/*
 *  Licensed to the Apache Software Foundation (ASF) under one or more
 *  contributor license agreements.  See the NOTICE file distributed with
 *  this work for additional information regarding copyright ownership.
 *  The ASF licenses this file to You under the Apache License, Version 2.0
 *  (the "License"); you may not use this file except in compliance with
 *  the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 */
package org.apache.coyote.http11.filters;

import java.io.IOException;
import java.nio.ByteBuffer;

import org.apache.coyote.OutputBuffer;
import org.apache.coyote.Response;
import org.apache.coyote.http11.OutputFilter;
import org.apache.tomcat.util.buf.HexUtils;

/**
 * Chunked output filter.
 *
 * @author Remy Maucherat
 */
public class ChunkedOutputFilter implements OutputFilter {

    private static final byte[] END_CHUNK_BYTES =
        {(byte) '0', (byte) '\r', (byte) '\n', (byte) '\r', (byte) '\n'};


    /**
     * Next buffer in the pipeline.
     */
    protected OutputBuffer buffer;


    /**
     * Chunk header.
     */
    protected final ByteBuffer chunkHeader = ByteBuffer.allocate(10);


    /**
     * End chunk.
     */
    protected final ByteBuffer endChunk = ByteBuffer.wrap(END_CHUNK_BYTES);


    public ChunkedOutputFilter() {
        chunkHeader.put(8, (byte) '\r');
        chunkHeader.put(9, (byte) '\n');
    }


    // --------------------------------------------------- OutputBuffer Methods

    @Override
    public int doWrite(ByteBuffer chunk) throws IOException {

        int result = chunk.remaining();

        if (result <= 0) {
            return 0;
        }

        int pos = calculateChunkHeader(result);

        chunkHeader.position(pos + 1).limit(chunkHeader.position() + 9 - pos);
        buffer.doWrite(chunkHeader);

        buffer.doWrite(chunk);

        chunkHeader.position(8).limit(10);
        buffer.doWrite(chunkHeader);

        return result;
    }


    private int calculateChunkHeader(int len) {
        // Calculate chunk header
        int pos = 7;
        int current = len;
        while (current > 0) {
            int digit = current % 16;
            current = current / 16;
            chunkHeader.put(pos--, HexUtils.getHex(digit));
        }
        return pos;
    }


    @Override
    public long getBytesWritten() {
        return buffer.getBytesWritten();
    }


    // --------------------------------------------------- OutputFilter Methods

    /**
     * Some filters need additional parameters from the response. All the
     * necessary reading can occur in that method, as this method is called
     * after the response header processing is complete.
     */
    @Override
    public void setResponse(Response response) {
        // NOOP: No need for parameters from response in this filter
    }


    /**
     * Set the next buffer in the filter pipeline.
     */
    @Override
    public void setBuffer(OutputBuffer buffer) {
        this.buffer = buffer;
    }


    /**
     * End the current request. It is acceptable to write extra bytes using
     * buffer.doWrite during the execution of this method.
     */
    @Override
    public long end() throws IOException {

        // Write end chunk
        buffer.doWrite(endChunk);
        endChunk.position(0).limit(endChunk.capacity());

        return 0;
    }


    /**
     * Make the filter ready to process the next request.
     */
    @Override
    public void recycle() {
        // NOOP: Nothing to recycle
    }
}