/**
 ******************************************************************************
 *                    HOMEWORK     15-211      COMPRESSION
 ******************************************************************************
 *
 *  Represents a node in the Huffman tree.
 *
 *
 *****************************************************************************/
 /*****************************************************************************

               There is no need to modify this file.

 *****************************************************************************/


public class HuffmanNode implements Comparable<HuffmanNode>
{
	private byte value;
	private int freq;
	private HuffmanNode left, right, parent;

	/**
	* Creates a leaf node with a given frequency
	*
	* @throws IllegalArgumentException
	*             if freq is negative
	*/
	public HuffmanNode (byte value, int freq)
	{
		if (freq < 0)
			throw new IllegalArgumentException ("frequence needs to be non-negative");

		this.value = value;
		this.freq = freq;
	}

	/**
	* Creates an internal node with the given childern.
	*
	* @param l
	*            The left child
	* @param r
	*            The right child
	* @throws IllegalArgumentException
	*             If either l or r is null.
	*/
	public HuffmanNode (HuffmanNode l, HuffmanNode r)
	{
		if (l == null || r == null)
			throw new IllegalArgumentException ("Trying to create an internal node with a null child");

		left = l;
		right = r;

		left.parent = right.parent = this;

		this.freq = l.getFreq () + r.getFreq ();
	}

	/**
	* Compares two nodes by their frequences
	*/
	public int compareTo(HuffmanNode node)
	{
		return freq - node.freq;
	}

	/**
	* Checks if this is a leaf node
	*/
	public boolean isLeaf ()
	{
		return left == null && right == null;
	}

	/** Checks if this is the root of the Huffman tree. */
	public boolean isRoot ()
	{
		return parent == null;
	}

	/** Gets the frequency of this node. */
	public int getFreq ()
	{
		return freq;
	}

	/**
	* Gets the value of this node, or null if this is an internal node
	*/
	public byte getValue ()
	{
		return value;
	}

	/**
	* Gets the parent of this node, or null if this is the root of the Huffman
	* tree.
	*/
	public HuffmanNode getParent ()
	{
		return parent;
	}

	/**
	* Gets the left child of this node, or null if this is a leaf.
	*/
	public HuffmanNode getLeft ()
	{
		return left;
	}

	/**
	* Gets the right child of this node, or null if this is a leaf.
	*/
	public HuffmanNode getRight ()
	{
		return right;
	}
}