    // Copyright (C) 2003  Davis E. King (davis@dlib.net)
    // License: Boost Software License   See LICENSE.txt for the full license.
    #ifndef DLIB_QUEUE_KERNEl_1_
    #define DLIB_QUEUE_KERNEl_1_

    #include "queue_kernel_abstract.h"
    #include "../algs.h"
    #include "../interfaces/enumerable.h"
    #include "../interfaces/remover.h"
    #include "../serialize.h"

    namespace dlib
    {

        template <
            typename T,
            typename mem_manager = default_memory_manager
            >
        class queue_kernel_1 : public enumerable<T>,
                               public remover<T>
        {

            /*!
                INITIAL VALUE
                    queue_size == 0
                    current_element == 0
                    at_start_ == true

                CONVENTION
                    queue_size == the number of elements in the queue
                    at_start() == at_start_
                    current_element_valid() == (current_element != 0)
                    element() == current_element->item

                    if (queue_size > 0)
                    {
                        in points to the last element to be inserted into the queue
                        out points to the next element to be dequeued

                        each node points to the node inserted after it except for the most
                        recently inserted node

                        current_element == 0
                    }

            !*/

            struct node
            {
                node* last;

                T item;
            };

            public:

                typedef T type;
                typedef mem_manager mem_manager_type;

                queue_kernel_1 (
                ) :
                    in(0),
                    out(0),
                    queue_size(0),
                    current_element(0),
                    at_start_(true)
                {
                }

                virtual ~queue_kernel_1 (
                );

                inline void clear(
                );

                void enqueue (
                    T& item
                );

                void dequeue (
                    T& item
                );

                void cat (
                    queue_kernel_1& item
                );

                T& current (
                );

                const T& current (
                ) const;

                void swap (
                    queue_kernel_1& item
                );

                // functions from the remover interface
                inline void remove_any (
                    T& item
                );

                // functions from the enumerable interface
                inline unsigned long size (
                ) const;

                inline bool at_start (
                ) const;

                inline void reset (
                ) const;

                bool current_element_valid (
                ) const;

                inline const T& element (
                ) const;

                inline T& element (
                );

                bool move_next (
                ) const;

            private:

                void delete_nodes (
                    node* start,
                    unsigned long length
                );
                /*!
                    requires
                        - start points to a node in a singly linked list
                        - start->last points to the next node in the list
                        - there are at least length nodes in the list begining with start
                    ensures
                        - length nodes have been deleted starting with the node pointed
                          to by start
                !*/

                // data members

                node* in;
                node* out;
                unsigned long queue_size;
                mutable node* current_element;
                mutable bool at_start_;

                // restricted functions
                queue_kernel_1(queue_kernel_1&);        // copy constructor
                queue_kernel_1& operator=(queue_kernel_1&);    // assignment operator

        };

        template <
            typename T,
            typename mem_manager
            >
        inline void swap (
            queue_kernel_1<T,mem_manager>& a,
            queue_kernel_1<T,mem_manager>& b
        ) { a.swap(b); }

        template <
            typename T,
            typename mem_manager
            >
        void deserialize (
            queue_kernel_1<T,mem_manager>& item,
            std::istream& in
        )
        {
            try
            {
                item.clear();
                unsigned long size;
                deserialize(size,in);
                T temp;
                for (unsigned long i = 0; i < size; ++i)
                {
                    deserialize(temp,in);
                    item.enqueue(temp);
                }
            }
            catch (serialization_error e)
            {
                item.clear();
                throw serialization_error(e.info + "\n   while deserializing object of type queue_kernel_1");
            }
        }

    // ----------------------------------------------------------------------------------------
    // ----------------------------------------------------------------------------------------
        // member function definitions
    // ----------------------------------------------------------------------------------------
    // ----------------------------------------------------------------------------------------

        template <
            typename T,
            typename mem_manager
            >
        queue_kernel_1<T,mem_manager>::
        ~queue_kernel_1 (
        )
        {
            delete_nodes(out,queue_size);
        }

    // ----------------------------------------------------------------------------------------

        template <
            typename T,
            typename mem_manager
            >
        void queue_kernel_1<T,mem_manager>::
        clear (
        )
        {
            delete_nodes(out,queue_size);
            queue_size = 0;

            // put the enumerator at the start
            reset();
        }

    // ----------------------------------------------------------------------------------------

        template <
            typename T,
            typename mem_manager
            >
        void queue_kernel_1<T,mem_manager>::
        enqueue (
            T& item
        )
        {
            // make new node
            node* temp = new node;

            // swap item into new node
            exchange(item,temp->item);

            if (queue_size == 0)
                out = temp;
            else
                in->last = temp;

            // make in point to the new node
            in = temp;

            ++queue_size;

            // put the enumerator at the start
            reset();
        }

    // ----------------------------------------------------------------------------------------

        template <
            typename T,
            typename mem_manager
            >
        void queue_kernel_1<T,mem_manager>::
        dequeue (
            T& item
        )
        {
            // swap out into item
            exchange(item,out->item);

            --queue_size;

            if (queue_size == 0)
            {
                delete out;
            }
            else
            {
                node* temp = out;

                // move out pointer to the next element in the queue
                out = out->last;

                // delete old node
                delete temp;
            }

            // put the enumerator at the start
            reset();
        }

    // ----------------------------------------------------------------------------------------

        template <
            typename T,
            typename mem_manager
            >
        void queue_kernel_1<T,mem_manager>::
        cat (
            queue_kernel_1<T,mem_manager>& item
        )
        {
            if (item.queue_size > 0)
            {
                if (queue_size > 0)
                {
                    in->last = item.out;
                }
                else
                {
                    out = item.out;
                }

                in = item.in;
                queue_size += item.queue_size;
                item.queue_size = 0;
            }

            // put the enumerator at the start
            reset();
        }

    // ----------------------------------------------------------------------------------------

        template <
            typename T,
            typename mem_manager
            >
        T& queue_kernel_1<T,mem_manager>::
        current (
        )
        {
            return out->item;
        }

    // ----------------------------------------------------------------------------------------

        template <
            typename T,
            typename mem_manager
            >
        const T& queue_kernel_1<T,mem_manager>::
        current (
        ) const
        {
            return out->item;
        }

    // ----------------------------------------------------------------------------------------

        template <
            typename T,
            typename mem_manager
            >
        void queue_kernel_1<T,mem_manager>::
        swap (
            queue_kernel_1<T,mem_manager>& item
        )
        {
            node* in_temp = in;
            node* out_temp = out;
            unsigned long queue_size_temp = queue_size;
            node* current_element_temp = current_element;
            bool at_start_temp = at_start_;

            in = item.in;
            out = item.out;
            queue_size = item.queue_size;
            current_element = item.current_element;
            at_start_ = item.at_start_;

            item.in = in_temp;
            item.out = out_temp;
            item.queue_size = queue_size_temp;
            item.current_element = current_element_temp;
            item.at_start_ = at_start_temp;
        }

    // ----------------------------------------------------------------------------------------
    // ----------------------------------------------------------------------------------------
        // enumerable function definitions
    // ----------------------------------------------------------------------------------------
    // ----------------------------------------------------------------------------------------

        template <
            typename T,
            typename mem_manager
            >
        bool queue_kernel_1<T,mem_manager>::
        at_start (
        ) const
        {
            return at_start_;
        }

    // ----------------------------------------------------------------------------------------

        template <
            typename T,
            typename mem_manager
            >
        unsigned long queue_kernel_1<T,mem_manager>::
        size (
        ) const
        {
            return queue_size;
        }

    // ----------------------------------------------------------------------------------------

        template <
            typename T,
            typename mem_manager
            >
        void queue_kernel_1<T,mem_manager>::
        reset (
        ) const
        {
            at_start_ = true;
            current_element = 0;
        }

    // ----------------------------------------------------------------------------------------

        template <
            typename T,
            typename mem_manager
            >
        bool queue_kernel_1<T,mem_manager>::
        current_element_valid (
        ) const
        {
            return (current_element != 0);
        }

    // ----------------------------------------------------------------------------------------

        template <
            typename T,
            typename mem_manager
            >
        const T& queue_kernel_1<T,mem_manager>::
        element (
        ) const
        {
            return current_element->item;
        }

    // ----------------------------------------------------------------------------------------

        template <
            typename T,
            typename mem_manager
            >
        T& queue_kernel_1<T,mem_manager>::
        element (
        )
        {
            return current_element->item;
        }

    // ----------------------------------------------------------------------------------------

        template <
            typename T,
            typename mem_manager
            >
        bool queue_kernel_1<T,mem_manager>::
        move_next (
        ) const
        {
            if (at_start_)
            {
                at_start_ = false;
                // if the queue is empty then there is nothing to do
                if (queue_size == 0)
                {
                    return false;
                }
                else
                {
                    current_element = out;
                    return true;
                }
            }
            else
            {
                // if we are at the last element then the enumeration has finished
                if (current_element == in || current_element == 0)
                {
                    current_element = 0;
                    return false;
                }
                else
                {
                    current_element = current_element->last;
                    return true;
                }
            }
        }

    // ----------------------------------------------------------------------------------------
    // ----------------------------------------------------------------------------------------
        // remover function definitions
    // ----------------------------------------------------------------------------------------
    // ----------------------------------------------------------------------------------------

        template <
            typename T,
            typename mem_manager
            >
        void queue_kernel_1<T,mem_manager>::
        remove_any (
            T& item
        )
        {
            dequeue(item);
        }

    // ----------------------------------------------------------------------------------------
    // ----------------------------------------------------------------------------------------
        // private member function definitions
    // ----------------------------------------------------------------------------------------
    // ----------------------------------------------------------------------------------------

        template <
            typename T,
            typename mem_manager
            >
        void queue_kernel_1<T,mem_manager>::
        delete_nodes (
            node* start,
            unsigned long length
        )
        {
            node* temp;
            while (length)
            {
                temp = start->last;
                delete start;
                start = temp;
                --length;
            }
        }

    // ----------------------------------------------------------------------------------------

    }

    #endif // DLIB_QUEUE_KERNEl_1_