//Dstl (c) Crown Copyright 2017
package uk.gov.dstl.baleen.collectionreaders.helpers;

import java.io.IOException;
import java.util.Iterator;

import org.apache.uima.UimaContext;
import org.apache.uima.collection.CollectionException;
import org.apache.uima.jcas.JCas;
import org.apache.uima.resource.ResourceInitializationException;

import uk.gov.dstl.baleen.exceptions.BaleenException;
import uk.gov.dstl.baleen.uima.BaleenCollectionReader;

/**
 * A collection reader that can be represented by an iterator, where each call to next() generates a
 * new document.
 *
 * @param <T>
 *            the generic type
 */
public abstract class AbstractIteratatorCollectionReader<T> extends BaleenCollectionReader {

	private Iterator<T> iterator;

	@Override
	protected final void doInitialize(UimaContext context) throws ResourceInitializationException {
		try {
			iterator = initializeIterator(context);
		} catch (final BaleenException e) {
			throw new ResourceInitializationException(e);
		}
	}

	@Override
	protected final void doGetNext(JCas jCas) throws IOException, CollectionException {
		final T next = iterator.next();
		apply(next, jCas);
	}

	@Override
	public final boolean doHasNext() throws IOException, CollectionException {
		return iterator.hasNext();
	}

	/**
	 * Create the iterator (called once)
	 *
	 * @param context
	 *            the context
	 * @return the iterator
	 * @throws BaleenException
	 *             the baleen exception
	 */
	protected abstract Iterator<T> initializeIterator(UimaContext context) throws BaleenException;

	/**
	 * Convert the return item from the iterator to a jcas.
	 *
	 * @param next
	 *            the next
	 * @param jCas
	 *            the j cas
	 */
	protected abstract void apply(T next, JCas jCas);

}