// Allison Obourn
// CSE 143 - Lecture 26
// A LinkedList object stores a list of values using
// a linked list as its underlying data structure.
// This version uses "generics" so that it can store any type of value, not 
// just integers.  It also implements the same interface as ArrayList,
// so that the two can be used interchangeably in client code.

public class LinkedList<E> implements List<E> {
   private ListNode front;
   
   // Initializes a new empty list
   public LinkedList() {
      front = null;
   }
      
   // Adds the given value to the end of the list.
   public void add(E value) {
      if(front == null) {
         front = new ListNode(value);
      } else {
         ListNode current = front;
         while(current.next != null) {
            current = current.next;
         }
         current.next = new ListNode(value);
      }
   }
   
   // Adds a value at a given index.
   // Pre: 0 <= index <= size, throws a NullPointerException if index > size.
   public void add(int index, E value) {
      if (index == 0) {
         front = new ListNode(value, front);
      } else {
         ListNode current = front;
         for (int i = 0; i < index - 1; i++) {
            current = current.next;
         }
         ListNode temp = new ListNode(value, current.next);
         current.next = temp;
         // also ok: current.next = new ListNode(value, current.next);
      }
   }
   
   // Sets the element at the specified index in the list to have the given value.
   // Precondition: 0 <= index < size
   // Throws a NullPointerException if index >= size.
   public void set(int index, E value) {
      ListNode current = goTo(index);
      current.data = value;
   }
   
   // Returns the index of the first occurrence of the given value in the list,
   // or -1 if the value is not found in the list.
   public int indexOf(E value) {
      int index = 0;
      ListNode current = front;
      while (current != null) {
         if (current.data.equals(value)) {
            return index;
         }
         index++;
         current = current.next;
      }
      return -1;
   }
   
   //TODO: change <> to compareTo - incomplete!
   // Adds the value in sorted (non-decreasing) order.
   // Pre: list is sorted
   // Post: list is sorted
   public void addSorted(E value) {
      if(front == null || value < front.data) {
         front = new ListNode(value, front);
      } else {
         ListNode current = front;
         while(current.next != null && current.next.data < value) {
            current = current.next;
         }
         current.next = new ListNode(value, current.next);
      }
   }
      
   // Returns the value at the given index.
   // Pre: 0 <= index < size
   public E get(int index) {
      ListNode current = front;
      for(int i = 0; i < index; i++) {
         current = current.next;
      }
      return current.data;
   }
   
   // Returns a comma-separated String representation of this list.
   public String toString() {
      if (front == null) {
         return "[]";
      } else {
         String result = "[" + front.data;
         ListNode current = front.next;
         while (current != null) {
            result += ", " + current.data;
            current = current.next;
         }
         result += "]";
         return result;
      }
   }
   
   // Returns the size of this list (inefficient -- could use a size field).
   public int size() {
      ListNode current = front;
      int size = 0;
      while(current != null) {
         size++;
         current = current.next;
      }
      return size;
   }  
   
   // True if the list is empty, false otherwise
   public boolean isEmpty() {
      return front == null;
   }
   
   // Removes the value at the given index.
   // Pre: 0 <= index < size
   public void remove(int index) {
      if (index == 0) {
         front = front.next;
      } else {
         ListNode current = front;
         for (int i = 0; i < index - 1; i++) {
            current = current.next;
         }
         current.next = current.next.next;
      }
   }
   
   // Returns a reference to the node object representing the index'th element
   // in the list.  Used as a helper by many of the public methods.
   private ListNode goTo(int index) {
      ListNode current = front;
      for (int i = 0; i < index; i++) {
         current = current.next;
      }
      return current;
   }
   
   // A ListNode represents a single node in a linked list.  It stores a 
   // value and a link to the next node.
   
   private class ListNode {
      E data;
      ListNode next; 
      
      // Creates a terminal ListNode containing null as data.
      public ListNode() {
         this(null, null);
      }
      
      // Creates a terminal ListNode with the specified data.
      public ListNode(E data) {
         this(data, null);
      }
   
      // Creates a ListNode with the specified data and next node.
      public ListNode(E data, ListNode next) {
         this.data = data;
         this.next = next;
      }   
   }
}