/**
 * MIT License
 *
 * Copyright (c) 2017 Tessil
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in all
 * copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */
#ifndef TSL_ORDERED_MAP_H
#define TSL_ORDERED_MAP_H


#include <cstddef>
#include <deque>
#include <functional>
#include <initializer_list>
#include <memory>
#include <type_traits>
#include <utility>
#include <vector>
#include "ordered_hash.h"


namespace tsl {


/**
 * Implementation of an hash map using open adressing with robin hood with backshift delete to resolve collisions.
 *
 * The particularity of this hash map is that it remembers the order in which the elements were added and
 * provide a way to access the structure which stores these values through the 'values_container()' method.
 * The used container is defined by ValueTypeContainer, by default a std::deque is used (grows faster) but
 * a std::vector may be used. In this case the map provides a 'data()' method which give a direct access
 * to the memory used to store the values (which can be usefull to communicate with C API's).
 *
 * The Key and T must be copy constructible and/or move constructible. To use `unordered_erase` they both
 * must be swappable.
 *
 * The behaviour of the hash map is undefinded if the destructor of Key or T throws an exception.
 *
 * Iterators invalidation:
 *  - clear, operator=, reserve, rehash: always invalidate the iterators (also invalidate end()).
 *  - insert, emplace, emplace_hint, operator[]: when a std::vector is used as ValueTypeContainer
 *                                               and if size() < capacity(), only end().
 *                                               Otherwise all the iterators are invalidated if an insert occurs.
 *  - erase, unordered_erase: when a std::vector is used as ValueTypeContainer invalidate the iterator of
 *                            the erased element and all the ones after the erased element (including end()).
 *                            Otherwise all the iterators are invalidated if an erase occurs.
 */
template<class Key,
         class T,
         class Hash = std::hash<Key>,
         class KeyEqual = std::equal_to<Key>,
         class Allocator = std::allocator<std::pair<Key, T>>,
         class ValueTypeContainer = std::deque<std::pair<Key, T>, Allocator>>
class ordered_map {
private:
    template<typename U>
    using has_is_transparent = tsl::detail_ordered_hash::has_is_transparent<U>;

    class KeySelect {
    public:
        using key_type = Key;

        const key_type& operator()(const std::pair<Key, T>& key_value) const noexcept {
            return key_value.first;
        }

        key_type& operator()(std::pair<Key, T>& key_value) noexcept {
            return key_value.first;
        }
    };

    class ValueSelect {
    public:
        using value_type = T;

        const value_type& operator()(const std::pair<Key, T>& key_value) const noexcept {
            return key_value.second;
        }

        value_type& operator()(std::pair<Key, T>& key_value) noexcept {
            return key_value.second;
        }
    };

    using ht = detail_ordered_hash::ordered_hash<std::pair<Key, T>, KeySelect, ValueSelect,
                                                 Hash, KeyEqual, Allocator, ValueTypeContainer>;

public:
    using key_type = typename ht::key_type;
    using mapped_type = T;
    using value_type = typename ht::value_type;
    using size_type = typename ht::size_type;
    using difference_type = typename ht::difference_type;
    using hasher = typename ht::hasher;
    using key_equal = typename ht::key_equal;
    using allocator_type = typename ht::allocator_type;
    using reference = typename ht::reference;
    using const_reference = typename ht::const_reference;
    using pointer = typename ht::pointer;
    using const_pointer = typename ht::const_pointer;
    using iterator = typename ht::iterator;
    using const_iterator = typename ht::const_iterator;
    using reverse_iterator = typename ht::reverse_iterator;
    using const_reverse_iterator = typename ht::const_reverse_iterator;

    using values_container_type = typename ht::values_container_type;


    /*
     * Constructors
     */
    ordered_map(): ordered_map(ht::DEFAULT_INIT_BUCKETS_SIZE) {
    }

    explicit ordered_map(size_type bucket_count,
                         const Hash& hash = Hash(),
                         const KeyEqual& equal = KeyEqual(),
                         const Allocator& alloc = Allocator()):
                     m_ht(bucket_count, hash, equal, alloc, ht::DEFAULT_MAX_LOAD_FACTOR)
    {
    }

    ordered_map(size_type bucket_count,
                const Allocator& alloc): ordered_map(bucket_count, Hash(), KeyEqual(), alloc)
    {
    }

    ordered_map(size_type bucket_count,
                const Hash& hash,
                const Allocator& alloc): ordered_map(bucket_count, hash, KeyEqual(), alloc)
    {
    }

    explicit ordered_map(const Allocator& alloc): ordered_map(ht::DEFAULT_INIT_BUCKETS_SIZE, alloc) {
    }

    template<class InputIt>
    ordered_map(InputIt first, InputIt last,
                size_type bucket_count = ht::DEFAULT_INIT_BUCKETS_SIZE,
                const Hash& hash = Hash(),
                const KeyEqual& equal = KeyEqual(),
                const Allocator& alloc = Allocator()): ordered_map(bucket_count, hash, equal, alloc)
    {
        insert(first, last);
    }

    template<class InputIt>
    ordered_map(InputIt first, InputIt last,
                size_type bucket_count,
                const Allocator& alloc): ordered_map(first, last, bucket_count, Hash(), KeyEqual(), alloc)
    {
    }

    template<class InputIt>
    ordered_map(InputIt first, InputIt last,
                size_type bucket_count,
                const Hash& hash,
                const Allocator& alloc): ordered_map(first, last, bucket_count, hash, KeyEqual(), alloc)
    {
    }

    ordered_map(std::initializer_list<value_type> init,
                size_type bucket_count = ht::DEFAULT_INIT_BUCKETS_SIZE,
                const Hash& hash = Hash(),
                const KeyEqual& equal = KeyEqual(),
                const Allocator& alloc = Allocator()):
            ordered_map(init.begin(), init.end(), bucket_count, hash, equal, alloc)
    {
    }

    ordered_map(std::initializer_list<value_type> init,
                size_type bucket_count,
                const Allocator& alloc):
            ordered_map(init.begin(), init.end(), bucket_count, Hash(), KeyEqual(), alloc)
    {
    }

    ordered_map(std::initializer_list<value_type> init,
                size_type bucket_count,
                const Hash& hash,
                const Allocator& alloc):
            ordered_map(init.begin(), init.end(), bucket_count, hash, KeyEqual(), alloc)
    {
    }


    ordered_map& operator=(std::initializer_list<value_type> ilist) {
        m_ht.clear();

        m_ht.reserve(ilist.size());
        m_ht.insert(ilist.begin(), ilist.end());

        return *this;
    }

    allocator_type get_allocator() const { return m_ht.get_allocator(); }



    /*
     * Iterators
     */
    iterator begin() noexcept { return m_ht.begin(); }
    const_iterator begin() const noexcept { return m_ht.begin(); }
    const_iterator cbegin() const noexcept { return m_ht.cbegin(); }

    iterator end() noexcept { return m_ht.end(); }
    const_iterator end() const noexcept { return m_ht.end(); }
    const_iterator cend() const noexcept { return m_ht.cend(); }

    reverse_iterator rbegin() noexcept { return m_ht.rbegin(); }
    const_reverse_iterator rbegin() const noexcept { return m_ht.rbegin(); }
    const_reverse_iterator rcbegin() const noexcept { return m_ht.rcbegin(); }

    reverse_iterator rend() noexcept { return m_ht.rend(); }
    const_reverse_iterator rend() const noexcept { return m_ht.rend(); }
    const_reverse_iterator rcend() const noexcept { return m_ht.rcend(); }


    /*
     * Capacity
     */
    bool empty() const noexcept { return m_ht.empty(); }
    size_type size() const noexcept { return m_ht.size(); }
    size_type max_size() const noexcept { return m_ht.max_size(); }

    /*
     * Modifiers
     */
    void clear() noexcept { m_ht.clear(); }



    std::pair<iterator, bool> insert(const value_type& value) { return m_ht.insert(value); }

    template<class P, typename std::enable_if<std::is_constructible<value_type, P&&>::value>::type* = nullptr>
    std::pair<iterator, bool> insert(P&& value) { return m_ht.emplace(std::forward<P>(value)); }

    std::pair<iterator, bool> insert(value_type&& value) { return m_ht.insert(std::move(value)); }


    iterator insert(const_iterator hint, const value_type& value) {
        return m_ht.insert(hint, value);
    }

    template<class P, typename std::enable_if<std::is_constructible<value_type, P&&>::value>::type* = nullptr>
    iterator insert(const_iterator hint, P&& value) {
        return m_ht.emplace_hint(hint, std::forward<P>(value));
    }

    iterator insert(const_iterator hint, value_type&& value) {
        return m_ht.insert(hint, std::move(value));
    }


    template<class InputIt>
    void insert(InputIt first, InputIt last) { m_ht.insert(first, last); }
    void insert(std::initializer_list<value_type> ilist) { m_ht.insert(ilist.begin(), ilist.end()); }




    template<class M>
    std::pair<iterator, bool> insert_or_assign(const key_type& k, M&& obj) {
        return m_ht.insert_or_assign(k, std::forward<M>(obj));
    }

    template<class M>
    std::pair<iterator, bool> insert_or_assign(key_type&& k, M&& obj) {
        return m_ht.insert_or_assign(std::move(k), std::forward<M>(obj));
    }


    template<class M>
    iterator insert_or_assign(const_iterator hint, const key_type& k, M&& obj) {
        return m_ht.insert_or_assign(hint, k, std::forward<M>(obj));
    }

    template<class M>
    iterator insert_or_assign(const_iterator hint, key_type&& k, M&& obj) {
        return m_ht.insert_or_assign(hint, std::move(k), std::forward<M>(obj));
    }

    /**
     * Due to the way elements are stored, emplace will need to move or copy the key-value once.
     * The method is equivalent to insert(value_type(std::forward<Args>(args)...));
     *
     * Mainly here for compatibility with the std::unordered_map interface.
     */
    template<class... Args>
    std::pair<iterator, bool> emplace(Args&&... args) { return m_ht.emplace(std::forward<Args>(args)...); }

    /**
     * Due to the way elements are stored, emplace_hint will need to move or copy the key-value once.
     * The method is equivalent to insert(hint, value_type(std::forward<Args>(args)...));
     *
     * Mainly here for compatibility with the std::unordered_map interface.
     */
    template <class... Args>
    iterator emplace_hint(const_iterator hint, Args&&... args) {
        return m_ht.emplace_hint(hint, std::forward<Args>(args)...);
    }




    template<class... Args>
    std::pair<iterator, bool> try_emplace(const key_type& k, Args&&... args) {
        return m_ht.try_emplace(k, std::forward<Args>(args)...);
    }

    template<class... Args>
    std::pair<iterator, bool> try_emplace(key_type&& k, Args&&... args) {
        return m_ht.try_emplace(std::move(k), std::forward<Args>(args)...);
    }

    template<class... Args>
    iterator try_emplace(const_iterator hint, const key_type& k, Args&&... args) {
        return m_ht.try_emplace(hint, k, std::forward<Args>(args)...);
    }

    template<class... Args>
    iterator try_emplace(const_iterator hint, key_type&& k, Args&&... args) {
        return m_ht.try_emplace(hint, std::move(k), std::forward<Args>(args)...);
    }




    /**
     * When erasing an element, the insert order will be preserved and no holes will be present in the container
     * returned by 'values_container()'.
     *
     * The method is in O(n), if the order is not important 'unordered_erase(...)' method is faster with an O(1)
     * average complexity.
     */
    iterator erase(iterator pos) { return m_ht.erase(pos); }

    /**
     * @copydoc erase(iterator pos)
     */
    iterator erase(const_iterator pos) { return m_ht.erase(pos); }

    /**
     * @copydoc erase(iterator pos)
     */
    iterator erase(const_iterator first, const_iterator last) { return m_ht.erase(first, last); }

    /**
     * @copydoc erase(iterator pos)
     */
    size_type erase(const key_type& key) { return m_ht.erase(key); }

    /**
     * @copydoc erase(iterator pos)
     *
     * Use the hash value 'precalculated_hash' instead of hashing the key. The hash value should be the same
     * as hash_function()(key). Usefull to speed-up the lookup to the value if you already have the hash.
     */
    size_type erase(const key_type& key, std::size_t precalculated_hash) {
        return m_ht.erase(key, precalculated_hash);
    }

    /**
     * @copydoc erase(iterator pos)
     *
     * This overload only participates in the overload resolution if the typedef KeyEqual::is_transparent exists.
     * If so, K must be hashable and comparable to Key.
     */
    template<class K, class KE = KeyEqual, typename std::enable_if<has_is_transparent<KE>::value>::type* = nullptr>
    size_type erase(const K& key) { return m_ht.erase(key); }

    /**
     * @copydoc erase(const key_type& key, std::size_t precalculated_hash)
     *
     * This overload only participates in the overload resolution if the typedef KeyEqual::is_transparent exists.
     * If so, K must be hashable and comparable to Key.
     */
    template<class K, class KE = KeyEqual, typename std::enable_if<has_is_transparent<KE>::value>::type* = nullptr>
    size_type erase(const K& key, std::size_t precalculated_hash) {
        return m_ht.erase(key, precalculated_hash);
    }


    void swap(ordered_map& other) noexcept { other.m_ht.swap(m_ht); }

    /*
     * Lookup
     */
    T& at(const Key& key) { return m_ht.at(key); }

    /**
     * Use the hash value 'precalculated_hash' instead of hashing the key. The hash value should be the same
     * as hash_function()(key). Usefull to speed-up the lookup if you already have the hash.
     */
    T& at(const Key& key, std::size_t precalculated_hash) { return m_ht.at(key, precalculated_hash); }


    const T& at(const Key& key) const { return m_ht.at(key); }

    /**
     * @copydoc at(const Key& key, std::size_t precalculated_hash)
     */
    const T& at(const Key& key, std::size_t precalculated_hash) const { return m_ht.at(key, precalculated_hash); }


    /**
     * This overload only participates in the overload resolution if the typedef KeyEqual::is_transparent exists.
     * If so, K must be hashable and comparable to Key.
     */
    template<class K, class KE = KeyEqual, typename std::enable_if<has_is_transparent<KE>::value>::type* = nullptr>
    T& at(const K& key) { return m_ht.at(key); }

    /**
     * @copydoc at(const K& key)
     *
     * Use the hash value 'precalculated_hash' instead of hashing the key. The hash value should be the same
     * as hash_function()(key). Usefull to speed-up the lookup if you already have the hash.
     */
    template<class K, class KE = KeyEqual, typename std::enable_if<has_is_transparent<KE>::value>::type* = nullptr>
    T& at(const K& key, std::size_t precalculated_hash) { return m_ht.at(key, precalculated_hash); }

    /**
     * @copydoc at(const K& key)
     */
    template<class K, class KE = KeyEqual, typename std::enable_if<has_is_transparent<KE>::value>::type* = nullptr>
    const T& at(const K& key) const { return m_ht.at(key); }

    /**
     * @copydoc at(const K& key, std::size_t precalculated_hash)
     */
    template<class K, class KE = KeyEqual, typename std::enable_if<has_is_transparent<KE>::value>::type* = nullptr>
    const T& at(const K& key, std::size_t precalculated_hash) const { return m_ht.at(key, precalculated_hash); }



    T& operator[](const Key& key) { return m_ht[key]; }
    T& operator[](Key&& key) { return m_ht[std::move(key)]; }



    size_type count(const Key& key) const { return m_ht.count(key); }

    /**
     * Use the hash value 'precalculated_hash' instead of hashing the key. The hash value should be the same
     * as hash_function()(key). Usefull to speed-up the lookup if you already have the hash.
     */
    size_type count(const Key& key, std::size_t precalculated_hash) const {
        return m_ht.count(key, precalculated_hash);
    }

    /**
     * This overload only participates in the overload resolution if the typedef KeyEqual::is_transparent exists.
     * If so, K must be hashable and comparable to Key.
     */
    template<class K, class KE = KeyEqual, typename std::enable_if<has_is_transparent<KE>::value>::type* = nullptr>
    size_type count(const K& key) const { return m_ht.count(key); }

    /**
     * @copydoc count(const K& key) const
     *
     * Use the hash value 'precalculated_hash' instead of hashing the key. The hash value should be the same
     * as hash_function()(key). Usefull to speed-up the lookup if you already have the hash.
     */
    template<class K, class KE = KeyEqual, typename std::enable_if<has_is_transparent<KE>::value>::type* = nullptr>
    size_type count(const K& key, std::size_t precalculated_hash) const {
        return m_ht.count(key, precalculated_hash);
    }



    iterator find(const Key& key) { return m_ht.find(key); }

    /**
     * Use the hash value 'precalculated_hash' instead of hashing the key. The hash value should be the same
     * as hash_function()(key). Usefull to speed-up the lookup if you already have the hash.
     */
    iterator find(const Key& key, std::size_t precalculated_hash) { return m_ht.find(key, precalculated_hash); }

    const_iterator find(const Key& key) const { return m_ht.find(key); }

    /**
     * @copydoc find(const Key& key, std::size_t precalculated_hash)
     */
    const_iterator find(const Key& key, std::size_t precalculated_hash) const {
        return m_ht.find(key, precalculated_hash);
    }

    /**
     * This overload only participates in the overload resolution if the typedef KeyEqual::is_transparent exists.
     * If so, K must be hashable and comparable to Key.
     */
    template<class K, class KE = KeyEqual, typename std::enable_if<has_is_transparent<KE>::value>::type* = nullptr>
    iterator find(const K& key) { return m_ht.find(key); }

    /**
     * @copydoc find(const K& key)
     *
     * Use the hash value 'precalculated_hash' instead of hashing the key. The hash value should be the same
     * as hash_function()(key). Usefull to speed-up the lookup if you already have the hash.
     */
    template<class K, class KE = KeyEqual, typename std::enable_if<has_is_transparent<KE>::value>::type* = nullptr>
    iterator find(const K& key, std::size_t precalculated_hash) { return m_ht.find(key, precalculated_hash); }

    /**
     * @copydoc find(const K& key)
     */
    template<class K, class KE = KeyEqual, typename std::enable_if<has_is_transparent<KE>::value>::type* = nullptr>
    const_iterator find(const K& key) const { return m_ht.find(key); }

    /**
     * @copydoc find(const K& key)
     *
     * Use the hash value 'precalculated_hash' instead of hashing the key. The hash value should be the same
     * as hash_function()(key). Usefull to speed-up the lookup if you already have the hash.
     */
    template<class K, class KE = KeyEqual, typename std::enable_if<has_is_transparent<KE>::value>::type* = nullptr>
    const_iterator find(const K& key, std::size_t precalculated_hash) const {
        return m_ht.find(key, precalculated_hash);
    }



    std::pair<iterator, iterator> equal_range(const Key& key) { return m_ht.equal_range(key); }

    /**
     * Use the hash value 'precalculated_hash' instead of hashing the key. The hash value should be the same
     * as hash_function()(key). Usefull to speed-up the lookup if you already have the hash.
     */
    std::pair<iterator, iterator> equal_range(const Key& key, std::size_t precalculated_hash) {
        return m_ht.equal_range(key, precalculated_hash);
    }

    std::pair<const_iterator, const_iterator> equal_range(const Key& key) const { return m_ht.equal_range(key); }

    /**
     * @copydoc equal_range(const Key& key, std::size_t precalculated_hash)
     */
    std::pair<const_iterator, const_iterator> equal_range(const Key& key, std::size_t precalculated_hash) const {
        return m_ht.equal_range(key, precalculated_hash);
    }

    /**
     * This overload only participates in the overload resolution if the typedef KeyEqual::is_transparent exists.
     * If so, K must be hashable and comparable to Key.
     */
    template<class K, class KE = KeyEqual, typename std::enable_if<has_is_transparent<KE>::value>::type* = nullptr>
    std::pair<iterator, iterator> equal_range(const K& key) { return m_ht.equal_range(key); }

    /**
     * @copydoc equal_range(const K& key)
     *
     * Use the hash value 'precalculated_hash' instead of hashing the key. The hash value should be the same
     * as hash_function()(key). Usefull to speed-up the lookup if you already have the hash.
     */
    template<class K, class KE = KeyEqual, typename std::enable_if<has_is_transparent<KE>::value>::type* = nullptr>
    std::pair<iterator, iterator> equal_range(const K& key, std::size_t precalculated_hash) {
        return m_ht.equal_range(key, precalculated_hash);
    }

    /**
     * @copydoc equal_range(const K& key)
     */
    template<class K, class KE = KeyEqual, typename std::enable_if<has_is_transparent<KE>::value>::type* = nullptr>
    std::pair<const_iterator, const_iterator> equal_range(const K& key) const { return m_ht.equal_range(key); }

    /**
     * @copydoc equal_range(const K& key, std::size_t precalculated_hash)
     */
    template<class K, class KE = KeyEqual, typename std::enable_if<has_is_transparent<KE>::value>::type* = nullptr>
    std::pair<const_iterator, const_iterator> equal_range(const K& key, std::size_t precalculated_hash) const {
        return m_ht.equal_range(key, precalculated_hash);
    }



    /*
     * Bucket interface
     */
    size_type bucket_count() const { return m_ht.bucket_count(); }
    size_type max_bucket_count() const { return m_ht.max_bucket_count(); }


    /*
     * Hash policy
     */
    float load_factor() const { return m_ht.load_factor(); }
    float max_load_factor() const { return m_ht.max_load_factor(); }
    void max_load_factor(float ml) { m_ht.max_load_factor(ml); }

    void rehash(size_type count) { m_ht.rehash(count); }
    void reserve(size_type count) { m_ht.reserve(count); }


    /*
     * Observers
     */
    hasher hash_function() const { return m_ht.hash_function(); }
    key_equal key_eq() const { return m_ht.key_eq(); }



    /*
     * Other
     */

    /**
     * Convert a const_iterator to an iterator.
     */
    iterator mutable_iterator(const_iterator pos) {
        return m_ht.mutable_iterator(pos);
    }

    /**
     * Requires index <= size().
     *
     * Return an iterator to the element at index. Return end() if index == size().
     */
    iterator nth(size_type index) { return m_ht.nth(index); }

    /**
     * @copydoc nth(size_type index)
     */
    const_iterator nth(size_type index) const { return m_ht.nth(index); }


    /**
     * Return const_reference to the first element. Requires the container to not be empty.
     */
    const_reference front() const { return m_ht.front(); }

    /**
     * Return const_reference to the last element. Requires the container to not be empty.
     */
    const_reference back() const { return m_ht.back(); }


    /**
     * Only available if ValueTypeContainer is a std::vector. Same as calling 'values_container().data()'.
     */
    template<class U = values_container_type, typename std::enable_if<tsl::detail_ordered_hash::is_vector<U>::value>::type* = nullptr>
    const typename values_container_type::value_type* data() const noexcept { return m_ht.data(); }

    /**
     * Return the container in which the values are stored. The values are in the same order as the insertion order
     * and are contiguous in the structure, no holes (size() == values_container().size()).
     */
    const values_container_type& values_container() const noexcept { return m_ht.values_container(); }

    template<class U = values_container_type, typename std::enable_if<tsl::detail_ordered_hash::is_vector<U>::value>::type* = nullptr>
    size_type capacity() const noexcept { return m_ht.capacity(); }

    void shrink_to_fit() { m_ht.shrink_to_fit(); }



    /**
     * Insert the value before pos shifting all the elements on the right of pos (including pos) one position
     * to the right.
     *
     * Amortized linear time-complexity in the distance between pos and end().
     */
    std::pair<iterator, bool> insert_at_position(const_iterator pos, const value_type& value) {
        return m_ht.insert_at_position(pos, value);
    }

    /**
     * @copydoc insert_at_position(const_iterator pos, const value_type& value)
     */
    std::pair<iterator, bool> insert_at_position(const_iterator pos, value_type&& value) {
        return m_ht.insert_at_position(pos, std::move(value));
    }

    /**
     * @copydoc insert_at_position(const_iterator pos, const value_type& value)
     *
     * Same as insert_at_position(pos, value_type(std::forward<Args>(args)...), mainly
     * here for coherence.
     */
    template<class... Args>
    std::pair<iterator, bool> emplace_at_position(const_iterator pos, Args&&... args) {
        return m_ht.emplace_at_position(pos, std::forward<Args>(args)...);
    }

    /**
     * @copydoc insert_at_position(const_iterator pos, const value_type& value)
     */
    template<class... Args>
    std::pair<iterator, bool> try_emplace_at_position(const_iterator pos, const key_type& k, Args&&... args) {
        return m_ht.try_emplace_at_position(pos, k, std::forward<Args>(args)...);
    }

    /**
     * @copydoc insert_at_position(const_iterator pos, const value_type& value)
     */
    template<class... Args>
    std::pair<iterator, bool> try_emplace_at_position(const_iterator pos, key_type&& k, Args&&... args) {
        return m_ht.try_emplace_at_position(pos, std::move(k), std::forward<Args>(args)...);
    }



    void pop_back() { m_ht.pop_back(); }

    /**
     * Faster erase operation with an O(1) average complexity but it doesn't preserve the insertion order.
     *
     * If an erasure occurs, the last element of the map will take the place of the erased element.
     */
    iterator unordered_erase(iterator pos) { return m_ht.unordered_erase(pos); }

    /**
     * @copydoc unordered_erase(iterator pos)
     */
    iterator unordered_erase(const_iterator pos) { return m_ht.unordered_erase(pos); }

    /**
     * @copydoc unordered_erase(iterator pos)
     */
    size_type unordered_erase(const key_type& key) { return m_ht.unordered_erase(key); }

    /**
     * @copydoc unordered_erase(iterator pos)
     *
     * Use the hash value 'precalculated_hash' instead of hashing the key. The hash value should be the same
     * as hash_function()(key). Usefull to speed-up the lookup if you already have the hash.
     */
    size_type unordered_erase(const key_type& key, std::size_t precalculated_hash) {
        return m_ht.unordered_erase(key, precalculated_hash);
    }

    /**
     * @copydoc unordered_erase(iterator pos)
     *
     * This overload only participates in the overload resolution if the typedef KeyEqual::is_transparent exists.
     * If so, K must be hashable and comparable to Key.
     */
    template<class K, class KE = KeyEqual, typename std::enable_if<has_is_transparent<KE>::value>::type* = nullptr>
    size_type unordered_erase(const K& key) { return m_ht.unordered_erase(key); }

    /**
     * @copydoc unordered_erase(const K& key)
     *
     * Use the hash value 'precalculated_hash' instead of hashing the key. The hash value should be the same
     * as hash_function()(key). Usefull to speed-up the lookup if you already have the hash.
     */
    template<class K, class KE = KeyEqual, typename std::enable_if<has_is_transparent<KE>::value>::type* = nullptr>
    size_type unordered_erase(const K& key, std::size_t precalculated_hash) {
        return m_ht.unordered_erase(key, precalculated_hash);
    }



    friend bool operator==(const ordered_map& lhs, const ordered_map& rhs) { return lhs.m_ht == rhs.m_ht; }
    friend bool operator!=(const ordered_map& lhs, const ordered_map& rhs) { return lhs.m_ht != rhs.m_ht; }
    friend bool operator<(const ordered_map& lhs, const ordered_map& rhs) { return lhs.m_ht < rhs.m_ht; }
    friend bool operator<=(const ordered_map& lhs, const ordered_map& rhs) { return lhs.m_ht <= rhs.m_ht; }
    friend bool operator>(const ordered_map& lhs, const ordered_map& rhs) { return lhs.m_ht > rhs.m_ht; }
    friend bool operator>=(const ordered_map& lhs, const ordered_map& rhs) { return lhs.m_ht >= rhs.m_ht; }

    friend void swap(ordered_map& lhs, ordered_map& rhs) { lhs.swap(rhs); }

private:
    ht m_ht;
};

} // end namespace tsl

#endif