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ARQ is a SPARQL 1.1 query engine for Apache Jena
There is a newer version: 5.1.0
/*
 * 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.sparql.expr;

import java.util.Objects;

import org.apache.jena.atlas.lib.Lib ;
import org.apache.jena.atlas.logging.Log ;
import org.apache.jena.graph.Node ;
import org.apache.jena.sparql.ARQInternalErrorException ;
import org.apache.jena.sparql.core.Var ;
import org.apache.jena.sparql.engine.binding.Binding ;
import org.apache.jena.sparql.expr.aggregate.Aggregator ;
import org.apache.jena.sparql.function.FunctionEnv ;
import org.apache.jena.sparql.graph.NodeTransform;
import org.apache.jena.sparql.serializer.SerializationContext ;

/** Group aggregation functions calculated a value during grouping and
 *  placed in the output binding.  This class is relationship of 
 *  an aggregation expression and that variable.  Evaluation returns
 *  the variable's bound value. 
 */

public class ExprAggregator extends ExprNode
{
    protected Aggregator aggregator ;
    protected Var var ;
    protected ExprVar exprVar = null ;
    
    public ExprAggregator(Var v, Aggregator agg)          { _setVar(v) ; aggregator = agg ; }
    public Var getVar()                                 { return var ; }
    
    public void setVar(Var v)
    {
        if (this.var != null) 
            throw new ARQInternalErrorException(Lib.className(this)+ ": Attempt to set variable to " + v + " when already set as " + this.var) ;
        if (v == null) 
            throw new ARQInternalErrorException(Lib.className(this)+ ": Attempt to set variable to null") ;
        _setVar(v) ;
    }

    private void _setVar(Var v)
    {
        this.var = v ;
        this.exprVar = new ExprVar(var) ;
    }

    public Aggregator getAggregator()   { return aggregator ; }
    
    @Override
    public int hashCode()
    { 
        int x = aggregator.hashCode() ;
        if ( var != null )
            x ^= var.hashCode() ;
        return x ;
    }
    
    @Override
    public boolean equals(Expr other, boolean bySyntax) {
        if ( other == null ) return false ;
        if ( this == other ) return true ;
        if ( ! ( other instanceof ExprAggregator ) )
            return false ;
        ExprAggregator agg = (ExprAggregator)other ;
        if ( ! Objects.equals(var, agg.var) )
            return false ;
        return Objects.equals(aggregator, agg.aggregator) ;
    }

    // Ensure no confusion - in an old design, an ExprAggregator was a subclass of ExprVar. 
    @Override
    public ExprVar getExprVar()
    { throw new ARQInternalErrorException() ; }
    
    @Override
    public Var asVar()
    { throw new ARQInternalErrorException() ; }
    
    public ExprVar getAggVar() { return exprVar ; }
    
    // As an expression suitable for outputting the calculation. 
    public String asSparqlExpr(SerializationContext sCxt)        
    { return aggregator.asSparqlExpr(sCxt) ; }
    
    @Override
    public ExprAggregator copySubstitute(Binding binding)
    {
        Var v = var ;
        Aggregator agg = aggregator ;
        return new ExprAggregator(v, agg) ;
    }
    
    @Override
    public ExprAggregator applyNodeTransform(NodeTransform transform)
    {
        // Can't rewrite this to a non-variable.
        Node node = transform.apply(var) ;
        if ( ! Var.isVar(node) )
        {
            Log.warn(this, "Attempt to convert an aggregation variable to a non-variable: ignored") ;
            node = var ;
        }
        
        Var v = (Var)node ;
        Aggregator agg = aggregator.copyTransform(transform) ;
        return new ExprAggregator(Var.alloc(node), agg) ;
    }
    
    // DEBUGGING
    @Override
    public String toString()
    { return "(AGG "+
                (var==null?"<>":"?"+var.getVarName())+
                " "+aggregator.toString()+")"; }
    
    public Expr copy(Var v)  { return new ExprAggregator(v, aggregator.copy(aggregator.getExprList())) ; }
    
    @Override
    public NodeValue eval(Binding binding, FunctionEnv env)
    {
       return ExprVar.eval(var, binding, env) ;
    }
    
    public Expr apply(ExprTransform transform)  { return transform.transform(this) ; }
    
    @Override
    public void visit(ExprVisitor visitor)
    { visitor.visit(this) ; }
    
}