//
//  ========================================================================
//  Copyright (c) 1995-2020 Mort Bay Consulting Pty Ltd and others.
//  ------------------------------------------------------------------------
//  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.spdy.parser;

import java.nio.ByteBuffer;

import org.eclipse.jetty.spdy.api.DataInfo;
import org.eclipse.jetty.spdy.frames.DataFrame;

public abstract class DataFrameParser
{
    private State state = State.STREAM_ID;
    private int cursor;
    private int streamId;
    private byte flags;
    private int length;

    /**
     * <p>Parses the given {@link ByteBuffer} for a data frame.</p>
     *
     * @param buffer the {@link ByteBuffer} to parse
     * @return true if the data frame has been fully parsed, false otherwise
     */
    public boolean parse(ByteBuffer buffer)
    {
        while (buffer.hasRemaining())
        {
            switch (state)
            {
                case STREAM_ID:
                {
                    if (buffer.remaining() >= 4)
                    {
                        streamId = buffer.getInt() & 0x7F_FF_FF_FF;
                        state = State.FLAGS;
                    }
                    else
                    {
                        state = State.STREAM_ID_BYTES;
                        cursor = 4;
                    }
                    break;
                }
                case STREAM_ID_BYTES:
                {
                    byte currByte = buffer.get();
                    --cursor;
                    streamId += (currByte & 0xFF) << 8 * cursor;
                    if (cursor == 0)
                        state = State.FLAGS;
                    break;
                }
                case FLAGS:
                {
                    flags = buffer.get();
                    cursor = 3;
                    state = State.LENGTH;
                    break;
                }
                case LENGTH:
                {
                    byte currByte = buffer.get();
                    --cursor;
                    length += (currByte & 0xFF) << 8 * cursor;
                    if (cursor > 0)
                        break;
                    state = State.DATA;
                    // Fall down if length == 0: we can't loop because the buffer
                    // may be empty but we need to invoke the application anyway
                    if (length > 0)
                        break;
                }
                case DATA:
                {
                    // Length can only be at most 3 bytes, which is 16_777_215 i.e. 16 MiB.
                    // However, compliant clients should implement flow control, so it's
                    // unlikely that we will get that 16 MiB chunk.
                    // However, TCP may further split the flow control window, so we may
                    // only have part of the data at this point.

                    int size = Math.min(length, buffer.remaining());
                    int limit = buffer.limit();
                    buffer.limit(buffer.position() + size);
                    ByteBuffer bytes = buffer.slice();
                    buffer.limit(limit);
                    buffer.position(buffer.position() + size);
                    length -= size;
                    if (length == 0)
                    {
                        onDataFrame(bytes);
                        return true;
                    }
                    else
                    {
                        // We got only part of the frame data bytes,
                        // so we generate a synthetic data frame
                        onDataFragment(bytes);
                    }
                    break;
                }
                default:
                {
                    throw new IllegalStateException();
                }
            }
        }
        return false;
    }

    private void onDataFrame(ByteBuffer bytes)
    {
        DataFrame frame = new DataFrame(streamId, flags, bytes.remaining());
        onDataFrame(frame, bytes);
        reset();
    }

    private void onDataFragment(ByteBuffer bytes)
    {
        DataFrame frame = new DataFrame(streamId, (byte)(flags & ~DataInfo.FLAG_CLOSE), bytes.remaining());
        onDataFrame(frame, bytes);
        // Do not reset, we're expecting more data
    }

    protected abstract void onDataFrame(DataFrame frame, ByteBuffer data);

    private void reset()
    {
        state = State.STREAM_ID;
        cursor = 0;
        streamId = 0;
        flags = 0;
        length = 0;
    }

    private enum State
    {
        STREAM_ID, STREAM_ID_BYTES, FLAGS, LENGTH, DATA
    }
}
