include/list.h

#ifndef LIST_H
#define LIST_H

#include "generic.h"

namespace algo {
    template <typename Object>
    class List {
        private:
            class ListNode {
                public:
                    ListNode( const Object & obj = Object{ },
                              ListNode *pNext = nullptr,
                              ListNode *pPrev = nullptr )
                        : element{ obj }, next { pNext }, prev { pPrev } { }

                    ListNode( const Object && obj,
                              ListNode *pNext = nullptr,
                              ListNode *pPrev = nullptr )
                        : element( std::move( obj ) ), next ( pNext ), prev ( pPrev ) { }

                private:
                    Object element;
                    ListNode* next;
                    ListNode* prev;

                    friend class List<Object>;
            }; //end of class ListNode

        public:
            class const_iterator {
                public:
                    const_iterator( ) : current{ nullptr }
                    { }

                    const Object& operator* ( ) const
                    {
                        return retrieve( );
                    }

                    const_iterator& operator++ ( )
                    {
                        current = current->next;
                        return *this;
                    }

                    const_iterator operator++ ( int )
                    {
                        const_iterator old = *this;
                        ++ ( *this );
                        return old;
                    }

                    const_iterator & operator-- ( )
                    {
                        current = current->prev;
                        return *this;
                    }

                    const_iterator operator-- ( int )
                    {
                        const_iterator old = *this;
                        --( *this );
                        return old;
                    }

                    bool operator== ( const const_iterator& rhs ) const
                    {
                        return ( current == rhs.current );
                    }

                    bool operator!= ( const const_iterator& rhs ) const
                    {
                        return ( current != rhs.current );
                    }

                protected:
                    ListNode *current;

                    Object& retrieve ( ) const
                    {
                        return current->element;
                    }

                    const_iterator( ListNode *p )
                        : current{ p } { }

                    friend class List<Object>;

            }; //end of class const_iterator

            class iterator : public const_iterator {
                public:
                    iterator( ) { }

                    Object & operator*( )
                    {
                        return const_iterator::retrieve( );
                    }

                    const Object & operator*( ) const
                    {
                        return const_iterator::operator*( );
                    }
                
                    iterator &  operator++( )
                    {
                        this->current = this->current->next;
                        return *this;
                    }

                    iterator operator++ ( int )
                    {
                        iterator old = *this;
                        ++ ( *this );
                        return old;
                    }

                    iterator & operator--( )
                    {
                        this->current = this->current->prev;
                        return *this;
                    }

                    iterator operator-- ( int )
                    {
                        iterator old = *this;
                        -- ( *this );
                        return old;
                    }

                protected:
                    iterator( ListNode* node ) : const_iterator { node }
                    { }

                    friend class List<Object>;
            }; //end of class iterator

        public:
            List( )
            {
                initialize( );
            }
            
            ~List( )
            {
                clear( );
                delete _head;
                delete _tail;
            }

            List( const List& rhs )
            {
                initialize( );
                for (auto & elem : rhs ) {
                    push_back( elem );
                }
            }

            List ( List && rhs )
                : _size( rhs._size ), _head( rhs._head ), _tail( rhs._tail )
            {
                rhs._size = 0;
                rhs._head = rhs._tail = nullptr;
            }

            List& operator= ( const List & rhs )
            {
                List copy = rhs;
                algo::swap( copy, *this );
                return *this;
            }
        
            List& operator= ( List && rhs )
            {
                algo::swap( _size, rhs._size );
                algo::swap( _head, rhs._head );
                algo::swap( _tail, rhs._tail );
                return *this;
            }

            iterator begin( )
            {
                return iterator( _head->next );
            }

            const_iterator begin( ) const
            {
                return const_iterator( _head->next );
            }

            iterator end( )
            {
                return iterator( _tail );
            }

            const_iterator end( ) const
            {
                return const_iterator( _tail );
            }

            int size( ) const
            {
                return _size;
            }

            bool empty( ) const
            {
                return ( _size == 0 );

            }
            
            void clear( )
            {
                while ( !empty( ) )
                    pop_front( );
            }

            Object& front( )
            {
                return (*begin( ) );
            }

            const Object& front( ) const
            {
                return (*begin( ) );
            }

            Object& back( )
            {
                return (*--end( ) );
            }

            const Object& back( ) const
            {
                return (*--end( ) );
            }

            void push_front( const Object& obj )
            {
                insert( obj, begin( ) );
            }

            void push_front( Object && obj )
            {
                insert( std::move( obj ), begin( ) );
            }

            void push_back( const Object & obj )
            {
                insert( obj, end( ) ); 
            }

            void push_back ( Object && obj )
            {
                insert( std::move( obj ), end( ) );
            }

            void pop_front( )
            {
                erase( begin( ) );
            }

            void pop_back( )
            {
                erase( --end( ) );
            }

            iterator insert( const Object & obj, iterator it )
            {
                ListNode *currNode = it.current;
                ListNode *newNode = new ListNode{ obj, currNode, currNode->prev };
                currNode->prev->next = newNode;
                currNode->prev = newNode;
                ++_size;
                return iterator( newNode );
            }

            iterator erase( iterator it )
            {
                ListNode* currNode = it.current;
                iterator returnItr( currNode->next );
                currNode->prev->next = currNode->next;
                currNode->next->prev = currNode->prev;
                delete currNode;
                --_size;
                return returnItr;
            }

            iterator erase( iterator from, iterator to )
            {
                for( iterator it = from; it != to; ) {
                    it = erase( it );
                }
                return to;
            }

        private:
            int _size;
            ListNode *_head;
            ListNode *_tail;

            void initialize( )
            {
                _size = 0;
                _head = new ListNode;
                _tail = new ListNode;
                _head->next = _tail;
                _tail->prev = _head;
            }
    }; //end of class List
} //end of namespace algo

#endif