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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) 2018, Burton Computer Corporation
// All rights reserved.
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package org.javimmutable.collections.hash.collision_map;

import org.javimmutable.collections.Cursor;
import org.javimmutable.collections.Func1;
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.MutableDelta;
import org.javimmutable.collections.tree.BranchNode;
import org.javimmutable.collections.tree.ComparableComparator;
import org.javimmutable.collections.tree.LeafNode;
import org.javimmutable.collections.tree.Node;
import org.javimmutable.collections.tree.UpdateResult;

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

/**
 * Transforms implementation that stores values in Node objects (b-trees trees).
 * Usable with keys that implement Comparable.  Will fail with any other
 * type of key.
 */
@Immutable
public class TreeCollisionMap, V>
    implements CollisionMap, K, V>
{
    private final Comparator comparator = ComparableComparator.of();

    @Nonnull
    @Override
    public Node update(Node leaf,
                             @Nonnull K key,
                             V value,
                             @Nonnull MutableDelta delta)
    {
        if (leaf == null) {
            delta.add(1);
            return new LeafNode<>(key, value);
        } else {
            return resultForUpdate(leaf, delta, leaf.assign(comparator, key, value));
        }
    }

    @Nonnull
    @Override
    public Node update(@Nullable Node leaf,
                             @Nonnull K key,
                             @Nonnull Func1, V> generator,
                             @Nonnull MutableDelta delta)
    {
        if (leaf == null) {
            delta.add(1);
            return new LeafNode<>(key, generator.apply(Holders.of()));
        } else {
            return resultForUpdate(leaf, delta, leaf.update(comparator, key, generator));
        }
    }

    @Override
    public Node delete(@Nonnull Node leaf,
                             @Nonnull K key,
                             @Nonnull MutableDelta delta)
    {
        final Node newLeaf = leaf.delete(comparator, key);
        if (newLeaf == leaf) {
            return leaf;
        } else {
            delta.add(-1);
            return newLeaf.isEmpty() ? null : newLeaf.compress();
        }
    }

    @Override
    public V getValueOr(@Nonnull Node leaf,
                        @Nonnull K key,
                        V defaultValue)
    {
        return leaf.getValueOr(comparator, key, defaultValue);
    }

    @Override
    public Holder findValue(@Nonnull Node leaf,
                               @Nonnull K key)
    {
        return leaf.find(comparator, key);
    }

    @Override
    public Holder> findEntry(@Nonnull Node leaf,
                                                       @Nonnull K key)
    {
        return leaf.findEntry(comparator, key);
    }

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

    @Override
    public SplitableIterator> iterator(@Nonnull Node leaf)
    {
        return leaf.iterator();
    }

    private Node resultForUpdate(Node leaf,
                                       @Nonnull MutableDelta delta,
                                       UpdateResult result)
    {
        switch (result.type) {
            case UNCHANGED:
                return leaf;
            case INPLACE:
                delta.add(result.sizeDelta);
                return result.newNode;
            case SPLIT:
                delta.add(result.sizeDelta);
                return new BranchNode<>(result.newNode, result.extraNode);
            default:
                throw new IllegalStateException("unknown UpdateResult.Type value");
        }
    }
}