/*

   Derby - Class org.apache.derby.impl.sql.compile.BaseTableNumbersVisitor

   Licensed to the Apache Software Foundation (ASF) under one or more
   contributor license agreements.  See the NOTICE file distributed with
   this work for additional information regarding copyright ownership.
   The ASF licenses this file to you under the Apache License, Version 2.0
   (the "License"); you may not use this file except in compliance with
   the License.  You may obtain a copy of the License at

      http://www.apache.org/licenses/LICENSE-2.0

   Unless required by applicable law or agreed to in writing, software
   distributed under the License is distributed on an "AS IS" BASIS,
   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   See the License for the specific language governing permissions and
   limitations under the License.

 */

package	org.apache.derby.impl.sql.compile;

import org.apache.derby.iapi.error.StandardException;
import org.apache.derby.iapi.sql.compile.Visitable; 
import org.apache.derby.iapi.sql.compile.Visitor;
import org.apache.derby.iapi.util.JBitSet;

/**
 * Walk through a subtree and build a list of the assigned numbers for
 * all tables that exist in that subtree.  We do this by looking for any
 * column references in the subtree and, for each column reference, we
 * walk down the ColumnReference-ResultColumn chain until we find the
 * the bottom-most table number, which should correspond to a base
 * table.
 */
class BaseTableNumbersVisitor implements Visitor
{
	// JBitSet to hold the table numbers that we find.
	private JBitSet tableMap;

	/* Column number of the ColumnReference or ResultColumn
	 * for which we most recently found a base table number. 
	 * In cases where this visitor is only expected to find
	 * a single base table number, this field is useful for
	 * determining what the column position w.r.t. the found
	 * base table was.
	 */
	private int columnNumber;

	/**
	 * Constructor: takes a JBitSet to use as the holder for any base table
	 * numbers found while walking the subtree.
	 *
	 * @param tableMap JBitSet into which we put the table numbers we find.
	 */
    BaseTableNumbersVisitor(JBitSet tableMap)
	{
		this.tableMap = tableMap;
		columnNumber = -1;
	}

	/**
	 * Set a new JBitSet to serve as the holder for base table numbers
	 * we find while walking.
	 *
	 * @param tableMap JBitSet into which we put the table numbers we find.
	 */
	protected void setTableMap(JBitSet tableMap)
	{
		this.tableMap = tableMap;
	}

	/**
	 * Reset the state of this visitor.
	 */
	protected void reset()
	{
		tableMap.clearAll();
		columnNumber = -1;
	}

	/**
	 * Retrieve the the position of the ColumnReference or
	 * ResultColumn for which we most recently found a base
	 * table number.
	 */
	protected int getColumnNumber()
	{
		return columnNumber;
	}

	////////////////////////////////////////////////
	//
	// VISITOR INTERFACE
	//
	////////////////////////////////////////////////

	/**
	 * @see org.apache.derby.iapi.sql.compile.Visitor#visit
	 */
	public Visitable visit(Visitable node)
		throws StandardException
	{
		ResultColumn rc = null;
		if (node instanceof ColumnReference)
		{
			// Start by seeing if this column reference is the
			// bottom-most one, meaning that there are no column
			// references beneath this one.
			rc = ((ColumnReference)node).getSource();

			if (rc == null) {
			// this can happen if column reference is pointing to a column
			// that is not from a base table.  For example, if we have a
			// VALUES clause like
			//
			//    (values (1, 2), (3, 4)) V1 (i, j)
			//
			// and then a column reference to VI.i, the column reference
			// won't have a source.
				return node;
			}
		}
		else if (node instanceof ResultColumn)
			rc = (ResultColumn)node;
		else if (node instanceof SelectNode)
		{
			// If the node is a SelectNode we just need to look at its
			// FROM list.
			((SelectNode)node).getFromList().accept(this);
		}
		else if (node instanceof FromBaseTable) {
		// just grab the FBT's table number.
			tableMap.set(((FromBaseTable)node).getTableNumber());
		}

		if (rc != null)
		{
			// This next call will walk through the ResultColumn tree
			// until it finds another ColumnReference, and then will
			// return the table number for that column reference.  We
			// can't stop there, though, because the column reference
			// that we found might in turn have column references beneath
			// it, and we only want the table number of the bottom-most
			// column reference.  So once we find the column reference,
			// we have to recurse.

			int baseTableNumber = rc.getTableNumber();
			if (baseTableNumber >= 0) {
			// Move down to the column reference that has the table
			// number that we just found.  There may be one or more
			// VirtualColumnNode-to-ResultColumnNode links between
			// the current ResultColumn and the column reference we're
			// looking for, so we have to walk past those until we find
			// the desired column reference.

				ValueNode rcExpr = rc.getExpression();
				while (rcExpr instanceof VirtualColumnNode) {
					rc = ((VirtualColumnNode)rcExpr).getSourceColumn();
					rcExpr = rc.getExpression();
				}

				if (rcExpr instanceof ColumnReference)
				// we found our column reference; recurse using that.
					rcExpr.accept(this);
				else {
				// Else we must have found the table number someplace
				// other than within a ColumnReference (ex. we may
				// have pulled it from a VirtualColumnNode's source
				// table); so just set the number.
					tableMap.set(baseTableNumber);
					columnNumber = rc.getColumnPosition();
				}
			}
			else if (node instanceof ColumnReference) {
			// we couldn't find any other table numbers beneath the
			// ColumnReference, so just use the table number for
			// that reference.
				ColumnReference cr = (ColumnReference)node;
				cr.getTablesReferenced(tableMap);
				columnNumber = cr.getColumnNumber();
			}
		}

		return node;
	}

	/**
	 * @see org.apache.derby.iapi.sql.compile.Visitor#skipChildren
	 */
	public boolean skipChildren(Visitable node)
	{
		/* A SelectNode's children can include a where clause in the
		 * form of either a PredicateList or an AndNode.  In either
		 * case we don't want to descend into the where clause because
		 * it's possible that it references a base table that is not
		 * in the subtree we're walking.  So we skip the children of
		 * a SelectNode.  Similarly, any other PredicateList may contain
		 * references to base tables that we don't want to include, so
		 * we skip a PredicateList's children as well.  Note, though,
		 * that if this visitor is specifically targeted for a particular
		 * Predicate or AndNode (i.e. a call is directly made to
		 * Predicate.accept() or AndNode.accept()) then we _will_ descend
		 * into that predicate's operands and retrieve referenced base
		 * table numbers.
		 *
		 * And finally, if we visit a FromBaseTable we can just grab
		 * it's number and that's it--there's no need to go any further.
		 */
		return (node instanceof FromBaseTable) ||
			(node instanceof SelectNode) ||
			(node instanceof PredicateList);
	}

	/**
	 * @see org.apache.derby.iapi.sql.compile.Visitor#stopTraversal
	 */
	public boolean stopTraversal()
	{
		return false;
	}

	/**
	 * @see org.apache.derby.iapi.sql.compile.Visitor#visitChildrenFirst
	 */
	public boolean visitChildrenFirst(Visitable node)
	{
		return false;
	}

}	
