/*
 * Copyright (C) 2007-2012 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;

namespace Com.Xagasoft.Gats
{
    /// <summary>
    /// Encapsulates a single floating point value.
    /// </summary>
    /// <remarks>
    /// The GATS floating point encoding is bit-exact with any standard
    /// floating point encoding similar to the IEEE encoding.  This means that
    /// unlike textual encoding you will always get the exact same floating
    /// point value back that you encoded.  This format is arbitrary precision
    /// and not dependant on platform or hardware.
    ///
    /// Although the format is arbitrary precision, the backend in C# uses a
    /// double for maximum precision without resorting to a software arbitrary
    /// precision library.
    ///
    /// Interestingly, unlike many other languages, C# provides a decimal type
    /// that is also floating point, however the decimal type is encoded using
    /// a bcd-like scheme.  This makes it an excellent choice for many human
    /// activities, but it cannot be encoded precisely as a GatsFloat.  If you
    /// would like to preserve the decimal nature of those types it may be
    /// better to encode them as strings.
    ///
    /// In encoding, the GATS float uses two different type specifiers, an 'f'
    /// indicates a normal floating point value.  An 'F' represents a special
    /// value: positive or negative NaN, infinity, or zero.
    /// </remarks>
    public class GatsFloat : GatsObject
    {
        private static readonly double Log256 = Math.Log( 256.0 );
        public double Value { get; set; }

        public GatsFloat()
        {
            Value = 0.0;
        }

        public GatsFloat( double val )
        {
            Value = val;
        }

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

        public override void Read( Stream s, char type )
        {
            if( type == 'F' )
            {
                int subType = s.ReadByte();
                if( subType == -1 )
                    throw new GatsException( GatsException.Type.PrematureEnd );
                switch( (char)subType )
                {
                    case 'N': Value = -Double.NaN;                  break;
                    case 'n': Value = Double.NaN;                   break;
                    case 'I': Value = Double.NegativeInfinity;      break;
                    case 'i': Value = Double.PositiveInfinity;      break;
                    case 'Z': Value = -0.0;                         break;
                    case 'z': Value = 0.0;                          break;
                }
            }
            else if( type == 'f' )
            {
                int len = (int)GatsInteger.ReadPackedInt( s );
                bool neg = false;
                if( len < 0 )
                {
                    neg = true;
                    len = -len;
                }
                int[] buf = new int[len];
                for( int j = 0; j < len; j++ )
                {
                    buf[j] = s.ReadByte();
                }
                Value = 0.0;
                for( int j = len-1; j > 0; j-- )
                {
                    Value = (Value+(double)buf[j]) * (1.0/256.0);
                }
                Value += buf[0];
                long scale = GatsInteger.ReadPackedInt( s );
                Value *= Math.Pow( 256.0, scale );
                if( neg )
                    Value = -Value;
            }
        }

        public override void Write( Stream s )
        {
            if( Value == 0.0 )
            {
                s.WriteByte( (int)'F' );
                s.WriteByte( (int)'z' );
            }
            else if( Double.IsInfinity( Value ) )
            {
                s.WriteByte( (int)'F' );
                if( Double.IsNegativeInfinity( Value ) )
                    s.WriteByte( (int)'I' );
                else
                    s.WriteByte( (int)'i' );
            }
            else if( Double.IsNaN( Value ) )
            {
                s.WriteByte( (int)'F' );
                s.WriteByte( (int)'n' );
            }
            else
            {
                s.WriteByte( (int)'f' );
                double d = Value;
                bool neg = false;
                if( d < 0.0 )
                {
                    neg = true;
                    d = -d;
                }
               
                MemoryStream ms = new MemoryStream();
                long scale = (long)(Math.Log( d ) / Log256);
                if( scale < 0 ) scale--;
                d /= Math.Pow( 256.0, scale );
                ms.WriteByte( (byte)d );
                d -= (int)d;
                for( int j = 0; j < 150 && d != 0.0; j++ )
                {
                    d = d*256.0;
                    ms.WriteByte( (byte)d );
                    d -= (int)d;
                }
                byte[] msbuf = ms.ToArray();
                if( neg )
                    GatsInteger.WritePackedInt( s, -msbuf.Length );
                else
                    GatsInteger.WritePackedInt( s, msbuf.Length );
                s.Write( msbuf, 0, msbuf.Length );
                GatsInteger.WritePackedInt( s, scale );
            }
        }
    }
}