/**
* Licensed to Odiago, Inc. under one or more contributor license
* agreements. See the NOTICE.txt file distributed with this work for
* additional information regarding copyright ownership. Odiago, Inc.
* 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 com.odiago.flumebase.lang;
import com.odiago.flumebase.exec.AssignedSymbol;
import com.odiago.flumebase.exec.WindowSymbol;
import com.odiago.flumebase.parser.IdentifierExpr;
import com.odiago.flumebase.parser.SQLStatement;
import com.odiago.flumebase.parser.WindowSpec;
/**
* SELECT statements may contain named WINDOW definitions which are
* referenced as identifiers elsewhere in the statement. An identifier,
* when evaluated, will attempt to read the named field from the
* event being processed. WindowSymbol instances are pointers to the
* WindowSpec they define; such IdentifierExpr instances should be
* replaced by the WindowSpec instances they reference.
*/
public class ReplaceWindows extends TreeWalkVisitor {
/**
* When we find an IdentifierExpr that should be replaced by a WindowSpec,
* this is filled with the WindowSpec to replace it with. After visiting
* the IdentifierExpr, we do the replacement and set this field to null.
*/
private WindowSpec mReplaceWith;
@Override
public void after(SQLStatement parent, SQLStatement child) throws VisitException {
if (null != mReplaceWith) {
// Do the replacement.
replace(parent, child, mReplaceWith);
mReplaceWith = null;
}
}
@Override
public void visit(IdentifierExpr ident) {
AssignedSymbol assignedSym = ident.getAssignedSymbol();
if (assignedSym instanceof WindowSymbol) {
// We have found an IdentifierExpr that should be replaced.
WindowSymbol windowSym = (WindowSymbol) assignedSym;
mReplaceWith = windowSym.getWindowSpec();
}
}
}