/*
Research Project:   Graphical Database for Category Theory
                    J. Bradbury, Dr. R. Rosebrugh, I. Rutherford
                    Mount Allison University 2001
File:               CategoryList.java
Description:	      This class implements a list of ListNode classes which
                    contain categories.
*/

//import statements
import java.awt.*;
import java.applet.Applet;

class CategoryList
//class DefList definition
{

  CategoryNode head;   //Points to front of LinkedList
  CategoryNode tail;   //Points to back of LinkedList

  public void CategoryList()
  //List Constructor
  {
    head = tail = null;
  }

  public void insertNode(Category insertItem)
  //Inserts node at end of linked list
  {
    if (isEmpty())
       head = tail = new CategoryNode(insertItem);
    else
       tail = tail.next = new CategoryNode(insertItem);
  }

 public void getList(TextArea view)
 //Retrieves list of categorys in linked list
 {
   int count = 0;
   CategoryNode current = head;
   view.append("\nOpen Categories\n");
   view.append("------------------\n");
   while(current != null)
   {
        count++;
        view.append(" - " +current.cat.name + "\n");
        //view.appendText(count + ". " + current.cat.name + "\n");
        current = current.next;
   }
   view.append("------------------\n\n");
 }



 public void replaceNode(Category c)
 //Replaces a node with an updated version of the same node
 {
   CategoryNode current = head;
   while(current !=null)
   {
        if (c.name.equals(current.cat.name))
        {
           current.cat = c;
        }
        current = current.next;
   }
 }

  public Category getNode(String name)
  //returns a Category when given Category's name
  {
   Category getItem = null;
   CategoryNode current = head;
   while(current != null)
   {
        if (name.equals(current.cat.name))
        {
           getItem = current.cat;
           return getItem;
        }
       current = current.next;
   }
   getItem = new Category();
   getItem.name = "";
   return getItem; //return null if category not in list
  }

  public boolean removeNode(String name) throws EmptyListException
  //Removes node from end of linked list
  {
    Category removeItem = null;
    CategoryNode current = head;
    CategoryNode previous = null;

    if (isEmpty())
       throw new EmptyListException();

    if (name.equals(head.cat.name))
    {
      if (head.equals(tail))
          head = tail = null;
      else
          head = head.next;
      return true;
    }
    else
    {
     //current.next = head;
     while(current != null)
     {
        if (name.equals(current.next.cat.name))
        {
           current.next = current.next.next;
           //previous = current;  //previous is node before one being removed
           //current = current.next; //current is node being removed
           //previous.next = current.next; //previous.next points to current.next
           return true;
        }
        current = current.next;
     }
   }
   return false;
  //if (head.equals(tail))
  //head = tail = null;
  }

  public boolean isEmpty()
  //Returns if the linked list is empty
  //That is, if the head of the list points to null
  {
    return head == null;
  }

/*  public void displayAll()
  {
   //if (isEmpty())
   //{
     //Message saying is empty displayed on the screen
   //}

   ListNode current = head;
   while (current != null)
   {
         //display category
         current = current.next;
   }
  } */


  public Category removeHead()
  //Removes the category at the front of the list and
  //returns it
  {
    Category removeItem = head.cat;
    if (head.equals(tail))
      head = tail = null;
    else
      head = head.next;
    return removeItem;
  }

  public boolean doesExist(String name)
  // Returns true if a category of the given name is in
  // the list. Otherwise returns false.
  {
    if (head == null)
      return false;
    CategoryNode temp = head;
    while (temp.next != null)
    {
      if (temp.cat.name.equals(name))
        return true;
      temp = temp.next;
    }
    return false;
  }
}