memgraph/include/utils/iterator/inspect.hpp

#pragma once

#include "utils/iterator/composable.hpp"
#include "utils/iterator/iterator_base.hpp"

namespace iter
{

// Class which inspects values returned by I iterator
// before passing them as a result.
// function.
// T - type of return value
// I - iterator type
// OP - type of inspector function. OP: T&->void
template <class T, class I, class OP>
class Inspect : public IteratorBase<T>,
                public Composable<T, Inspect<T, I, OP>>
{
public:
    Inspect() = delete;

    // Inspect operation is designed to be used
    // in chained calls which operate on an
    // iterator. Inspect will in that usecase 
    // receive other iterator by value and
    // std::move is a optimization for it.
    Inspect(I &&iter, OP &&op) : 
        iter(std::move(iter)), 
        op(std::move(op))
    {}

    Inspect(Inspect &&m) :
        iter(std::move(m.iter)), op(std::move(m.op)) {}

    ~Inspect() final {}

    Option<T> next() final
    {
        auto item = iter.next();
        if (item.is_present()) {
            op(item.get());
            return std::move(item);
        } else {
            return Option<T>();
        }
    }

    Count count() final { return iter.count(); }

private:
    I iter;
    OP op;
};

template <class I, class OP>
auto make_inspect(I &&iter, OP &&op)
{
    // Compiler cant deduce type T. decltype is here to help with it.
    return Inspect<decltype(iter.next().take()), I, OP>
        (std::move(iter), std::move(op));
}
}