//
// example of using recursive linked-list class:
//
// define and illustrate use of "shopping list" class.
//
// version 1
//
#include <iostream.h>
#include <stdlib.h>             // has EXIT_SUCCESS
#include <string>
#include "seq.h"                // has Seq template class

//
// "shopping list" class
//
class ShopList {

public:

  // public interface for class:

  // constructor.
  // post:  constructed ShopList has no items.
  ShopList() { 
    items = Seq<string>();
  }

  // function to print items.
  // post:  all items in list printed to stdout.
  void printItems() const {
    print(items);
  }

  // function to search for item.
  // post:  returns true if itm is in list, false otherwise.
  bool hasItem(const string & itm) const {
    return has(itm, items);
  }

  // function to add item.
  // post:  "itm" added to list.
  void addItem(const string & itm) {
    items = Seq<string>(itm, items);
  }

  // function to remove item.
  // post:  "itm" removed from list if present. 
  //          (removes first occurrence only.)
  void removeItem(const string & itm) {
    items = remove(itm, items);
  }

private:

  // list of items.
  Seq<string> items;

  // helper functions:

  // function to print list of strings.
  // post:  l printed to stdout.
  static void print(const Seq<string> & l) {
    if (l.empty())
      return;
    else {
      cout << l.hd() << endl;
      print(l.tl());
    }
  }

  // function to find item in list of strings.
  // post:  returns true if itm is in l, false otherwise.
  static bool has(const string & itm, const Seq<string> & l) {
    if (l.empty())
      return false;
    else
      return (l.hd() == itm) || has(itm, l.tl());
  }

  // function to remove item from list of strings.
  // post:  returns l with first occurrence of itm removed.
  static Seq<string> remove(const string & itm, 
			    const Seq<string> & l) {
    if (l.empty())
      return l;
    else if (l.hd() == itm)
      return l.tl();
    else
      return Seq<string>(l.hd(), remove(itm, l.tl()));
  }
};

//
// main program:
//
// illustrates use of ShopList class.
//
int main(void) {

  ShopList myList;
  cout << "Items on my list:\n";
  myList.printItems();
  myList.addItem("soda pop");
  myList.addItem("paper towels");
  cout << "Items on my list after add:\n";
  myList.printItems();
  cout << "Is soda pop on my list?  ";
  if (myList.hasItem("soda pop"))
    cout << "yes\n";
  else
    cout << "no\n";
  cout << "Is beer on my list?  ";
  if (myList.hasItem("beer"))
    cout << "yes\n";
  else
    cout << "no\n";
  myList.removeItem("paper towels");
  cout << "Items on my list after remove:\n";
  myList.printItems();

  return EXIT_SUCCESS;
}