/*
* Licensed 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.facebook.presto.operator.window;
import com.facebook.presto.spi.block.BlockBuilder;
import com.facebook.presto.spi.function.ValueWindowFunction;
import com.facebook.presto.spi.function.WindowFunctionSignature;
import java.util.List;
import static com.google.common.collect.Iterables.getOnlyElement;
@WindowFunctionSignature(name = "first_value", typeVariable = "T", returnType = "T", argumentTypes = "T")
public class FirstValueFunction
extends ValueWindowFunction
{
private final int argumentChannel;
public FirstValueFunction(List<Integer> argumentChannels)
{
this.argumentChannel = getOnlyElement(argumentChannels);
}
@Override
public void processRow(BlockBuilder output, int frameStart, int frameEnd, int currentPosition)
{
if (frameStart < 0) {
output.appendNull();
return;
}
windowIndex.appendTo(argumentChannel, frameStart, output);
}
}