/*

 *   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 {