src/java/org/apache/cassandra/cql3/functions/PartiallyAppliedScalarFunction.java

/*
 * 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.cassandra.cql3.functions;

import java.nio.ByteBuffer;
import java.util.ArrayList;
import java.util.List;

import org.apache.cassandra.cql3.CqlBuilder;
import org.apache.cassandra.db.marshal.AbstractType;
import org.apache.cassandra.exceptions.InvalidRequestException;
import org.apache.cassandra.transport.ProtocolVersion;

/**
 * An internal function used to hold the partial application of another function to only some of its parameters.
 *
 * @see ScalarFunction#partialApplication(ProtocolVersion, List)
 */
final class PartiallyAppliedScalarFunction extends NativeScalarFunction implements PartialScalarFunction
{
    private final ScalarFunction function;
    private final List<ByteBuffer> partialParameters;

    PartiallyAppliedScalarFunction(ScalarFunction function, List<ByteBuffer> partialParameters, int unresolvedCount)
    {
        // Note that we never register those function, there are just used internally, so the name doesn't matter much
        super("__partial_application__", function.returnType(), computeArgTypes(function, partialParameters, unresolvedCount));
        this.function = function;
        this.partialParameters = partialParameters;
    }

    @Override
    public boolean isMonotonic()
    {
        return function.isNative() ? ((NativeScalarFunction) function).isPartialApplicationMonotonic(partialParameters)
                                   : function.isMonotonic();
    }

    @Override
    public boolean isPure()
    {
        return function.isPure();
    }

    @Override
    public Function getFunction()
    {
        return function;
    }

    @Override
    public List<ByteBuffer> getPartialParameters()
    {
        return partialParameters;
    }

    private static AbstractType<?>[] computeArgTypes(ScalarFunction function, List<ByteBuffer> partialParameters, int unresolvedCount)
    {
        AbstractType<?>[] argTypes = new AbstractType<?>[unresolvedCount];
        int arg = 0;
        for (int i = 0; i < partialParameters.size(); i++)
        {
            if (partialParameters.get(i) == UNRESOLVED)
                argTypes[arg++] = function.argTypes().get(i);
        }
        return argTypes;
    }

    public ByteBuffer execute(ProtocolVersion protocolVersion, List<ByteBuffer> parameters) throws InvalidRequestException
    {
        List<ByteBuffer> fullParameters = new ArrayList<>(partialParameters);
        int arg = 0;
        for (int i = 0; i < fullParameters.size(); i++)
        {
            if (fullParameters.get(i) == UNRESOLVED)
                fullParameters.set(i, parameters.get(arg++));
        }
        return function.execute(protocolVersion, fullParameters);
    }

    @Override
    public String toString()
    {
        CqlBuilder b = new CqlBuilder().append(function.name()).append(" : (");

        List<AbstractType<?>> types = function.argTypes();
        for (int i = 0, m = types.size(); i < m; i++)
        {
            if (i > 0)
                b.append(", ");
            b.append(toCqlString(types.get(i)));
            if (partialParameters.get(i) != Function.UNRESOLVED)
                b.append("(constant)");
        }
        b.append(") -> ").append(returnType);
        return b.toString();
    }
}