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// Burton Computer Corporation
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package org.javimmutable.collections.cursors;

import org.javimmutable.collections.Cursor;
import org.javimmutable.collections.Cursorable;
import org.javimmutable.collections.Func1;
import org.javimmutable.collections.Indexed;
import org.javimmutable.collections.SplitCursor;

import javax.annotation.Nonnull;

public class LazyMultiCursor
    extends AbstractStartedCursor
{
    @Nonnull
    private final Cursor> source;
    @Nonnull
    private final Cursor cursor;

    private LazyMultiCursor(@Nonnull Cursor> source,
                            @Nonnull Cursor cursor)
    {
        this.source = source;
        this.cursor = cursor;
    }

    /**
     * Constructs a cursor that visits all of the values reachable from all of the
     * Cursorables visited by source.
     */
    public static  Cursor cursor(@Nonnull Cursor> source)
    {
        return new AbstractStartCursor()
        {
            @Nonnull
            @Override
            public Cursor next()
            {
                return advance(source.start());
            }
        };
    }

    /**
     * Constructs a cursor that visits all of the values reachable from all of the
     * Cursorables contained in source.
     */
    public static  Cursor cursor(@Nonnull Indexed> source)
    {
        return cursor(StandardCursor.of(source));
    }

    /**
     * Constructs a cursor that visits all of the values reachable from all of the
     * Cursorables contained in source.  All values are transformed using the provided method.
     */
    public static  Cursor transformed(Indexed source,
                                               Func1> transforminator)
    {
        return transformed(StandardCursor.of(source), transforminator);
    }

    /**
     * Constructs a cursor that visits all of the values reachable from all of the
     * Cursorables visited by source.  All values are transformed using the provided method.
     */
    public static  Cursor transformed(Cursor source,
                                               Func1> transforminator)
    {
        return cursor(TransformCursor.of(source, transforminator));
    }

    /**
     * Constructs a Cursorable with a cursor() method that returns a LazyMultiCursor from the
     * provided sources.  Note: the type signature has changed from v1.9.1 to require a
     * Cursorable of type T rather than a super class.
     */
    public static  Cursorable cursorable(@Nonnull final Cursor> sources)
    {
        return () -> LazyMultiCursor.cursor(sources);
    }

    /**
     * Constructs a Cursorable with a cursor() method that returns a LazyMultiCursor from the
     * provided sources.  Note: the type signature has changed from v1.9.1 to require a
     * Cursorable of type T rather than a super class.
     */
    public static  Cursorable cursorable(@Nonnull final Indexed> sources)
    {
        return () -> LazyMultiCursor.cursor(sources);
    }

    /**
     * Used internally to create a LazyMultiCursor with already started source and cursor fields.
     */
    private static  Cursor resumeAfterSplitCursor(@Nonnull Cursor> source,
                                                        @Nonnull Cursor cursor)
    {
        return new AbstractStartCursor()
        {
            @Nonnull
            @Override
            public Cursor next()
            {
                return new LazyMultiCursor<>(source, cursor);
            }
        };
    }

    private static  Cursor advance(Cursor> source)
    {
        while (source.hasValue()) {
            Cursor cursor = source.getValue().cursor().start();
            if (cursor.hasValue()) {
                return new LazyMultiCursor<>(source, cursor);
            }
            source = source.next();
        }
        return EmptyStartedCursor.of();
    }

    @Nonnull
    @Override
    public Cursor next()
    {
        if (cursor.hasValue()) {
            Cursor nextCursor = cursor.next();
            if (nextCursor.hasValue()) {
                return new LazyMultiCursor<>(source, nextCursor);
            }
        }

        return advance(source.next());
    }

    @Override
    public boolean hasValue()
    {
        return cursor.hasValue();
    }

    @Override
    public T getValue()
    {
        return cursor.getValue();
    }

    @Override
    public boolean isSplitAllowed()
    {
        return source.isSplitAllowed();
    }

    @Override
    public SplitCursor splitCursor()
    {
        final SplitCursor> split = source.splitCursor();
        return new SplitCursor<>(resumeAfterSplitCursor(split.getLeft().start(), cursor), cursor(split.getRight()));
    }
}