// Copyright 2022 The Dawn & Tint Authors
//
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#ifndef SRC_DAWN_COMMON_REFCOUNTEDWITHEXTERNALCOUNT_H_
#define SRC_DAWN_COMMON_REFCOUNTEDWITHEXTERNALCOUNT_H_

#include "src/dawn/common/RefCounted.h"

namespace dawn {

// RecCountedWithExternalCountBase is a version of RefCounted which tracks a separate
// refcount for calls to APIAddRef/APIRelease (refs added/removed by the application).
// The external refcount starts at 0, and the total refcount starts at 1 - i.e. the first
// ref isn't an external ref.
// When the external refcount is incremented from 0 to 1, WillAddFirstExternalRef is called, and it
// can be called more than once.
// When the external refcount drops to zero, WillDropLastExternalRef is called, and it can be called
// more than once.
// The derived class must override the behavior of WillDropLastExternalRef, overriding
// WillAddFirstExternalRef is optional.
template <typename T>
class RefCountedWithExternalCount : public T {
  public:
    static constexpr bool HasExternalRefCount = true;

    using T::T;

    void APIAddRef() {
        IncrementExternalRefCount();
        T::APIAddRef();
    }

    void APIRelease() {
        if (mExternalRefCount.Decrement()) {
            WillDropLastExternalRef();
        }
        T::APIRelease();
    }

    void IncrementExternalRefCount() {
        if (mExternalRefCount.Increment()) {
            WillAddFirstExternalRef();
        }
    }

    uint64_t GetExternalRefCountForTesting() const {
        return mExternalRefCount.GetValueForTesting();
    }

  protected:
    bool HasExternalRef() const {
        // Note that we call the "ForTesting" function here but this is a use case where it is not
        // for testing, and we are allowing it as a special case for external reference counting.
        return mExternalRefCount.GetValueForTesting() > 0;
    }

  private:
    virtual void WillAddFirstExternalRef() {}
    virtual void WillDropLastExternalRef() = 0;

    RefCount mExternalRefCount{/*initCount=*/0, /*payload=*/0};
};

}  // namespace dawn

#endif  // SRC_DAWN_COMMON_REFCOUNTEDWITHEXTERNALCOUNT_H_