/*

 *   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.daemon;

import java.io.IOException;

import java.net.InetSocketAddress;

import java.net.SocketException;

import java.nio.ByteBuffer;

import java.nio.CharBuffer;

import java.nio.channels.ClosedChannelException;

import java.nio.channels.SelectionKey;

import java.nio.channels.SocketChannel;

import java.nio.charset.Charset;

import java.util.Arrays;

import java.util.Timer;

import java.util.TimerTask;

import java.util.logging.Level;

import org.sonews.daemon.command.Command;

import org.sonews.storage.Article;

import org.sonews.storage.Group;

import org.sonews.storage.StorageBackendException;

import org.sonews.util.Log;

import org.sonews.util.Stats;

/**

 * For every SocketChannel (so TCP/IP connection) there is an instance of

 * this class.

 * @author Christian Lins

 * @since sonews/0.5.0

 */

public final class NNTPConnection {

	public static final String NEWLINE = "\r\n";    // RFC defines this as newline

	public static final String MESSAGE_ID_PATTERN = "<[^>]+>";

	private static final Timer cancelTimer = new Timer(true); // Thread-safe? True for run as daemon

	/** SocketChannel is generally thread-safe */

	private SocketChannel channel = null;

	private Charset charset = Charset.forName("UTF-8");

	private Command command = null;

	private Article currentArticle = null;

	private Group currentGroup = null;

	private volatile long lastActivity = System.currentTimeMillis();

	private ChannelLineBuffers lineBuffers = new ChannelLineBuffers();

	private int readLock = 0;

	private final Object readLockGate = new Object();

	private SelectionKey writeSelKey = null;

	public NNTPConnection(final SocketChannel channel)

			throws IOException {

		if (channel == null) {

			throw new IllegalArgumentException("channel is null");

		}

		this.channel = channel;

		Stats.getInstance().clientConnect();

	}

	/**

	 * Tries to get the read lock for this NNTPConnection. This method is Thread-

	 * safe and returns true of the read lock was successfully set. If the lock

	 * is still hold by another Thread the method returns false.

	 */

	boolean tryReadLock() {

		// As synchronizing simple types may cause deadlocks,

		// we use a gate object.

		synchronized (readLockGate) {

			if (readLock != 0) {

				return false;

			} else {

				readLock = Thread.currentThread().hashCode();

				return true;

			}

		}

	}

	/**

	 * Releases the read lock in a Thread-safe way.

	 * @throws IllegalMonitorStateException if a Thread not holding the lock

	 * tries to release it.

	 */

	void unlockReadLock() {

		synchronized (readLockGate) {

			if (readLock == Thread.currentThread().hashCode()) {

				readLock = 0;

			} else {

				throw new IllegalMonitorStateException();

			}

		}

	}

	/**

	 * @return Current input buffer of this NNTPConnection instance.

	 */

	public ByteBuffer getInputBuffer() {

		return this.lineBuffers.getInputBuffer();

	}

	/**

	 * @return Output buffer of this NNTPConnection which has at least one byte

	 * free storage.

	 */

	public ByteBuffer getOutputBuffer() {

		return this.lineBuffers.getOutputBuffer();

	}

	/**

	 * @return ChannelLineBuffers instance associated with this NNTPConnection.

	 */

	public ChannelLineBuffers getBuffers() {

		return this.lineBuffers;

	}

	/**

	 * @return true if this connection comes from a local remote address.

	 */

	public boolean isLocalConnection() {

		return ((InetSocketAddress) this.channel.socket().getRemoteSocketAddress()).getHostName().equalsIgnoreCase("localhost");

	}

	void setWriteSelectionKey(SelectionKey selKey) {

		this.writeSelKey = selKey;

	}

	public void shutdownInput() {

		try {

			// Closes the input line of the channel's socket, so no new data

			// will be received and a timeout can be triggered.

			this.channel.socket().shutdownInput();

		} catch (IOException ex) {

			Log.get().warning("Exception in NNTPConnection.shutdownInput(): " + ex);

		}

	}

	public void shutdownOutput() {

		cancelTimer.schedule(new TimerTask() {

			@Override

			public void run() {

				try {

					// Closes the output line of the channel's socket.

					channel.socket().shutdownOutput();

					channel.close();

				} catch (SocketException ex) {

					// Socket was already disconnected

					Log.get().info("NNTPConnection.shutdownOutput(): " + ex);

				} catch (Exception ex) {

					Log.get().warning("NNTPConnection.shutdownOutput(): " + ex);

				}

			}

		}, 3000);

	}

	public SocketChannel getSocketChannel() {

		return this.channel;

	}

	public Article getCurrentArticle() {

		return this.currentArticle;

	}

	public Charset getCurrentCharset() {

		return this.charset;

	}

	/**

	 * @return The currently selected communication channel (not SocketChannel)

	 */

	public Group getCurrentChannel() {

		return this.currentGroup;

	}

	public void setCurrentArticle(final Article article) {

		this.currentArticle = article;

	}

	public void setCurrentGroup(final Group group) {

		this.currentGroup = group;

	}

	public long getLastActivity() {

		return this.lastActivity;

	}

	/**

	 * Due to the readLockGate there is no need to synchronize this method.

	 * @param raw

	 * @throws IllegalArgumentException if raw is null.

	 * @throws IllegalStateException if calling thread does not own the readLock.

	 */

	void lineReceived(byte[] raw) {

		if (raw == null) {

			throw new IllegalArgumentException("raw is null");

		}

		if (readLock == 0 || readLock != Thread.currentThread().hashCode()) {

			throw new IllegalStateException("readLock not properly set");

		}

		this.lastActivity = System.currentTimeMillis();

		String line = new String(raw, this.charset);

		// There might be a trailing \r, but trim() is a bad idea

		// as it removes also leading spaces from long header lines.

		if (line.endsWith("\r")) {

			line = line.substring(0, line.length() - 1);

			raw = Arrays.copyOf(raw, raw.length - 1);

		}

		Log.get().fine("<< " + line);

		if (command == null) {

			command = parseCommandLine(line);

			assert command != null;

		}

		try {

			// The command object will process the line we just received

			try {

				command.processLine(this, line, raw);

			} catch (StorageBackendException ex) {

				Log.get().info("Retry command processing after StorageBackendException");

				// Try it a second time, so that the backend has time to recover

				command.processLine(this, line, raw);

			}

		} catch (ClosedChannelException ex0) {

			try {

				StringBuilder strBuf = new StringBuilder();

				strBuf.append("Connection to ");

				strBuf.append(channel.socket().getRemoteSocketAddress());

				strBuf.append(" closed: ");

				strBuf.append(ex0);

				Log.get().info(strBuf.toString());

			} catch (Exception ex0a) {

				ex0a.printStackTrace();

			}

		} catch (Exception ex1) { // This will catch a second StorageBackendException

			try {

				command = null;

				Log.get().log(Level.WARNING, ex1.getLocalizedMessage(), ex1);

				println("403 Internal server error");

				// Should we end the connection here?

				// RFC says we MUST return 400 before closing the connection

				shutdownInput();

				shutdownOutput();

			} catch (Exception ex2) {

				ex2.printStackTrace();

			}

		}

		if (command == null || command.hasFinished()) {

			command = null;

			charset = Charset.forName("UTF-8"); // Reset to default

		}

	}

	/**

	 * This method determines the fitting command processing class.

	 * @param line

	 * @return

	 */

	private Command parseCommandLine(String line) {

		String cmdStr = line.split(" ")[0];

		return CommandSelector.getInstance().get(cmdStr);

	}

	/**

	 * Puts the given line into the output buffer, adds a newline character

	 * and returns. The method returns immediately and does not block until

	 * the line was sent. If line is longer than 510 octets it is split up in

	 * several lines. Each line is terminated by \r\n (NNTPConnection.NEWLINE).

	 * @param line

	 */

	public void println(final CharSequence line, final Charset charset)

			throws IOException {

		writeToChannel(CharBuffer.wrap(line), charset, line);

		writeToChannel(CharBuffer.wrap(NEWLINE), charset, null);

	}

	/**

	 * Writes the given raw lines to the output buffers and finishes with

	 * a newline character (\r\n).

	 * @param rawLines

	 */

	public void println(final byte[] rawLines)

			throws IOException {

		this.lineBuffers.addOutputBuffer(ByteBuffer.wrap(rawLines));

		writeToChannel(CharBuffer.wrap(NEWLINE), charset, null);

	}

	/**

	 * Encodes the given CharBuffer using the given Charset to a bunch of

	 * ByteBuffers (each 512 bytes large) and enqueues them for writing at the

	 * connected SocketChannel.

	 * @throws java.io.IOException

	 */

	private void writeToChannel(CharBuffer characters, final Charset charset,

			CharSequence debugLine)

			throws IOException {

		if (!charset.canEncode()) {

			Log.get().severe("FATAL: Charset " + charset + " cannot encode!");

			return;

		}

		// Write characters to output buffers

		LineEncoder lenc = new LineEncoder(characters, charset);

		lenc.encode(lineBuffers);

		enableWriteEvents(debugLine);

	}

	private void enableWriteEvents(CharSequence debugLine) {

		// Enable OP_WRITE events so that the buffers are processed

		try {

			this.writeSelKey.interestOps(SelectionKey.OP_WRITE);

			ChannelWriter.getInstance().getSelector().wakeup();

		} catch (Exception ex) // CancelledKeyException and ChannelCloseException

		{

			Log.get().warning("NNTPConnection.writeToChannel(): " + ex);

			return;

		}

		// Update last activity timestamp

		this.lastActivity = System.currentTimeMillis();

		if (debugLine != null) {

			Log.get().fine(">> " + debugLine);

		}

	}

	public void println(final CharSequence line)

			throws IOException {

		println(line, charset);

	}

	public void print(final String line)

			throws IOException {

		writeToChannel(CharBuffer.wrap(line), charset, line);

	}

	public void setCurrentCharset(final Charset charset) {

		this.charset = charset;

	}

	void setLastActivity(long timestamp) {

		this.lastActivity = timestamp;

	}

}