//
//  ========================================================================
//  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.hpack;

import java.nio.ByteBuffer;
import java.nio.charset.StandardCharsets;
import java.util.EnumSet;
import java.util.HashSet;
import java.util.Set;

import org.eclipse.jetty.http.HttpField;
import org.eclipse.jetty.http.HttpFields;
import org.eclipse.jetty.http.HttpHeader;
import org.eclipse.jetty.http.HttpScheme;
import org.eclipse.jetty.http.HttpStatus;
import org.eclipse.jetty.http.HttpVersion;
import org.eclipse.jetty.http.MetaData;
import org.eclipse.jetty.http.PreEncodedHttpField;
import org.eclipse.jetty.http2.hpack.HpackContext.Entry;
import org.eclipse.jetty.http2.hpack.HpackContext.StaticEntry;
import org.eclipse.jetty.util.StringUtil;
import org.eclipse.jetty.util.TypeUtil;
import org.eclipse.jetty.util.log.Log;
import org.eclipse.jetty.util.log.Logger;

public class HpackEncoder
{
    private static final Logger LOG = Log.getLogger(HpackEncoder.class);
    private static final HttpField[] STATUSES = new HttpField[599];
    static final EnumSet<HttpHeader> DO_NOT_HUFFMAN =
        EnumSet.of(
            HttpHeader.AUTHORIZATION,
            HttpHeader.CONTENT_MD5,
            HttpHeader.PROXY_AUTHENTICATE,
            HttpHeader.PROXY_AUTHORIZATION);
    static final EnumSet<HttpHeader> DO_NOT_INDEX =
        EnumSet.of(
            // HttpHeader.C_PATH,  // TODO more data needed
            // HttpHeader.DATE,    // TODO more data needed
            HttpHeader.AUTHORIZATION,
            HttpHeader.CONTENT_MD5,
            HttpHeader.CONTENT_RANGE,
            HttpHeader.ETAG,
            HttpHeader.IF_MODIFIED_SINCE,
            HttpHeader.IF_UNMODIFIED_SINCE,
            HttpHeader.IF_NONE_MATCH,
            HttpHeader.IF_RANGE,
            HttpHeader.IF_MATCH,
            HttpHeader.LOCATION,
            HttpHeader.RANGE,
            HttpHeader.RETRY_AFTER,
            // HttpHeader.EXPIRES,
            HttpHeader.LAST_MODIFIED,
            HttpHeader.SET_COOKIE,
            HttpHeader.SET_COOKIE2);
    static final EnumSet<HttpHeader> NEVER_INDEX =
        EnumSet.of(
            HttpHeader.AUTHORIZATION,
            HttpHeader.SET_COOKIE,
            HttpHeader.SET_COOKIE2);
    private static final EnumSet<HttpHeader> IGNORED_HEADERS = EnumSet.of(HttpHeader.CONNECTION, HttpHeader.KEEP_ALIVE,
        HttpHeader.PROXY_CONNECTION, HttpHeader.TRANSFER_ENCODING, HttpHeader.UPGRADE);
    private static final PreEncodedHttpField TE_TRAILERS = new PreEncodedHttpField(HttpHeader.TE, "trailers");

    static
    {
        for (HttpStatus.Code code : HttpStatus.Code.values())
        {
            STATUSES[code.getCode()] = new PreEncodedHttpField(HttpHeader.C_STATUS, Integer.toString(code.getCode()));
        }
    }

    private final HpackContext _context;
    private final boolean _debug;
    private int _remoteMaxDynamicTableSize;
    private int _localMaxDynamicTableSize;
    private int _maxHeaderListSize;
    private int _headerListSize;

    public HpackEncoder()
    {
        this(4096, 4096, -1);
    }

    public HpackEncoder(int localMaxDynamicTableSize)
    {
        this(localMaxDynamicTableSize, 4096, -1);
    }

    public HpackEncoder(int localMaxDynamicTableSize, int remoteMaxDynamicTableSize)
    {
        this(localMaxDynamicTableSize, remoteMaxDynamicTableSize, -1);
    }

    public HpackEncoder(int localMaxDynamicTableSize, int remoteMaxDynamicTableSize, int maxHeaderListSize)
    {
        _context = new HpackContext(remoteMaxDynamicTableSize);
        _remoteMaxDynamicTableSize = remoteMaxDynamicTableSize;
        _localMaxDynamicTableSize = localMaxDynamicTableSize;
        _maxHeaderListSize = maxHeaderListSize;
        _debug = LOG.isDebugEnabled();
    }

    public int getMaxHeaderListSize()
    {
        return _maxHeaderListSize;
    }

    public void setMaxHeaderListSize(int maxHeaderListSize)
    {
        _maxHeaderListSize = maxHeaderListSize;
    }

    public HpackContext getHpackContext()
    {
        return _context;
    }

    public void setRemoteMaxDynamicTableSize(int remoteMaxDynamicTableSize)
    {
        _remoteMaxDynamicTableSize = remoteMaxDynamicTableSize;
    }

    public void setLocalMaxDynamicTableSize(int localMaxDynamicTableSize)
    {
        _localMaxDynamicTableSize = localMaxDynamicTableSize;
    }

    public void encode(ByteBuffer buffer, MetaData metadata)
    {
        if (LOG.isDebugEnabled())
            LOG.debug(String.format("CtxTbl[%x] encoding", _context.hashCode()));

        _headerListSize = 0;
        int pos = buffer.position();

        // Check the dynamic table sizes!
        int maxDynamicTableSize = Math.min(_remoteMaxDynamicTableSize, _localMaxDynamicTableSize);
        if (maxDynamicTableSize != _context.getMaxDynamicTableSize())
            encodeMaxDynamicTableSize(buffer, maxDynamicTableSize);

        // Add Request/response meta fields
        if (metadata.isRequest())
        {
            MetaData.Request request = (MetaData.Request)metadata;

            // TODO optimise these to avoid HttpField creation
            String scheme = request.getURI().getScheme();
            encode(buffer, new HttpField(HttpHeader.C_SCHEME, scheme == null ? HttpScheme.HTTP.asString() : scheme));
            encode(buffer, new HttpField(HttpHeader.C_METHOD, request.getMethod()));
            encode(buffer, new HttpField(HttpHeader.C_AUTHORITY, request.getURI().getAuthority()));
            encode(buffer, new HttpField(HttpHeader.C_PATH, request.getURI().getPathQuery()));
        }
        else if (metadata.isResponse())
        {
            MetaData.Response response = (MetaData.Response)metadata;
            int code = response.getStatus();
            HttpField status = code < STATUSES.length ? STATUSES[code] : null;
            if (status == null)
                status = new HttpField.IntValueHttpField(HttpHeader.C_STATUS, code);
            encode(buffer, status);
        }

        // Remove fields as specified in RFC 7540, 8.1.2.2.
        HttpFields fields = metadata.getFields();
        if (fields != null)
        {
            // For example: Connection: Close, TE, Upgrade, Custom.
            Set<String> hopHeaders = null;
            for (String value : fields.getCSV(HttpHeader.CONNECTION, false))
            {
                if (hopHeaders == null)
                    hopHeaders = new HashSet<>();
                hopHeaders.add(StringUtil.asciiToLowerCase(value));
            }
            for (HttpField field : fields)
            {
                HttpHeader header = field.getHeader();
                if (header != null && IGNORED_HEADERS.contains(header))
                    continue;
                if (header == HttpHeader.TE)
                {
                    if (field.contains("trailers"))
                        encode(buffer, TE_TRAILERS);
                    continue;
                }
                if (hopHeaders != null && hopHeaders.contains(StringUtil.asciiToLowerCase(field.getName())))
                    continue;
                encode(buffer, field);
            }
        }

        // Check size
        if (_maxHeaderListSize > 0 && _headerListSize > _maxHeaderListSize)
        {
            LOG.warn("Header list size too large {} > {} for {}", _headerListSize, _maxHeaderListSize);
            if (LOG.isDebugEnabled())
                LOG.debug("metadata={}", metadata);
        }

        if (LOG.isDebugEnabled())
            LOG.debug(String.format("CtxTbl[%x] encoded %d octets", _context.hashCode(), buffer.position() - pos));
    }

    public void encodeMaxDynamicTableSize(ByteBuffer buffer, int maxDynamicTableSize)
    {
        if (maxDynamicTableSize > _remoteMaxDynamicTableSize)
            throw new IllegalArgumentException();
        buffer.put((byte)0x20);
        NBitInteger.encode(buffer, 5, maxDynamicTableSize);
        _context.resize(maxDynamicTableSize);
    }

    public void encode(ByteBuffer buffer, HttpField field)
    {
        if (field.getValue() == null)
            field = new HttpField(field.getHeader(), field.getName(), "");

        int fieldSize = field.getName().length() + field.getValue().length();
        _headerListSize += fieldSize + 32;

        final int p = _debug ? buffer.position() : -1;

        String encoding = null;

        // Is there an entry for the field?
        Entry entry = _context.get(field);
        if (entry != null)
        {
            // Known field entry, so encode it as indexed
            if (entry.isStatic())
            {
                buffer.put(((StaticEntry)entry).getEncodedField());
                if (_debug)
                    encoding = "IdxFieldS1";
            }
            else
            {
                int index = _context.index(entry);
                buffer.put((byte)0x80);
                NBitInteger.encode(buffer, 7, index);
                if (_debug)
                    encoding = "IdxField" + (entry.isStatic() ? "S" : "") + (1 + NBitInteger.octectsNeeded(7, index));
            }
        }
        else
        {
            // Unknown field entry, so we will have to send literally.
            final boolean indexed;

            // But do we know it's name?
            HttpHeader header = field.getHeader();

            // Select encoding strategy
            if (header == null)
            {
                // Select encoding strategy for unknown header names
                Entry name = _context.get(field.getName());

                if (field instanceof PreEncodedHttpField)
                {
                    int i = buffer.position();
                    ((PreEncodedHttpField)field).putTo(buffer, HttpVersion.HTTP_2);
                    byte b = buffer.get(i);
                    indexed = b < 0 || b >= 0x40;
                    if (_debug)
                        encoding = indexed ? "PreEncodedIdx" : "PreEncoded";
                }
                // has the custom header name been seen before?
                else if (name == null)
                {
                    // unknown name and value, so let's index this just in case it is
                    // the first time we have seen a custom name or a custom field.
                    // unless the name is changing, this is worthwhile
                    indexed = true;
                    encodeName(buffer, (byte)0x40, 6, field.getName(), null);
                    encodeValue(buffer, true, field.getValue());
                    if (_debug)
                        encoding = "LitHuffNHuffVIdx";
                }
                else
                {
                    // known custom name, but unknown value.
                    // This is probably a custom field with changing value, so don't index.
                    indexed = false;
                    encodeName(buffer, (byte)0x00, 4, field.getName(), null);
                    encodeValue(buffer, true, field.getValue());
                    if (_debug)
                        encoding = "LitHuffNHuffV!Idx";
                }
            }
            else
            {
                // Select encoding strategy for known header names
                Entry name = _context.get(header);

                if (field instanceof PreEncodedHttpField)
                {
                    // Preencoded field
                    int i = buffer.position();
                    ((PreEncodedHttpField)field).putTo(buffer, HttpVersion.HTTP_2);
                    byte b = buffer.get(i);
                    indexed = b < 0 || b >= 0x40;
                    if (_debug)
                        encoding = indexed ? "PreEncodedIdx" : "PreEncoded";
                }
                else if (DO_NOT_INDEX.contains(header))
                {
                    // Non indexed field
                    indexed = false;
                    boolean neverIndex = NEVER_INDEX.contains(header);
                    boolean huffman = !DO_NOT_HUFFMAN.contains(header);
                    encodeName(buffer, neverIndex ? (byte)0x10 : (byte)0x00, 4, header.asString(), name);
                    encodeValue(buffer, huffman, field.getValue());

                    if (_debug)
                        encoding = "Lit" +
                            ((name == null) ? "HuffN" : ("IdxN" + (name.isStatic() ? "S" : "") + (1 + NBitInteger.octectsNeeded(4, _context.index(name))))) +
                            (huffman ? "HuffV" : "LitV") +
                            (neverIndex ? "!!Idx" : "!Idx");
                }
                else if (fieldSize >= _context.getMaxDynamicTableSize() || header == HttpHeader.CONTENT_LENGTH && field.getValue().length() > 2)
                {
                    // Non indexed if field too large or a content length for 3 digits or more
                    indexed = false;
                    encodeName(buffer, (byte)0x00, 4, header.asString(), name);
                    encodeValue(buffer, true, field.getValue());
                    if (_debug)
                        encoding = "LitIdxNS" + (1 + NBitInteger.octectsNeeded(4, _context.index(name))) + "HuffV!Idx";
                }
                else
                {
                    // indexed
                    indexed = true;
                    boolean huffman = !DO_NOT_HUFFMAN.contains(header);
                    encodeName(buffer, (byte)0x40, 6, header.asString(), name);
                    encodeValue(buffer, huffman, field.getValue());
                    if (_debug)
                        encoding = ((name == null) ? "LitHuffN" : ("LitIdxN" + (name.isStatic() ? "S" : "") + (1 + NBitInteger.octectsNeeded(6, _context.index(name))))) +
                            (huffman ? "HuffVIdx" : "LitVIdx");
                }
            }

            // If we want the field referenced, then we add it to our table and reference set.
            if (indexed)
                _context.add(field);
        }

        if (_debug)
        {
            int e = buffer.position();
            if (LOG.isDebugEnabled())
                LOG.debug("encode {}:'{}' to '{}'", encoding, field, TypeUtil.toHexString(buffer.array(), buffer.arrayOffset() + p, e - p));
        }
    }

    private void encodeName(ByteBuffer buffer, byte mask, int bits, String name, Entry entry)
    {
        buffer.put(mask);
        if (entry == null)
        {
            // leave name index bits as 0
            // Encode the name always with lowercase huffman
            buffer.put((byte)0x80);
            NBitInteger.encode(buffer, 7, Huffman.octetsNeededLC(name));
            Huffman.encodeLC(buffer, name);
        }
        else
        {
            NBitInteger.encode(buffer, bits, _context.index(entry));
        }
    }

    static void encodeValue(ByteBuffer buffer, boolean huffman, String value)
    {
        if (huffman)
        {
            // huffman literal value
            buffer.put((byte)0x80);

            int needed = Huffman.octetsNeeded(value);
            if (needed >= 0)
            {
                NBitInteger.encode(buffer, 7, needed);
                Huffman.encode(buffer, value);
            }
            else
            {
                // Not iso_8859_1
                byte[] bytes = value.getBytes(StandardCharsets.UTF_8);
                NBitInteger.encode(buffer, 7, Huffman.octetsNeeded(bytes));
                Huffman.encode(buffer, bytes);
            }
        }
        else
        {
            // add literal assuming iso_8859_1
            buffer.put((byte)0x00).mark();
            NBitInteger.encode(buffer, 7, value.length());
            for (int i = 0; i < value.length(); i++)
            {
                char c = value.charAt(i);
                if (c < ' ' || c > 127)
                {
                    // Not iso_8859_1, so re-encode as UTF-8
                    buffer.reset();
                    byte[] bytes = value.getBytes(StandardCharsets.UTF_8);
                    NBitInteger.encode(buffer, 7, bytes.length);
                    buffer.put(bytes, 0, bytes.length);
                    return;
                }
                buffer.put((byte)c);
            }
        }
    }
}
