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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
// http://www.burton-computer.com
//
// Copyright (c) 2014, Burton Computer Corporation
// All rights reserved.
//
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//     Redistributions of source code must retain the above copyright
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//
//     Redistributions in binary form must reproduce the above copyright
//     notice, this list of conditions and the following disclaimer in
//     the documentation and/or other materials provided with the
//     distribution.
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package org.javimmutable.collections.listmap;

import org.javimmutable.collections.Cursor;
import org.javimmutable.collections.Holder;
import org.javimmutable.collections.Insertable;
import org.javimmutable.collections.JImmutableList;
import org.javimmutable.collections.JImmutableListMap;
import org.javimmutable.collections.JImmutableMap;
import org.javimmutable.collections.common.Conditions;
import org.javimmutable.collections.common.IteratorAdaptor;
import org.javimmutable.collections.list.JImmutableArrayList;

import javax.annotation.Nonnull;
import javax.annotation.Nullable;
import javax.annotation.concurrent.Immutable;
import java.util.Iterator;

@Immutable
public abstract class AbstractJImmutableListMap
        implements JImmutableListMap
{
    private final JImmutableMap> contents;

    protected AbstractJImmutableListMap(JImmutableMap> contents)
    {
        this.contents = contents;
    }

    @Nonnull
    @Override
    public JImmutableList getList(@Nonnull K key)
    {
        Conditions.stopNull(key);
        Holder> current = contents.find(key);
        return current.isFilled() ? current.getValue() : emptyList();
    }

    @Nonnull
    @Override
    public JImmutableListMap assign(@Nonnull K key,
                                          @Nonnull JImmutableList value)
    {
        Conditions.stopNull(key, value);
        return create(contents.assign(key, copyList(value)));
    }

    @Nonnull
    @Override
    public JImmutableListMap insert(@Nonnull K key,
                                          @Nullable V value)
    {
        return create(contents.assign(key, insertInList(getList(key), value)));
    }

    @Nonnull
    @Override
    public JImmutableListMap delete(@Nonnull K key)
    {
        return create(contents.delete(key));
    }

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

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

    @Nonnull
    @Override
    public Cursor keysCursor()
    {
        return contents.keysCursor();
    }

    @Nonnull
    @Override
    public Cursor valuesCursor(@Nonnull K key)
    {
        return getList(key).cursor();
    }

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

    @Override
    @Nonnull
    public Insertable> insert(@Nonnull JImmutableMap.Entry e)
    {
        return insert(e.getKey(), e.getValue());
    }

    @Override
    public Iterator>> iterator()
    {
        return IteratorAdaptor.of(cursor());
    }

    @Nullable
    @Override
    public JImmutableList get(K key)
    {
        return contents.get(key);
    }

    @Override
    public JImmutableList getValueOr(K key,
                                        JImmutableList defaultValue)
    {
        return contents.getValueOr(key, defaultValue);
    }

    @Nonnull
    @Override
    public Holder> find(K key)
    {
        return contents.find(key);
    }

    @Nonnull
    @Override
    public JImmutableListMap deleteAll()
    {
        return create(contents.deleteAll());
    }

    /**
     * Implemented by derived classes to create a new instance of the appropriate class.
     *
     * @param map
     * @return
     */
    protected abstract JImmutableListMap create(JImmutableMap> map);

    /**
     * Overridable by derived classes to create a compatible copy of the specified list.
     * Default implementation simply returns the original.
     *
     * @return
     */
    protected JImmutableList copyList(JImmutableList original)
    {
        return original;
    }

    /**
     * Overridable by derived classes to create a new empty list
     *
     * @return
     */
    @Nonnull
    protected JImmutableList emptyList()
    {
        return JImmutableArrayList.of();
    }

    /**
     * Overridable by derived classes to insert a value into a list in some way.
     * Default implementation appends to end of the list.
     *
     * @return
     */
    protected JImmutableList insertInList(JImmutableList list,
                                             V value)
    {
        return list.insertLast(value);
    }
}