/*
 *****************************************************************************
 *		File Name: ParNode.java
 *		Purpose: class representing internal node in b+-tree
 *		Authors: Han Don, Jeff Xing, Carol Cheung
 *		Version: 1
 *		Last Date Updated: Feb. 27, 2001
 ****************************************************************************/

/**
 *  ParNode holds information of a parent node.
 *  It provides the services that the
 *  BTreeString requires.  
 */
public class ParNode {
	
	/**
	 *  The order of the tree.
	 */
	public final static int ORDER = 4;
	
	/**
	 *  An empty key.
	 */
	private final static long EMPTY = -1;
	
	/**
	 *  Pointer array if my children are leaves.
	 */
	private LeafNode [] leaves;
	
	/**
	 *  Pointer array if my children are parent 
	 *  nodes as well.
	 */
	private ParNode [] nextLevel;
	
	/**
	 *  The keys that I am holding.
	 */
	private long [] keys;
	
	/**
	 *  Class constructor
	 */
	public ParNode () {
		leaves = new LeafNode [ORDER];
		nextLevel = new ParNode [ORDER];
		keys = new long[ORDER];
		for (int i = 0; i < ORDER; i++) {
			nextLevel[i] = null;
			leaves[i] = null;
			keys[i] = EMPTY;
		}
	}


	/**
	 * returns the index of the next available slot for a child
	 */
	public int nextAvailable() {
		for(int i = 0; i < ORDER; i++){
			if(keys[i] == EMPTY) return i;
		}
		return -1;
	}
	
	/**
	 *  Replace my last key with 'key'.
	 */
	public void updateLastKey(long key) {
		int last = nextAvailable();
		if (last == -1)
			keys[ORDER-1] = key;
		else					
			keys[last-1] = key;
	}
	
	/**
	 *  Return my last key.
	 */
	public long getLastKey() { return keys[ORDER - 1]; }
	
	/**
	 *  Return my leaf child at index i.
	 *  precondition: 0 <= i < ORDER
	 */
	public LeafNode getLeafAt(int i) { return leaves[i]; }	
	
	/**
	 *  Return my ParNode child at index i.
	 *  precondition: 0<= i < ORDER	
	 */
	public ParNode getNextLevelAt(int i) { 
		return nextLevel[i]; }	
	
	/**
	 *  Return my key at index i.
	 *  precondition: 0 <= i < ORDER
	 */
	public long getKeyAt(int i) { return keys[i]; }
	
	/**
	 *  Set a new key and point to my ParNode child 'par'.
	 */
	public void setParNode(long newKey, ParNode par) {
		boolean added = false;
		for(int i = 0; i < ORDER && !added; i++){
			if(keys[i] == EMPTY) {
				keys[i] = newKey;
				nextLevel[i] = par;
				added = true;
			}
		}
	}
	
	/**
	 *  Set a new key and point to my leaf child 'par'.
	 */
	public void setLeafNode (long newKey, LeafNode leaf) {
		boolean added = false;
		for(int i = 0; i < ORDER && !added; i++){
			if(keys[i] == EMPTY) {
				keys[i] = newKey;
				leaves[i] = leaf;
				added = true;
			}
		}
	}
	
}