//
// Copyright (c) ZeroC, Inc. All rights reserved.
//

namespace IceInternal
{
    public sealed class Protocol
    {
        //
        // Size of the Ice protocol header
        //
        // Magic number (4 bytes)
        // Protocol version major (Byte)
        // Protocol version minor (Byte)
        // Encoding version major (Byte)
        // Encoding version minor (Byte)
        // Message type (Byte)
        // Compression status (Byte)
        // Message size (Int)
        //
        internal const int headerSize = 14;

        //
        // The magic number at the front of each message
        //
        internal static readonly byte[] magic = new byte[] { 0x49, 0x63, 0x65, 0x50 }; // 'I', 'c', 'e', 'P'

        //
        // The current Ice protocol and encoding version
        //
        internal const byte protocolMajor = 1;
        internal const byte protocolMinor = 0;
        internal const byte protocolEncodingMajor = 1;
        internal const byte protocolEncodingMinor = 0;

        internal const byte encodingMajor = 1;
        internal const byte encodingMinor = 1;

        public const byte OPTIONAL_END_MARKER           = 0xFF;

        public const byte FLAG_HAS_TYPE_ID_STRING       = (1<<0);
        public const byte FLAG_HAS_TYPE_ID_INDEX        = (1<<1);
        public const byte FLAG_HAS_TYPE_ID_COMPACT      = (1<<1 | 1<<0);
        public const byte FLAG_HAS_OPTIONAL_MEMBERS     = (1<<2);
        public const byte FLAG_HAS_INDIRECTION_TABLE    = (1<<3);
        public const byte FLAG_HAS_SLICE_SIZE           = (1<<4);
        public const byte FLAG_IS_LAST_SLICE            = (1<<5);

        //
        // The Ice protocol message types
        //
        internal const byte requestMsg = 0;
        internal const byte requestBatchMsg = 1;
        internal const byte replyMsg = 2;
        internal const byte validateConnectionMsg = 3;
        internal const byte closeConnectionMsg = 4;

        internal static readonly byte[] requestHdr = new byte[]
        {
            magic[0], magic[1], magic[2], magic[3],
            protocolMajor, protocolMinor,
            protocolEncodingMajor, protocolEncodingMinor,
            requestMsg,
            0, // Compression status.
            0, 0, 0, 0, // Message size (placeholder).
            0, 0, 0, 0  // Request ID (placeholder).
        };

        internal static readonly byte[] requestBatchHdr = new byte[]
        {
            magic[0], magic[1], magic[2], magic[3],
            protocolMajor, protocolMinor,
            protocolEncodingMajor, protocolEncodingMinor,
            requestBatchMsg,
            0, // Compression status.
            0, 0, 0, 0, // Message size (placeholder).
            0, 0, 0, 0  // Number of requests in batch (placeholder).
        };

        internal static readonly byte[] replyHdr = new byte[]
        {
            magic[0], magic[1], magic[2], magic[3],
            protocolMajor, protocolMinor,
            protocolEncodingMajor, protocolEncodingMinor,
            replyMsg,
            0, // Compression status.
            0, 0, 0, 0 // Message size (placeholder).
        };

        internal static void
        checkSupportedProtocol(Ice.ProtocolVersion v)
        {
            if(v.major != protocolMajor || v.minor > protocolMinor)
            {
                throw new Ice.UnsupportedProtocolException("", v, Ice.Util.currentProtocol);
            }
        }

        public static void
        checkSupportedProtocolEncoding(Ice.EncodingVersion v)
        {
            if(v.major != protocolEncodingMajor || v.minor > protocolEncodingMinor)
            {
                throw new Ice.UnsupportedEncodingException("", v, Ice.Util.currentProtocolEncoding);
            }
        }

        internal static void
        checkSupportedEncoding(Ice.EncodingVersion v)
        {
            if(v.major != encodingMajor || v.minor > encodingMinor)
            {
                throw new Ice.UnsupportedEncodingException("", v, Ice.Util.currentEncoding);
            }
        }

        //
        // Either return the given protocol if not compatible, or the greatest
        // supported protocol otherwise.
        //
        internal static Ice.ProtocolVersion
        getCompatibleProtocol(Ice.ProtocolVersion v)
        {
            if(v.major != Ice.Util.currentProtocol.major)
            {
                return v; // Unsupported protocol, return as is.
            }
            else if(v.minor < Ice.Util.currentProtocol.minor)
            {
                return v; // Supported protocol.
            }
            else
            {
                //
                // Unsupported but compatible, use the currently supported
                // protocol, that's the best we can do.
                //
                return Ice.Util.currentProtocol;
            }
        }

        //
        // Either return the given encoding if not compatible, or the greatest
        // supported encoding otherwise.
        //
        internal static Ice.EncodingVersion
        getCompatibleEncoding(Ice.EncodingVersion v)
        {
            if(v.major != Ice.Util.currentEncoding.major)
            {
                return v; // Unsupported encoding, return as is.
            }
            else if(v.minor < Ice.Util.currentEncoding.minor)
            {
                return v; // Supported encoding.
            }
            else
            {
                //
                // Unsupported but compatible, use the currently supported
                // encoding, that's the best we can do.
                //
                return Ice.Util.currentEncoding;
            }
        }

        internal static bool
        isSupported(Ice.ProtocolVersion version, Ice.ProtocolVersion supported)
        {
            return version.major == supported.major && version.minor <= supported.minor;
        }

        internal static bool
        isSupported(Ice.EncodingVersion version, Ice.EncodingVersion supported)
        {
            return version.major == supported.major && version.minor <= supported.minor;
        }

        private Protocol()
        {
        }
    }

}