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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) 2017, Burton Computer Corporation
// All rights reserved.
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package org.javimmutable.collections.inorder;

import org.javimmutable.collections.Cursor;
import org.javimmutable.collections.Func1;
import org.javimmutable.collections.Holder;
import org.javimmutable.collections.Holders;
import org.javimmutable.collections.JImmutableArray;
import org.javimmutable.collections.JImmutableMap;
import org.javimmutable.collections.MapEntry;
import org.javimmutable.collections.array.trie32.TrieArray;
import org.javimmutable.collections.common.AbstractJImmutableMap;
import org.javimmutable.collections.cursors.TransformCursor;
import org.javimmutable.collections.hash.JImmutableHashMap;

import javax.annotation.Nonnull;
import javax.annotation.concurrent.Immutable;

/**
 * JImmutableMap implementation that allows iteration over members in the order in which they
 * were inserted into the map.  Maintains two parallel data structures, one for sorting and
 * the other for storing entries.  Gets are approximately as fast as hash map gets but updates
 * are significantly slower.   Iteration is comparable to sorted map iteration.
 * 
 * Use a hash or tree map whenever possible but this class performs well enough for most cases
 * where insertion order is important to an algorithm.
 *
 * @param 
 * @param 
 */
@Immutable
public class JImmutableInsertOrderMap
        extends AbstractJImmutableMap
{
    @SuppressWarnings("unchecked")
    public static final JImmutableInsertOrderMap EMPTY = new JImmutableInsertOrderMap(TrieArray.of(), JImmutableHashMap.of(), 1);

    private final JImmutableArray> sortedNodes;
    private final JImmutableMap> hashedNodes;
    private final int nextIndex;

    private JImmutableInsertOrderMap(JImmutableArray> sortedNodes,
                                     JImmutableMap> hashedNodes,
                                     int nextIndex)
    {
        assert sortedNodes.size() == hashedNodes.size();
        this.sortedNodes = sortedNodes;
        this.hashedNodes = hashedNodes;
        this.nextIndex = nextIndex;
    }

    @SuppressWarnings("unchecked")
    public static  JImmutableInsertOrderMap of()
    {
        return (JImmutableInsertOrderMap)EMPTY;
    }

    @Override
    public V getValueOr(K key,
                        V defaultValue)
    {
        final Node current = hashedNodes.get(key);
        return (current != null) ? current.getValue() : defaultValue;
    }

    @Nonnull
    @Override
    public Holder find(@Nonnull K key)
    {
        final Node current = hashedNodes.get(key);
        return (current != null) ? current : Holders.of();
    }

    @Nonnull
    @Override
    public Holder> findEntry(@Nonnull K key)
    {
        final Node current = hashedNodes.get(key);
        return (current != null) ? Holders.>of(current) : Holders.>of();
    }

    @Nonnull
    @Override
    public JImmutableInsertOrderMap assign(@Nonnull K key,
                                                 V value)
    {
        final Node current = hashedNodes.get(key);
        if (current == null) {
            final Node newNode = new Node(key, value, nextIndex);
            return new JImmutableInsertOrderMap(sortedNodes.assign(newNode.index, newNode),
                                                      hashedNodes.assign(key, newNode),
                                                      nextIndex + 1);
        } else if (current.getValue() == value) {
            return this;
        } else {
            final Node newNode = current.withValue(value);
            return new JImmutableInsertOrderMap(sortedNodes.assign(newNode.index, newNode),
                                                      hashedNodes.assign(key, newNode),
                                                      nextIndex);
        }
    }

    @Nonnull
    @Override
    public JImmutableInsertOrderMap delete(@Nonnull K key)
    {
        final Node current = hashedNodes.get(key);
        if (current != null) {
            return new JImmutableInsertOrderMap(sortedNodes.delete(current.index),
                                                      hashedNodes.delete(key),
                                                      nextIndex);
        } else {
            return this;
        }
    }

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

    @Nonnull
    @Override
    public JImmutableInsertOrderMap deleteAll()
    {
        return of();
    }

    @Override
    @Nonnull
    public Cursor> cursor()
    {
        return TransformCursor.of(sortedNodes.valuesCursor(), new Func1, Entry>()
        {
            @Override
            public Entry apply(Node node)
            {
                return node;
            }
        });
    }

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

    /**
     * An Entry implementation that also stores the sortedKeys index corresponding to this node's key.
     *
     * @param 
     * @param 
     */
    @Immutable
    private static class Node
            extends MapEntry
            implements Holder
    {
        private final int index;

        private Node(K key,
                     V value,
                     int index)
        {
            super(key, value);
            this.index = index;
        }

        @Override
        public boolean isEmpty()
        {
            return false;
        }

        @Override
        public boolean isFilled()
        {
            return true;
        }

        @Override
        public V getValueOrNull()
        {
            return value;
        }

        @Override
        public V getValueOr(V defaultValue)
        {
            return value;
        }

        private Node withValue(V value)
        {
            return new Node(key, value, index);
        }
    }
}