#region CPL License
/*
Nuclex Framework
Copyright (C) 2002-2009 Nuclex Development Labs

This library is free software; you can redistribute it and/or
modify it under the terms of the IBM Common Public License as
published by the IBM Corporation; either version 1.0 of the
License, or (at your option) any later version.

This library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
IBM Common Public License for more details.

You should have received a copy of the IBM Common Public
License along with this library
*/
#endregion

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Text;

namespace Nuclex.Support {

  /// <summary>Contains helper methods for the string builder class</summary>
  public class StringBuilderHelper {

    /// <summary>Predefined unicode characters for the numbers 0 to 9</summary>
    private static readonly char[] numbers = new char[] {
      '0', '1', '2', '3', '4', '5', '6', '7', '8', '9'
    };

    /// <summary>Clears the contents of a string builder</summary>
    /// <param name="builder">String builder that will be cleared</param>
    public static void Clear(StringBuilder builder) {
      builder.Remove(0, builder.Length);
    }

    /// <summary>
    ///   Appends an integer to a string builder without generating garbage
    /// </summary>
    /// <param name="builder">String builder to which an integer will be appended</param>
    /// <param name="value">Byte that will be appended to the string builder</param>
    /// <remarks>
    ///   The normal StringBuilder.Append() method generates garbage when converting
    ///   integer arguments whereas this method will avoid any garbage, albeit probably
    ///   with a small performance impact compared to the built-in method.
    /// </remarks>
    public static void Append(StringBuilder builder, byte value) {
      recursiveAppend(builder, value);
    }

    /// <summary>
    ///   Appends an integer to a string builder without generating garbage
    /// </summary>
    /// <param name="builder">String builder to which an integer will be appended</param>
    /// <param name="value">Integer that will be appended to the string builder</param>
    /// <remarks>
    ///   The normal StringBuilder.Append() method generates garbage when converting
    ///   integer arguments whereas this method will avoid any garbage, albeit probably
    ///   with a small performance impact compared to the built-in method.
    /// </remarks>
    public static void Append(StringBuilder builder, int value) {
      if(value < 0) {
        builder.Append('-');
        recursiveAppend(builder, -value);
      } else {
        recursiveAppend(builder, value);
      }
    }

    /// <summary>
    ///   Appends an long integer to a string builder without generating garbage
    /// </summary>
    /// <param name="builder">String builder to which an integer will be appended</param>
    /// <param name="value">Long integer that will be appended to the string builder</param>
    /// <remarks>
    ///   The normal StringBuilder.Append() method generates garbage when converting
    ///   integer arguments whereas this method will avoid any garbage, albeit probably
    ///   with a small performance impact compared to the built-in method.
    /// </remarks>
    public static void Append(StringBuilder builder, long value) {
      if(value < 0) {
        builder.Append('-');
        recursiveAppend(builder, -value);
      } else {
        recursiveAppend(builder, value);
      }
    }

    /// <summary>
    ///   Appends a floating point value to a string builder without generating garbage
    /// </summary>
    /// <param name="builder">String builder the value will be appended to</param>
    /// <param name="value">Value that will be appended to the string builder</param>
    public static void Append(StringBuilder builder, float value) {
      const int ExponentBits = 0xFF; // Bit mask for the exponent bits
      const int FractionalBitCount = 23; // Number of bits for fractional part
      const int ExponentBias = 127; // Bias subtraced from exponent
      const int NumericBitCount = 31; // Bits without sign
      
      // You do not modify these as they're calculated based on the 
      const int FractionalBits = (2 << FractionalBitCount) - 1;
      const int HighestFractionalBit = (1 << FractionalBitCount);
      const int FractionalBitCountPlusOne = FractionalBitCount + 1;

      int intValue = FloatHelper.ReinterpretAsInt(value);

      int exponent = ((intValue >> FractionalBitCount) & ExponentBits) - ExponentBias;
      int mantissa = (intValue & FractionalBits) | HighestFractionalBit;

      int integral;
      int fractional;
      if(exponent >= 0) {
        if(exponent >= FractionalBitCount) {
          Debug.Assert(exponent < NumericBitCount);
          integral = mantissa << (exponent - FractionalBitCount);
          fractional = 0;
        } else {
          integral = mantissa >> (FractionalBitCount - exponent);
          fractional = (mantissa << (exponent + 1)) & FractionalBits;
        }
      } else {
        Debug.Assert(exponent >= -FractionalBitCount);
        integral = 0;
        fractional = (mantissa & FractionalBits) >> -(exponent + 1);
      }
/*      
      if(exponent >= NumericBitCount) {
        throw new ArgumentException("Value too large", "value");
      } else if(exponent < -FractionalBitCount) {
        throw new ArgumentException("Value too small", "value");
      } else if(exponent >= FractionalBitCount) {
        integral = mantissa << (exponent - FractionalBitCount);
        fractional = 0;
      } else if(exponent >= 0) {
        integral = mantissa >> (FractionalBitCount - exponent);
        fractional = (mantissa << (exponent + 1)) & FractionalBits;
      } else { // exp2 < 0
        integral = 0;
        fractional = (mantissa & FractionalBits) >> -(exponent + 1);
      }
*/
      // Build the integral part      
      if(intValue < 0) {
        builder.Append('-');
      }
      if(integral == 0) {
        builder.Append('0');
      } else {
        recursiveAppend(builder, integral);
      }

      builder.Append('.');

      // Build the fractional part
      if(fractional == 0) {
        builder.Append('0');
      } else {
        while(fractional != 0) {
          fractional *= 10;
          int digit = (fractional >> FractionalBitCountPlusOne);
          builder.Append(numbers[digit]);
          fractional &= FractionalBits;
        }
      }
    }

    /// <summary>Recursively appends a number's characters to a string builder</summary>
    /// <param name="builder">String builder the number will be appended to</param>
    /// <param name="remaining">Remaining digits that will be recursively processed</param>
    private static void recursiveAppend(StringBuilder builder, int remaining) {
      int digit;
      int tenth = Math.DivRem(remaining, 10, out digit);

      if(tenth > 0) {
        recursiveAppend(builder, tenth);
      }

      builder.Append(numbers[digit]);
    }

    /// <summary>Recursively appends a number's characters to a string builder</summary>
    /// <param name="builder">String builder the number will be appended to</param>
    /// <param name="remaining">Remaining digits that will be recursively processed</param>
    private static void recursiveAppend(StringBuilder builder, long remaining) {
      long digit;
      long tenth = Math.DivRem(remaining, 10, out digit);

      if(tenth > 0) {
        recursiveAppend(builder, tenth);
      }

      builder.Append(numbers[digit]);
    }

  }

} // namespace Nuclex.Support