/**********************************************************
* A Generic Linked List class with a private static inner Node class.
*********************************************************/
// We want to "throw" Java exceptions in our code,
// so we must import them first:
import java.util.NoSuchElementException;


// make class name of generic type
public class GenericLinkedList<T> implements SimpleList<T>
{
   /*******************************************************
     The private inner class "Node" 
    *******************************************************/
   // make Node class name of generic type
   private class Node<T>
   {
      // Node instance variable is generic
      private T item;
      private Node<T> next;

      // parameters in constructor generic
      public Node(T item, Node<T> next)
      {
         this.item = item;
         this.next = next;
      }

      public String toString(){ return "" + this.item; }
   } // End of private inner class "Node"


   /********************************************************/
   // SimpleLinkedList instance variable "first" is declared of
   // type "Node", i.e. the inner class defined above
   // first is generic node

   private Node<T> first;

   // Constructs an empty list
   public GenericLinkedList()
   {
      first = null;
   }

   // Returns true if the list is empty
   public boolean isEmpty()
   {
      return first==null;
   }

   // Returns a string representation
   public String toString()
   {
      String output = "";

      if(first == null) 
         return "[NULL]";

      Node<T> tmp = first;
      while(tmp != null) 
      {
         output += tmp + " -> ";
         tmp = tmp.next;
      }
      output += "[NULL]";
      return output;
   }

   // Inserts a new node at the beginning of this list
   // take in generic item; Nodes are generic
   public void addFirst(T item)
   {
      Node<T> newNode = new Node<T>(item, first);
      first = newNode;
   }


   // Removes and returns the first element (item) in the list.
   // returns generic type
   public T removeFirst()
   {
      if(isEmpty())
      {
         throw new NoSuchElementException();
      }

      T toReturn = first.item;
      first = first.next;
      return toReturn;
   }


   // Inserts a new node to the end of this list
   // take in generic item; Nodes are generic
   public void addLast(T item)
   {
      if(isEmpty())
      {
         first = new Node<T>(item,null);
         //equivalent: addFirst(item)
      }
      else
      {
         Node<T> current = first;
         while(current.next!=null)
         {
            current = current.next;
         }
         current.next = new Node<T>(item,null);
      }
   }

   // Delete the node at the end of this list
   public T removeLast()
   {
      if(isEmpty())                         // Edge case 1: empty list
      { // empty list can't remove anything
         throw new NoSuchElementException();
      }

      if( first.next == null )             // Edge case 2: list has 1 elem
      {
         Node<T> ret = first;
         first = null;
         return ret.item;
      }

      // General case

      // Find the last node while remembering the previous node
      Node<T> current = first;
      Node<T> previous = first;
      while( current.next != null )
      {
         previous = current;
         current = current.next;
      }

      // Unlink the last node (from its predecessor)
      previous.next = null;

      // Return the last node
      return current.item;
   }


   // Returns the first element (item) in the list
   // returns generic type
   public T getFirst()
   {
      if(isEmpty())
      {
         throw new NoSuchElementException();
      }
      return first.item;
   }

   // Returns the last element (item) in the list
   // returns generic type; Nodes are generic
   public T getLast()
   {
      if(isEmpty())
      {
         throw new NoSuchElementException();
      }

      Node<T> current = first;
      while(current.next!=null)
      {
         current = current.next;
      }
      return current.item;
   }


   // Returns the item at the specified position in the list.
   // Note: Assume that pos is the index of the node, and that
   // node indexes start at zero!
   // returns generic type; Nodes are generic
   public T get(int pos)
   {
      // Coding strategy: Start by solving the general case, then add checks
      // for edge cases (e.g. What if "pos" is out-of-bound?)

      if(isEmpty())
      { // empty list
         throw new NoSuchElementException();
      }

      int i = 0;
      Node<T> current = first;
      while(i<pos)
      {
         i++;
         current = current.next;

         if(current==null)
         { // pos past end of list
            throw new NoSuchElementException();
         }
      }
      return current.item;
   }




   // Removes the first occurrence of the specified element in this list.
   // key is generic type; Nodes are generic
   public void remove(T key)
   {
      if(isEmpty())
      { // empty list can't remove anything
         throw new NoSuchElementException();
      }
      // key is the first element
      if(first.item.equals(key))
      {
         first = first.next;
      }
      else
      {
         Node<T> current = first;
         Node<T> previous = first;
         while(current!=null && !current.item.equals(key))
         {
            previous = current;
            current = current.next;
         }
         if(current==null)
         { // key not found
            throw new NoSuchElementException();
         }
         previous.next = current.next;
      }
   }


   // Reverse the linked list!
   // Example LL before reversing:
   // A => B => C => D => NULL
   // Example LL after reversing:
   // D => C => B => A => NULL
   // Nodes are generic
   public void reverse()
   {
      if(isEmpty())
      {
         throw new NoSuchElementException();
      }
      Node<T> current1 = first; // iterate through old list in old order
      Node<T> current2 = first; // iterate through new list to make new links
      while(current1.next != null)
      {
         Node<T> newNode = new Node<T>(current1.next.item, current2);
         current2 = newNode;
         current1 = current1.next;
      }
      first.next = null;
      first = current2;
   }

   // TESTING
   public static void main(String[] args)
   {
      System.out.println("GenericLinkedList<String>");

      GenericLinkedList<String> stringList = new GenericLinkedList<String>();

      stringList.addFirst("A");
      stringList.addFirst("B");
      stringList.addLast("C");
      System.out.println(stringList); // B -> A -> C

      System.out.println("getFirst: " + stringList.getFirst()); // B
      System.out.println("getLast: " + stringList.getLast()); // C
      System.out.println("get(1): " + stringList.get(1)); // A

      stringList.remove("A");
      System.out.println("List after remove(\"A\")");
      System.out.println(stringList); // B -> C
      System.out.println();

      // ===========================================================
      System.out.println("GenericLinkedList<Integer>");
      GenericLinkedList<Integer> intList = new GenericLinkedList<Integer>();

      intList.addFirst(1); // ooh fancy word for this?
      intList.addFirst(2);
      intList.addLast(3);
      System.out.println(intList); // 2 -> 1 -> 3

      System.out.println("getFirst: " + intList.getFirst()); // 2
      System.out.println("getLast: " + intList.getLast()); // 3
      System.out.println("get(1): " + intList.get(1)); // 1

      intList.remove(1);
      System.out.println("List after remove(1)");

      System.out.println(intList); // 2 -> 3
   }
} // End of class