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Library providing immutable/persistent collection classes for Java. While collections are immutable they provide methods for adding and removing values by creating new modified copies of themselves. Each copy shares almost all of its structure with other copies to minimize memory consumption.
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// Burton Computer Corporation
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// Copyright (c) 2021, Burton Computer Corporation
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package org.javimmutable.collections.common;

import org.javimmutable.collections.Holder;
import org.javimmutable.collections.IterableStreamable;
import org.javimmutable.collections.JImmutableMap;
import org.javimmutable.collections.MapEntry;
import org.javimmutable.collections.iterators.TransformStreamable;

import javax.annotation.Nonnull;
import javax.annotation.concurrent.Immutable;
import java.util.AbstractCollection;
import java.util.AbstractMap;
import java.util.AbstractSet;
import java.util.Collection;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;
import java.util.Spliterator;

/**
 * An immutable Map implementation backed by a JImmutableMap.
 */
@SuppressWarnings({"unchecked", "NullableProblems"})
@Immutable
public class MapAdaptor
    extends AbstractMap
{
    private final JImmutableMap map;

    public MapAdaptor(JImmutableMap map)
    {
        this.map = map;
    }

    public static  MapAdaptor of(JImmutableMap map)
    {
        return new MapAdaptor<>(map);
    }

    @Override
    public int size()
    {
        return map.size();
    }

    @Override
    public boolean isEmpty()
    {
        return map.isEmpty();
    }

    @Override
    public boolean containsKey(Object o)
    {
        return map.find((K)o).isFilled();
    }

    /**
     * Uses O(n) traversal of the JImmutableMap to search for a matching value.
     */
    @Override
    public boolean containsValue(Object o)
    {
        for (JImmutableMap.Entry entry : map) {
            V value = entry.getValue();
            if (o == null) {
                if (value == null) {
                    return true;
                }
            } else {
                if ((value != null) && value.equals(o)) {
                    return true;
                }
            }
        }
        return false;
    }

    @Override
    public V get(Object o)
    {
        return map.getValueOr((K)o, null);
    }

    @Override
    public V put(K k,
                 V v)
    {
        throw new UnsupportedOperationException();
    }

    @Override
    public V remove(Object o)
    {
        throw new UnsupportedOperationException();
    }

    @Override
    public void putAll(Map map)
    {
        throw new UnsupportedOperationException();
    }

    @Override
    public void clear()
    {
        throw new UnsupportedOperationException();
    }

    @Override
    public Set keySet()
    {
        return new AbstractSet()
        {
            @Override
            public boolean isEmpty()
            {
                return map.isEmpty();
            }

            @Override
            public boolean contains(Object o)
            {
                return map.find((K)o).isFilled();
            }

            @Override
            public Iterator iterator()
            {
                return map.keys().iterator();
            }

            @Override
            public Spliterator spliterator()
            {
                return map.keys().spliterator();
            }

            @Override
            public int size()
            {
                return map.size();
            }
        };
    }

    @Override
    public Collection values()
    {
        return new AbstractCollection()
        {
            @Override
            public Iterator iterator()
            {
                return map.values().iterator();
            }

            @Override
            public Spliterator spliterator()
            {
                return map.values().spliterator();
            }

            @Override
            public int size()
            {
                return map.size();
            }
        };
    }

    @Override
    public Set> entrySet()
    {
        return new AbstractSet>()
        {
            @Override
            public boolean isEmpty()
            {
                return map.isEmpty();
            }

            @Override
            public boolean contains(Object o)
            {
                if (!(o instanceof Entry)) {
                    return false;
                }
                Entry oEntry = (Entry)o;
                Holder> eHolder = map.findEntry(oEntry.getKey());
                return eHolder.isFilled() && new MapEntry(eHolder.getValue()).equals(oEntry);
            }

            @Override
            public Iterator> iterator()
            {
                return streamable().iterator();
            }

            @Override
            public Spliterator> spliterator()
            {
                return streamable().spliterator();
            }

            @Override
            public int size()
            {
                return map.size();
            }

            @Nonnull
            private IterableStreamable> streamable()
            {
                return TransformStreamable.of(map, e -> MapEntry.of(e));
            }
        };
    }
}