/**
* Inserts a new directory entry into the B-tree block. If the block is at level 0, then the entry
* is inserted there. Otherwise, the entry is inserted into the appropriate child node, and the
* return value is examined. A non-null return value indicates that the child node split, and so
* the returned entry is inserted into this block. If this block splits, then the method similarly
* returns the entry information of the new block to its caller; otherwise, the method returns
* null.
*
* @param e the directory entry to be inserted
* @return the directory entry of the newly-split block, if one exists; otherwise, null
*/
public DirEntry insert(DirEntry e) {
if (contents.getFlag() == 0) return insertEntry(e);
Block childblk = findChildBlock(e.dataVal());
BTreeDir child = new BTreeDir(childblk, ti, tx);
DirEntry myentry = child.insert(e);
child.close();
return (myentry != null) ? insertEntry(myentry) : null;
}
/**
* Creates a new root block for the B-tree. The new root will have two children: the old root, and
* the specified block. Since the root must always be in block 0 of the file, the contents of the
* old root will get transferred to a new block.
*
* @param e the directory entry to be added as a child of the new root
*/
public void makeNewRoot(DirEntry e) {
Constant firstval = contents.getDataVal(0);
int level = contents.getFlag();
Block newblk = contents.split(0, level); // ie, transfer all the records
DirEntry oldroot = new DirEntry(firstval, newblk.number());
insertEntry(oldroot);
insertEntry(e);
contents.setFlag(level + 1);
}
/**
* Returns the block number of the B-tree leaf block that contains the specified search key.
*
* @param searchkey the search key value
* @return the block number of the leaf block containing that search key
*/
public int search(Constant searchkey) {
Block childblk = findChildBlock(searchkey);
while (contents.getFlag() > 0) {
contents.close();
contents = new BTreePage(childblk, ti, tx);
childblk = findChildBlock(searchkey);
}
return childblk.number();
}
private DirEntry insertEntry(DirEntry e) {
int newslot = 1 + contents.findSlotBefore(e.dataVal());
contents.insertDir(newslot, e.dataVal(), e.blockNumber());
if (!contents.isFull()) return null;
// else page is full, so split it
int level = contents.getFlag();
int splitpos = contents.getNumRecs() / 2;
Constant splitval = contents.getDataVal(splitpos);
Block newblk = contents.split(splitpos, level);
return new DirEntry(splitval, newblk.number());
}