// Copyright (c) 2011 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 MUL_REF_COUNTED_
#define MUL_REF_COUNTED_

#include <assert.h>

namespace base {

  namespace subtle {

    class RefCountedBase {
    public:
      bool HasOneRef() const { return ref_count_ == 1; }

    protected:
      RefCountedBase()
        : ref_count_(0) {
      }
      ~RefCountedBase() {
      }


      void AddRef() const {
        ++ref_count_;
      }

      // Returns true if the object should self-delete.
      bool Release() const {

        if (--ref_count_ == 0) {
          return true;
        }
        return false;
      }
    private:
      mutable int ref_count_;
      DISALLOW_COPY_AND_ASSIGN_(RefCountedBase);
    };

    class RefCountedThreadSafeBase {

    public:
      bool HasOneRef() const;
    protected:
      RefCountedThreadSafeBase();
      ~RefCountedThreadSafeBase();

      void AddRef() const;

      // Returns true if the object should self-delete.
      bool Release() const;

    private:
      mutable int ref_count_;
      DISALLOW_COPY_AND_ASSIGN_(RefCountedThreadSafeBase);
    };

  }  // namespace subtle

  template <class T>
  class RefCounted : public subtle::RefCountedBase {
  public:
    RefCounted() {}

    void AddRef() const {
      subtle::RefCountedBase::AddRef();
    }

    void Release() const {
      if (subtle::RefCountedBase::Release()) {
        delete static_cast<const T*>(this);
      }
    }

  protected:
    ~RefCounted() {}

  private:
    DISALLOW_COPY_AND_ASSIGN_(RefCounted<T>);
  };

  // Forward declaration.
  template <class T, typename Traits> class RefCountedThreadSafe;

  // Default traits for RefCountedThreadSafe<T>.  Deletes the object when its ref
  // count reaches 0.  Overload to delete it on a different thread etc.
  template<typename T>
  struct DefaultRefCountedThreadSafeTraits {
    static void Destruct(const T* x) {
      // Delete through RefCountedThreadSafe to make child classes only need to be
      // friend with RefCountedThreadSafe instead of this struct, which is an
      // implementation detail.
      RefCountedThreadSafe<T,
        DefaultRefCountedThreadSafeTraits>::DeleteInternal(x);
    }
  };

  //
  // A thread-safe variant of RefCounted<T>
  //
  //   class MyFoo : public base::RefCountedThreadSafe<MyFoo> {
  //    ...
  //   };
  //
  // If you're using the default trait, then you should add compile time
  // asserts that no one else is deleting your object.  i.e.
  //    private:
  //     friend class base::RefCountedThreadSafe<MyFoo>;
  //     ~MyFoo();
  template <class T, typename Traits = DefaultRefCountedThreadSafeTraits<T> >
  class RefCountedThreadSafe : public subtle::RefCountedThreadSafeBase {
  public:
    RefCountedThreadSafe() {}

    void AddRef() const {
      subtle::RefCountedThreadSafeBase::AddRef();
    }

    void Release() const {
      if (subtle::RefCountedThreadSafeBase::Release()) {
        Traits::Destruct(static_cast<const T*>(this));
      }
    }

  protected:
    ~RefCountedThreadSafe() {}

  private:
    friend struct DefaultRefCountedThreadSafeTraits<T>;
    static void DeleteInternal(const T* x) { delete x; }

    DISALLOW_COPY_AND_ASSIGN_(RefCountedThreadSafe);
  };

  //
  // A thread-safe wrapper for some piece of data so we can place other
  // things in scoped_refptrs<>.
  //
  template<typename T>
  class RefCountedData
    : public base::RefCountedThreadSafe< base::RefCountedData<T> > {
  public:
    RefCountedData() : data() {}
    RefCountedData(const T& in_value) : data(in_value) {}

    T data;

  private:
    friend class base::RefCountedThreadSafe<base::RefCountedData<T> >;
    ~RefCountedData() {}
  };

}  // namespace base

//
// A smart pointer class for reference counted objects.  Use this class instead
// of calling AddRef and Release manually on a reference counted object to
// avoid common memory leaks caused by forgetting to Release an object
// reference.  Sample usage:
//
//   class MyFoo : public RefCounted<MyFoo> {
//    ...
//   };
//
//   void some_function() {
//     scoped_refptr<MyFoo> foo = new MyFoo();
//     foo->Method(param);
//     // |foo| is released when this function returns
//   }
//
//   void some_other_function() {
//     scoped_refptr<MyFoo> foo = new MyFoo();
//     ...
//     foo = NULL;  // explicitly releases |foo|
//     ...
//     if (foo)
//       foo->Method(param);
//   }
//
// The above examples show how scoped_refptr<T> acts like a pointer to T.
// Given two scoped_refptr<T> classes, it is also possible to exchange
// references between the two objects, like so:
//
//   {
//     scoped_refptr<MyFoo> a = new MyFoo();
//     scoped_refptr<MyFoo> b;
//
//     b.swap(a);
//     // now, |b| references the MyFoo object, and |a| references NULL.
//   }
//
// To make both |a| and |b| in the above example reference the same MyFoo
// object, simply use the assignment operator:
//
//   {
//     scoped_refptr<MyFoo> a = new MyFoo();
//     scoped_refptr<MyFoo> b;
//
//     b = a;
//     // now, |a| and |b| each own a reference to the same MyFoo object.
//   }
//
template <class T>
class scoped_refptr {
public:
  typedef T element_type;

  scoped_refptr() : ptr_(NULL) {
  }

  scoped_refptr(T* p) : ptr_(p) {
    if (ptr_)
      ptr_->AddRef();
  }

  scoped_refptr(const scoped_refptr<T>& r) : ptr_(r.ptr_) {
    if (ptr_)
      ptr_->AddRef();
  }

  template <typename U>
  scoped_refptr(const scoped_refptr<U>& r) : ptr_(r.get()) {
    if (ptr_)
      ptr_->AddRef();
  }

  ~scoped_refptr() {
    if (ptr_)
      ptr_->Release();
  }

  T* get() const { return ptr_; }

  // Allow scoped_refptr<C> to be used in boolean expression
  // and comparison operations.
  operator T*() const { return ptr_; }

  T* operator->() const {
    assert(ptr_ != NULL);
    return ptr_;
  }

  scoped_refptr<T>& operator=(T* p) {
    // AddRef first so that self assignment should work
    if (p)
      p->AddRef();
    T* old_ptr = ptr_;
    ptr_ = p;
    if (old_ptr)
      old_ptr->Release();
    return *this;
  }

  scoped_refptr<T>& operator=(const scoped_refptr<T>& r) {
    return *this = r.ptr_;
  }

  template <typename U>
  scoped_refptr<T>& operator=(const scoped_refptr<U>& r) {
    return *this = r.get();
  }

  void swap(T** pp) {
    T* p = ptr_;
    ptr_ = *pp;
    *pp = p;
  }

  void swap(scoped_refptr<T>& r) {
    swap(&r.ptr_);
  }

protected:
  T* ptr_;
};

// Handy utility for creating a scoped_refptr<T> out of a T* explicitly without
// having to retype all the template arguments
template <typename T>
scoped_refptr<T> make_scoped_refptr(T* t) {
  return scoped_refptr<T>(t);
}

#endif