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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.Func0;

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

/**
 * Cursor that creates and returns a real Cursor for a specific iterable only when start() or next() is
 * called for the first time.
 *
 * @param 
 */
@Immutable
public class LazyCursor
        extends AbstractStartCursor
{
    private final Func0> factory;

    /**
     * Creates a new LazyCursor for the specified factory.
     *
     * @param factory a function to return an actual Cursor to use for iteration
     */
    public LazyCursor(Func0> factory)
    {
        this.factory = factory;
    }

    /**
     * Creates a new LazyCursor for the specified cursorable.
     *
     * @param cursorable to return an actual Cursor to use for iteration
     */
    public LazyCursor(final Cursorable cursorable)
    {
        this.factory = new Func0>()
        {
            @Override
            public Cursor apply()
            {
                return cursorable.cursor();
            }
        };
    }

    /**
     * Creates a new LazyCursor using the specified factory.
     *
     * @param factory a Func0 capable of creating a real Cursor
     */
    public static  LazyCursor of(Func0> factory)
    {
        return new LazyCursor(factory);
    }

    /**
     * Creates a new LazyCursor for the specified cursorable.
     *
     * @param cursorable a Cursorable capable of producing a non-empty LazyCursor
     */
    public static  LazyCursor of(Cursorable cursorable)
    {
        return new LazyCursor(cursorable);
    }

    /**
     * Creates the real cursor using the factory and returns its start() method's result.
     * Thus when the lazy cursor creates the real cursor it always immediately calls its
     * start() method to start its iteration and get it into the state expected by the
     * caller of this method.
     *
     * @return real cursor's start() value
     */
    @Nonnull
    @Override
    public Cursor next()
    {
        return factory.apply().start();
    }
}