/*************************************************************************************

   Extended WPF Toolkit

   Copyright (C) 2007-2013 Xceed Software Inc.

   This program is provided to you under the terms of the Microsoft Public
   License (Ms-PL) as published at http://wpftoolkit.codeplex.com/license 

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   pick up the Plus Edition at http://xceed.com/wpf_toolkit

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  ***********************************************************************************/


namespace Standard
{
  using System;
  using System.Diagnostics.CodeAnalysis;

  /// <summary>
  /// DoubleUtil uses fixed eps to provide fuzzy comparison functionality for doubles.
  /// Note that FP noise is a big problem and using any of these compare 
  /// methods is not a complete solution, but rather the way to reduce 
  /// the probability of repeating unnecessary work.
  /// </summary>
  internal static class DoubleUtilities
  {
    /// <summary>
    /// Epsilon - more or less random, more or less small number.
    /// </summary>
    private const double Epsilon = 0.00000153;

    /// <summary>
    /// AreClose returns whether or not two doubles are "close".  That is, whether or 
    /// not they are within epsilon of each other.
    /// There are plenty of ways for this to return false even for numbers which
    /// are theoretically identical, so no code calling this should fail to work if this 
    /// returns false. 
    /// </summary>
    /// <param name="value1">The first double to compare.</param>
    /// <param name="value2">The second double to compare.</param>
    /// <returns>The result of the AreClose comparision.</returns>
    [SuppressMessage( "Microsoft.Performance", "CA1811:AvoidUncalledPrivateCode" )]
    public static bool AreClose( double value1, double value2 )
    {
      if( value1 == value2 )
      {
        return true;
      }

      double delta = value1 - value2;
      return ( delta < Epsilon ) && ( delta > -Epsilon );
    }

    /// <summary>
    /// LessThan returns whether or not the first double is less than the second double.
    /// That is, whether or not the first is strictly less than *and* not within epsilon of
    /// the other number.
    /// There are plenty of ways for this to return false even for numbers which
    /// are theoretically identical, so no code calling this should fail to work if this 
    /// returns false.
    /// </summary>
    /// <param name="value1">The first double to compare.</param>
    /// <param name="value2">The second double to compare.</param>
    /// <returns>The result of the LessThan comparision.</returns>
    [SuppressMessage( "Microsoft.Performance", "CA1811:AvoidUncalledPrivateCode" )]
    public static bool LessThan( double value1, double value2 )
    {
      return ( value1 < value2 ) && !AreClose( value1, value2 );
    }

    /// <summary>
    /// GreaterThan returns whether or not the first double is greater than the second double.
    /// That is, whether or not the first is strictly greater than *and* not within epsilon of
    /// the other number.
    /// There are plenty of ways for this to return false even for numbers which
    /// are theoretically identical, so no code calling this should fail to work if this 
    /// returns false.
    /// </summary>
    /// <param name="value1">The first double to compare.</param>
    /// <param name="value2">The second double to compare.</param>
    /// <returns>The result of the GreaterThan comparision.</returns>
    [SuppressMessage( "Microsoft.Performance", "CA1811:AvoidUncalledPrivateCode" )]
    public static bool GreaterThan( double value1, double value2 )
    {
      return ( value1 > value2 ) && !AreClose( value1, value2 );
    }

    /// <summary>
    /// LessThanOrClose returns whether or not the first double is less than or close to
    /// the second double.  That is, whether or not the first is strictly less than or within
    /// epsilon of the other number.
    /// There are plenty of ways for this to return false even for numbers which
    /// are theoretically identical, so no code calling this should fail to work if this 
    /// returns false.
    /// </summary>
    /// <param name="value1">The first double to compare.</param>
    /// <param name="value2">The second double to compare.</param>
    /// <returns>The result of the LessThanOrClose comparision.</returns>
    [SuppressMessage( "Microsoft.Performance", "CA1811:AvoidUncalledPrivateCode" )]
    public static bool LessThanOrClose( double value1, double value2 )
    {
      return ( value1 < value2 ) || AreClose( value1, value2 );
    }

    /// <summary>
    /// GreaterThanOrClose returns whether or not the first double is greater than or close to
    /// the second double.  That is, whether or not the first is strictly greater than or within
    /// epsilon of the other number.
    /// There are plenty of ways for this to return false even for numbers which
    /// are theoretically identical, so no code calling this should fail to work if this 
    /// returns false.
    /// </summary>
    /// <param name="value1">The first double to compare.</param>
    /// <param name="value2">The second double to compare.</param>
    /// <returns>The result of the GreaterThanOrClose comparision.</returns>
    [SuppressMessage( "Microsoft.Performance", "CA1811:AvoidUncalledPrivateCode" )]
    public static bool GreaterThanOrClose( double value1, double value2 )
    {
      return ( value1 > value2 ) || AreClose( value1, value2 );
    }

    /// <summary>
    /// Test to see if a double is a finite number (is not NaN or Infinity).
    /// </summary>
    /// <param name='value'>The value to test.</param>
    /// <returns>Whether or not the value is a finite number.</returns>
    [SuppressMessage( "Microsoft.Performance", "CA1811:AvoidUncalledPrivateCode" )]
    public static bool IsFinite( double value )
    {
      return !double.IsNaN( value ) && !double.IsInfinity( value );
    }

    /// <summary>
    /// Test to see if a double a valid size value (is finite and > 0).
    /// </summary>
    /// <param name='value'>The value to test.</param>
    /// <returns>Whether or not the value is a valid size value.</returns>
    [SuppressMessage( "Microsoft.Performance", "CA1811:AvoidUncalledPrivateCode" )]
    public static bool IsValidSize( double value )
    {
      return IsFinite( value ) && GreaterThanOrClose( value, 0 );
    }
  }
}