//
//  ========================================================================
//  Copyright (c) 1995-2017 Mort Bay Consulting Pty. Ltd.
//  ------------------------------------------------------------------------
//  All rights reserved. This program and the accompanying materials
//  are made available under the terms of the Eclipse Public License v1.0
//  and Apache License v2.0 which accompanies this distribution.
//
//      The Eclipse Public License is available at
//      http://www.eclipse.org/legal/epl-v10.html
//
//      The Apache License v2.0 is available at
//      http://www.opensource.org/licenses/apache2.0.php
//
//  You may elect to redistribute this code under either of these licenses.
//  ========================================================================
//

package org.eclipse.jetty.websocket.common.extensions.compress;

import java.io.ByteArrayOutputStream;
import java.nio.ByteBuffer;
import java.util.ArrayDeque;
import java.util.Queue;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.zip.DataFormatException;
import java.util.zip.Deflater;
import java.util.zip.Inflater;
import java.util.zip.ZipException;

import org.eclipse.jetty.util.BufferUtil;
import org.eclipse.jetty.util.IteratingCallback;
import org.eclipse.jetty.util.log.Log;
import org.eclipse.jetty.util.log.Logger;
import org.eclipse.jetty.websocket.api.BatchMode;
import org.eclipse.jetty.websocket.api.WriteCallback;
import org.eclipse.jetty.websocket.api.extensions.Frame;
import org.eclipse.jetty.websocket.common.OpCode;
import org.eclipse.jetty.websocket.common.extensions.AbstractExtension;
import org.eclipse.jetty.websocket.common.frames.DataFrame;

public abstract class CompressExtension extends AbstractExtension
{
    protected static final byte[] TAIL_BYTES = new byte[] { 0x00, 0x00, (byte)0xFF, (byte)0xFF };
    protected static final ByteBuffer TAIL_BYTES_BUF = ByteBuffer.wrap(TAIL_BYTES);
    private static final Logger LOG = Log.getLogger(CompressExtension.class);

    /** Never drop tail bytes 0000FFFF, from any frame type */
    protected static final int TAIL_DROP_NEVER = 0;
    /** Always drop tail bytes 0000FFFF, from all frame types */
    protected static final int TAIL_DROP_ALWAYS = 1;
    /** Only drop tail bytes 0000FFFF, from fin==true frames */
    protected static final int TAIL_DROP_FIN_ONLY = 2;

    /** Always set RSV flag, on all frame types */
    protected static final int RSV_USE_ALWAYS = 0;
    /**
     * Only set RSV flag on first frame in multi-frame messages.
     * <p>
     * Note: this automatically means no-continuation frames have the RSV bit set
     */
    protected static final int RSV_USE_ONLY_FIRST = 1;

    /** Inflater / Decompressed Buffer Size */
    protected static final int INFLATE_BUFFER_SIZE = 8 * 1024;

    /** Deflater / Inflater: Maximum Input Buffer Size */
    protected static final int INPUT_MAX_BUFFER_SIZE = 8 * 1024;

    /** Inflater : Output Buffer Size */
    private static final int DECOMPRESS_BUF_SIZE = 8 * 1024;
    
    private final static boolean NOWRAP = true;

    private final Queue<FrameEntry> entries = new ArrayDeque<>();
    private final IteratingCallback flusher = new Flusher();
    private Deflater deflaterImpl;
    private Inflater inflaterImpl;
    protected AtomicInteger decompressCount = new AtomicInteger(0);
    private int tailDrop = TAIL_DROP_NEVER;
    private int rsvUse = RSV_USE_ALWAYS;

    protected CompressExtension()
    {
        tailDrop = getTailDropMode();
        rsvUse = getRsvUseMode();
    }

    public Deflater getDeflater()
    {
        if (deflaterImpl == null)
        {
            deflaterImpl = new Deflater(Deflater.DEFAULT_COMPRESSION,NOWRAP);
        }
        return deflaterImpl;
    }

    public Inflater getInflater()
    {
        if (inflaterImpl == null)
        {
            inflaterImpl = new Inflater(NOWRAP);
        }
        return inflaterImpl;
    }

    /**
     * Indicates use of RSV1 flag for indicating deflation is in use.
     */
    @Override
    public boolean isRsv1User()
    {
        return true;
    }

    /**
     * Return the mode of operation for dropping (or keeping) tail bytes in frames generated by compress (outgoing)
     * 
     * @return either {@link #TAIL_DROP_ALWAYS}, {@link #TAIL_DROP_FIN_ONLY}, or {@link #TAIL_DROP_NEVER}
     */
    abstract int getTailDropMode();

    /**
     * Return the mode of operation for RSV flag use in frames generate by compress (outgoing)
     * 
     * @return either {@link #RSV_USE_ALWAYS} or {@link #RSV_USE_ONLY_FIRST}
     */
    abstract int getRsvUseMode();

    protected void forwardIncoming(Frame frame, ByteAccumulator accumulator)
    {
        DataFrame newFrame = new DataFrame(frame);
        // Unset RSV1 since it's not compressed anymore.
        newFrame.setRsv1(false);

        ByteBuffer buffer = getBufferPool().acquire(accumulator.getLength(),false);
        try
        {
            BufferUtil.flipToFill(buffer);
            accumulator.transferTo(buffer);
            newFrame.setPayload(buffer);
            nextIncomingFrame(newFrame);
        }
        finally
        {
            getBufferPool().release(buffer);
        }
    }

    protected ByteAccumulator newByteAccumulator()
    {
        int maxSize = Math.max(getPolicy().getMaxTextMessageSize(),getPolicy().getMaxBinaryMessageBufferSize());
        return new ByteAccumulator(maxSize);
    }

    protected void decompress(ByteAccumulator accumulator, ByteBuffer buf) throws DataFormatException
    {
        if ((buf == null) || (!buf.hasRemaining()))
        {
            return;
        }
        byte[] output = new byte[DECOMPRESS_BUF_SIZE];
        
        Inflater inflater = getInflater();
        
        while(buf.hasRemaining() && inflater.needsInput())
        {
            if (!supplyInput(inflater,buf))
            {
                LOG.debug("Needed input, but no buffer could supply input");
                return;
            }
    
            int read;
            while ((read = inflater.inflate(output)) >= 0)
            {
                if (read == 0)
                {
                    LOG.debug("Decompress: read 0 {}",toDetail(inflater));
                    break;
                }
                else
                {
                    // do something with output
                    if (LOG.isDebugEnabled())
                    {
                        LOG.debug("Decompressed {} bytes: {}",read,toDetail(inflater));
                    }
    
                    accumulator.copyChunk(output,0,read);
                }
            }
        }

        if (LOG.isDebugEnabled())
        {
            LOG.debug("Decompress: exiting {}",toDetail(inflater));
        }
    }

    @Override
    public void outgoingFrame(Frame frame, WriteCallback callback, BatchMode batchMode)
    {
        // We use a queue and an IteratingCallback to handle concurrency.
        // We must compress and write atomically, otherwise the compression
        // context on the other end gets confused.

        if (flusher.isFailed())
        {
            notifyCallbackFailure(callback,new ZipException());
            return;
        }

        FrameEntry entry = new FrameEntry(frame,callback,batchMode);
        if (LOG.isDebugEnabled())
            LOG.debug("Queuing {}",entry);
        offerEntry(entry);
        flusher.iterate();
    }

    private void offerEntry(FrameEntry entry)
    {
        synchronized (this)
        {
            entries.offer(entry);
        }
    }

    private FrameEntry pollEntry()
    {
        synchronized (this)
        {
            return entries.poll();
        }
    }

    protected void notifyCallbackSuccess(WriteCallback callback)
    {
        try
        {
            if (callback != null)
                callback.writeSuccess();
        }
        catch (Throwable x)
        {
            if (LOG.isDebugEnabled())
                LOG.debug("Exception while notifying success of callback " + callback,x);
        }
    }

    protected void notifyCallbackFailure(WriteCallback callback, Throwable failure)
    {
        try
        {
            if (callback != null)
                callback.writeFailed(failure);
        }
        catch (Throwable x)
        {
            if (LOG.isDebugEnabled())
                LOG.debug("Exception while notifying failure of callback " + callback,x);
        }
    }

    private static boolean supplyInput(Inflater inflater, ByteBuffer buf)
    {
        if (buf.remaining() <= 0)
        {
            if (LOG.isDebugEnabled())
            {
                LOG.debug("No data left left to supply to Inflater");
            }
            return false;
        }

        byte input[];
        int inputOffset;
        int len;

        if (buf.hasArray())
        {
            // no need to create a new byte buffer, just return this one.
            len = buf.remaining();
            input = buf.array();
            inputOffset = buf.position() + buf.arrayOffset();
            buf.position(buf.position() + len);
        }
        else
        {
            // Only create an return byte buffer that is reasonable in size
            len = Math.min(INPUT_MAX_BUFFER_SIZE,buf.remaining());
            input = new byte[len];
            inputOffset = 0;
            buf.get(input,0,len);
        }

        inflater.setInput(input,inputOffset,len);
        if (LOG.isDebugEnabled())
        {
            LOG.debug("Supplied {} input bytes: {}",input.length,toDetail(inflater));
        }
        return true;
    }

    private static boolean supplyInput(Deflater deflater, ByteBuffer buf)
    {
        if (buf.remaining() <= 0)
        {
            if (LOG.isDebugEnabled())
            {
                LOG.debug("No data left left to supply to Deflater");
            }
            return false;
        }

        byte input[];
        int inputOffset;
        int len;

        if (buf.hasArray())
        {
            // no need to create a new byte buffer, just return this one.
            len = buf.remaining();
            input = buf.array();
            inputOffset = buf.position() + buf.arrayOffset();
            buf.position(buf.position() + len);
        }
        else
        {
            // Only create an return byte buffer that is reasonable in size
            len = Math.min(INPUT_MAX_BUFFER_SIZE,buf.remaining());
            input = new byte[len];
            inputOffset = 0;
            buf.get(input,0,len);
        }

        deflater.setInput(input,inputOffset,len);
        if (LOG.isDebugEnabled())
        {
            LOG.debug("Supplied {} input bytes: {}",input.length,toDetail(deflater));
        }
        return true;
    }

    private static String toDetail(Inflater inflater)
    {
        return String.format("Inflater[finished=%b,read=%d,written=%d,remaining=%d,in=%d,out=%d]",inflater.finished(),inflater.getBytesRead(),
                inflater.getBytesWritten(),inflater.getRemaining(),inflater.getTotalIn(),inflater.getTotalOut());
    }

    private static String toDetail(Deflater deflater)
    {
        return String.format("Deflater[finished=%b,read=%d,written=%d,in=%d,out=%d]",deflater.finished(),deflater.getBytesRead(),deflater.getBytesWritten(),
                deflater.getTotalIn(),deflater.getTotalOut());
    }

    public static boolean endsWithTail(ByteBuffer buf)
    {
        if ((buf == null) || (buf.remaining() < TAIL_BYTES.length))
        {
            return false;
        }
        int limit = buf.limit();
        for (int i = TAIL_BYTES.length; i > 0; i--)
        {
            if (buf.get(limit - i) != TAIL_BYTES[TAIL_BYTES.length - i])
            {
                return false;
            }
        }
        return true;
    }
    
    @Override
    protected void doStop() throws Exception
    {
        if(deflaterImpl != null)
            deflaterImpl.end();
        if(inflaterImpl != null)
            inflaterImpl.end();
        super.doStop();
    }

    @Override
    public String toString()
    {
        return getClass().getSimpleName();
    }

    private static class FrameEntry
    {
        private final Frame frame;
        private final WriteCallback callback;
        private final BatchMode batchMode;

        private FrameEntry(Frame frame, WriteCallback callback, BatchMode batchMode)
        {
            this.frame = frame;
            this.callback = callback;
            this.batchMode = batchMode;
        }

        @Override
        public String toString()
        {
            return frame.toString();
        }
    }

    private class Flusher extends IteratingCallback implements WriteCallback
    {
        private FrameEntry current;
        private boolean finished = true;
        
        @Override
        public void failed(Throwable x)
        {
            LOG.warn(x);
            super.failed(x);
        }

        @Override
        protected Action process() throws Exception
        {
            if (finished)
            {
                current = pollEntry();
                LOG.debug("Processing {}",current);
                if (current == null)
                    return Action.IDLE;
                deflate(current);
            }
            else
            {
                compress(current,false);
            }
            return Action.SCHEDULED;
        }

        private void deflate(FrameEntry entry)
        {
            Frame frame = entry.frame;
            BatchMode batchMode = entry.batchMode;
            if (OpCode.isControlFrame(frame.getOpCode()))
            {
                // Do not deflate control frames
                nextOutgoingFrame(frame,this,batchMode);
                return;
            }
            
            compress(entry,true);
        }

        private void compress(FrameEntry entry, boolean first)
        {
            // Get a chunk of the payload to avoid to blow
            // the heap if the payload is a huge mapped file.
            Frame frame = entry.frame;
            ByteBuffer data = frame.getPayload();
            int remaining = data.remaining();
            int outputLength = Math.max(256,data.remaining());
            if (LOG.isDebugEnabled())
                LOG.debug("Compressing {}: {} bytes in {} bytes chunk",entry,remaining,outputLength);

            boolean needsCompress = true;
            
            Deflater deflater = getDeflater();

            if (deflater.needsInput() && !supplyInput(deflater,data))
            {
                // no input supplied
                needsCompress = false;
            }
            
            ByteArrayOutputStream out = new ByteArrayOutputStream();

            byte[] output = new byte[outputLength];

            boolean fin = frame.isFin();

            // Compress the data
            while (needsCompress)
            {
                int compressed = deflater.deflate(output,0,outputLength,Deflater.SYNC_FLUSH);

                // Append the output for the eventual frame.
                if (LOG.isDebugEnabled())
                    LOG.debug("Wrote {} bytes to output buffer",compressed);
                out.write(output,0,compressed);

                if (compressed < outputLength)
                {
                    needsCompress = false;
                }
            }

            ByteBuffer payload = ByteBuffer.wrap(out.toByteArray());

            if (payload.remaining() > 0)
            {
                // Handle tail bytes generated by SYNC_FLUSH.
                if (LOG.isDebugEnabled())
                    LOG.debug("compressed bytes[] = {}",BufferUtil.toDetailString(payload));

                if (tailDrop == TAIL_DROP_ALWAYS)
                {
                    if (endsWithTail(payload))
                    {
                        payload.limit(payload.limit() - TAIL_BYTES.length);
                    }
                    if (LOG.isDebugEnabled())
                        LOG.debug("payload (TAIL_DROP_ALWAYS) = {}",BufferUtil.toDetailString(payload));
                }
                else if (tailDrop == TAIL_DROP_FIN_ONLY)
                {
                    if (frame.isFin() && endsWithTail(payload))
                    {
                        payload.limit(payload.limit() - TAIL_BYTES.length);
                    }
                    if (LOG.isDebugEnabled())
                        LOG.debug("payload (TAIL_DROP_FIN_ONLY) = {}",BufferUtil.toDetailString(payload));
                }
            }
            else if (fin)
            {
                // Special case: 7.2.3.6.  Generating an Empty Fragment Manually
                // https://tools.ietf.org/html/rfc7692#section-7.2.3.6
                payload = ByteBuffer.wrap(new byte[] { 0x00 });
            }

            if (LOG.isDebugEnabled())
            {
                LOG.debug("Compressed {}: input:{} -> payload:{}",entry,outputLength,payload.remaining());
            }

            boolean continuation = frame.getType().isContinuation() || !first;
            DataFrame chunk = new DataFrame(frame,continuation);
            if (rsvUse == RSV_USE_ONLY_FIRST)
            {
                chunk.setRsv1(!continuation);
            }
            else
            {
                // always set
                chunk.setRsv1(true);
            }
            chunk.setPayload(payload);
            chunk.setFin(fin);

            nextOutgoingFrame(chunk,this,entry.batchMode);
        }

        @Override
        protected void onCompleteSuccess()
        {
            // This IteratingCallback never completes.
        }

        @Override
        protected void onCompleteFailure(Throwable x)
        {
            // Fail all the frames in the queue.
            FrameEntry entry;
            while ((entry = pollEntry()) != null)
                notifyCallbackFailure(entry.callback,x);
        }

        @Override
        public void writeSuccess()
        {
            if (finished)
                notifyCallbackSuccess(current.callback);
            succeeded();
        }

        @Override
        public void writeFailed(Throwable x)
        {
            notifyCallbackFailure(current.callback,x);
            // If something went wrong, very likely the compression context
            // will be invalid, so we need to fail this IteratingCallback.
            failed(x);
        }
    }
}
