/*
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/.
 *
 * Copyright 2021, Danny Robson <danny@nerdcruft.net>
 */


#pragma once

#include "../iterator/unordered_insert.hpp"
#include "../iterator/placement_output.hpp"
#include "../iterator/tuple_picker.hpp"
#include "../cast.hpp"

#include <algorithm>
#include <functional>

#include <cstddef>


namespace cruft::map {
    /// A multi-map with a compile-time fixed-size backing store.
    template <
        std::size_t SizeV,
        typename KeyT,
        typename ValueT,
        typename ComparatorT = std::less<>
    >
    class multi_fixed {
    public:
        static constexpr auto elements = SizeV;

        using key_type = KeyT;
        using mapped_type = ValueT;
        using value_type = std::pair<key_type, mapped_type>;

        using key_compare = ComparatorT;
        using reference = value_type&;
        using const_reference = value_type const&;
        using pointer = value_type*;
        using const_pointer = value_type const*;

        using iterator = pointer;
        using const_iterator = const_pointer;

        multi_fixed () = default;
        ~multi_fixed ()
        {
            for (std::size_t i = 0; i < m_size; ++i)
                m_store.data[i].~value_type ();
        }

        multi_fixed (std::initializer_list<value_type> const &src)
        {
            if (src.size () > capacity ())
                throw std::bad_alloc ();

            std::copy (
                std::make_move_iterator (std::begin (src)),
                std::make_move_iterator (std::end   (src)),
                m_store.data + 0
            );

            m_size = src.size ();

            std::sort (
                m_store.data +      0,
                m_store.data + m_size,
                ComparatorT {}
            );
        }

        multi_fixed (multi_fixed const&);

        multi_fixed (multi_fixed &&rhs) noexcept (std::is_nothrow_move_constructible_v<value_type>)
        {
            clear ();

            while (m_size != rhs.m_size) {
                new (m_store.data + m_size) value_type (std::move (rhs.m_store.data[m_size]));
                ++m_size;
            }
        }

        multi_fixed& operator= (multi_fixed&&) noexcept (std::is_nothrow_move_assignable_v<value_type>) = default;
        multi_fixed& operator= (multi_fixed const&) noexcept (std::is_nothrow_assignable_v<value_type>) = default;

        iterator begin (void)& { return m_store.data +      0; }
        iterator end   (void)& { return m_store.data + m_size; }

        const_iterator begin (void) const& { return m_store.data +      0; }
        const_iterator end   (void) const& { return m_store.data + m_size; }

        const_iterator cbegin (void) const& { return cbegin (); }
        const_iterator cend   (void) const& { return cend   (); }

        iterator
        insert (value_type const &kv)
        {
            // Don't overrun our static buffer
            if (size () == capacity ())
                throw std::bad_alloc ();

            // Find the insert position. We prefer lte comparison so that we
            // avoid moving too many key-value pairs backwards to make room
            // for the data.
            auto cursor = begin ();
            ComparatorT cmp {};
            while (cmp (cursor->first, kv.first) && cursor != end ())
                ++cursor;

            // Shuffle the items back in the storage.
            auto offset = std::distance (begin (), cursor);
            auto remain = size () - offset;
            std::move_backward (cursor, cursor + remain, cursor + remain + 1);

            // Insert the new data and return
            new (cursor) value_type (kv);
            ++m_size;
            return cursor;
        }

        iterator
        insert (value_type &&kv)
        {
            return insert (kv);
        }

        template <typename RandomT>
        void
        insert (RandomT first, RandomT last)
        {
            static_assert (
                std::is_same_v<
                    typename std::iterator_traits<RandomT>::iterator_category,
                    std::random_access_iterator_tag
                >,
                "We assume random iterators here to simplify offset "
                "calculations and make copying a little more efficient. "
                "There's no reason it needs to be restricted though."
            );

            auto const count = std::distance (first, last);
            if (cruft::cast::sign<size_t> (count) > capacity () - size ())
                throw std::bad_alloc ();

            std::copy (
                first,
                last,
                cruft::iterator::placement_output {m_store.data + size ()}
            );

            std::sort (
                m_store.data + size (),
                m_store.data + size () + count
            );

            std::inplace_merge (
                m_store.data + 0,
                m_store.data + size (),
                m_store.data + size () + count
            );

            m_size += count;
        }

        template <typename K>
        bool contains (K const&) const;

        template <typename K>
        iterator find (K const &k)&
        {
            ComparatorT cmp {};

            for (auto cursor = begin (); cursor != end (); ++cursor)
                if (!cmp (cursor->first, k) && !cmp (k, cursor->first))
                    return cursor;

            return end ();
        }

        template <typename K>
        const_iterator find (K const&) const&;

        template <typename K>
        iterator
        lower_bound (K const &k)&
        {
            ComparatorT cmp {};
            return std::find_if (
                begin (),
                end   (),
                [&] (auto const &val) { return !cmp (val.first, k); }
            );
        }

        template <typename K>
        iterator
        upper_bound (K const &k)&
        {
            ComparatorT cmp {};
            return std::find_if (
                begin (),
                end   (),
                [&] (auto const &val) { return cmp (k, val.first); }
            );
        }

        template <typename K>
        std::pair<iterator, iterator>
        equal_range (K const &key)&
        {
            return {
                lower_bound (key),
                upper_bound (key)
            };
        }

        void clear (void)
        {
            for (std::size_t i = 0; i < m_size; ++i)
                m_store.data[i].~value_type ();
            m_size = 0;
        }

        void erase (iterator it)
        {
            CHECK_GE (it, begin ());
            CHECK_LT (it, end   ());
            CHECK (!empty ());

            std::move (it + 1, end (), it);
            --m_size;
            m_store.data[m_size].~value_type ();
        }


        /// Erases the keys pointed at by the supplied iterator range.
        ///
        /// If a key does not exist it is silently ignored.
        ///
        /// \return The number of keys erased.
        template <typename IteratorT>
        std::size_t
        erase_keys (IteratorT first, IteratorT last)
        {
            CHECK (std::is_sorted (first, last));

            std::size_t tally = 0;

            // HACK: This is hopelessly naive, but it works.
            for (auto cursor = first; cursor != last; ++cursor) {
                if (auto pos = find (*cursor); pos != end ()) {
                    erase (pos);
                    ++tally;
                }
            }

            return tally;
        }

        void
        erase_item (value_type const &kv)
        {
            auto [first, last] = equal_range (kv.first);

            auto const pos = std::find_if (
                first,
                last,
                [&kv] (auto const &candidate) { return candidate.second == kv.second; }
            );

            if (pos == last)
                throw std::out_of_range ("unknown key-value");

            erase (pos);
        }


        std::size_t erase (key_type const&);

        bool empty (void) const { return m_size == 0; }
        auto size (void) const { return m_size; }
        auto capacity (void) const { return elements; }

        void swap (multi_fixed &rhs)
        {
            // To save duplicating the code which moves the trailing excess
            // items between containers we instead just reverse the direction
            // here.
            if (rhs.size () > size ())
                rhs.swap (*this);

            using std::swap;

            // Swap the commonly held indices
            std::size_t const common = std::min (size (), rhs.size ());
            for (std::size_t i = 0; i != common; ++i)
                swap (m_store.data[i], rhs.m_store.data[i]);

            // Move our indices to the rhs if we're larger. We don't need the
            // reverse case because we took care of that earlier.
            CHECK_GE (size (), rhs.size ());
            if (size () > common) {
                for (std::size_t i = common; i < size (); ++i)
                    new (rhs.m_store.data + i) value_type (std::move (m_store.data[i]));

                swap (m_size, rhs.m_size);
            }
        }

        /// A helper class that allows iteration over the keys of a
        /// multi_fixed map.
        ///
        /// The iterators it provides may be invalidated if any mutating
        /// operations are performed on the underlying multi_fixed object.
        class keys_proxy {
        public:
            using iterator_category = std::random_access_iterator_tag;
            using value_type = KeyT;
            using difference_type = std::ptrdiff_t;
            using pointer = value_type*;
            using reference = value_type&;

            keys_proxy (multi_fixed const &_parent)
                : m_parent (&_parent)
            { ; }

            auto begin (void) const { return cruft::iterator::make_tuple_picker<0> (m_parent->begin ()); }
            auto end   (void) const { return cruft::iterator::make_tuple_picker<0> (m_parent->end   ()); }

        private:
            multi_fixed const *m_parent;
        };

        /// Returns a container that allows traversal of the underlying keys
        /// of the store.
        keys_proxy keys (void) const& { return keys_proxy (*this); }

    private:
        std::size_t m_size = 0;

        union store {
             store () { ; }
            ~store () { ; }

            char defer;
            value_type data[elements];
        } m_store;
    };


    template <
        std::size_t SizeV,
        typename KeyT,
        typename ValueT,
        typename ComparatorT
    >
    void swap (
        multi_fixed<SizeV, KeyT, ValueT, ComparatorT> &a,
        multi_fixed<SizeV, KeyT, ValueT, ComparatorT> &b
    ) {
        a.swap (b);
    }


    /// Returns a concatenation of two multi_fixed maps. ie, a copy of
    /// all entries in the first map, and all entries in the second map.
    ///
    /// If both maps have the same value then the output will have duplicates.
    ///
    /// If the combined size of the maps exceeds the static capacity a
    /// std::bad_alloc will be thrown.
    template <std::size_t SizeV, typename KeyT, typename ValueT, typename ComparatorT>
    multi_fixed<SizeV, KeyT, ValueT, ComparatorT>
    operator+ (
        multi_fixed<SizeV, KeyT, ValueT, ComparatorT> const &a,
        multi_fixed<SizeV, KeyT, ValueT, ComparatorT> const &b
    ) {
        multi_fixed<SizeV, KeyT, ValueT, ComparatorT> res;
        res.insert (a.begin (), a.end ());
        res.insert (b.begin (), b.end ());
        return res;
    }


    /// Returns the difference between two multi_fixed maps.
    ///
    /// ie, the entries found in the first but not the second.
    template <std::size_t SizeV, typename KeyT, typename ValueT, typename ComparatorT>
    multi_fixed<SizeV, KeyT, ValueT, ComparatorT>
    operator- (
        multi_fixed<SizeV, KeyT, ValueT, ComparatorT> const &a,
        multi_fixed<SizeV, KeyT, ValueT, ComparatorT> const &b
    ) {

        multi_fixed<SizeV, KeyT, ValueT, ComparatorT> res;
        std::set_difference (
            std::begin (a), std::end (a),
            std::begin (b), std::end (b),
            cruft::iterator::unordered_insert (res)
        );
        return res;
    }


    template <std::size_t SizeV, typename KeyT, typename ValueT, typename ComparatorT>
    bool
    operator== (
        multi_fixed<SizeV, KeyT, ValueT, ComparatorT> const &a,
        multi_fixed<SizeV, KeyT, ValueT, ComparatorT> const &b
    ) {
        return std::equal (
            std::begin (a), std::end (a),
            std::begin (b), std::end (b)
        );
    }
}