/*
* 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.jena.arq.querybuilder.rewriters;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Stack;
import org.apache.jena.graph.Node ;
import org.apache.jena.graph.Triple ;
import org.apache.jena.sparql.core.TriplePath ;
import org.apache.jena.sparql.core.Var ;
import org.apache.jena.sparql.core.VarExprList ;
import org.apache.jena.sparql.engine.binding.Binding ;
import org.apache.jena.sparql.engine.binding.BindingHashMap ;
import org.apache.jena.sparql.expr.Expr ;
import org.apache.jena.sparql.util.ExprUtils ;
/**
* The base class for rewriters.
*
* Rewriters push and pop items on the stack during processing.
*
* @param <T> The type of object being rewritten.
*/
public class AbstractRewriter<T> {
// The map of variables to nodes.
protected final Map<Var, Node> values;
// A stack used in processing.
private final Stack<T> result = new Stack<T>();
/**
* Constructor
* @param values The values to map.
*/
protected AbstractRewriter(Map<Var, Node> values) {
this.values = values;
}
/**
* Push the value on the stack.
* @param value The value to push.
*/
protected final void push(T value) {
result.push(value);
}
/**
* pop the value from the stack.
* @return The value from the top of the stack.
*/
protected final T pop() {
return result.pop();
}
/**
* Return true if the stack is empty.
* @return true if the stack is empty, false otherwise.
*/
protected final boolean isEmpty() {
return result.isEmpty();
}
/**
* Get the result from the rewriter.
* Returns the top of the stack.
* @return The final result or null if there is no answer.
*/
public final T getResult() {
if (isEmpty()) {
return null;
}
return pop();
}
/**
* Rewrite a triple path.
* @param t The triple path to rewrite.
* @return the triple path after rewriting.
*/
protected final TriplePath rewrite(TriplePath t) {
if (t.getPath() == null) {
return new TriplePath(new Triple(changeNode(t.getSubject()),
changeNode(t.getPredicate()), changeNode(t.getObject())));
} else {
PathRewriter transform = new PathRewriter(values);
t.getPath().visit(transform);
return new TriplePath(changeNode(t.getSubject()),
transform.getResult(), changeNode(t.getObject()));
}
}
/**
* Rewrite a triple.
* @param t The triple to rewrite.
* @return The rewritten triple.
*/
protected final Triple rewrite(Triple t) {
return new Triple(changeNode(t.getSubject()),
changeNode(t.getPredicate()), changeNode(t.getObject()));
}
/**
* If the node is a variable perform any necessary rewrite, otherwise return the node.
* @param n The node to to rewrite.
* @return the rewriten node.
*/
protected final Node changeNode(Node n) {
if (n.isVariable()) {
Var v = Var.alloc(n);
if (values.containsKey(v)) {
return values.get(v);
}
}
return n;
}
/**
* Change all the nodes in the list.
* If a node is a variable perform any necessary rewrite, otherwise return the node.
* @param src a list of nodes to change.
* @return The list of nodes.
*/
protected final List<Node> changeNodes(List<Node> src) {
List<Node> lst = new ArrayList<Node>();
for (Node t : src) {
lst.add(changeNode(t));
}
return lst;
}
/**
* Rewrite a list of triples.
* @param src The list of triples to rewrite.
* @return The list of rewritten triples.
*/
public final List<Triple> rewrite(List<Triple> src) {
List<Triple> lst = new ArrayList<Triple>();
for (Triple t : src) {
lst.add(rewrite(t));
}
return lst;
}
/**
* Rewrite a binding.
* @param binding The binding to rewrite
* @return The rewritten binding.
*/
protected final Binding rewrite(Binding binding) {
BindingHashMap retval = new BindingHashMap();
Iterator<Var> iter = binding.vars();
while (iter.hasNext()) {
Var v = iter.next();
Node n = changeNode(binding.get(v));
n = n.equals(v) ? binding.get(v) : n;
retval.add(v, n);
}
return retval;
}
/**
* Rewrite a variable expression list.
* @param lst The variable expression list.
* @return the rewritten variable expresson list.
*/
public final VarExprList rewrite(VarExprList lst) {
VarExprList retval = new VarExprList();
for (Var v : lst.getVars()) {
Node n = values.get(v);
if (n != null) {
if (n.isVariable()) {
retval.add(Var.alloc(n));
}
} else {
retval.add(v);
}
}
for (Map.Entry<Var, Expr> entry : lst.getExprs().entrySet()) {
Expr target = ExprUtils.nodeToExpr(entry.getKey());
Node n = values.get(entry.getKey());
Var v = entry.getKey();
Expr e = entry.getValue();
if (n != null) {
if (n.isVariable()) {
v = Var.alloc(n);
if (target.equals(e)) {
e = ExprUtils.nodeToExpr(n);
}
} else {
v = null;
}
}
if (v != null) {
retval.add(v, e);
}
}
return retval;
}
}