/* Copyright (C) 2014 Tal Aloni <tal.aloni.il@gmail.com>. All rights reserved.
 * 
 * You can redistribute this program and/or modify it under the terms of
 * the GNU Lesser Public License as published by the Free Software Foundation,
 * either version 3 of the License, or (at your option) any later version.
 */
using System;
using System.Collections.Generic;
using System.IO;
using System.Text;
using Utilities;

namespace SMBLibrary.NetBios
{
    public class NetBiosUtils
    {
        /// <summary>
        /// The NetBIOS naming convention allows for 16 characters in a NetBIOS name.
        /// Microsoft, however, limits NetBIOS names to 15 characters and uses the 16th character as a NetBIOS suffix
        /// See http://support.microsoft.com/kb/163409/en-us
        /// </summary>
        public static string GetMSNetBiosName(string name, NetBiosSuffix suffix)
        {
            if (name.Length > 15)
            {
                name = name.Substring(0, 15);
            }
            else if (name.Length < 15)
            {
                name = name.PadRight(15);
            }

            return name + (char)suffix;
        }

        public static string GetNameFromMSNetBiosName(string netBiosName)
        {
            if (netBiosName.Length != 16)
            {
                throw new ArgumentException("Invalid MS NetBIOS name");
            }

            netBiosName = netBiosName.Substring(0, 15);
            return netBiosName.TrimEnd(' ');
        }

        public static byte[] EncodeName(string name, NetBiosSuffix suffix, string scopeID)
        {
            string netBiosName = GetMSNetBiosName(name, suffix);
            return EncodeName(netBiosName, scopeID);
        }

        /// <param name="name">NetBIOS name</param>
        /// <param name="scopeID">dot-separated labels, formatted per DNS naming rules</param>
        public static byte[] EncodeName(string netBiosName, string scopeID)
        {
            string domainName = FirstLevelEncoding(netBiosName, scopeID);
            return SecondLevelEncoding(domainName);
        }

        // The conversion of a NetBIOS name to a format complying with DNS "best practices".
        // NetBIOS names may contain characters which are not considered valid for use in DNS names,
        // yet RFC 1001 and RFC 1002 attempted to map the NetBIOS name space into the DNS name space.
        // To work around this conflict, NetBIOS names are encoded by splitting each byte of the name
        // into two nibbles and then adding the value of 'A' (0x41).
        // Thus, the '&' character (0x26) would be encoded as "CG".
        // NetBIOS names are usually padded with spaces before being encoded. 
        /// <param name="name">NetBIOS name</param>
        /// <param name="scopeID">dot-separated labels, formatted per DNS naming rules</param>
        public static string FirstLevelEncoding(string netBiosName, string scopeID)
        {
            // RFC 1001: NetBIOS names as seen across the client interface to NetBIOS are exactly 16 bytes long
            if (netBiosName.Length != 16)
            {
                throw new ArgumentException("Invalid MS NetBIOS name");
            }

            StringBuilder builder = new StringBuilder();
            for (int index = 0; index < netBiosName.Length; index++)
            {
                byte c = (byte)netBiosName[index];
                byte high = (byte)(0x41 + (c >> 4));
                byte low = (byte)(0x41 + (c & 0x0F));
                builder.Append((char)high);
                builder.Append((char)low);
            }

            if (scopeID.Length > 0)
            {
                builder.Append(".");
                builder.Append(scopeID);
            }

            return builder.ToString();
        }

        // Domain names messages are expressed in terms of a sequence
        // of labels.  Each label is represented as a one octet length
        // field followed by that number of octets.  Since every domain
        // name ends with the null label of the root, a compressed
        // domain name is terminated by a length byte of zero
        /// <summary>
        /// The on-the-wire format of an NBT name. The encoding scheme replaces the familiar dot characters
        /// used in DNS names with a byte containing the length of the next label.
        /// </summary>
        public static byte[] SecondLevelEncoding(string domainName)
        {
            string[] labels = domainName.Split('.');
            int length = 1; // null terminator
            for (int index = 0; index < labels.Length; index++)
            {
                length += 1 + labels[index].Length;
                if (labels[index].Length > 63)
                {
                    throw new ArgumentException("Invalid NetBIOS label length");
                }
            }
            
            byte[] result = new byte[length];
            int offset = 0;
            foreach(string label in labels)
            {
                result[offset] = (byte)label.Length;
                offset++;
                ByteWriter.WriteAnsiString(result, offset, label, label.Length);
                offset += label.Length;
            }

            result[offset] = 0; // null termination
            return result;
        }

        public static string DecodeName(byte[] buffer, ref int offset)
        {
            string domainName = SecondLevelDecoding(buffer, ref offset);
            string name = domainName.Split('.')[0];
            return FirstLevelDecoding(name);
        }

        public static string SecondLevelDecoding(byte[] buffer, ref int offset)
        {
            StringBuilder builder = new StringBuilder();

            byte labelLength = ByteReader.ReadByte(buffer, ref offset);
            while (labelLength > 0)
            {
                if (builder.Length > 0)
                {
                    builder.Append(".");
                }

                // The high order two bits of the length field must be zero
                if (labelLength > 63)
                {
                    throw new ArgumentException("Invalid NetBIOS label length");
                }

                string label = ByteReader.ReadAnsiString(buffer, offset, labelLength);
                builder.Append(label);
                offset += labelLength;

                labelLength = ByteReader.ReadByte(buffer, ref offset);
            }

            return builder.ToString();
        }

        public static string FirstLevelDecoding(string name)
        {
            StringBuilder builder = new StringBuilder();

            for(int index = 0; index < name.Length; index += 2)
            {
                byte c0 = (byte)name[index];
                byte c1 = (byte)name[index + 1];
                byte high = (byte)(((c0 - 0x41) & 0xF) << 4);
                byte low = (byte)((c1 - 0x41) & 0xF);
                byte c = (byte)(high | low);
                builder.Append((char)c);
            }

            return builder.ToString();
        }

        public static void WriteNamePointer(byte[] buffer, ref int offset, int nameOffset)
        {
            WriteNamePointer(buffer, offset, nameOffset);
            offset += 2;
        }

        /// <summary>
        /// Will write a 2 bytes pointer to a name
        /// Note: NetBIOS implementations can only use label string pointers in Name Service packets
        /// </summary>
        public static void WriteNamePointer(byte[] buffer, int offset, int nameOffset)
        {
            ushort pointer = (ushort)(0xC000 | (nameOffset & 0x3FFF));
            BigEndianWriter.WriteUInt16(buffer, offset, pointer);
        }

        public static void WriteNamePointer(Stream stream, int nameOffset)
        {
            ushort pointer = (ushort)(0xC000 | (nameOffset & 0x3FFF));
            BigEndianWriter.WriteUInt16(stream, pointer);
        }
    }
}