package eu.dnetlib.enabling.database.resultset;

import java.util.Iterator;
import java.util.Map;
import java.util.NoSuchElementException;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.TimeUnit;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import eu.dnetlib.enabling.database.rmi.DatabaseException;
import eu.dnetlib.enabling.database.utils.DatabaseUtils;
import eu.dnetlib.enabling.resultset.SizedIterable;

public class IterableRowSet implements SizedIterable<String> {

	private String db;
	private String sql;
	private String sqlForCount;
	private DatabaseUtils dbUtils;
	private Integer size = null;

	private static final Log log = LogFactory.getLog(IterableRowSet.class); // NOPMD by marko on 11/24/08 5:02 PM

	public IterableRowSet(final String db, final String sql, final String sqlForCount, final DatabaseUtils dbUtils) {
		super();
		this.db = db;
		this.sql = sql;
		this.sqlForCount = sqlForCount;
		this.dbUtils = dbUtils;
	}

	@Override
	@SuppressWarnings("unchecked")
	public Iterator<String> iterator() {
		try {
			final BlockingQueue<Map<String, Object>> queue = dbUtils.executeSql(db, sql, BlockingQueue.class);
			return new QueueIterator(queue);
		} catch (Exception e) {
			throw new RuntimeException("Error creating iterator for query: " + sql, e);
		}
	}

	@Override
	public int getNumberOfElements() {
		if (size != null) { return size; }

		String query = (sqlForCount == null) || sqlForCount.isEmpty() ? "SELECT count(*) FROM ( " + sql + " ) AS TABLELISTENER" : sqlForCount;

		try {
			log.debug("Calculating size using query: " + query);
			this.size = dbUtils.executeSql(db, query, Integer.class);
			return size;
		} catch (DatabaseException e) {
			log.error("Error in getSize, query: " + query, e);
			throw new IllegalStateException("Error in getSize, query: " + query, e);
		}

	}

	private class QueueIterator implements Iterator<String> {

		private Map<String, Object> curr;
		private BlockingQueue<Map<String, Object>> queue;

		public QueueIterator(final BlockingQueue<Map<String, Object>> queue) throws InterruptedException {
			super();
			this.queue = queue;
			this.curr = queue.poll(DatabaseUtils.BLOCKING_QUEUE_TIMEOUT, TimeUnit.SECONDS);
		}

		@Override
		public String next() {
			log.debug("Reading Next Element from queue");

			try {
				if ((curr == null) || curr.isEmpty()) { throw new NoSuchElementException(
						"Value from queue is null or empty, probably the producer doesn't produce"); }
				String res = dbUtils.rowToDocument(curr).asXML();
				curr = queue.poll(DatabaseUtils.BLOCKING_QUEUE_TIMEOUT, TimeUnit.SECONDS);
				return res;
			} catch (Exception e) {
				throw new NoSuchElementException("Error navigating rowset for query: " + sql + "\n" + e.getMessage());
			}
		}

		@Override
		public boolean hasNext() {
			// An empty Map indicates the end of the Queue
			return (curr != null) && !curr.isEmpty();
		}

		@Override
		public void remove() {}

	}

}