#ifndef ITER_UNIQUE_EVERSEEN_HPP_

#define ITER_UNIQUE_EVERSEEN_HPP_

#include "internal/iterbase.hpp"

#include "filter.hpp"

#include <type_traits>

#include <functional>

#include <utility>

#include <unordered_set>

#include <iterator>

namespace iter {

// the container type must be usable in an unordered_map to achieve constant

// performance checking if it has ever been seen

template <typename Container>

auto unique_everseen(Container&& container)

-> impl::Filtered<std::function<bool(impl::iterator_deref<Container>)>,

Container> {

using elem_t = impl::iterator_deref<Container>;

std::unordered_set<typename std::decay<elem_t>::type> elem_seen;

std::function<bool(elem_t)> func =

// has to be captured by value because it goes out of scope when the

// function returns

[elem_seen](elem_t e) mutable {

if (elem_seen.find(e) == std::end(elem_seen)) {

elem_seen.insert(e);

return true;

}

return false;

};

return filter(func, std::forward<Container>(container));

}

template <typename T>

auto unique_everseen(std::initializer_list<T> il)

-> impl::Filtered<std::function<bool(T)>, std::initializer_list<T>> {

std::unordered_set<T> elem_seen;

std::function<bool(T)> func = [elem_seen](const T& e) mutable {

if (elem_seen.find(e) == std::end(elem_seen)) {

elem_seen.insert(e);

return true;

}

return false;

};

return filter(func, il);

}

}

#endif