDomain[domain].$length++;
+        }
+      }
+
       let key;
       do {
         key = Math.random().toFixed(15).substr(5);
@@ -164,6 +199,26 @@
       if (!(filter.text in keyByFilter))
         return;
 
+      if (!canUseStylesheets)
+      {
+        let domains = filter.domains;
+        if (!domains)
+        {
+          domains = Object.create(null);
+          domains[""] = true;
+        }
+
+        for (let domain in domains)
+        {
+          if (domain in filtersByDomain && filter.text in filtersByDomain[domain])
+          {
+            delete filtersByDomain[domain][filter.text];
+            if (!--filtersByDomain[domain].$length)
+              delete filtersByDomain[domain];
+          }
+        }
+      }
+
       let key = keyByFilter[filter.text];
       delete filterByKey[key];
       delete keyByFilter[filter.text];
@@ -282,7 +337,7 @@
     this._applying = true;
   },
 
-  _generateCSSContent: function*()
+  _generateCSSContent: function()
   {
     // Grouping selectors by domains
     let domains = Object.create(null);
@@ -372,22 +427,65 @@
   },
 
   /**
-   * Returns a list of all selectors active on a particular domain (currently
-   * used only in Chrome, Opera and Safari).
+   * Returns a list of all selectors active on a particular domain (it cannot
+   * be used in Firefox).
    */
   getSelectorsForDomain: function(/**String*/ domain, /**Boolean*/ specificOnly)
   {
-    let result = [];
-    let keys = Object.getOwnPropertyNames(filterByKey);
-    for (let key of keys)
+    if (canUseStylesheets)
+      throw new Error("Use of getSelectorsForDomain is limited to platforms which cannot inject stylesheets");
+
+    let selectors = [];
+    domain = domain.toUpperCase();
+
+    if (!specificOnly)
     {
-      let filter = filterByKey[key];
-      if (specificOnly && (!filter.domains || filter.domains[""]))
-        continue;
+      let filterTexts = filtersByDomain[""];
+      if (filterTexts)
+      {
+        for (let filterText in filterTexts)
+        {
+          if (filterTexts[filterText] && filterText != "$length")
+          {
+            let filter = Filter.fromText(filterText);
+            if (!this.getException(filter, domain))
+              selectors[selectors.length] = filter.selector;
+          }
+        }
+      }
+    }
 
-      if (filter.isActiveOnDomain(domain) && !this.getException(filter, domain))
-        result.push(filter.selector);
+    let ignorableFilters = [];
+    while (true)
+    {
+      if (domain && domain in filtersByDomain)
+      {
+        let filterTexts = filtersByDomain[domain];
+        for (let filterText in filterTexts)
+        {
+          if (ignorableFilters.indexOf(filterText) > -1)
+            continue;
+          
+          if (filterTexts[filterText])
+          {
+            if (filterText == "$length")
+              continue;
+
+            let filter = Filter.fromText(filterText);
+            if (!this.getException(filter, domain))
+              selectors[selectors.length] = filter.selector;
+          }
+          else
+            ignorableFilters[ignorableFilters.length] = filterText;
+        }
+      }
+
+      let nextDot = domain.indexOf(".");
+      if (nextDot < 0)
+        break;
+      domain = domain.substr(nextDot + 1);
     }
-    return result;
+
+    return selectors;
   }
 };