/*
 * Copyright (C) 2010 Google Inc. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are
 * met:
 *
 *     * Redistributions of source code must retain the above copyright
 * notice, this list of conditions and the following disclaimer.
 *     * Redistributions in binary form must reproduce the above
 * copyright notice, this list of conditions and the following disclaimer
 * in the documentation and/or other materials provided with the
 * distribution.
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 * contributors may be used to endorse or promote products derived from
 * this software without specific prior written permission.
 * 
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#ifndef ScriptWrappable_h
#define ScriptWrappable_h

#include "WebCoreMemoryInstrumentation.h"
#include "WrapperTypeInfo.h"
#include <v8.h>

namespace WebCore {

class ScriptWrappable {
public:
    ScriptWrappable() { }

    v8::Handle<v8::Object> wrapper() const
    {
        return v8::Handle<v8::Object>(maskOrUnmaskPointer(*m_maskedWrapper));
    }

    void setWrapper(v8::Handle<v8::Object> wrapper, v8::Isolate* isolate, const WrapperConfiguration& configuration)
    {
        ASSERT(m_maskedWrapper.IsEmpty());
        v8::Persistent<v8::Object> persistent = v8::Persistent<v8::Object>::New(isolate, wrapper);
        configuration.configureWrapper(persistent, isolate);
        persistent.MakeWeak(isolate, this, weakCallback);
        m_maskedWrapper = maskOrUnmaskPointer(*persistent);
    }

    void reportMemoryUsage(MemoryObjectInfo* memoryObjectInfo) const
    {
        MemoryClassInfo info(memoryObjectInfo, this, WebCoreMemoryTypes::DOM);
        info.ignoreMember(m_maskedWrapper);
    }

private:
    inline void disposeWrapper(v8::Persistent<v8::Value> value, v8::Isolate* isolate)
    {
        ASSERT(!m_maskedWrapper.IsEmpty());
        ASSERT(*value == maskOrUnmaskPointer(*m_maskedWrapper));
        value.Dispose(isolate);
        m_maskedWrapper.Clear();
    }

    // Stores a masked wrapper to prevent attackers from overwriting this field
    // with a phony wrapper.
    v8::Persistent<v8::Object> m_maskedWrapper;

    static inline v8::Object* maskOrUnmaskPointer(const v8::Object* object)
    {
        const uintptr_t objectPointer = reinterpret_cast<uintptr_t>(object);
        const uintptr_t randomMask = ~(reinterpret_cast<uintptr_t>(&WebCoreMemoryTypes::DOM) >> 13); // Entropy via ASLR.
        return reinterpret_cast<v8::Object*>((objectPointer ^ randomMask) & (!objectPointer - 1)); // Preserve null without branching.
    }

    static void weakCallback(v8::Isolate* isolate, v8::Persistent<v8::Value> value, void* context)
    {
        ScriptWrappable* key = static_cast<ScriptWrappable*>(context);
        ASSERT(value->IsObject());
        v8::Persistent<v8::Object> wrapper = v8::Persistent<v8::Object>::Cast(value);
        ASSERT(key->wrapper() == wrapper);

        // Note: |object| might not be equal to |key|, e.g., if ScriptWrappable isn't a left-most base class.
        void* object = toNative(wrapper);
        WrapperTypeInfo* info = toWrapperTypeInfo(wrapper);
        ASSERT(info->derefObjectFunction);

        key->disposeWrapper(value, isolate);
        // FIXME: I noticed that 50%~ of minor GC cycle times can be consumed
        // inside key->deref(), which causes Node destructions. We should
        // make Node destructions incremental.
        info->derefObject(object);
    }
};

} // namespace WebCore

#endif // ScriptWrappable_h