''' <summary>
''' To use this class do the following assignment 
''' Value = StringCalculator.Calculate("Formula String")
''' </summary>
''' <remarks></remarks>
Public Class StringCalculator

  ' Updated to VB.net 2005 by Jerry W. A. Dusing
  ' Email : jerrydusing@yahoo.com

  ' Refactored from code initially created by Visal 
  ' Email : invisal@gmail.com'
  ' Vote for Visal in PSCODE through the link:
  ' http://www.pscode.com/vb/scripts/showcode.asp?txtCodeId=59600&lngWId=1 

#Region "Public methods"

  ''' <summary>
  ''' Computes the value of a given formula.
  ''' 
  ''' </summary>
  ''' <param name="pFormula">string formula</param>
  ''' <returns>Double</returns>
  ''' <remarks>
  ''' Supports the functions: cos, sin, log, abs,  and mod.
  ''' For example : [10*2+(2+3)]/(5 mod 4)
  ''' </remarks>
  Public Shared Function Calculate(ByVal pFormula As String) As Double
    Try
      If FoundParenthesis(pFormula) Then

        Return Calculate(ExpressionInParenthesis(pFormula))

      ElseIf InStr(1, pFormula, "abs", vbTextCompare) > 0 Then

        Return Absolute(pFormula)

      ElseIf InStr(1, pFormula, "cos", vbTextCompare) > 0 Then

        Return Cosine(pFormula)

      ElseIf InStr(1, pFormula, "sin", vbTextCompare) > 0 Then

        Return Sine(pFormula)

      ElseIf InStr(1, pFormula, "log", vbTextCompare) > 0 Then

        Return Logarithm(pFormula)

      ElseIf InStr(1, pFormula, "mod") > 1 Then

        Return Modulo(pFormula)

      ElseIf InStr(1, pFormula, "+") > 1 Then

        Return Plus(pFormula)

      ElseIf InStr(1, pFormula, "-") > 1 Then

        Return Minus(pFormula)

      ElseIf InStr(1, pFormula, "*") > 1 Then

        Return Multiply(pFormula)

      ElseIf InStr(1, pFormula, "/") > 1 Then

        Return Divide(pFormula)

      ElseIf InStr(1, pFormula, "^") > 1 Then

        Return Exponential(pFormula)

      Else

        If IsNumeric(pFormula) = True Then
          Return CDbl(pFormula)
        Else
          Throw New Exception("Unrecognized formula expresion.")
        End If
      End If

    Catch ex As Exception
      Throw New Exception(ex.Message)
    End Try

  End Function

#End Region

#Region "Private methods"

  Private Shared Function Absolute( _
    ByVal pExp As String _
  ) As Double
    Dim index As Integer = InStr(1, pExp, "abs", vbTextCompare)
    Dim exp As String = ""
    For i As Integer = index + 3 To Len(pExp)
      Dim cmid As String = Mid(pExp, i, 1)
      If IsNumeric(cmid) = True Or cmid = "." Or cmid = "," Then
        exp = exp & cmid
      Else
        Exit For
      End If
    Next
    If exp <> "" Then
      ' replace the adsolute number with the answer            
      exp = Replace(pExp, "abs" & exp, Math.Abs(CDbl(exp)).ToString())
      Return Calculate(exp)
    Else
      Mid(pExp, index, 3) = "000"
      Return Calculate(pExp)
    End If
  End Function

  Private Shared Function Cosine( _
    ByVal pExp As String _
  ) As Double
    Dim index As Integer = InStr(1, pExp, "cos", vbTextCompare)
    ' clear all the text in exp2        
    Dim exp As String = ""
    ' get cosines angle        
    For i As Integer = index + 3 To Len(pExp)
      Dim cmid As String = Mid(pExp, i, 1)
      If IsNumeric(cmid) = True Or cmid = "." Or cmid = "," Then
        exp = exp & cmid
      Else
        Exit For
      End If
    Next
    If exp <> "" Then
      ' replace cosines with the answer            
      exp = Replace(pExp, "cos" & exp, Math.Cos(CDbl(exp)).ToString())
      Return Calculate(exp)
    Else
      Mid(pExp, index, 3) = "000"
      Return Calculate(pExp)
    End If
  End Function

  Private Shared Function Divide( _
    ByVal pExp As String _
  ) As Double
    Dim index As Integer = InStr(1, pExp, "/")
    Dim divisor As Double = Calculate(Right(pExp, Len(pExp) - index))
    If divisor = 0.0! Then
      Throw New Exception("Division by zero!")
    Else
      Return Calculate(Left(pExp, index - 1)) / divisor
    End If
  End Function

  Private Shared Function Exponential( _
    ByVal pExp As String _
  ) As Double
    Dim index As Integer = InStr(1, pExp, "^")
    Return Calculate(Left(pExp, index - 1)) ^ Calculate(Right(pExp, Len(pExp) - index))
  End Function

  Private Shared Function ExpressionInParenthesis( _
    ByVal pExp As String _
  ) As String
    Dim sIndex, eIndex As Integer
    'searching for ")"      
    MatchClosingParenthesis(pExp, sIndex, eIndex)

    If eIndex <= sIndex + 1 Then ' check if () is empty or not
      Return Replace(pExp, "()", "0")
    Else
      ' get expression between "(" and ")"            
      Dim RetVal As String = Mid(pExp, sIndex + 1, eIndex - (sIndex + 1))
      Return Replace(pExp, "(" & RetVal & ")", Calculate(RetVal).ToString())
    End If
  End Function

  Private Shared Function FoundParenthesis( _
    ByRef pExp As String _
  ) As Boolean
    pExp = Replace(pExp, "\", "/") ' \ and / are same division 
    pExp = Replace(pExp, "[", "(") ' "[" and "(" are the same also "]" and ")"
    pExp = Replace(pExp, "]", ")")
    Return InStr(1, pExp, "(") > 0
  End Function

  Private Shared Function Logarithm( _
    ByVal pExp As String) As Double
    Dim index As Integer = InStr(1, pExp, "log", vbTextCompare)
    ' clear all the text in exp2        
    Dim exp As String = ""
    ' get number        
    For i As Integer = index + 3 To Len(pExp)
      Dim cmid As String = Mid(pExp, i, 1)
      If IsNumeric(cmid) = True Or cmid = "." Or cmid = "," Then
        exp = exp & cmid
      Else
        Exit For
      End If
    Next i
    If exp <> "" Then
      ' replace logarithmic with the answer           
      exp = Replace(pExp, "log" & exp, Math.Log(CDbl(exp)).ToString())
      Return Calculate(exp)
    Else
      Mid(pExp, index, 3) = "000"
      Return Calculate(pExp)
    End If
  End Function

  Private Shared Sub MatchClosingParenthesis( _
    ByRef pExp As String, _
    ByRef pStart As Integer, _
    ByRef pEnd As Integer _
  )
    Dim count As Integer
    For pEnd = (pStart + 1) To Len(pExp)
      Select Case Mid(pExp, pEnd, 1)
        Case "("
          count += 1
        Case ")"
          If count = 0 Then Exit For
          count -= 1
      End Select
    Next pEnd

    If count > 0 Then ' if no ")" create ")" automatically
      pExp = pExp & Replace(Space(count + 1), " ", ")")
      pEnd = pEnd + count
    End If
  End Sub

  Private Shared Function Minus( _
    ByVal pExp As String _
  ) As Double
    Dim index As Integer = InStr(1, pExp, "-")
    Return Calculate(Left(pExp, index - 1)) - Calculate(Right(pExp, Len(pExp) - index))
  End Function

  Private Shared Function Modulo( _
    ByVal pExp As String _
  ) As Double
    Dim index As Integer = InStr(1, pExp, "mod")
    Return Calculate(Left(pExp, index - 1)) Mod Calculate(Right(pExp, Len(pExp) - (index + 2)))
  End Function

  Private Shared Function Multiply( _
    ByVal pExp As String _
  ) As Double
    Dim index As Integer = InStr(1, pExp, "*")
    Return Calculate(Left(pExp, index - 1)) * Calculate(Right(pExp, Len(pExp) - index))
  End Function

  Private Shared Function Plus( _
    ByVal pExp As String _
  ) As Double
    Dim index As Integer = InStr(1, pExp, "+")
    Return Calculate(Left(pExp, index - 1)) + Calculate(Right(pExp, Len(pExp) - index))
  End Function

  Private Shared Function Sine( _
    ByVal pExp As String _
  ) As Double
    Dim index As Integer = InStr(1, pExp, "sin", vbTextCompare)
    ' clear all the text in exp2        
    Dim exp As String = ""
    ' get sines angle        
    For i As Integer = index + 3 To Len(pExp)
      Dim cmid As String = Mid(pExp, i, 1)
      If IsNumeric(cmid) = True Or cmid = "." Or cmid = "," Then
        exp = exp & cmid
      Else
        Exit For
      End If
    Next i
    If exp <> "" Then
      ' replace Sines with the answer            
      exp = Replace(pExp, "sin" & exp, Math.Sin(CDbl(exp)).ToString())
      Return Calculate(exp)
    Else
      Mid(pExp, index, 3) = "000"
      Return Calculate(pExp)
    End If
  End Function

#End Region

End Class