#ifndef DL_LIST_H
#define DL_LIST_H
#include <iostream>
#include <initializer_list>

namespace cop4530 {

 template <typename T>
    class List {
        private:
          // nested Node class
          struct Node {
             T data;
             Node *prev;
             Node *next;

             Node(const T & d = T{}, Node *p = nullptr, Node *n = nullptr) 
                : data{d}, prev{p}, next{n} {}
             Node(T && d, Node *p = nullptr, Node *n = nullptr)
                : data{std::move(d)}, prev{p}, next{n} {}
          };

       public:
          //nested const_iterator class
          class const_iterator {
             public:
                const_iterator();            // default zero parameter constructor
                const T & operator*() const; // operator*() to return element
 
                // increment/decrement operators
                const_iterator & operator++();
                const_iterator operator++(int);
                const_iterator & operator--();
                const_iterator operator--(int);

                // comparison operators
                bool operator==(const const_iterator &rhs) const;
                bool operator!=(const const_iterator &rhs) const;

             protected:
                Node *current;              // pointer to node in List
                T & retrieve() const;       // retrieve the element refers to
                const_iterator(Node *p);    // protected constructor

                friend class List<T>;
          };

          // nested iterator class
          class iterator : public const_iterator {
             public:
                iterator();
                T & operator*();
                const T & operator*() const;

                // increment/decrement operators
                iterator & operator++();
                iterator operator++(int);
                iterator & operator--();
                iterator operator--(int);

             protected:
                iterator(Node *p);
                friend class List<T>;
          };

       public:
          // constructor, desctructor, copy constructor
          List();                  // default zero parameter constructor
          List(const List &rhs);   // copy constructor
          List(List && rhs);       // move constructor

          // num elements with value of val
          explicit List(int num, const T& val = T{});

          // constructs with elements [start, end)
          List(const_iterator start, const_iterator end); 

	  // constructs with a copy of each of the elements in the initalizer_list
	  List (std::initializer_list<T> iList);

          ~List(); // destructor

          // copy assignment operator
          const List& operator=(const List &rhs);

          // move assignment operator
          List & operator=(List && rhs);

	  // sets list to the elements of the initializer_list
          List& operator= (std::initializer_list<T> iList);


          // member functions
          int size() const;       // number of elements
          bool empty() const;     // check if list is empty
          void clear();           // delete all elements
          void reverse();         // reverse the order of the elements

          T& front();             // reference to the first element
          const T& front() const;
          T& back();              // reference to the last element
          const T& back() const; 

          void push_front(const T & val); // insert to the beginning
          void push_front(T && val);      // move version of insert
          void push_back(const T & val);  // insert to the end
          void push_back(T && val);       // move version of insert
          void pop_front();               // delete first element
          void pop_back();                // delete last element

          void remove(const T &val);      // remove all elements with value = val

	  template <typename PREDICATE>
	  void remove_if(PREDICATE pred);	// remove all elements for which Predicate pred
						//  returns true. pred can take in a function object

          // print out all elements. ofc is deliminitor
          void print(std::ostream& os, char ofc = ' ') const; 

          iterator begin();               // iterator to first element
          const_iterator begin() const;
          iterator end();                 // end marker iterator
          const_iterator end() const; 
          iterator insert(iterator itr, const T& val);  // insert val ahead of itr
          iterator insert(iterator itr, T && val);      // move version of insert
          iterator erase(iterator itr);                 // erase one element
          iterator erase(iterator start, iterator end); // erase [start, end)


       private:
          int theSize;           // number of elements
          Node *head;            // head node
          Node *tail;            // tail node
      
          void init();           // initialization
    };

   // overloading comparison operators
   template <typename T>
      bool operator==(const List<T> & lhs, const List<T> &rhs);

   template <typename T>
      bool operator!=(const List<T> & lhs, const List<T> &rhs);

   // overloading output operator
   template <typename T>
      std::ostream & operator<<(std::ostream &os, const List<T> &l);

   // include the implementation file here

#include "List.hpp"

} // end of namespace 4530

#endif