//
//  ========================================================================
//  Copyright (c) 1995-2019 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.http2.parser;

import java.nio.ByteBuffer;
import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.atomic.AtomicReference;

import org.eclipse.jetty.http2.ErrorCode;
import org.eclipse.jetty.http2.Flags;
import org.eclipse.jetty.http2.frames.Frame;
import org.eclipse.jetty.http2.frames.SettingsFrame;
import org.eclipse.jetty.util.log.Log;
import org.eclipse.jetty.util.log.Logger;

public class SettingsBodyParser extends BodyParser
{
    private static final Logger LOG = Log.getLogger(SettingsBodyParser.class);

    private final int maxKeys;
    private State state = State.PREPARE;
    private int cursor;
    private int length;
    private int settingId;
    private int settingValue;
    private int keys;
    private Map<Integer, Integer> settings;

    public SettingsBodyParser(HeaderParser headerParser, Parser.Listener listener)
    {
        this(headerParser, listener, SettingsFrame.DEFAULT_MAX_KEYS);
    }

    public SettingsBodyParser(HeaderParser headerParser, Parser.Listener listener, int maxKeys)
    {
        super(headerParser, listener);
        this.maxKeys = maxKeys;
    }

    protected void reset()
    {
        state = State.PREPARE;
        cursor = 0;
        length = 0;
        settingId = 0;
        settingValue = 0;
        settings = null;
    }

    public int getMaxKeys()
    {
        return maxKeys;
    }

    @Override
    protected void emptyBody(ByteBuffer buffer)
    {
        onSettings(buffer, new HashMap<>());
    }

    @Override
    public boolean parse(ByteBuffer buffer)
    {
        while (buffer.hasRemaining())
        {
            switch (state)
            {
                case PREPARE:
                {
                    // SPEC: wrong streamId is treated as connection error.
                    if (getStreamId() != 0)
                        return connectionFailure(buffer, ErrorCode.PROTOCOL_ERROR.code, "invalid_settings_frame");
                    length = getBodyLength();
                    settings = new HashMap<>();
                    state = State.SETTING_ID;
                    break;
                }
                case SETTING_ID:
                {
                    if (buffer.remaining() >= 2)
                    {
                        settingId = buffer.getShort() & 0xFF_FF;
                        state = State.SETTING_VALUE;
                        length -= 2;
                        if (length <= 0)
                            return connectionFailure(buffer, ErrorCode.FRAME_SIZE_ERROR.code, "invalid_settings_frame");
                    }
                    else
                    {
                        cursor = 2;
                        settingId = 0;
                        state = State.SETTING_ID_BYTES;
                    }
                    break;
                }
                case SETTING_ID_BYTES:
                {
                    int currByte = buffer.get() & 0xFF;
                    --cursor;
                    settingId += currByte << (8 * cursor);
                    --length;
                    if (length <= 0)
                        return connectionFailure(buffer, ErrorCode.FRAME_SIZE_ERROR.code, "invalid_settings_frame");
                    if (cursor == 0)
                    {
                        state = State.SETTING_VALUE;
                    }
                    break;
                }
                case SETTING_VALUE:
                {
                    if (buffer.remaining() >= 4)
                    {
                        settingValue = buffer.getInt();
                        if (LOG.isDebugEnabled())
                            LOG.debug(String.format("setting %d=%d",settingId, settingValue));
                        if (!onSetting(buffer, settings, settingId, settingValue))
                            return false;
                        state = State.SETTING_ID;
                        length -= 4;
                        if (length == 0)
                            return onSettings(buffer, settings);
                    }
                    else
                    {
                        cursor = 4;
                        settingValue = 0;
                        state = State.SETTING_VALUE_BYTES;
                    }
                    break;
                }
                case SETTING_VALUE_BYTES:
                {
                    int currByte = buffer.get() & 0xFF;
                    --cursor;
                    settingValue += currByte << (8 * cursor);
                    --length;
                    if (cursor > 0 && length <= 0)
                        return connectionFailure(buffer, ErrorCode.FRAME_SIZE_ERROR.code, "invalid_settings_frame");
                    if (cursor == 0)
                    {
                        if (LOG.isDebugEnabled())
                            LOG.debug(String.format("setting %d=%d",settingId, settingValue));
                        if (!onSetting(buffer, settings, settingId, settingValue))
                            return false;
                        state = State.SETTING_ID;
                        if (length == 0)
                            return onSettings(buffer, settings);
                    }
                    break;
                }
                default:
                {
                    throw new IllegalStateException();
                }
            }
        }
        return false;
    }

    protected boolean onSetting(ByteBuffer buffer, Map<Integer, Integer> settings, int key, int value)
    {
        ++keys;
        if (keys > getMaxKeys())
            return connectionFailure(buffer, ErrorCode.ENHANCE_YOUR_CALM_ERROR.code, "invalid_settings_frame");
        settings.put(key, value);
        return true;
    }

    protected boolean onSettings(ByteBuffer buffer, Map<Integer, Integer> settings)
    {
        Integer enablePush = settings.get(SettingsFrame.ENABLE_PUSH);
        if (enablePush != null && enablePush != 0 && enablePush != 1)
            return connectionFailure(buffer, ErrorCode.PROTOCOL_ERROR.code, "invalid_settings_enable_push");

        Integer initialWindowSize = settings.get(SettingsFrame.INITIAL_WINDOW_SIZE);
        // Values greater than Integer.MAX_VALUE will overflow to negative.
        if (initialWindowSize != null && initialWindowSize < 0)
            return connectionFailure(buffer, ErrorCode.FLOW_CONTROL_ERROR.code, "invalid_settings_initial_window_size");

        Integer maxFrameLength = settings.get(SettingsFrame.MAX_FRAME_SIZE);
        if (maxFrameLength != null && (maxFrameLength < Frame.DEFAULT_MAX_LENGTH || maxFrameLength > Frame.MAX_MAX_LENGTH))
            return connectionFailure(buffer, ErrorCode.PROTOCOL_ERROR.code, "invalid_settings_max_frame_size");

        SettingsFrame frame = new SettingsFrame(settings, hasFlag(Flags.ACK));
        reset();
        notifySettings(frame);
        return true;
    }

    public static SettingsFrame parseBody(final ByteBuffer buffer)
    {
        final int bodyLength = buffer.remaining();
        final AtomicReference<SettingsFrame> frameRef = new AtomicReference<>();
        SettingsBodyParser parser = new SettingsBodyParser(null, null)
        {
            @Override
            protected int getStreamId()
            {
                return 0;
            }

            @Override
            protected int getBodyLength()
            {
                return bodyLength;
            }

            @Override
            protected boolean onSettings(ByteBuffer buffer, Map<Integer, Integer> settings)
            {
                frameRef.set(new SettingsFrame(settings, false));
                return true;
            }

            @Override
            protected boolean connectionFailure(ByteBuffer buffer, int error, String reason)
            {
                frameRef.set(null);
                return false;
            }
        };
        if (bodyLength == 0)
            parser.emptyBody(buffer);
        else
            parser.parse(buffer);
        return frameRef.get();
    }

    private enum State
    {
        PREPARE, SETTING_ID, SETTING_ID_BYTES, SETTING_VALUE, SETTING_VALUE_BYTES
    }
}
