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/*
 * Copyright 2016-2019 Crown Copyright
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package uk.gov.gchq.gaffer.commonutil.iterable;

import uk.gov.gchq.gaffer.commonutil.exception.LimitExceededException;

import java.util.Iterator;
import java.util.NoSuchElementException;

/**
 * An {@code LimitedCloseableIterator} is an {@link java.util.Iterator} which is
 * limited to a maximum size. This is achieved by iterating through the objects
 * contained in the iterator until the preconfigured starting point is reached
 * (and discarding these), then by retrieving objects until either:
 * 
 *     the end of the iterator is reached, or
 *     the iterator pointer exceeds the specified limit
 * 
 *
 * @param  the type of items in the iterator.
 */
public class LimitedCloseableIterator implements CloseableIterator {
    private final CloseableIterator iterator;
    private final Integer end;
    private int index = 0;
    private Boolean truncate = true;

    public LimitedCloseableIterator(final Iterator iterator, final int start, final Integer end) {
        this(iterator, start, end, true);
    }

    public LimitedCloseableIterator(final Iterator iterator, final int start, final Integer end, final Boolean truncate) {
        this(new WrappedCloseableIterator<>(iterator), start, end, truncate);
    }

    public LimitedCloseableIterator(final CloseableIterator iterator, final int start, final Integer end) {
        this(iterator, start, end, true);
    }

    public LimitedCloseableIterator(final CloseableIterator iterator, final int start, final Integer end, final Boolean truncate) {
        if (null != end && start > end) {
            throw new IllegalArgumentException("start should be less than end");
        }

        if (null == iterator) {
            this.iterator = new EmptyCloseableIterator<>();
        } else {
            this.iterator = iterator;
        }
        this.end = end;
        this.truncate = truncate;

        while (index < start && hasNext()) {
            next();
        }
    }

    @Override
    public void close() {
        iterator.close();
    }

    @Override
    public boolean hasNext() {
        final boolean withinLimit = (null == end || index < end);

        if (!withinLimit && !truncate && iterator.hasNext()) {
            // Throw an exception if we are - not within the limit, we don't want to truncate and there are items remaining.
            throw new LimitExceededException("Limit of " + end + " exceeded.");
        }

        final boolean hasNext = withinLimit && iterator.hasNext();
        if (!hasNext) {
            close();
        }

        return hasNext;
    }

    @Override
    public T next() {
        if (!hasNext()) {
            throw new NoSuchElementException();
        }

        index++;
        return iterator.next();
    }

    @Override
    public void remove() {
        throw new UnsupportedOperationException();
    }
}