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// Burton Computer Corporation
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package org.javimmutable.collections.hash;

import org.javimmutable.collections.Cursor;
import org.javimmutable.collections.Holder;
import org.javimmutable.collections.Holders;
import org.javimmutable.collections.JImmutableMap;
import org.javimmutable.collections.SplitableIterator;
import org.javimmutable.collections.common.AbstractJImmutableMap;
import org.javimmutable.collections.common.StreamConstants;
import org.javimmutable.collections.cursors.StandardCursor;
import org.javimmutable.collections.iterators.EmptyIterator;
import org.javimmutable.collections.serialization.JImmutableHashMapProxy;

import javax.annotation.Nonnull;
import javax.annotation.concurrent.Immutable;
import java.io.Serializable;

/**
 * Singleton implementation of JImmutableMap that contains no elements.
 * When a value is assigned to the map a JImmutableHashMap is created that
 * manages hash collisions using a tree if key is Comparable or a list otherwise.
 */
@Immutable
public class EmptyHashMap
    extends AbstractJImmutableMap
    implements Serializable
{
    static final EmptyHashMap INSTANCE = new EmptyHashMap();

    private static final long serialVersionUID = -121805;

    private EmptyHashMap()
    {
    }

    @Nonnull
    @Override
    public Holder find(@Nonnull K key)
    {
        return Holders.of();
    }

    @Nonnull
    @Override
    public Holder> findEntry(@Nonnull K key)
    {
        return Holders.of();
    }

    @Nonnull
    @Override
    public JImmutableMap assign(@Nonnull K key,
                                      V value)
    {
        return JImmutableHashMap.forKey(key).assign(key, value);
    }

    @Nonnull
    @Override
    public JImmutableMap delete(@Nonnull K key)
    {
        return this;
    }

    @Override
    public int size()
    {
        return 0;
    }

    @Nonnull
    @Override
    public JImmutableMap deleteAll()
    {
        return this;
    }

    @Override
    @Nonnull
    public Cursor> cursor()
    {
        return StandardCursor.of();
    }

    @Nonnull
    @Override
    public SplitableIterator> iterator()
    {
        return EmptyIterator.of();
    }

    @Override
    public int getSpliteratorCharacteristics()
    {
        return StreamConstants.SPLITERATOR_UNORDERED;
    }

    @Override
    public V getValueOr(K key,
                        V defaultValue)
    {
        return defaultValue;
    }

    @Override
    public void checkInvariants()
    {
        //TODO: fix empty checkInvariants()
    }

    private Object writeReplace()
    {
        return new JImmutableHashMapProxy(this);
    }
}