/*
 * Copyright (C) 2007-2013 Xagasoft, All rights reserved.
 *
 * This file is part of the libgats library and is released under the
 * terms of the license contained in the file LICENSE.
 */

using System.IO;
using System.Net;
using System;

namespace Com.Xagasoft.Gats
{
    /// <summary>
    /// Main I/O interface.  Use this to read and write GATS.
    /// </summary>
    /// <remarks>
    /// GatsStream is not a traditional Stream class, it only can read and
    /// write complete GATS packets.  A GATS packet consists of a version,
    /// size, and a single encoded GATS object (which can be a container).
    ///
    /// This one class handles both reading and writing.  Writing is fairly
    /// straight forward, but for volatile streams like network sockets you'll
    /// probably want to wrap your stream with a buffer before handing it to
    /// GatsStream.
    ///
    /// Reading handles it's own buffering, and will remember what has been
    /// read between calls if it cannot get enough data at once to complete
    /// a single packet.  See the ReadObject docs for more details.
    /// </remarks>
    public class GatsStream
    {
        private Stream s;
        private MemoryStream ReadBuf;
        private int size = -1;
        private int version;
        private BinaryWriter bw = null;
        private BinaryReader br = null;

        /// <summary>
        /// Construct a new GatsStream around a given Stream class.
        /// </summary>
        /// <remarks>
        /// The provided Stream does not need to be opened for both reading and
        /// writing, you can construct a GatsStream around a read only or
        /// write only stream.
        /// </remarks>
        /// <param name="s">Stream to operate on.</param>
        public GatsStream( Stream s )
        {
            this.s = s;
            this.ReadBuf = new MemoryStream();
        }

        /// <summary>
        /// Read a GATS packet and return the contained GatsObject.
        /// </summary>
        /// <remarks>
        /// This reads a complete packet into an internal buffer, parses the
        /// gats object within it, and returns it.  This method will read as
        /// much data as it needs from the stream, but no more.  Not a single
        /// extra byte will be read.
        ///
        /// In the event that an end of stream is encountered, or a partial
        /// packet has been read but no more data can be read at the moment,
        /// this method will maintain it's buffer but return null to the caller.
        /// </remarks>
        /// <returns>
        /// The read object, or null if no object could be read yet.
        /// </returns>
        public GatsObject ReadObject()
        {
            if( size == -1 )
            {
                for(;;)
                {
                    version = s.ReadByte();
                    if( version == -1 )
                        return null;
                    if( version > 0 )
                        break;
                }
            }

            if( br == null )
                this.br = new BinaryReader( s );

            switch( version )
            {
                case 1:
                    // Verion 1 of gats
                    if( size == -1 )
                        size = IPAddress.NetworkToHostOrder( br.ReadInt32() )-5;
                    byte[] buf = new byte[4096];
                    while( ReadBuf.Length < size )
                    {
                        int goal = (int)(size-ReadBuf.Length);
                        if( goal > 4096 )
                            goal = 4096;
                        int amnt = s.Read( buf, 0, goal );
                        if( amnt <= 0 )
                            return null;
                        ReadBuf.Write( buf, 0, amnt );
                    }
                    ReadBuf.Seek( 0, SeekOrigin.Begin );
                    GatsObject ret = GatsObject.Read( ReadBuf );
                    ReadBuf.SetLength( 0 );
                    size = version = -1;
                    return ret;
            }

            return null;
        }

        /// <summary>
        /// Write a GatsObject to the stream in a proper GATS packet.
        /// </summary>
        /// <remarks>
        /// The object passed in is first written to an internal buffer, and
        /// then to the output in several write operations.  This means that
        /// for many applications you will want to buffer the output.  In the
        /// case of writing to files, it could be faster to buffer the output.
        /// In the case of writing to a socket buffering could prevent sending
        /// many small packets.
        ///
        /// No flushing is done by this method, it is left to the caller to
        /// determine the proper time to flush their streams.
        /// </remarks>
        /// <param name="obj">The object to be written.</param>
        public void WriteObject( GatsObject obj )
        {
            MemoryStream ms = new MemoryStream();
            obj.Write( ms );

            if( bw == null )
                this.bw = new BinaryWriter( s );
            bw.Write( (byte)1 );
            bw.Write( IPAddress.HostToNetworkOrder( (int)ms.Length+5 ) );
            bw.Write( ms.GetBuffer(), 0, (int)ms.Length );
        }
    }
}