Extending the NthIndexCache to support caching for the type of index.

Source/core/dom/NthIndexCache.h

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef NthIndexCache_h
 #define NthIndexCache_h
 
 #include "core/CoreExport.h"
 #include "core/dom/Element.h"
 #include "core/dom/ElementTraversal.h"
 #include "platform/heap/Handle.h"
 #include "wtf/HashMap.h"
 #include "wtf/OwnPtr.h"
 #include "wtf/RefPtr.h"
 
 namespace blink {
 
 class Document;
+class HasTagName {
+public:
+    explicit HasTagName(const QualifiedName& tagName) : m_tagName(tagName) { }
+    bool operator() (const Element& element) const { return element.hasTagName(m_tagName); }
+private:
+    const QualifiedName m_tagName;
+};
 
 class CORE_EXPORT NthIndexCache final {
     STACK_ALLOCATED();
     WTF_MAKE_NONCOPYABLE(NthIndexCache);
 public:
     explicit NthIndexCache(Document&);
     ~NthIndexCache();
 
     inline unsigned nthChildIndex(Element&);
+    inline unsigned nthChildIndexOfType(Element&, const QualifiedName&);
     inline unsigned nthLastChildIndex(Element&);
+    inline unsigned nthLastChildIndexOfType(Element&, const QualifiedName&);
 
 private:
     class NthIndexData final : public NoBaseWillBeGarbageCollected<NthIndexData> {
         WTF_MAKE_NONCOPYABLE(NthIndexData);
         DECLARE_EMPTY_DESTRUCTOR_WILL_BE_REMOVED(NthIndexData);
     public:
         NthIndexData() { }
 
         inline unsigned nthIndex(Element&);
+        inline unsigned nthIndexOfType(Element&, const QualifiedName&);
         inline unsigned nthLastIndex(Element&);
+        inline unsigned nthLastIndexOfType(Element&, const QualifiedName&);
 
         unsigned cacheNthIndices(Element&);
+        unsigned cacheNthIndicesOfType(Element&, const QualifiedName&);
 
         WillBeHeapHashMap<RawPtrWillBeMember<Element>, unsigned> m_elementIndexMap;
         unsigned m_count = 0;
 
         DECLARE_TRACE();
     };
 
+    using ParentMap = WillBeHeapHashMap<RefPtrWillBeMember<Node>, OwnPtrWillBeMember<NthIndexData>>;
+    OwnPtrWillBeMember<ParentMap> m_parentMap;
+
+    using IndexByType = WillBeHeapHashMap<String, OwnPtrWillBeMember<NthIndexData>>;
+
+    using ParentMapForType = WillBeHeapHashMap<RefPtrWillBeMember<Node>, OwnPtrWillBeMember<IndexByType>>;
+    OwnPtrWillBeMember<ParentMapForType> m_parentMapForType;
+
+
     NthIndexData& ensureNthIndexDataFor(Node&);
+    NthIndexCache::IndexByType& ensureTypeIndexMap(Node&);
 
-    using ParentMap = WillBeHeapHashMap<RefPtrWillBeMember<Node>, OwnPtrWillBeMember<NthIndexData>>;
+    NthIndexCache::NthIndexData& nthIndexDataWithTagName(Element&);
 
-    OwnPtrWillBeMember<ParentMap> m_parentMap;
     RawPtrWillBeMember<Document> m_document;
     uint64_t m_domTreeVersion;
 };
 
 inline unsigned NthIndexCache::NthIndexData::nthIndex(Element& element)
 {
     if (element.isPseudoElement())
         return 1;
     if (!m_count)
         return cacheNthIndices(element);
 
     unsigned index = 0;
     for (Element* sibling = &element; sibling; sibling = ElementTraversal::previousSibling(*sibling), index++) {
         auto it = m_elementIndexMap.find(sibling);
         if (it != m_elementIndexMap.end())
             return it->value + index;
     }
     return index;
 }
 
+inline unsigned NthIndexCache::NthIndexData::nthIndexOfType(Element& element, const QualifiedName& type)
+{
+    if (element.isPseudoElement())
+        return 1;
+    if (!m_count)
+        return cacheNthIndicesOfType(element, type);
+    unsigned index = 0;
+    for (Element* sibling = &element; sibling; sibling = ElementTraversal::previousSibling(*sibling, HasTagName(type)), index++) {
+        auto it = m_elementIndexMap.find(sibling);
+        if (it != m_elementIndexMap.end())
+            return it->value + index;
+    }
+    return index;
+}
+
 inline unsigned NthIndexCache::NthIndexData::nthLastIndex(Element& element)
 {
     if (element.isPseudoElement())
         return 1;
     unsigned index = nthIndex(element);
     return m_count - index + 1;
 }
 
+inline unsigned NthIndexCache::NthIndexData::nthLastIndexOfType(Element& element, const QualifiedName& type)
+{
+    if (element.isPseudoElement())
+        return 1;
+    unsigned index = nthIndexOfType(element, type);
+    return m_count - index + 1;
+}
+
 inline unsigned NthIndexCache::nthChildIndex(Element& element)
 {
     ASSERT(element.parentNode());
     return ensureNthIndexDataFor(*element.parentNode()).nthIndex(element);
 }
 
+inline unsigned NthIndexCache::nthChildIndexOfType(Element& element, const QualifiedName& type)
+{
+    ASSERT(element.parentNode());
+    return nthIndexDataWithTagName(element).nthIndexOfType(element, type);
+}
+
 inline unsigned NthIndexCache::nthLastChildIndex(Element& element)
 {
     ASSERT(element.parentNode());
     return ensureNthIndexDataFor(*element.parentNode()).nthLastIndex(element);
 }
 
+inline unsigned NthIndexCache::nthLastChildIndexOfType(Element& element, const QualifiedName& type)
+{
+    ASSERT(element.parentNode());
+    return nthIndexDataWithTagName(element).nthLastIndexOfType(element, type);
+}
+
+
 } // namespace blink
 
 #endif // NthIndexCache_h