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#pragma once
/// @file
#include <cassert>
#include <functional>
#include <memory>
namespace nix {
template<std::integral T>
class NotifyingCounter
{
private:
T counter;
std::function<void()> notify;
public:
class Bump
{
friend class NotifyingCounter;
struct SubOnFree
{
T delta;
void operator()(NotifyingCounter * c) const
{
c->add(-delta);
}
};
// lightly misuse unique_ptr to get RAII types with destructor callbacks
std::unique_ptr<NotifyingCounter<T>, SubOnFree> at;
Bump(NotifyingCounter<T> & at, T delta) : at(&at, {delta}) {}
public:
Bump() = default;
Bump(decltype(nullptr)) {}
T delta() const
{
return at ? at.get_deleter().delta : 0;
}
void reset()
{
at.reset();
}
};
explicit NotifyingCounter(std::function<void()> notify, T initial = 0)
: counter(initial)
, notify(std::move(notify))
{
assert(this->notify);
}
// bumps hold pointers to this, so we should neither copy nor move.
NotifyingCounter(const NotifyingCounter &) = delete;
NotifyingCounter & operator=(const NotifyingCounter &) = delete;
NotifyingCounter(NotifyingCounter &&) = delete;
NotifyingCounter & operator=(NotifyingCounter &&) = delete;
T get() const
{
return counter;
}
operator T() const
{
return counter;
}
void add(T delta)
{
counter += delta;
notify();
}
NotifyingCounter & operator+=(T delta)
{
add(delta);
return *this;
}
NotifyingCounter & operator++(int)
{
return *this += 1;
}
Bump addTemporarily(T delta)
{
add(delta);
return Bump{*this, delta};
}
};
}
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