/*

  *   SONEWS News Server

  *   see AUTHORS for the list of contributors

  *

  *   This program is free software: you can redistribute it and/or modify

  *   it under the terms of the GNU General Public License as published by

  *   the Free Software Foundation, either version 3 of the License, or

  *   (at your option) any later version.

  *

  *   This program is distributed in the hope that it will be useful,

  *   but WITHOUT ANY WARRANTY; without even the implied warranty of

  *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

  *   GNU General Public License for more details.

  *

  *   You should have received a copy of the GNU General Public License

  *   along with this program.  If not, see <http://www.gnu.org/licenses/>.

  */

 package org.sonews.storage.impl;

 import java.sql.Connection;

 import java.sql.DriverManager;

 import java.sql.ResultSet;

 import java.sql.SQLException;

 import java.sql.Statement;

 import java.sql.PreparedStatement;

 import java.util.ArrayList;

 import java.util.Enumeration;

 import java.util.List;

 import java.util.logging.Level;

 import java.util.regex.Matcher;

 import java.util.regex.Pattern;

 import java.util.regex.PatternSyntaxException;

 import javax.mail.Header;

 import javax.mail.internet.MimeUtility;

 import org.sonews.config.Config;

 import org.sonews.util.Log;

 import org.sonews.feed.Subscription;

 import org.sonews.storage.Article;

 import org.sonews.storage.ArticleHead;

 import org.sonews.storage.Channel;

 import org.sonews.storage.Group;

 import org.sonews.storage.Storage;

 import org.sonews.storage.StorageBackendException;

 import org.sonews.util.Pair;

 /**

  * JDBCDatabase facade class.

  * @author Christian Lins

  * @since sonews/0.5.0

  */

 // TODO: Refactor this class to reduce size (e.g. ArticleDatabase GroupDatabase)

 public class JDBCDatabase implements Storage

 {

 	public static final int MAX_RESTARTS = 2;

 	protected Connection conn = null;

 	protected PreparedStatement pstmtAddArticle1 = null;

 	protected PreparedStatement pstmtAddArticle2 = null;

 	protected PreparedStatement pstmtAddArticle3 = null;

 	protected PreparedStatement pstmtAddArticle4 = null;

 	protected PreparedStatement pstmtAddGroup0 = null;

 	protected PreparedStatement pstmtAddEvent = null;

 	protected PreparedStatement pstmtCountArticles = null;

 	protected PreparedStatement pstmtCountGroups = null;

 	protected PreparedStatement pstmtDeleteArticle0 = null;

 	protected PreparedStatement pstmtDeleteArticle1 = null;

 	protected PreparedStatement pstmtDeleteArticle2 = null;

 	protected PreparedStatement pstmtDeleteArticle3 = null;

 	protected PreparedStatement pstmtGetArticle0 = null;

 	protected PreparedStatement pstmtGetArticle1 = null;

 	protected PreparedStatement pstmtGetArticleHeaders0 = null;

 	protected PreparedStatement pstmtGetArticleHeaders1 = null;

 	protected PreparedStatement pstmtGetArticleHeads = null;

 	protected PreparedStatement pstmtGetArticleIDs = null;

 	protected PreparedStatement pstmtGetArticleIndex = null;

 	protected PreparedStatement pstmtGetConfigValue = null;

 	protected PreparedStatement pstmtGetEventsCount0 = null;

 	protected PreparedStatement pstmtGetEventsCount1 = null;

 	protected PreparedStatement pstmtGetGroupForList = null;

 	protected PreparedStatement pstmtGetGroup0 = null;

 	protected PreparedStatement pstmtGetGroup1 = null;

 	protected PreparedStatement pstmtGetFirstArticleNumber = null;

 	protected PreparedStatement pstmtGetListForGroup = null;

 	protected PreparedStatement pstmtGetLastArticleNumber = null;

 	protected PreparedStatement pstmtGetMaxArticleID = null;

 	protected PreparedStatement pstmtGetMaxArticleIndex = null;

 	protected PreparedStatement pstmtGetOldestArticle = null;

 	protected PreparedStatement pstmtGetPostingsCount = null;

 	protected PreparedStatement pstmtGetSubscriptions = null;

 	protected PreparedStatement pstmtIsArticleExisting = null;

 	protected PreparedStatement pstmtIsGroupExisting = null;

 	protected PreparedStatement pstmtPurgeGroup0 = null;

 	protected PreparedStatement pstmtPurgeGroup1 = null;

 	protected PreparedStatement pstmtSetConfigValue0 = null;

 	protected PreparedStatement pstmtSetConfigValue1 = null;

 	protected PreparedStatement pstmtUpdateGroup = null;

 	/** How many times the database connection was reinitialized */

 	protected int restarts = 0;

 	protected void prepareAddGroupStatement() throws SQLException {

 		this.pstmtAddGroup0 = conn.prepareStatement(

 				"INSERT INTO groups (name, flags) VALUES (?, ?)");

 	}

 	protected void prepareCountGroupsStatement() throws SQLException {

 		this.pstmtCountGroups = conn.prepareStatement(

 				"SELECT Count(group_id) FROM groups WHERE "

 				+ "flags & " + Channel.DELETED + " = 0");

 	}

 	protected void prepareGetPostingsCountStatement() throws SQLException {

 		this.pstmtGetPostingsCount = conn.prepareStatement(

 				"SELECT Count(*) FROM postings NATURAL JOIN groups "

 				+ "WHERE groups.name = ?");

 	}

 	protected void prepareGetSubscriptionsStatement() throws SQLException {

 		this.pstmtGetSubscriptions = conn.prepareStatement(

 				"SELECT host, port, name FROM peers NATURAL JOIN "

 				+ "peer_subscriptions NATURAL JOIN groups WHERE feedtype = ?");

 	}

 	/**

 	 * Rises the database: reconnect and recreate all prepared statements.

 	 * @throws java.lang.SQLException

 	 */

 	protected void arise()

 		throws SQLException

 	{

 		try {

 			// Load database driver

 			Class.forName(

 				Config.inst().get(Config.LEVEL_FILE, Config.STORAGE_DBMSDRIVER, "java.lang.Object"));

 			// Establish database connection

 			this.conn = DriverManager.getConnection(

 				Config.inst().get(Config.LEVEL_FILE, Config.STORAGE_DATABASE, "<not specified>"),

 				Config.inst().get(Config.LEVEL_FILE, Config.STORAGE_USER, "root"),

 				Config.inst().get(Config.LEVEL_FILE, Config.STORAGE_PASSWORD, ""));

 			this.conn.setTransactionIsolation(Connection.TRANSACTION_SERIALIZABLE);

 			if (this.conn.getTransactionIsolation() != Connection.TRANSACTION_SERIALIZABLE) {

 				Log.get().warning("Database is NOT fully serializable!");

 			}

 			// Prepare statements for method addArticle()

 			this.pstmtAddArticle1 = conn.prepareStatement(

 				"INSERT INTO articles (article_id, body) VALUES(?, ?)");

 			this.pstmtAddArticle2 = conn.prepareStatement(

 				"INSERT INTO headers (article_id, header_key, header_value, header_index) "

 				+ "VALUES (?, ?, ?, ?)");

 			this.pstmtAddArticle3 = conn.prepareStatement(

 				"INSERT INTO postings (group_id, article_id, article_index)"

 				+ "VALUES (?, ?, ?)");

 			this.pstmtAddArticle4 = conn.prepareStatement(

 				"INSERT INTO article_ids (article_id, message_id) VALUES (?, ?)");

 			// Prepare statement for method addStatValue()

 			this.pstmtAddEvent = conn.prepareStatement(

 				"INSERT INTO events VALUES (?, ?, ?)");

 			// Prepare statement for method addGroup()

 			prepareAddGroupStatement();

 			// Prepare statement for method countArticles()

 			this.pstmtCountArticles = conn.prepareStatement(

 				"SELECT Count(article_id) FROM article_ids");

 			// Prepare statement for method countGroups()

 			prepareCountGroupsStatement();

 			// Prepare statements for method delete(article)

 			this.pstmtDeleteArticle0 = conn.prepareStatement(

 				"DELETE FROM articles WHERE article_id = "

 				+ "(SELECT article_id FROM article_ids WHERE message_id = ?)");

 			this.pstmtDeleteArticle1 = conn.prepareStatement(

 				"DELETE FROM headers WHERE article_id = "

 				+ "(SELECT article_id FROM article_ids WHERE message_id = ?)");

 			this.pstmtDeleteArticle2 = conn.prepareStatement(

 				"DELETE FROM postings WHERE article_id = "

 				+ "(SELECT article_id FROM article_ids WHERE message_id = ?)");

 			this.pstmtDeleteArticle3 = conn.prepareStatement(

 				"DELETE FROM article_ids WHERE message_id = ?");

 			// Prepare statements for methods getArticle()

 			this.pstmtGetArticle0 = conn.prepareStatement(

 				"SELECT * FROM articles  WHERE article_id = "

 				+ "(SELECT article_id FROM article_ids WHERE message_id = ?)");

 			this.pstmtGetArticle1 = conn.prepareStatement(

 				"SELECT * FROM articles WHERE article_id = "

 				+ "(SELECT article_id FROM postings WHERE "

 				+ "article_index = ? AND group_id = ?)");

 			// Prepare statement for method getArticleHeaders()

 			this.pstmtGetArticleHeaders0 = conn.prepareStatement(

 				"SELECT header_key, header_value FROM headers WHERE article_id = ? "

 				+ "ORDER BY header_index ASC");

 			// Prepare statement for method getArticleHeaders(regular expr pattern)

 			this.pstmtGetArticleHeaders1 = conn.prepareStatement(

 				"SELECT p.article_index, h.header_value FROM headers h "

 				+ "INNER JOIN postings p ON h.article_id = p.article_id "

 				+ "INNER JOIN groups g ON p.group_id = g.group_id "

 				+ "WHERE g.name          =  ? AND "

 				+ "h.header_key    =  ? AND "

 				+ "p.article_index >= ? "

 				+ "ORDER BY p.article_index ASC");

 			this.pstmtGetArticleIDs = conn.prepareStatement(

 				"SELECT article_index FROM postings WHERE group_id = ?");

 			// Prepare statement for method getArticleIndex

 			this.pstmtGetArticleIndex = conn.prepareStatement(

 				"SELECT article_index FROM postings WHERE "

 				+ "article_id = (SELECT article_id FROM article_ids "

 				+ "WHERE message_id = ?) "

 				+ " AND group_id = ?");

 			// Prepare statements for method getArticleHeads()

 			this.pstmtGetArticleHeads = conn.prepareStatement(

 				"SELECT article_id, article_index FROM postings WHERE "

 				+ "postings.group_id = ? AND article_index >= ? AND "

 				+ "article_index <= ?");

 			// Prepare statements for method getConfigValue()

 			this.pstmtGetConfigValue = conn.prepareStatement(

 				"SELECT config_value FROM config WHERE config_key = ?");

 			// Prepare statements for method getEventsCount()

 			this.pstmtGetEventsCount0 = conn.prepareStatement(

 				"SELECT Count(*) FROM events WHERE event_key = ? AND "

 				+ "event_time >= ? AND event_time < ?");

 			this.pstmtGetEventsCount1 = conn.prepareStatement(

 				"SELECT Count(*) FROM events WHERE event_key = ? AND "

 				+ "event_time >= ? AND event_time < ? AND group_id = ?");

 			// Prepare statement for method getGroupForList()

 			this.pstmtGetGroupForList = conn.prepareStatement(

 				"SELECT name FROM groups INNER JOIN groups2list "

 				+ "ON groups.group_id = groups2list.group_id "

 				+ "WHERE groups2list.listaddress = ?");

 			// Prepare statement for method getGroup()

 			this.pstmtGetGroup0 = conn.prepareStatement(

 				"SELECT group_id, flags FROM groups WHERE Name = ?");

 			this.pstmtGetGroup1 = conn.prepareStatement(

 				"SELECT name FROM groups WHERE group_id = ?");

 			// Prepare statement for method getLastArticleNumber()

 			this.pstmtGetLastArticleNumber = conn.prepareStatement(

 				"SELECT Max(article_index) FROM postings WHERE group_id = ?");

 			// Prepare statement for method getListForGroup()

 			this.pstmtGetListForGroup = conn.prepareStatement(

 				"SELECT listaddress FROM groups2list INNER JOIN groups "

 				+ "ON groups.group_id = groups2list.group_id WHERE name = ?");

 			// Prepare statement for method getMaxArticleID()

 			this.pstmtGetMaxArticleID = conn.prepareStatement(

 				"SELECT Max(article_id) FROM articles");

 			// Prepare statement for method getMaxArticleIndex()

 			this.pstmtGetMaxArticleIndex = conn.prepareStatement(

 				"SELECT Max(article_index) FROM postings WHERE group_id = ?");

 			// Prepare statement for method getOldestArticle()

 			this.pstmtGetOldestArticle = conn.prepareStatement(

 				"SELECT message_id FROM article_ids WHERE article_id = "

 				+ "(SELECT Min(article_id) FROM article_ids)");

 			// Prepare statement for method getFirstArticleNumber()

 			this.pstmtGetFirstArticleNumber = conn.prepareStatement(

 				"SELECT Min(article_index) FROM postings WHERE group_id = ?");

 			// Prepare statement for method getPostingsCount()

 			prepareGetPostingsCountStatement();

 			// Prepare statement for method getSubscriptions()

 			prepareGetSubscriptionsStatement();

 			// Prepare statement for method isArticleExisting()

 			this.pstmtIsArticleExisting = conn.prepareStatement(

 				"SELECT Count(article_id) FROM article_ids WHERE message_id = ?");

 			// Prepare statement for method isGroupExisting()

 			this.pstmtIsGroupExisting = conn.prepareStatement(

 				"SELECT * FROM groups WHERE name = ?");

 			// Prepare statement for method setConfigValue()

 			this.pstmtSetConfigValue0 = conn.prepareStatement(

 				"DELETE FROM config WHERE config_key = ?");

 			this.pstmtSetConfigValue1 = conn.prepareStatement(

 				"INSERT INTO config VALUES(?, ?)");

 			// Prepare statements for method purgeGroup()

 			this.pstmtPurgeGroup0 = conn.prepareStatement(

 				"DELETE FROM peer_subscriptions WHERE group_id = ?");

 			this.pstmtPurgeGroup1 = conn.prepareStatement(

 				"DELETE FROM groups WHERE group_id = ?");

 			// Prepare statement for method update(Group)

 			this.pstmtUpdateGroup = conn.prepareStatement(

 				"UPDATE groups SET flags = ?, name = ? WHERE group_id = ?");

 		} catch (ClassNotFoundException ex) {

 			throw new Error("JDBC Driver not found!", ex);

 		}

 	}

 	/**

 	 * Adds an article to the database.

 	 * @param article

 	 * @return

 	 * @throws java.sql.SQLException

 	 */

 	@Override

 	public void addArticle(final Article article)

 		throws StorageBackendException

 	{

 		try {

 			this.conn.setAutoCommit(false);

 			int newArticleID = getMaxArticleID() + 1;

 			addArticle(article, newArticleID);

 			this.conn.commit();

 			this.conn.setAutoCommit(true);

 			this.restarts = 0; // Reset error count

 		} catch (SQLException ex) {

 			try {

 				this.conn.rollback();  // Rollback changes

 			} catch (SQLException ex2) {

 				Log.get().severe("Rollback of addArticle() failed: " + ex2);

 			}

 			try {

 				this.conn.setAutoCommit(true); // and release locks

 			} catch (SQLException ex2) {

 				Log.get().severe("setAutoCommit(true) of addArticle() failed: " + ex2);

 			}

 			restartConnection(ex);

 			addArticle(article);

 		}

 	}

 	/**

 	 * Adds an article to the database.

 	 * @param article

 	 * @return

 	 * @throws java.sql.SQLException

 	 */

 	void addArticle(final Article article, final int newArticleID)

 		throws SQLException, StorageBackendException

 	{

 		// Fill prepared statement with values;

 		// writes body to article table

 		pstmtAddArticle1.setInt(1, newArticleID);

 		pstmtAddArticle1.setBytes(2, article.getBody());

 		pstmtAddArticle1.execute();

 		// Add headers

 		Enumeration headers = article.getAllHeaders();

 		for (int n = 0; headers.hasMoreElements(); n++) {

 			Header header = (Header) headers.nextElement();

 			pstmtAddArticle2.setInt(1, newArticleID);

 			pstmtAddArticle2.setString(2, header.getName().toLowerCase());

 			pstmtAddArticle2.setString(3,

 				header.getValue().replaceAll("[\r\n]", ""));

 			pstmtAddArticle2.setInt(4, n);

 			pstmtAddArticle2.execute();

 		}

 		// For each newsgroup add a reference

 		List<Group> groups = article.getGroups();

 		for (Group group : groups) {

 			pstmtAddArticle3.setLong(1, group.getInternalID());

 			pstmtAddArticle3.setInt(2, newArticleID);

 			pstmtAddArticle3.setLong(3, getMaxArticleIndex(group.getInternalID()) + 1);

 			pstmtAddArticle3.execute();

 		}

 		// Write message-id to article_ids table

 		this.pstmtAddArticle4.setInt(1, newArticleID);

 		this.pstmtAddArticle4.setString(2, article.getMessageID());

 		this.pstmtAddArticle4.execute();

 	}

 	/**

 	 * Adds a group to the JDBCDatabase. This method is not accessible via NNTP.

 	 * @param name

 	 * @throws java.sql.SQLException

 	 */

 	@Override

 	public void addGroup(String name, int flags)

 		throws StorageBackendException

 	{

 		try {

 			this.conn.setAutoCommit(false);

 			pstmtAddGroup0.setString(1, name);

 			pstmtAddGroup0.setInt(2, flags);

 			pstmtAddGroup0.executeUpdate();

 			this.conn.commit();

 			this.conn.setAutoCommit(true);

 			this.restarts = 0; // Reset error count

 		} catch (SQLException ex) {

 			try {

 				this.conn.rollback();

 				this.conn.setAutoCommit(true);

 			} catch (SQLException ex2) {

 				ex2.printStackTrace();

 			}

 			restartConnection(ex);

 			addGroup(name, flags);

 		}

 	}

 	@Override

 	public void addEvent(long time, int type, long gid)

 		throws StorageBackendException

 	{

 		try {

 			this.conn.setAutoCommit(false);

 			this.pstmtAddEvent.setLong(1, time);

 			this.pstmtAddEvent.setInt(2, type);

 			this.pstmtAddEvent.setLong(3, gid);

 			this.pstmtAddEvent.executeUpdate();

 			this.conn.commit();

 			this.conn.setAutoCommit(true);

 			this.restarts = 0;

 		} catch (SQLException ex) {

 			try {

 				this.conn.rollback();

 				this.conn.setAutoCommit(true);

 			} catch (SQLException ex2) {

 				ex2.printStackTrace();

 			}

 			restartConnection(ex);

 			addEvent(time, type, gid);

 		}

 	}

 	@Override

 	public int countArticles()

 		throws StorageBackendException

 	{

 		ResultSet rs = null;

 		try {

 			rs = this.pstmtCountArticles.executeQuery();

 			if (rs.next()) {

 				return rs.getInt(1);

 			} else {

 				return -1;

 			}

 		} catch (SQLException ex) {

 			restartConnection(ex);

 			return countArticles();

 		} finally {

 			if (rs != null) {

 				try {

 					rs.close();

 				} catch (SQLException ex) {

 					ex.printStackTrace();

 				}

 				restarts = 0;

 			}

 		}

 	}

 	@Override

 	public int countGroups()

 		throws StorageBackendException

 	{

 		ResultSet rs = null;

 		try {

 			rs = this.pstmtCountGroups.executeQuery();

 			if (rs.next()) {

 				return rs.getInt(1);

 			} else {

 				return -1;

 			}

 		} catch (SQLException ex) {

 			restartConnection(ex);

 			return countGroups();

 		} finally {

 			if (rs != null) {

 				try {

 					rs.close();

 				} catch (SQLException ex) {

 					ex.printStackTrace();

 				}

 				restarts = 0;

 			}

 		}

 	}

 	@Override

 	public void delete(final String messageID)

 		throws StorageBackendException

 	{

 		try {

 			this.conn.setAutoCommit(false);

 			this.pstmtDeleteArticle0.setString(1, messageID);

 			int rs = this.pstmtDeleteArticle0.executeUpdate();

 			// We do not trust the ON DELETE CASCADE functionality to delete

 			// orphaned references...

 			this.pstmtDeleteArticle1.setString(1, messageID);

 			rs = this.pstmtDeleteArticle1.executeUpdate();

 			this.pstmtDeleteArticle2.setString(1, messageID);

 			rs = this.pstmtDeleteArticle2.executeUpdate();

 			this.pstmtDeleteArticle3.setString(1, messageID);

 			rs = this.pstmtDeleteArticle3.executeUpdate();

 			this.conn.commit();

 			this.conn.setAutoCommit(true);

 		} catch (SQLException ex) {

 			throw new StorageBackendException(ex);

 		}

 	}

 	@Override

 	public Article getArticle(String messageID)

 		throws StorageBackendException

 	{

 		ResultSet rs = null;

 		try {

 			pstmtGetArticle0.setString(1, messageID);

 			rs = pstmtGetArticle0.executeQuery();

 			if (!rs.next()) {

 				return null;

 			} else {

 				byte[] body = rs.getBytes("body");

 				String headers = getArticleHeaders(rs.getInt("article_id"));

 				return new Article(headers, body);

 			}

 		} catch (SQLException ex) {

 			restartConnection(ex);

 			return getArticle(messageID);

 		} finally {

 			if (rs != null) {

 				try {

 					rs.close();

 				} catch (SQLException ex) {

 					ex.printStackTrace();

 				}

 				restarts = 0; // Reset error count

 			}

 		}

 	}

 	/**

 	 * Retrieves an article by its ID.

 	 * @param articleID

 	 * @return

 	 * @throws StorageBackendException

 	 */

 	@Override

 	public Article getArticle(long articleIndex, long gid)

 		throws StorageBackendException

 	{

 		ResultSet rs = null;

 		try {

 			this.pstmtGetArticle1.setLong(1, articleIndex);

 			this.pstmtGetArticle1.setLong(2, gid);

 			rs = this.pstmtGetArticle1.executeQuery();

 			if (rs.next()) {

 				byte[] body = rs.getBytes("body");

 				String headers = getArticleHeaders(rs.getInt("article_id"));

 				return new Article(headers, body);

 			} else {

 				return null;

 			}

 		} catch (SQLException ex) {

 			restartConnection(ex);

 			return getArticle(articleIndex, gid);

 		} finally {

 			if (rs != null) {

 				try {

 					rs.close();

 				} catch (SQLException ex) {

 					ex.printStackTrace();

 				}

 				restarts = 0;

 			}

 		}

 	}

 	/**

 	 * Searches for fitting header values using the given regular expression.

 	 * @param group

 	 * @param start

 	 * @param end

 	 * @param headerKey

 	 * @param pattern

 	 * @return

 	 * @throws StorageBackendException

 	 */

 	@Override

 	public List<Pair<Long, String>> getArticleHeaders(Channel group, long start,

 		long end, String headerKey, String patStr)

 		throws StorageBackendException, PatternSyntaxException

 	{

 		ResultSet rs = null;

 		List<Pair<Long, String>> heads = new ArrayList<Pair<Long, String>>();

 		try {

 			this.pstmtGetArticleHeaders1.setString(1, group.getName());

 			this.pstmtGetArticleHeaders1.setString(2, headerKey);

 			this.pstmtGetArticleHeaders1.setLong(3, start);

 			rs = this.pstmtGetArticleHeaders1.executeQuery();

 			// Convert the "NNTP" regex to Java regex

 			patStr = patStr.replace("*", ".*");

 			Pattern pattern = Pattern.compile(patStr);

 			while (rs.next()) {

 				Long articleIndex = rs.getLong(1);

 				if (end < 0 || articleIndex <= end) // Match start is done via SQL

 				{

 					String headerValue = rs.getString(2);

 					Matcher matcher = pattern.matcher(headerValue);

 					if (matcher.matches()) {

 						heads.add(new Pair<Long, String>(articleIndex, headerValue));

 					}

 				}

 			}

 		} catch (SQLException ex) {

 			restartConnection(ex);

 			return getArticleHeaders(group, start, end, headerKey, patStr);

 		} finally {

 			if (rs != null) {

 				try {

 					rs.close();

 				} catch (SQLException ex) {

 					ex.printStackTrace();

 				}

 			}

 		}

 		return heads;

 	}

 	private String getArticleHeaders(long articleID)

 		throws StorageBackendException

 	{

 		ResultSet rs = null;

 		try {

 			this.pstmtGetArticleHeaders0.setLong(1, articleID);

 			rs = this.pstmtGetArticleHeaders0.executeQuery();

 			StringBuilder buf = new StringBuilder();

 			if (rs.next()) {

 				for (;;) {

 					buf.append(rs.getString(1)); // key

 					buf.append(": ");

 					String foldedValue = MimeUtility.fold(0, rs.getString(2));

 					buf.append(foldedValue); // value

 					if (rs.next()) {

 						buf.append("\r\n");

 					} else {

 						break;

 					}

 				}

 			}

 			return buf.toString();

 		} catch (SQLException ex) {

 			restartConnection(ex);

 			return getArticleHeaders(articleID);

 		} finally {

 			if (rs != null) {

 				try {

 					rs.close();

 				} catch (SQLException ex) {

 					ex.printStackTrace();

 				}

 			}

 		}

 	}

 	@Override

 	public long getArticleIndex(Article article, Group group)

 		throws StorageBackendException

 	{

 		ResultSet rs = null;

 		try {

 			this.pstmtGetArticleIndex.setString(1, article.getMessageID());

 			this.pstmtGetArticleIndex.setLong(2, group.getInternalID());

 			rs = this.pstmtGetArticleIndex.executeQuery();

 			if (rs.next()) {

 				return rs.getLong(1);

 			} else {

 				return -1;

 			}

 		} catch (SQLException ex) {

 			restartConnection(ex);

 			return getArticleIndex(article, group);

 		} finally {

 			if (rs != null) {

 				try {

 					rs.close();

 				} catch (SQLException ex) {

 					ex.printStackTrace();

 				}

 			}

 		}

 	}

 	/**

 	 * Returns a list of Long/Article Pairs.

 	 * @throws java.sql.SQLException

 	 */

 	@Override

 	public List<Pair<Long, ArticleHead>> getArticleHeads(Group group, long first,

 		long last)

 		throws StorageBackendException

 	{

 		ResultSet rs = null;

 		try {

 			this.pstmtGetArticleHeads.setLong(1, group.getInternalID());

 			this.pstmtGetArticleHeads.setLong(2, first);

 			this.pstmtGetArticleHeads.setLong(3, last);

 			rs = pstmtGetArticleHeads.executeQuery();

 			List<Pair<Long, ArticleHead>> articles = new ArrayList<Pair<Long, ArticleHead>>();

 			while (rs.next()) {

 				long aid = rs.getLong("article_id");

 				long aidx = rs.getLong("article_index");

 				String headers = getArticleHeaders(aid);

 				articles.add(new Pair<Long, ArticleHead>(aidx,

 					new ArticleHead(headers)));

 			}

 			return articles;

 		} catch (SQLException ex) {

 			restartConnection(ex);

 			return getArticleHeads(group, first, last);

 		} finally {

 			if (rs != null) {

 				try {

 					rs.close();

 				} catch (SQLException ex) {

 					ex.printStackTrace();

 				}

 			}

 		}

 	}

 	@Override

 	public List<Long> getArticleNumbers(long gid)

 		throws StorageBackendException

 	{

 		ResultSet rs = null;

 		try {

 			List<Long> ids = new ArrayList<Long>();

 			this.pstmtGetArticleIDs.setLong(1, gid);

 			rs = this.pstmtGetArticleIDs.executeQuery();

 			while (rs.next()) {

 				ids.add(rs.getLong(1));

 			}

 			return ids;

 		} catch (SQLException ex) {

 			restartConnection(ex);

 			return getArticleNumbers(gid);

 		} finally {

 			if (rs != null) {

 				try {

 					rs.close();

 					restarts = 0; // Clear the restart count after successful request

 				} catch (SQLException ex) {

 					ex.printStackTrace();

 				}

 			}

 		}

 	}

 	@Override

 	public String getConfigValue(String key)

 		throws StorageBackendException

 	{

 		ResultSet rs = null;

 		try {

 			this.pstmtGetConfigValue.setString(1, key);

 			rs = this.pstmtGetConfigValue.executeQuery();

 			if (rs.next()) {

 				return rs.getString(1); // First data on index 1 not 0

 			} else {

 				return null;

 			}

 		} catch (SQLException ex) {

 			restartConnection(ex);

 			return getConfigValue(key);

 		} finally {

 			if (rs != null) {

 				try {

 					rs.close();

 				} catch (SQLException ex) {

 					ex.printStackTrace();

 				}

 				restarts = 0; // Clear the restart count after successful request

 			}

 		}

 	}

 	@Override

 	public int getEventsCount(int type, long start, long end, Channel channel)

 		throws StorageBackendException

 	{

 		ResultSet rs = null;

 		try {

 			if (channel == null) {

 				this.pstmtGetEventsCount0.setInt(1, type);

 				this.pstmtGetEventsCount0.setLong(2, start);

 				this.pstmtGetEventsCount0.setLong(3, end);

 				rs = this.pstmtGetEventsCount0.executeQuery();

 			} else {

 				this.pstmtGetEventsCount1.setInt(1, type);

 				this.pstmtGetEventsCount1.setLong(2, start);

 				this.pstmtGetEventsCount1.setLong(3, end);

 				this.pstmtGetEventsCount1.setLong(4, channel.getInternalID());

 				rs = this.pstmtGetEventsCount1.executeQuery();

 			}

 			if (rs.next()) {

 				return rs.getInt(1);

 			} else {

 				return -1;

 			}

 		} catch (SQLException ex) {

 			restartConnection(ex);

 			return getEventsCount(type, start, end, channel);

 		} finally {

 			if (rs != null) {

 				try {

 					rs.close();

 				} catch (SQLException ex) {

 					ex.printStackTrace();

 				}

 			}

 		}

 	}

 	/**

 	 * Reads all Groups from the JDBCDatabase.

 	 * @return

 	 * @throws StorageBackendException

 	 */

 	@Override

 	public List<Channel> getGroups()

 		throws StorageBackendException

 	{

 		ResultSet rs;

 		List<Channel> buffer = new ArrayList<Channel>();

 		Statement stmt = null;

 		try {

 			stmt = conn.createStatement();

 			rs = stmt.executeQuery("SELECT * FROM groups ORDER BY name");

 			while (rs.next()) {

 				String name = rs.getString("name");

 				long id = rs.getLong("group_id");

 				int flags = rs.getInt("flags");

 				Group group = new Group(name, id, flags);

 				buffer.add(group);

 			}

 			return buffer;

 		} catch (SQLException ex) {

 			restartConnection(ex);

 			return getGroups();

 		} finally {

 			if (stmt != null) {

 				try {

 					stmt.close(); // Implicitely closes ResultSets

 				} catch (SQLException ex) {

 					ex.printStackTrace();

 				}

 			}

 		}

 	}

 	@Override

 	public List<String> getGroupsForList(String listAddress)

 		throws StorageBackendException

 	{

 		ResultSet rs = null;

 		try {

 			this.pstmtGetGroupForList.setString(1, listAddress);

 			rs = this.pstmtGetGroupForList.executeQuery();

 			List<String> groups = new ArrayList<String>();

 			while (rs.next()) {

 				String group = rs.getString(1);

 				groups.add(group);

 			}

 			return groups;

 		} catch (SQLException ex) {

 			restartConnection(ex);

 			return getGroupsForList(listAddress);

 		} finally {

 			if (rs != null) {

 				try {

 					rs.close();

 				} catch (SQLException ex) {

 					ex.printStackTrace();

 				}

 			}

 		}

 	}

 	/**

 	 * Returns the Group that is identified by the name.

 	 * @param name

 	 * @return

 	 * @throws StorageBackendException

 	 */

 	@Override

 	public Group getGroup(String name)

 		throws StorageBackendException

 	{

 		ResultSet rs = null;

 		try {

 			this.pstmtGetGroup0.setString(1, name);

 			rs = this.pstmtGetGroup0.executeQuery();

 			if (!rs.next()) {

 				return null;

 			} else {

 				long id = rs.getLong("group_id");

 				int flags = rs.getInt("flags");

 				return new Group(name, id, flags);

 			}

 		} catch (SQLException ex) {

 			restartConnection(ex);

 			return getGroup(name);

 		} finally {

 			if (rs != null) {

 				try {

 					rs.close();

 				} catch (SQLException ex) {

 					ex.printStackTrace();

 				}

 			}

 		}

 	}

 	@Override

 	public List<String> getListsForGroup(String group)

 		throws StorageBackendException

 	{

 		ResultSet rs = null;

 		List<String> lists = new ArrayList<String>();

 		try {

 			this.pstmtGetListForGroup.setString(1, group);

 			rs = this.pstmtGetListForGroup.executeQuery();

 			while (rs.next()) {

 				lists.add(rs.getString(1));

 			}

 			return lists;

 		} catch (SQLException ex) {

 			restartConnection(ex);

 			return getListsForGroup(group);

 		} finally {

 			if (rs != null) {

 				try {

 					rs.close();

 				} catch (SQLException ex) {

 					ex.printStackTrace();

 				}

 			}

 		}

 	}

 	private int getMaxArticleIndex(long groupID)

 		throws StorageBackendException

 	{

 		ResultSet rs = null;

 		try {

 			this.pstmtGetMaxArticleIndex.setLong(1, groupID);

 			rs = this.pstmtGetMaxArticleIndex.executeQuery();

 			int maxIndex = 0;

 			if (rs.next()) {

 				maxIndex = rs.getInt(1);

 			}

 			return maxIndex;

 		} catch (SQLException ex) {

 			restartConnection(ex);

 			return getMaxArticleIndex(groupID);

 		} finally {

 			if (rs != null) {

 				try {

 					rs.close();

 				} catch (SQLException ex) {

 					ex.printStackTrace();

 				}

 			}

 		}

 	}

 	private int getMaxArticleID()

 		throws StorageBackendException

 	{

 		ResultSet rs = null;

 		try {

 			rs = this.pstmtGetMaxArticleID.executeQuery();

 			int maxIndex = 0;

 			if (rs.next()) {

 				maxIndex = rs.getInt(1);

 			}

 			return maxIndex;

 		} catch (SQLException ex) {

 			restartConnection(ex);

 			return getMaxArticleID();

 		} finally {

 			if (rs != null) {

 				try {

 					rs.close();

 				} catch (SQLException ex) {

 					ex.printStackTrace();

 				}

 			}

 		}

 	}

 	@Override

 	public int getLastArticleNumber(Group group)

 		throws StorageBackendException

 	{

 		ResultSet rs = null;

 		try {

 			this.pstmtGetLastArticleNumber.setLong(1, group.getInternalID());

 			rs = this.pstmtGetLastArticleNumber.executeQuery();

 			if (rs.next()) {

 				return rs.getInt(1);

 			} else {

 				return 0;

 			}

 		} catch (SQLException ex) {

 			restartConnection(ex);

 			return getLastArticleNumber(group);

 		} finally {

 			if (rs != null) {

 				try {

 					rs.close();

 				} catch (SQLException ex) {

 					ex.printStackTrace();

 				}

 			}

 		}

 	}

 	@Override

 	public int getFirstArticleNumber(Group group)

 		throws StorageBackendException

 	{

 		ResultSet rs = null;

 		try {

 			this.pstmtGetFirstArticleNumber.setLong(1, group.getInternalID());

 			rs = this.pstmtGetFirstArticleNumber.executeQuery();

 			if (rs.next()) {

 				return rs.getInt(1);

 			} else {

 				return 0;

 			}

 		} catch (SQLException ex) {

 			restartConnection(ex);

 			return getFirstArticleNumber(group);

 		} finally {

 			if (rs != null) {

 				try {

 					rs.close();

 				} catch (SQLException ex) {

 					ex.printStackTrace();

 				}

 			}

 		}

 	}

 	/**

 	 * Returns a group name identified by the given id.

 	 * @param id

 	 * @return

 	 * @throws StorageBackendException

 	 */

 	public String getGroup(int id)

 		throws StorageBackendException

 	{

 		ResultSet rs = null;

 		try {

 			this.pstmtGetGroup1.setInt(1, id);

 			rs = this.pstmtGetGroup1.executeQuery();

 			if (rs.next()) {

 				return rs.getString(1);

 			} else {

 				return null;

 			}

 		} catch (SQLException ex) {

 			restartConnection(ex);

 			return getGroup(id);

 		} finally {

 			if (rs != null) {

 				try {

 					rs.close();

 				} catch (SQLException ex) {

 					ex.printStackTrace();

 				}

 			}

 		}

 	}

 	@Override

 	public double getEventsPerHour(int key, long gid)

 		throws StorageBackendException

 	{

 		String gidquery = "";

 		if (gid >= 0) {

 			gidquery = " AND group_id = " + gid;

 		}

 		Statement stmt = null;

 		ResultSet rs = null;

 		try {

 			stmt = this.conn.createStatement();

 			rs = stmt.executeQuery("SELECT Count(*) / (Max(event_time) - Min(event_time))"

 				+ " * 1000 * 60 * 60 FROM events WHERE event_key = " + key + gidquery);

 			if (rs.next()) {

 				restarts = 0; // reset error count

 				return rs.getDouble(1);

 			} else {

 				return Double.NaN;

 			}

 		} catch (SQLException ex) {

 			restartConnection(ex);

 			return getEventsPerHour(key, gid);

 		} finally {

 			try {

 				if (stmt != null) {

 					stmt.close(); // Implicitely closes the result sets

 				}

 			} catch (SQLException ex) {

 				ex.printStackTrace();

 			}

 		}

 	}

 	@Override

 	public String getOldestArticle()

 		throws StorageBackendException

 	{

 		ResultSet rs = null;

 		try {

 			rs = this.pstmtGetOldestArticle.executeQuery();

 			if (rs.next()) {

 				return rs.getString(1);

 			} else {

 				return null;

 			}

 		} catch (SQLException ex) {

 			restartConnection(ex);

 			return getOldestArticle();

 		} finally {

 			if (rs != null) {

 				try {

 					rs.close();

 				} catch (SQLException ex) {

 					ex.printStackTrace();

 				}

 			}

 		}

 	}

 	@Override

 	public int getPostingsCount(String groupname)

 		throws StorageBackendException

 	{

 		ResultSet rs = null;

 		try {

 			this.pstmtGetPostingsCount.setString(1, groupname);

 			rs = this.pstmtGetPostingsCount.executeQuery();

 			if (rs.next()) {

 				return rs.getInt(1);

 			} else {

 				Log.get().warning("Count on postings return nothing!");

 				return 0;

 			}

 		} catch (SQLException ex) {

 			restartConnection(ex);

 			return getPostingsCount(groupname);

 		} finally {

 			if (rs != null) {

 				try {

 					rs.close();

 				} catch (SQLException ex) {

 					ex.printStackTrace();

 				}

 			}

 		}

 	}

 	@Override

 	public List<Subscription> getSubscriptions(int feedtype)

 		throws StorageBackendException

 	{

 		ResultSet rs = null;

 		try {

 			List<Subscription> subs = new ArrayList<Subscription>();

 			this.pstmtGetSubscriptions.setInt(1, feedtype);

 			rs = this.pstmtGetSubscriptions.executeQuery();

 			while (rs.next()) {

 				String host = rs.getString("host");

 				String group = rs.getString("name");

 				int port = rs.getInt("port");

 				subs.add(new Subscription(host, port, feedtype, group));

 			}

 			return subs;

 		} catch (SQLException ex) {

 			restartConnection(ex);

 			return getSubscriptions(feedtype);

 		} finally {

 			if (rs != null) {

 				try {

 					rs.close();

 				} catch (SQLException ex) {

 					ex.printStackTrace();

 				}

 			}

 		}

 	}

 	/**

 	 * Checks if there is an article with the given messageid in the JDBCDatabase.

 	 * @param name

 	 * @return

 	 * @throws StorageBackendException

 	 */

 	@Override

 	public boolean isArticleExisting(String messageID)

 		throws StorageBackendException

 	{

 		ResultSet rs = null;

 		try {

 			this.pstmtIsArticleExisting.setString(1, messageID);

 			rs = this.pstmtIsArticleExisting.executeQuery();

 			return rs.next() && rs.getInt(1) == 1;

 		} catch (SQLException ex) {

 			restartConnection(ex);

 			return isArticleExisting(messageID);

 		} finally {

 			if (rs != null) {

 				try {

 					rs.close();

 				} catch (SQLException ex) {

 					ex.printStackTrace();

 				}

 			}

 		}

 	}

 	/**

 	 * Checks if there is a group with the given name in the JDBCDatabase.

 	 * @param name

 	 * @return

 	 * @throws StorageBackendException

 	 */

 	@Override

 	public boolean isGroupExisting(String name)

 		throws StorageBackendException

 	{

 		ResultSet rs = null;

 		try {

 			this.pstmtIsGroupExisting.setString(1, name);

 			rs = this.pstmtIsGroupExisting.executeQuery();

 			return rs.next();

 		} catch (SQLException ex) {

 			restartConnection(ex);

 			return isGroupExisting(name);

 		} finally {

 			if (rs != null) {

 				try {

 					rs.close();

 				} catch (SQLException ex) {

 					ex.printStackTrace();

 				}

 			}

 		}

 	}

 	@Override

 	public void setConfigValue(String key, String value)

 		throws StorageBackendException

 	{

 		try {

 			conn.setAutoCommit(false);

 			this.pstmtSetConfigValue0.setString(1, key);

 			this.pstmtSetConfigValue0.execute();

 			this.pstmtSetConfigValue1.setString(1, key);

 			this.pstmtSetConfigValue1.setString(2, value);

 			this.pstmtSetConfigValue1.execute();

 			conn.commit();

 			conn.setAutoCommit(true);

 		} catch (SQLException ex) {

 			restartConnection(ex);

 			setConfigValue(key, value);

 		}

 	}

 	/**

 	 * Closes the JDBCDatabase connection.

 	 */

 	public void shutdown()

 		throws StorageBackendException

 	{

 		try {

 			if (this.conn != null) {

 				this.conn.close();

 			}

 		} catch (SQLException ex) {

 			throw new StorageBackendException(ex);

 		}

 	}

 	@Override

 	public void purgeGroup(Group group)

 		throws StorageBackendException

 	{

 		try {

 			this.pstmtPurgeGroup0.setLong(1, group.getInternalID());

 			this.pstmtPurgeGroup0.executeUpdate();

 			this.pstmtPurgeGroup1.setLong(1, group.getInternalID());

 			this.pstmtPurgeGroup1.executeUpdate();

 		} catch (SQLException ex) {

 			restartConnection(ex);

 			purgeGroup(group);

 		}

 	}

 	protected void restartConnection(SQLException cause)

 		throws StorageBackendException

 	{

 		restarts++;

 		Log.get().log(Level.SEVERE, Thread.currentThread()

 			+ ": Database connection was closed (restart " + restarts + ").", cause);

 		if (restarts >= MAX_RESTARTS) {

 			// Delete the current, probably broken JDBCDatabase instance.

 			// So no one can use the instance any more.

 			JDBCDatabaseProvider.instances.remove(Thread.currentThread());

 			// Throw the exception upwards

 			throw new StorageBackendException(cause);

 		}

 		try {

 			Thread.sleep(1500L * restarts);

 		} catch (InterruptedException ex) {

 			Log.get().warning("Interrupted: " + ex.getMessage());

 		}

 		// Try to properly close the old database connection

 		try {

 			if (this.conn != null) {

 				this.conn.close();

 			}

 		} catch (SQLException ex) {

 			Log.get().warning(ex.getMessage());

 		}

 		try {

 			// Try to reinitialize database connection

 			arise();

 		} catch (SQLException ex) {

 			Log.get().warning(ex.getMessage());

 			restartConnection(ex);

 		}

 	}

 	@Override

 	public boolean update(Article article)

 		throws StorageBackendException

 	{

 		ResultSet rs = null;

 		try {

 			// Retrieve internal article_id

 			this.pstmtGetArticle0.setString(1, article.getMessageID());

 			rs = this.pstmtGetArticle0.executeQuery();

 			int articleID = rs.getInt("article_id");

 			delete(article.getMessageID());

 			this.conn.setAutoCommit(false);

 			addArticle(article, articleID);

 			this.conn.commit();

 			this.conn.setAutoCommit(true);

 			return true;

 		} catch (SQLException ex) {

 			try {

 				this.conn.rollback();

 			} catch(SQLException ex2) {

 				Log.get().severe("Rollback failed: " + ex2.getMessage());

 			}

 			restartConnection(ex);

 			return update(article);

 		}

 	}

 	/**

 	 * Writes the flags and the name of the given group to the database.

 	 * @param group

 	 * @throws StorageBackendException

 	 */

 	@Override

 	public boolean update(Group group)

 		throws StorageBackendException

 	{

 		try {

 			this.pstmtUpdateGroup.setInt(1, group.getFlags());

 			this.pstmtUpdateGroup.setString(2, group.getName());

 			this.pstmtUpdateGroup.setLong(3, group.getInternalID());

 			int rs = this.pstmtUpdateGroup.executeUpdate();

 			return rs == 1;

 		} catch (SQLException ex) {

 			restartConnection(ex);

 			return update(group);

 		}

 	}

 }