// CSE 143, Winter 2011, Marty Stepp
// A LinkedIntList object stores a list of integers using a series of linked
// node objects.
// Today's version of the class implements an IntList interface
// so that both kinds of lists can be treated the same by client code.

import java.util.*;  // for NoSuchElementException

public class LinkedIntList implements IntList {
    private ListNode front;   // refers to first node in list (null if empty)
    
    // Constructs a new empty list.
    public LinkedIntList() {
        front = null;  // null front means empty
    }
    
    // Adds the given value to the end of this list.
    public void add(int value) {
        if (front == null) {
            // empty list
            front = new ListNode(value);
        } else {
            // non-empty list

            // example: change from:
            //     front  10 -> 20 -> 30 /
            // to: front  10 -> 20 -> 30 -> 40 /

            // walk to last node
            ListNode current = front;
            while (current.next != null) {
                current = current.next;
            }
            
            // add new node at end of list
            current.next = new ListNode(value);
        }
    }
    
    // Inserts the given value into this list at the specified index.
    // Precondition: 0 <= index <= size
    // Throws a NullPointerException if index > size.
    public void add(int index, int value) {
        if (index == 0) {
            // insert at front of list
            front = new ListNode(value, front);
        } else {
            // walk to node before the one to insert
            ListNode current = front;
            for (int i = 0; i < index - 1; i++) {
                current = current.next;
            }
            
            ListNode newNode = new ListNode(value, current.next);
            current.next = newNode;
            
            // shorter version of the above code
            // current.next = new ListNode(value, current.next);
        }
    }
    
    // Adds the given element value to the list at the appropriate index
    // so that the list will remain in sorted order.
    // Precondition: The existing elements of the list are already sorted.
    // Postcondition: The new element value will be added, and the elements
    //                of the list will still be sorted.
    // This method may add the value in an improper location if the list's
    // existing elements are not sorted when this method is called.
    public void addSorted(int value) {
        // two special cases: adding to empty list, and adding smallest value
        if (front == null || front.data > value) {
            front = new ListNode(value, front);
        } else {
            // two other cases: adding to middle and end of list
            // (end of list case is handled by the current.next != null test)
            
            // advance to node before the place to add
            ListNode current = front;
            while (current.next != null && current.next.data < value) {
                current = current.next;
            }
            
            // insert the new node at this location
            current.next = new ListNode(value, current.next);
        }
        
    }
    
    // Returns the element at the specified index from the list.
    // Precondition: 0 <= index < size
    // Throws a NullPointerException if index >= size.
    public int get(int index) {
        ListNode current = front;
        for (int i = 0; i < index; i++) {
            current = current.next;
        }
        return current.data;
    }
    
    // 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(int value) {
        ListNode current = front;
        int index = 0;
        while (current != null) {
            if (current.data == value) {
                return index;
            }
            current = current.next;
            index++;
        }

        return -1;
    }
    
    // Removes and returns the front element from the list.
    // Precondition: size > 0
    // Throws a NoSuchElementException if the list is empty.
    public int remove() {
        if (front == null) {
            throw new NoSuchElementException("cannot remove from empty list");
        }
        
        // retrieve/return first element's data, then move to next
        int result = front.data;
        front = front.next;
        return result;
    }
    
    // Removes the value at the specified index from this list.
    // Precondition: 0 <= index < size
    // Throws a NullPointerException if index > size.
    public void remove(int index) {
        if (index == 0) {
            // special case: remove front node
            front = front.next;
        } else {
            // walk to node before the one to remove
            ListNode current = front;
            for (int i = 0; i < index - 1; i++) {
                current = current.next;
            }
            
            // remove it (point the previous node's next link past it)
            current.next = current.next.next;
        }
    }
    
    // Sets the element at the specified index in the list to the given value.
    // Precondition: 0 <= index < size
    // Throws a NullPointerException if index >= size.
    public void set(int index, int value) {
        ListNode current = front;
        for (int i = 0; i < index; i++) {
            current = current.next;
        }
        current.data = value;
    }
    
    public int size() {
        return 0;
    }
    
    public boolean isEmpty() {
        return true;
    }
    
    public void clear() {
        
    }
    
    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;
        }
    }

}