/*
 * 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;

namespace Com.Xagasoft.Gats
{
    /// <summary>
    /// Encapsulates a single integer value.
    /// </summary>
    /// <remarks>
    /// The GATS integer encoding is arbitrary precision, and only consumes as
    /// many bytes as it needs to represent a given number.  There is no such
    /// thing as an unsigned GATS integer.
    ///
    /// Internally the GatsInteger stores it's value in a long.
    ///
    /// In encoding, the type specifier for a GATS integer is 'i'.
    /// </remarks>
    public class GatsInteger : GatsObject
    {
        public long Value { get; set; }

        public GatsInteger( long val=0 )
        {
            Value = val;
        }

        public override string ToString()
        {
            return Value.ToString();
        }

        public override void Read( Stream s, char cType )
        {
            Value = ReadPackedInt( s );
        }

        public override void Write( Stream s )
        {
            s.WriteByte( (int)'i' );
            WritePackedInt( s, Value );
        }

        public static long ReadPackedInt( Stream s )
        {
            int b;
            long rOut = 0;
            bool bNeg;

            b = s.ReadByte();
            if( b == -1 )
                throw new GatsException( GatsException.Type.PrematureEnd );
            bNeg = (b&0x40) == 0x40;
            rOut |= ((long)b)&0x3F;
            int c = 0;
            while( (b&0x80) == 0x80 )
            {
                b = s.ReadByte();
                if( b == -1 )
                    throw new GatsException( GatsException.Type.PrematureEnd );
                rOut |= (long)(b&0x7F) << (6+7*(c++));
            }
            if( bNeg )
                return -rOut;
            return rOut;
        }

        public static void WritePackedInt( Stream s, long iIn )
        {
            byte b;

            if( iIn < 0 )
            {
                iIn = -iIn;
                b = (byte)(iIn&0x3F);
                if( iIn > b )
                    b |= 0x80 | 0x40;
                else
                    b |= 0x40;
            }
            else
            {
                b = (byte)(iIn&0x3F);
                if( iIn > b )
                    b |= 0x80;
            }
            s.WriteByte( b );
            iIn = iIn >> 6;

            while( iIn > 0 )
            {
                b = (byte)(iIn&0x7F);
                if( iIn > b )
                    b |= 0x80;
                s.WriteByte( b );
                iIn = iIn >> 7;
            }
        }
    };
}