﻿Module Module1

    Dim atomicMass As New Dictionary(Of String, Double) From {
        {"H", 1.008},
        {"He", 4.002602},
        {"Li", 6.94},
        {"Be", 9.0121831},
        {"B", 10.81},
        {"C", 12.011},
        {"N", 14.007},
        {"O", 15.999},
        {"F", 18.998403163},
        {"Ne", 20.1797},
        {"Na", 22.98976928},
        {"Mg", 24.305},
        {"Al", 26.9815385},
        {"Si", 28.085},
        {"P", 30.973761998},
        {"S", 32.06},
        {"Cl", 35.45},
        {"Ar", 39.948},
        {"K", 39.0983},
        {"Ca", 40.078},
        {"Sc", 44.955908},
        {"Ti", 47.867},
        {"V", 50.9415},
        {"Cr", 51.9961},
        {"Mn", 54.938044},
        {"Fe", 55.845},
        {"Co", 58.933194},
        {"Ni", 58.6934},
        {"Cu", 63.546},
        {"Zn", 65.38},
        {"Ga", 69.723},
        {"Ge", 72.63},
        {"As", 74.921595},
        {"Se", 78.971},
        {"Br", 79.904},
        {"Kr", 83.798},
        {"Rb", 85.4678},
        {"Sr", 87.62},
        {"Y", 88.90584},
        {"Zr", 91.224},
        {"Nb", 92.90637},
        {"Mo", 95.95},
        {"Ru", 101.07},
        {"Rh", 102.9055},
        {"Pd", 106.42},
        {"Ag", 107.8682},
        {"Cd", 112.414},
        {"In", 114.818},
        {"Sn", 118.71},
        {"Sb", 121.76},
        {"Te", 127.6},
        {"I", 126.90447},
        {"Xe", 131.293},
        {"Cs", 132.90545196},
        {"Ba", 137.327},
        {"La", 138.90547},
        {"Ce", 140.116},
        {"Pr", 140.90766},
        {"Nd", 144.242},
        {"Pm", 145},
        {"Sm", 150.36},
        {"Eu", 151.964},
        {"Gd", 157.25},
        {"Tb", 158.92535},
        {"Dy", 162.5},
        {"Ho", 164.93033},
        {"Er", 167.259},
        {"Tm", 168.93422},
        {"Yb", 173.054},
        {"Lu", 174.9668},
        {"Hf", 178.49},
        {"Ta", 180.94788},
        {"W", 183.84},
        {"Re", 186.207},
        {"Os", 190.23},
        {"Ir", 192.217},
        {"Pt", 195.084},
        {"Au", 196.966569},
        {"Hg", 200.592},
        {"Tl", 204.38},
        {"Pb", 207.2},
        {"Bi", 208.9804},
        {"Po", 209},
        {"At", 210},
        {"Rn", 222},
        {"Fr", 223},
        {"Ra", 226},
        {"Ac", 227},
        {"Th", 232.0377},
        {"Pa", 231.03588},
        {"U", 238.02891},
        {"Np", 237},
        {"Pu", 244},
        {"Am", 243},
        {"Cm", 247},
        {"Bk", 247},
        {"Cf", 251},
        {"Es", 252},
        {"Fm", 257},
        {"Uue", 315},
        {"Ubn", 299}
    }

    Function Evaluate(s As String) As Double
        s += "["
        Dim sum = 0.0
        Dim symbol = ""
        Dim number = ""
        For i = 1 To s.Length
            Dim c = s(i - 1)
            If "@" <= c AndAlso c <= "[" Then
                ' @,A-Z
                Dim n = 1
                If number <> "" Then
                    n = Integer.Parse(number)
                End If
                If symbol <> "" Then
                    sum += atomicMass(symbol) * n
                End If
                If c = "[" Then
                    Exit For
                End If
                symbol = c.ToString
                number = ""
            ElseIf "a" <= c AndAlso c <= "z" Then
                symbol += c
            ElseIf "0" <= c AndAlso c <= "9" Then
                number += c
            Else
                Throw New Exception(String.Format("Unexpected symbol {0} in molecule", c))
            End If
        Next
        Return sum
    End Function

    Function ReplaceFirst(text As String, search As String, replace As String) As String
        Dim pos = text.IndexOf(search)
        If pos < 0 Then
            Return text
        Else
            Return text.Substring(0, pos) + replace + text.Substring(pos + search.Length)
        End If
    End Function

    Function ReplaceParens(s As String) As String
        Dim letter = "s"c
        While True
            Dim start = s.IndexOf("(")
            If start = -1 Then
                Exit While
            End If

            For i = start + 1 To s.Length - 1
                If s(i) = ")" Then
                    Dim expr = s.Substring(start + 1, i - start - 1)
                    Dim symbol = String.Format("@{0}", letter)
                    s = ReplaceFirst(s, s.Substring(start, i + 1 - start), symbol)
                    atomicMass(symbol) = Evaluate(expr)
                    letter = Chr(Asc(letter) + 1)
                    Exit For
                End If
                If s(i) = "(" Then
                    start = i
                    Continue For
                End If
            Next
        End While
        Return s
    End Function

    Sub Main()
        Dim molecules() As String = {
            "H", "H2", "H2O", "H2O2", "(HO)2", "Na2SO4", "C6H12",
            "COOH(C(CH3)2)3CH3", "C6H4O2(OH)4", "C27H46O", "Uue"
        }
        For Each molecule In molecules
            Dim mass = Evaluate(ReplaceParens(molecule))
            Console.WriteLine("{0,17} -> {1,7:0.000}", molecule, mass)
        Next
    End Sub

End Module
