/***************************************************************************
 *                              PacketReader.cs
 *                            -------------------
 *   begin                : May 1, 2002
 *   copyright            : (C) The RunUO Software Team
 *   email                : info@runuo.com
 *
 *   $Id$
 *
 ***************************************************************************/

/***************************************************************************
 *
 *   This program is free software; you can redistribute it and/or modify
 *   it under the terms of the GNU General Public License as published by
 *   the Free Software Foundation; either version 2 of the License, or
 *   (at your option) any later version.
 *
 ***************************************************************************/

using System;
using System.Buffers;
using System.IO;
using System.Text;

namespace Server.Network
{
  public ref struct PacketReader
  {
    private SequenceReader<byte> m_Reader;

    public SequencePosition Position => m_Reader.Position;
    public long Length => m_Reader.Length;
    public long Consumed => m_Reader.Consumed;
    public long Remaining => m_Reader.Remaining;

    public PacketReader(ReadOnlySequence<byte> seq) => m_Reader = new SequenceReader<byte>(seq);

    public byte Peek() => m_Reader.TryPeek(out byte value) ? value : (byte)0;

    public void Trace(NetState state)
    {
      try
      {
        using StreamWriter sw = new StreamWriter("Packets.log", true);
        byte[] buffer = m_Reader.Sequence.ToArray();

        if (buffer.Length > 0)
          sw.WriteLine("Client: {0}: Unhandled packet 0x{1:X2}", state, buffer[0]);

        using (MemoryStream ms = new MemoryStream(buffer))
        {
          Utility.FormatBuffer(sw, ms, buffer.Length);
        }

        sw.WriteLine();
        sw.WriteLine();
      }
      catch
      {
        // ignored
      }
    }

    public SequencePosition Seek(long offset, SeekOrigin origin)
    {
      switch (origin)
      {
        case SeekOrigin.Begin:
          if (offset < m_Reader.Consumed)
            m_Reader.Rewind(m_Reader.Consumed - Math.Max(offset, 0L));
          else
            m_Reader.Advance(offset - m_Reader.Consumed);
          break;
        case SeekOrigin.Current:
          if (offset < 0)
            m_Reader.Rewind(Math.Min(m_Reader.Consumed, offset * -1));
          else
            m_Reader.Advance(Math.Min(m_Reader.Remaining, offset));
          break;
        case SeekOrigin.End:
          long count = m_Reader.Remaining - offset;
          if (count < 0)
            m_Reader.Rewind(count * -1);
          else if (count > 0)
            m_Reader.Advance(count);
          break;
      }

      return m_Reader.Position;
    }

    public bool TryReadByte(out byte value) => m_Reader.TryRead(out value);

    public int ReadInt32() => m_Reader.TryReadBigEndian(out int value) ? value : 0;

    public short ReadInt16() => m_Reader.TryReadBigEndian(out short value) ? value : (short)0;

    public byte ReadByte() => m_Reader.TryRead(out byte value) ? value : (byte)0;

    public uint ReadUInt32() => (uint)ReadInt32();

    public ushort ReadUInt16() => (ushort)ReadInt16();

    public sbyte ReadSByte() => (sbyte)ReadByte();

    public bool ReadBoolean() => ReadByte() != 0;

    public bool IsSafeChar(int c) => c >= 0x20 && c < 0xFFFE;

    public string ReadUTF8StringSafe()
    {
      StringBuilder sb = new StringBuilder();
      bool end = false;

      while (!(end |= m_Reader.End))
      {
        ReadOnlySpan<byte> span = m_Reader.UnreadSpan;
        int count = 0;
        bool safe = true;
        while (count < span.Length)
        {
          byte chr = span[count];
          if (chr == 0)
          {
            end = true;
            break;
          }

          if (!IsSafeChar(chr))
          {
            safe = false;
            break;
          }

          count++;
        }

        sb.Append(Encoding.UTF8.GetString(span.Slice(0, count)));
        m_Reader.Advance(count + (safe ? 1 : 0));
      }

      return sb.ToString();
    }

    public string ReadUTF8String()
    {
      StringBuilder sb = new StringBuilder();
      bool end = false;

      while (!(end |= m_Reader.End))
      {
        ReadOnlySpan<byte> span = m_Reader.UnreadSpan;
        int count = 0;
        while (count < span.Length)
        {
          if (span[count] == 0)
          {
            end = true;
            break;
          }

          count++;
        }

        sb.Append(Encoding.UTF8.GetString(span.Slice(0, count)));
        m_Reader.Advance(count);
      }

      return sb.ToString();
    }

    public string ReadString()
    {
      StringBuilder sb = new StringBuilder();
      bool end = false;

      while (!(end |= m_Reader.End))
      {
        ReadOnlySpan<byte> span = m_Reader.UnreadSpan;
        int count = 0;
        while (count < span.Length)
        {
          if (span[count] == 0)
          {
            end = true;
            break;
          }

          count++;
        }

        sb.Append(Encoding.ASCII.GetString(span.Slice(0, count)));
        m_Reader.Advance(count);
      }

      return sb.ToString();
    }

    public string ReadString(int size)
    {
      StringBuilder sb = new StringBuilder();
      bool end = false;

      while (!(end |= m_Reader.End) && size > 0)
      {
        ReadOnlySpan<byte> span = m_Reader.UnreadSpan;
        int count = 0;
        while (count < span.Length && size > 0)
        {
          if (span[count] == 0)
          {
            end = true;
            break;
          }

          count++;
          size--;
        }

        sb.Append(Encoding.ASCII.GetString(span.Slice(0, count)));
        m_Reader.Advance(count);
      }

      if (size > 0)
        m_Reader.Advance(size);

      return sb.ToString();
    }

    public bool IsSafeChar(int c) => c >= 0x20 && c < 0xFFFE;

    public string ReadUTF8StringSafe(int fixedLength)
    {
      StringBuilder sb = new StringBuilder();
      bool end = false;

      while (!(end |= m_Reader.End))
      {
        ReadOnlySpan<byte> span = m_Reader.UnreadSpan;
        int count = 0;
        bool safe = true;
        while (count < span.Length)
        {
          byte chr = span[count];
          if (chr == 0)
          {
            end = true;
            break;
          }

          if (!IsSafeChar(chr))
          {
            safe = false;
            break;
          }

          count++;
        }

        sb.Append(Encoding.ASCII.GetString(span.Slice(0, count)));
        m_Reader.Advance(count + (safe ? 1 : 0));
      }

      return sb.ToString();
    }

    public string ReadStringSafe(int size)
    {
      StringBuilder sb = new StringBuilder();
      bool end = false;

      while (!(end |= m_Reader.End) && size > 0)
      {
        ReadOnlySpan<byte> span = m_Reader.UnreadSpan;
        int count = 0;
        bool safe = true;
        while (count < span.Length && size > 0)
        {
          byte chr = span[count];
          if (chr == 0)
          {
            end = true;
            break;
          }

          if (!IsSafeChar(chr))
          {
            safe = false;
            break;
          }

          count++;
          size--;
        }

        sb.Append(Encoding.ASCII.GetString(span.Slice(0, count)));
        m_Reader.Advance(size + (safe ? 1 : 0));
      }

    public string ReadUTF8String() =>
      Utility.UTF8.GetString(
        m_Reader.TryReadTo(out ReadOnlySpan<byte> span, (byte)'\0', true) ? span :
          m_Reader.Sequence.Slice(m_Reader.Position, m_Reader.Remaining).ToArray()
      );

    public string ReadUnicodeStringLESafe(int fixedLength)
    {
      StringBuilder sb = new StringBuilder();

      while (fixedLength-- > 0 && m_Reader.TryReadLittleEndian(out short c) && c != 0)
        if (IsSafeChar(c))
          sb.Append((char)c);

      if (fixedLength > 0)
        m_Reader.Advance(fixedLength * 2);

      return sb.ToString();
    }

    public string ReadUnicodeStringLESafe()
    {
      StringBuilder sb = new StringBuilder();

      while (m_Reader.TryReadLittleEndian(out short c) && c != 0)
        if (IsSafeChar(c))
          sb.Append((char)c);

      return sb.ToString();
    }

    public string ReadUnicodeString()
    {
      StringBuilder sb = new StringBuilder();

      while (m_Reader.TryReadBigEndian(out short c) && c != 0)
        sb.Append((char)c);

      return sb.ToString();
    }

    public string ReadUnicodeString(int fixedLength)
    {
      StringBuilder sb = new StringBuilder();

      while (fixedLength-- > 0 && m_Reader.TryReadBigEndian(out short c) && c != 0)
        sb.Append((char)c);

      if (fixedLength > 0)
        m_Reader.Advance(fixedLength * 2);

      return sb.ToString();
    }

    public string ReadUnicodeStringSafe()
    {
      StringBuilder sb = new StringBuilder();

      while (m_Reader.TryReadBigEndian(out short c) && c != 0)
        if (IsSafeChar(c))
          sb.Append((char)c);

      return sb.ToString();
    }

    public string ReadUnicodeStringSafe(int fixedLength)
    {
      StringBuilder sb = new StringBuilder();

      while (fixedLength-- > 0 && m_Reader.TryReadBigEndian(out short c) && c != 0)
        if (IsSafeChar(c))
          sb.Append((char)c);

      if (fixedLength > 0)
        m_Reader.Advance(fixedLength * 2);

      return sb.ToString();
    }
  }
}