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Neo4j property value system.
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/*
 * Copyright (c) "Neo4j"
 * Neo4j Sweden AB [http://neo4j.com]
 *
 * This file is part of Neo4j.
 *
 * Neo4j is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see .
 */
package org.neo4j.values.virtual;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Set;
import java.util.function.BiConsumer;
import java.util.function.BinaryOperator;
import java.util.function.Function;
import java.util.function.Supplier;
import java.util.stream.Collector;

import org.neo4j.values.AnyValue;
import org.neo4j.values.storable.ValueRepresentation;

import static org.neo4j.memory.HeapEstimator.shallowSizeOfInstance;

public abstract class ListValueBuilder
{
    /**
     * @return a collector for {@link ListValue}s
     */
    public static Collector collector()
    {
        return LIST_VALUE_COLLECTOR;
    }

    /**
     * Start building a list of known size
     * @param size the final size of the list
     * @return a new builder
     */
    public static ListValueBuilder newListBuilder( int size )
    {
        return new FixedSizeListValueBuilder( size );
    }

    /**
     * Start building a list of unknown size
     * @return a new builder
     */
    public static ListValueBuilder newListBuilder()
    {
        return new UnknownSizeListValueBuilder();
    }

    protected long estimatedHeapSize;
    protected ValueRepresentation valueRepresentation;

    public final void add( AnyValue value )
    {
        estimatedHeapSize += value.estimatedHeapUsage();
        valueRepresentation = valueRepresentation == null ? value.valueRepresentation() : valueRepresentation.coerce( value.valueRepresentation() );
        internalAdd( value );
    }

    public abstract ListValue build();

    protected abstract void internalAdd( AnyValue value );

    protected ValueRepresentation valueRepresentation()
    {
        return valueRepresentation == null ? ValueRepresentation.UNKNOWN : valueRepresentation;
    }

    private static class FixedSizeListValueBuilder extends ListValueBuilder
    {
        private final AnyValue[] values;
        private int index;

        private FixedSizeListValueBuilder( int size )
        {
            this.values = new AnyValue[size];
        }

        @Override
        public ListValue build()
        {
            return new ListValue.ArrayListValue( values, estimatedHeapSize, valueRepresentation() );
        }

        @Override
        public void internalAdd( AnyValue value )
        {
            values[index++] = value;
        }
    }

    private static final long ARRAY_LIST_SHALLOW_SIZE = shallowSizeOfInstance( ArrayList.class );
    private static class UnknownSizeListValueBuilder extends ListValueBuilder
    {
        private final List values = new ArrayList<>();

        UnknownSizeListValueBuilder()
        {
            super();
            estimatedHeapSize += ARRAY_LIST_SHALLOW_SIZE;
        }

        public UnknownSizeListValueBuilder combine( UnknownSizeListValueBuilder rhs )
        {
            values.addAll( rhs.values );
            estimatedHeapSize += rhs.estimatedHeapSize;
            return this;
        }

        @Override
        public ListValue build()
        {
            return new ListValue.JavaListListValue( values, estimatedHeapSize, valueRepresentation() );
        }

        @Override
        public void internalAdd( AnyValue value )
        {
            values.add( value );
        }
    }

    private static final Collector LIST_VALUE_COLLECTOR = new Collector<>()
    {
        @Override
        public Supplier supplier()
        {
            return UnknownSizeListValueBuilder::new;
        }

        @Override
        public BiConsumer accumulator()
        {
            return ListValueBuilder::add;
        }

        @Override
        public BinaryOperator combiner()
        {
            return UnknownSizeListValueBuilder::combine;
        }

        @Override
        public Function finisher()
        {
            return UnknownSizeListValueBuilder::build;
        }

        @Override
        public Set characteristics()
        {
            return Collections.emptySet();
        }
    };
}