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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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//
//     Redistributions in binary form must reproduce the above copyright
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package org.javimmutable.collections.cursors;

import org.javimmutable.collections.Cursor;
import org.javimmutable.collections.common.IteratorAdaptor;

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

/**
 * A Cursor that combines multiple Cursors into a single virtual Cursor
 * that visits all values from all Cursors in order.
 *
 * @param 
 */
@Immutable
public class MultiCursor
        implements Cursor
{
    private final Node nodes;
    private final Cursor cursor;

    public MultiCursor(Cursor... cursors)
    {
        Node nodes = null;
        for (int i = cursors.length - 1; i >= 0; --i) {
            nodes = new Node(cursors[i], nodes);
        }
        this.nodes = nodes;
        this.cursor = null;
    }

    private MultiCursor(Node nodes,
                        Cursor cursor)
    {
        this.nodes = nodes;
        this.cursor = cursor;
    }

    /**
     * Creates an object for building a MultiCursor from an arbitrary sequence of Cursors.
     *
     * @param 
     * @return
     */
    public static  Builder builder()
    {
        return new Builder();
    }

    public static > MultiCursor of(C cursor1,
                                                             C cursor2)
    {
        return new MultiCursor(new Node(cursor1, new Node(cursor2, null)), null);
    }

    public static > MultiCursor of(C cursor1,
                                                             C cursor2,
                                                             C cursor3)
    {
        return new MultiCursor(new Node(cursor1, new Node(cursor2, new Node(cursor3, null))), null);
    }

    public static > MultiCursor of(C... cursors)
    {
        return new MultiCursor(cursors);
    }

    @Nonnull
    @Override
    public Cursor start()
    {
        return (cursor == null) ? next() : this;
    }

    @Nonnull
    @Override
    public Cursor next()
    {
        if ((cursor != null) && cursor.hasValue()) {
            Cursor nextCursor = cursor.next();
            if (nextCursor.hasValue()) {
                return new MultiCursor(nodes, nextCursor);
            }
        }

        Node newNodes = nodes;
        while (newNodes != null) {
            Cursor nextCursor = newNodes.cursor.next();
            if (nextCursor.hasValue()) {
                return new MultiCursor(newNodes.next, nextCursor);
            }
            newNodes = newNodes.next;
        }

        return EmptyStartedCursor.of();
    }

    @Override
    public boolean hasValue()
    {
        if (cursor == null) {
            throw new NotStartedException();
        }
        return cursor.hasValue();
    }

    @Override
    public T getValue()
    {
        if (cursor == null) {
            throw new NotStartedException();
        }
        return cursor.getValue();
    }

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

    /**
     * Builder class to build a MultiCursor from an arbitrary sequence of Cursors.
     * Cursors will be visited in the same order that add() is called.
     *
     * @param 
     */
    public static class Builder
    {
        private final Node nodes;

        private Builder()
        {
            this(null);
        }

        private Builder(Node nodes)
        {
            this.nodes = nodes;
        }

        public Builder add(Cursor cursor)
        {
            return new Builder(new Node(cursor, nodes));
        }

        public MultiCursor build()
        {
            Node inOrderNodes = null;
            for (Node n = nodes; n != null; n = n.next) {
                inOrderNodes = new Node(n.cursor, inOrderNodes);
            }
            return new MultiCursor(inOrderNodes, null);
        }
    }

    @Immutable
    private static class Node
    {
        private final Cursor cursor;
        private final Node next;

        private Node(Cursor cursor,
                     Node next)
        {
            this.cursor = cursor;
            this.next = next;
        }
    }
}