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 /* -*- Mode: C++; tab-width: 20; indent-tabs-mode: nil; c-basic-offset: 2 -*-

  * This Source Code Form is subject to the terms of the Mozilla Public

  * License, v. 2.0. If a copy of the MPL was not distributed with this

  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

 #ifndef FRAMEPROPERTYTABLE_H_

 #define FRAMEPROPERTYTABLE_H_

 #include "mozilla/MemoryReporting.h"

 #include "nsTArray.h"

 #include "nsTHashtable.h"

 #include "nsHashKeys.h"

 class nsIFrame;

 namespace mozilla {

 struct FramePropertyDescriptor;

 typedef void (*FramePropertyDestructor)(void* aPropertyValue);

 typedef void (*FramePropertyDestructorWithFrame)(nsIFrame* aFrame,

                                                  void* aPropertyValue);

 /**

  * A pointer to a FramePropertyDescriptor serves as a unique property ID.

  * The FramePropertyDescriptor stores metadata about the property.

  * Currently the only metadata is a destructor function. The destructor

  * function is called on property values when they are overwritten or

  * deleted.

  * 

  * To use this class, declare a global (i.e., file, class or function-scope

  * static member) FramePropertyDescriptor and pass its address as

  * aProperty in the FramePropertyTable methods.

  */

 struct FramePropertyDescriptor {

   /**

    * mDestructor will be called if it's non-null.

    */

   FramePropertyDestructor          mDestructor;

   /**

    * mDestructorWithFrame will be called if it's non-null and mDestructor

    * is null. WARNING: The frame passed to mDestructorWithFrame may

    * be a dangling frame pointer, if this is being called during

    * presshell teardown. Do not use it except to compare against

    * other frame pointers. No frame will have been allocated with

    * the same address yet.

    */

   FramePropertyDestructorWithFrame mDestructorWithFrame;

   /**

    * mDestructor and mDestructorWithFrame may both be null, in which case

    * no value destruction is a no-op.

    */

 };

 /**

  * The FramePropertyTable is optimized for storing 0 or 1 properties on

  * a given frame. Storing very large numbers of properties on a single

  * frame will not be efficient.

  * 

  * Property values are passed as void* but do not actually have to be

  * valid pointers. You can use NS_INT32_TO_PTR/NS_PTR_TO_INT32 to

  * store int32_t values. Null/zero values can be stored and retrieved.

  * Of course, the destructor function (if any) must handle such values

  * correctly.

  */

 class FramePropertyTable {

 public:

   FramePropertyTable() : mLastFrame(nullptr), mLastEntry(nullptr)

   {

   }

   ~FramePropertyTable()

   {

     DeleteAll();

   }

   /**

    * Set a property value on a frame. This requires one hashtable

    * lookup (using the frame as the key) and a linear search through

    * the properties of that frame. Any existing value for the property

    * is destroyed.

    */

   void Set(nsIFrame* aFrame, const FramePropertyDescriptor* aProperty,

            void* aValue);

   /**

    * Get a property value for a frame. This requires one hashtable

    * lookup (using the frame as the key) and a linear search through

    * the properties of that frame. If the frame has no such property,

    * returns null.

    * @param aFoundResult if non-null, receives a value 'true' iff

    * the frame has a value for the property. This lets callers

    * disambiguate a null result, which can mean 'no such property' or

    * 'property value is null'.

    */

   void* Get(const nsIFrame* aFrame, const FramePropertyDescriptor* aProperty,

             bool* aFoundResult = nullptr);

   /**

    * Remove a property value for a frame. This requires one hashtable

    * lookup (using the frame as the key) and a linear search through

    * the properties of that frame. The old property value is returned

    * (and not destroyed). If the frame has no such property,

    * returns null.

    * @param aFoundResult if non-null, receives a value 'true' iff

    * the frame had a value for the property. This lets callers

    * disambiguate a null result, which can mean 'no such property' or

    * 'property value is null'.

    */

   void* Remove(nsIFrame* aFrame, const FramePropertyDescriptor* aProperty,

                bool* aFoundResult = nullptr);

   /**

    * Remove and destroy a property value for a frame. This requires one

    * hashtable lookup (using the frame as the key) and a linear search

    * through the properties of that frame. If the frame has no such

    * property, nothing happens.

    */

   void Delete(nsIFrame* aFrame, const FramePropertyDescriptor* aProperty);

   /**

    * Remove and destroy all property values for a frame. This requires one

    * hashtable lookup (using the frame as the key).

    */

   void DeleteAllFor(nsIFrame* aFrame);

   /**

    * Remove and destroy all property values for all frames.

    */

   void DeleteAll();

   size_t SizeOfExcludingThis(mozilla::MallocSizeOf aMallocSizeOf) const;

 protected:

   /**

    * Stores a property descriptor/value pair. It can also be used to

    * store an nsTArray of PropertyValues.

    */

   struct PropertyValue {

     PropertyValue() : mProperty(nullptr), mValue(nullptr) {}

     PropertyValue(const FramePropertyDescriptor* aProperty, void* aValue)

       : mProperty(aProperty), mValue(aValue) {}

     bool IsArray() { return !mProperty && mValue; }

     nsTArray<PropertyValue>* ToArray()

     {

       NS_ASSERTION(IsArray(), "Must be array");

       return reinterpret_cast<nsTArray<PropertyValue>*>(&mValue);

     }

     void DestroyValueFor(nsIFrame* aFrame) {

       if (mProperty->mDestructor) {

         mProperty->mDestructor(mValue);

       } else if (mProperty->mDestructorWithFrame) {

         mProperty->mDestructorWithFrame(aFrame, mValue);

       }

     }

     size_t SizeOfExcludingThis(mozilla::MallocSizeOf aMallocSizeOf) {

       size_t n = 0;

       // We don't need to measure mProperty because it always points to static

       // memory.  As for mValue:  if it's a single value we can't measure it,

       // because the type is opaque;  if it's an array, we measure the array

       // storage, but we can't measure the individual values, again because

       // their types are opaque.

       if (IsArray()) {

         nsTArray<PropertyValue>* array = ToArray();

         n += array->SizeOfExcludingThis(aMallocSizeOf);

       }

       return n;

     }

     const FramePropertyDescriptor* mProperty;

     void* mValue;

   };

   /**

    * Used with an array of PropertyValues to allow lookups that compare

    * only on the FramePropertyDescriptor.

    */

   class PropertyComparator {

   public:

     bool Equals(const PropertyValue& a, const PropertyValue& b) const {

       return a.mProperty == b.mProperty;

     }

     bool Equals(const FramePropertyDescriptor* a, const PropertyValue& b) const {

       return a == b.mProperty;

     }

     bool Equals(const PropertyValue& a, const FramePropertyDescriptor* b) const {

       return a.mProperty == b;

     }

   };

   /**

    * Our hashtable entry. The key is an nsIFrame*, the value is a

    * PropertyValue representing one or more property/value pairs.

    */

   class Entry : public nsPtrHashKey<nsIFrame>

   {

   public:

     Entry(KeyTypePointer aKey) : nsPtrHashKey<nsIFrame>(aKey) {}

     Entry(const Entry &toCopy) :

       nsPtrHashKey<nsIFrame>(toCopy), mProp(toCopy.mProp) {}

     PropertyValue mProp;

   };

   static void DeleteAllForEntry(Entry* aEntry);

   static PLDHashOperator DeleteEnumerator(Entry* aEntry, void* aArg);

   static size_t SizeOfPropertyTableEntryExcludingThis(Entry* aEntry,

                   mozilla::MallocSizeOf aMallocSizeOf, void *);

   nsTHashtable<Entry> mEntries;

   nsIFrame* mLastFrame;

   Entry* mLastEntry;

 };

 /**

  * This class encapsulates the properties of a frame.

  */

 class FrameProperties {

 public:

   FrameProperties(FramePropertyTable* aTable, nsIFrame* aFrame)

     : mTable(aTable), mFrame(aFrame) {}

   FrameProperties(FramePropertyTable* aTable, const nsIFrame* aFrame)

     : mTable(aTable), mFrame(const_cast<nsIFrame*>(aFrame)) {}

   void Set(const FramePropertyDescriptor* aProperty, void* aValue) const

   {

     mTable->Set(mFrame, aProperty, aValue);

   }

   void* Get(const FramePropertyDescriptor* aProperty,

             bool* aFoundResult = nullptr) const

   {

     return mTable->Get(mFrame, aProperty, aFoundResult);

   }

   void* Remove(const FramePropertyDescriptor* aProperty,

                bool* aFoundResult = nullptr) const

   {

     return mTable->Remove(mFrame, aProperty, aFoundResult);

   }

   void Delete(const FramePropertyDescriptor* aProperty)

   {

     mTable->Delete(mFrame, aProperty);

   }

 private:

   FramePropertyTable* mTable;

   nsIFrame* mFrame;

 };

 }

 #endif /* FRAMEPROPERTYTABLE_H_ */