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package org.javimmutable.collections.iterators;

import org.javimmutable.collections.Indexed;
import org.javimmutable.collections.SplitIterator;
import org.javimmutable.collections.SplitableIterable;
import org.javimmutable.collections.SplitableIterator;
import org.javimmutable.collections.indexed.IndexedHelper;

import javax.annotation.Nonnull;
import java.util.NoSuchElementException;

public final class IndexedIterator
{
    private IndexedIterator()
    {
    }

    public static  SplitableIterator forward(@Nonnull Indexed values)
    {
        return new Forward<>(values, -1, values.size() - 1);
    }

    public static  SplitableIterable fwd(@Nonnull Indexed values)
    {
        return () -> forward(values);
    }

    public static  SplitableIterator iterator(@Nonnull Indexed values)
    {
        return forward(values);
    }

    public static  SplitableIterator reverse(@Nonnull Indexed values)
    {
        return new Reverse<>(values, values.size(), 0);
    }

    public static  SplitableIterable rev(@Nonnull Indexed values)
    {
        return () -> reverse(values);
    }

    public static SplitableIterator forRange(int low,
                                                      int high)
    {
        return iterator(IndexedHelper.range(low, high));
    }

    private static class Forward
        extends AbstractSplitableIterator
    {
        @Nonnull
        private final Indexed values;
        private final int limit;
        private int index;

        public Forward(@Nonnull Indexed values,
                       int index,
                       int limit)
        {
            this.values = values;
            this.limit = limit;
            this.index = index;
        }

        @Override
        public boolean hasNext()
        {
            return index < limit;
        }

        @Override
        public T next()
        {
            if (index >= limit) {
                throw new NoSuchElementException();
            }
            index += 1;
            return values.get(index);
        }

        @Override
        public boolean isSplitAllowed()
        {
            return (limit - index) > 1;
        }

        @Nonnull
        @Override
        public SplitIterator splitIterator()
        {
            final int splitIndex = index + (limit - index) / 2;
            if (splitIndex == index) {
                throw new UnsupportedOperationException();
            }
            return new SplitIterator<>(new Forward<>(values, index, splitIndex),
                                       new Forward<>(values, splitIndex, limit));
        }
    }

    private static class Reverse
        extends AbstractSplitableIterator
    {
        @Nonnull
        private final Indexed values;
        private final int limit;
        private int index;

        public Reverse(@Nonnull Indexed values,
                       int index,
                       int limit)
        {
            this.values = values;
            this.limit = limit;
            this.index = index;
        }

        @Override
        public boolean hasNext()
        {
            return index > limit;
        }

        @Override
        public T next()
        {
            if (index <= limit) {
                throw new NoSuchElementException();
            }
            index -= 1;
            return values.get(index);
        }

        @Override
        public boolean isSplitAllowed()
        {
            return (index - limit) > 1;
        }

        @Nonnull
        @Override
        public SplitIterator splitIterator()
        {
            final int splitIndex = index - (index - limit) / 2;
            if (splitIndex == index) {
                throw new UnsupportedOperationException();
            }
            return new SplitIterator<>(new Reverse<>(values, index, splitIndex),
                                       new Reverse<>(values, splitIndex, limit));
        }
    }
}