//    OpenVPN -- An application to securely tunnel IP networks
//               over a single port, with support for SSL/TLS-based
//               session authentication and key exchange,
//               packet encryption, packet authentication, and
//               packet compression.
//
//    Copyright (C) 2012- OpenVPN Inc.
//
//    SPDX-License-Identifier: MPL-2.0 OR AGPL-3.0-only WITH openvpn3-openssl-exception
//

// Base class and factory for compression/decompression objects.
// Currently we support LZO, Snappy, and LZ4 implementations.

#ifndef OPENVPN_COMPRESS_COMPRESS_H
#define OPENVPN_COMPRESS_COMPRESS_H

#include <openvpn/common/size.hpp>
#include <openvpn/common/exception.hpp>
#include <openvpn/common/rc.hpp>
#include <openvpn/common/likely.hpp>
#include <openvpn/buffer/buffer.hpp>
#include <openvpn/frame/frame.hpp>
#include <openvpn/log/sessionstats.hpp>
#include <openvpn/log/logger.hpp>

namespace openvpn {

//! Debugging level for message emitted from compression
#if !defined(OPENVPN_DEBUG_COMPRESS)
#define OPENVPN_DEBUG_COMPRESS 1
#endif

class Compress : public RC<thread_unsafe_refcount>,
                 public logging::LoggingMixin<OPENVPN_DEBUG_COMPRESS, logging::LOG_LEVEL_TRACE, Compress>
{
  public:
    typedef RCPtr<Compress> Ptr;

    // Compressor name
    virtual const char *name() const = 0;

    // Compression method implemented by underlying compression class.
    // hint should normally be true to compress the data.  If hint is
    // false, the data may be uncompressible or already compressed,
    // so method shouldn't attempt compression.
    virtual void compress(BufferAllocated &buf, const bool hint) = 0;

    // Decompression method implemented by underlying compression class.
    virtual void decompress(BufferAllocated &buf) = 0;

  protected:
    // magic numbers to indicate no compression
    enum
    {
        NO_COMPRESS = 0xFA,
        NO_COMPRESS_SWAP = 0xFB, // for better alignment handling, replace this byte with last byte of packet
    };

    // Compress V2 constants
    enum
    {
        COMPRESS_V2_ESCAPE = 0x50,

        // Compression algs
        OVPN_COMPv2_NONE = 0,
        OVPN_COMPv2_LZ4 = 1,
    };

    Compress(const Frame::Ptr &frame_arg,
             const SessionStats::Ptr &stats_arg)
        : frame(frame_arg), stats(stats_arg)
    {
    }

    void error(BufferAllocated &buf)
    {
        stats->error(Error::COMPRESS_ERROR);
        buf.reset_size();
    }

    void do_swap(Buffer &buf, unsigned char op)
    {
        if (buf.size())
        {
            buf.push_back(buf[0]);
            buf[0] = op;
        }
        else
            buf.push_back(op);
    }

    void do_unswap(Buffer &buf)
    {
        if (buf.size() >= 2)
        {
            const unsigned char first = buf.pop_back();
            buf.push_front(first);
        }
    }

    // Push a COMPRESS_V2 header byte (value).
    // Pass value == 0 to omit push.
    void v2_push(Buffer &buf, unsigned char value)
    {
        unsigned char uc = buf[0];
        if (value == 0 && uc != COMPRESS_V2_ESCAPE)
            return;
        unsigned char *esc = buf.prepend_alloc(2);
        esc[0] = COMPRESS_V2_ESCAPE;
        esc[1] = value;
    }

    // Pull a COMPRESS_V2 header byte.
    // Returns the compress op (> 0) on success.
    // Returns 0 if no compress op.
    int v2_pull(Buffer &buf)
    {
        unsigned char uc = buf[0];
        if (uc != COMPRESS_V2_ESCAPE)
            return 0;
        uc = buf[1];
        buf.advance(2);
        return uc;
    }

    Frame::Ptr frame;
    SessionStats::Ptr stats;
};
} // namespace openvpn

// include compressor implementations here
#include <openvpn/compress/compnull.hpp>
#include <openvpn/compress/compstub.hpp>

#ifndef NO_LZO
#include <openvpn/compress/lzoselect.hpp>
#endif
#ifdef HAVE_LZ4
#include <openvpn/compress/lz4.hpp>
#endif
#ifdef HAVE_SNAPPY
#include <openvpn/compress/snappy.hpp>
#endif

namespace openvpn {
class CompressContext
{
  public:
    enum Type
    {
        NONE,
        COMP_STUB,   // generic compression stub
        COMP_STUBv2, // generic compression stub using v2 protocol
        ANY,         // placeholder for any method on client, before server assigns it
        ANY_LZO,     // placeholder for LZO or LZO_STUB methods on client, before server assigns it
        LZO,
        LZO_SWAP,
        LZO_STUB,
        LZ4,
        LZ4v2,
        SNAPPY,
    };

    OPENVPN_SIMPLE_EXCEPTION(compressor_unavailable);

    CompressContext()
    {
    }

    CompressContext(const Type t, const bool asym)
        : asym_(asym) // asym indicates asymmetrical compression where only downlink is compressed
    {
        if (!compressor_available(t))
            throw compressor_unavailable();
        type_ = t;
    }

    Type type() const
    {
        return type_;
    }
    bool asym() const
    {
        return asym_;
    }

    unsigned int extra_payload_bytes() const
    {
        switch (type_)
        {
        case NONE:
            return 0;
        case COMP_STUBv2:
        case LZ4v2:
            return 2; // worst case
        default:
            return 1;
        }
    }

    Compress::Ptr new_compressor(const Frame::Ptr &frame, const SessionStats::Ptr &stats)
    {
        switch (type_)
        {
        case NONE:
            return new CompressNull(frame, stats);
        case ANY_LZO:
        case LZO_STUB:
            return new CompressStub(frame, stats, false);
        case ANY:
        case COMP_STUB:
            return new CompressStub(frame, stats, true);
        case COMP_STUBv2:
            return new CompressStubV2(frame, stats);
#ifndef NO_LZO
        case LZO:
            return new CompressLZO(frame, stats, false, asym_);
        case LZO_SWAP:
            return new CompressLZO(frame, stats, true, asym_);
#endif
#ifdef HAVE_LZ4
        case LZ4:
            return new CompressLZ4(frame, stats, asym_);
        case LZ4v2:
            return new CompressLZ4v2(frame, stats, asym_);
#endif
#ifdef HAVE_SNAPPY
        case SNAPPY:
            return new CompressSnappy(frame, stats, asym_);
#endif
        default:
            throw compressor_unavailable();
        }
    }

    static bool compressor_available(const Type t)
    {
        switch (t)
        {
        case NONE:
        case ANY:
        case ANY_LZO:
        case LZO_STUB:
        case COMP_STUB:
        case COMP_STUBv2:
            return true;
        case LZO:
        case LZO_SWAP:
#ifndef NO_LZO
            return true;
#else
            return false;
#endif
        case LZ4:
#ifdef HAVE_LZ4
            return true;
#else
            return false;
#endif
        case LZ4v2:
#ifdef HAVE_LZ4
            return true;
#else
            return false;
#endif
        case SNAPPY:
#ifdef HAVE_SNAPPY
            return true;
#else
            return false;
#endif
        default:
            return false;
        }
    }

    // On the client, used to tell server which compression methods we support.
    // Includes compression V1 and V2 methods.
    const char *peer_info_string() const
    {
        switch (type_)
        {
#ifndef NO_LZO
        case LZO:
            return "IV_LZO=1\n";
        case LZO_SWAP:
            return "IV_LZO_SWAP=1\n";
#endif
#ifdef HAVE_LZ4
        case LZ4:
            return "IV_LZ4=1\n";
#endif
#ifdef HAVE_LZ4
        case LZ4v2:
            return "IV_LZ4v2=1\n";
#endif
#ifdef HAVE_SNAPPY
        case SNAPPY:
            return "IV_SNAPPY=1\n";
#endif
        case LZO_STUB:
        case COMP_STUB:
        case COMP_STUBv2:
            return "IV_LZO_STUB=1\n"
                   "IV_COMP_STUB=1\n"
                   "IV_COMP_STUBv2=1\n";
        case ANY:
            return
#ifdef HAVE_SNAPPY
                "IV_SNAPPY=1\n"
#endif
#ifndef NO_LZO
                "IV_LZO=1\n"
                "IV_LZO_SWAP=1\n"
#else
                "IV_LZO_STUB=1\n"
#endif
#ifdef HAVE_LZ4
                "IV_LZ4=1\n"
                "IV_LZ4v2=1\n"
#endif
                "IV_COMP_STUB=1\n"
                "IV_COMP_STUBv2=1\n";
        case ANY_LZO:
            return
#ifndef NO_LZO
                "IV_LZO=1\n"
                "IV_LZO_SWAP=1\n"
#else
                "IV_LZO_STUB=1\n"
#endif
                "IV_COMP_STUB=1\n"
                "IV_COMP_STUBv2=1\n";
        default:
            return nullptr;
        }
    }

    // On the client, used to tell server which compression methods we support.
    // Limited only to compression V1 methods.
    const char *peer_info_string_v1() const
    {
        switch (type_)
        {
#ifndef NO_LZO
        case LZO:
            return "IV_LZO=1\n";
        case LZO_SWAP:
            return "IV_LZO_SWAP=1\n";
#endif
#ifdef HAVE_LZ4
        case LZ4:
            return "IV_LZ4=1\n";
#endif
#ifdef HAVE_SNAPPY
        case SNAPPY:
            return "IV_SNAPPY=1\n";
#endif
        case LZO_STUB:
        case COMP_STUB:
            return "IV_LZO_STUB=1\n"
                   "IV_COMP_STUB=1\n";
        case ANY:
            return
#ifdef HAVE_SNAPPY
                "IV_SNAPPY=1\n"
#endif
#ifndef NO_LZO
                "IV_LZO=1\n"
                "IV_LZO_SWAP=1\n"
#else
                "IV_LZO_STUB=1\n"
#endif
#ifdef HAVE_LZ4
                "IV_LZ4=1\n"
#endif
                "IV_COMP_STUB=1\n";
        case ANY_LZO:
            return
#ifndef NO_LZO
                "IV_LZO=1\n"
                "IV_LZO_SWAP=1\n"
#else
                "IV_LZO_STUB=1\n"
#endif
                "IV_COMP_STUB=1\n";
        default:
            return nullptr;
        }
    }

    const char *options_string() const
    {
        switch (type_)
        {
        case LZO:
        case LZO_STUB:
        case SNAPPY:
        case LZ4:
        case LZ4v2:
        case LZO_SWAP:
        case COMP_STUB:
        case COMP_STUBv2:
        case ANY:
        case ANY_LZO:
            return "comp-lzo";
        default:
            return nullptr;
        }
    }

    const char *str() const
    {
        switch (type_)
        {
        case LZO:
            return "LZO";
        case LZO_SWAP:
            return "LZO_SWAP";
        case LZ4:
            return "LZ4";
        case LZ4v2:
            return "LZ4v2";
        case SNAPPY:
            return "SNAPPY";
        case LZO_STUB:
            return "LZO_STUB";
        case COMP_STUB:
            return "COMP_STUB";
        case COMP_STUBv2:
            return "COMP_STUBv2";
        case ANY:
            return "ANY";
        case ANY_LZO:
            return "ANY_LZO";
        default:
            return "NONE";
        }
    }

    /* This function returns a parseable string representation of the compress
     * method. NOTE: returns nullptr if no mapping is possible */
    const char *method_to_string() const
    {
        switch (type_)
        {
        case LZO:
            return "lzo";
        case LZO_SWAP:
            return "lzo-swap";
        case LZO_STUB:
            return "lzo-stub";
        case LZ4:
            return "lz4";
        case LZ4v2:
            return "lz4v2";
        case SNAPPY:
            return "snappy";
        case COMP_STUB:
            return "stub";
        case COMP_STUBv2:
            return "stub-v2";
        default:
            return nullptr;
        }
    }

    static Type parse_method(const std::string &method)
    {
        if (method == "stub-v2")
            return COMP_STUBv2;
        else if (method == "lz4-v2")
            return LZ4v2;
        else if (method == "lz4")
            return LZ4;
        else if (method == "lzo")
            return LZO;
        else if (method == "lzo-swap")
            return LZO_SWAP;
        else if (method == "lzo-stub")
            return LZO_STUB;
        else if (method == "snappy")
            return SNAPPY;
        else if (method == "stub")
            return COMP_STUB;
        else
            return NONE;
    }

    static Type stub(const Type t)
    {
        switch (t)
        {
        case COMP_STUBv2:
        case LZ4v2:
            return COMP_STUBv2;
        default:
            return COMP_STUB;
        }
    }

    /**
     *  Checks if the compression type is one of the available stub modes
     *
     * @param t  The CompressContext::Type value
     * @return   Returns true if the type is one of the *_STUB{,v2} types,
     *           otherwise false.
     */
    static bool is_any_stub(const Type t)
    {
        switch (t)
        {
        case LZO_STUB:
        case COMP_STUB:
        case COMP_STUBv2:
            return true;
        default:
            return false;
        }
    }

    static void init_static()
    {
#ifndef NO_LZO
        CompressLZO::init_static();
#endif
    }

  private:
    Type type_ = NONE;
    bool asym_ = false;
};

} // namespace openvpn

#endif // OPENVPN_COMPRESS_COMPRESS_H