  <Language("SearchGrammar", "1.0", "Google-to-SQL query converter")> _
    Public Class SearchGrammar
        Inherits Grammar
        Public Sub New()
            MyBase.New(False)
            Me.GrammarComments = "Google-to-SQL full-text query format converter. Based on original project by Michael Coles." & vbCr & vbLf & "http://www.sqlservercentral.com/articles/Full-Text+Search+(2008)/64248/ " & vbCr & vbLf & "Slightly revised to work with latest version of Irony. "

            ' Terminals
            Dim Term = CreateTerm("Term")
            Dim Phrase = New StringLiteral("Phrase", """")
            Dim ImpliedAnd = New ImpliedSymbolTerminal("ImpliedAnd")

            ' NonTerminals
            Dim BinaryExpression = New NonTerminal("BinaryExpression")
            Dim BinaryOp = New NonTerminal("BinaryOp")
            Dim Expression = New NonTerminal("Expression")
            Dim PrimaryExpression = New NonTerminal("PrimaryExpression")
            Dim ThesaurusExpression = New NonTerminal("ThesaurusExpression")
            Dim ThesaurusOperator = New NonTerminal("ThesaurusOperator")
            Dim ExactExpression = New NonTerminal("ExactExpression")
            Dim ParenthesizedExpression = New NonTerminal("ParenthesizedExpression")
            Dim ProximityExpression = New NonTerminal("ProximityExpression")
            Dim ProximityList = New NonTerminal("ProximityList")

            Me.Root = Expression
            Expression.Rule = PrimaryExpression Or BinaryExpression
            BinaryExpression.Rule = Expression + BinaryOp + Expression
            BinaryOp.Rule = ImpliedAnd Or "and" Or "&" Or "-" Or "or" Or "|"
            PrimaryExpression.Rule = Term Or ThesaurusExpression Or ExactExpression Or ParenthesizedExpression Or Phrase Or ProximityExpression
            ThesaurusExpression.Rule = "~" + Term
            ExactExpression.Rule = "+" + Term Or "+" + Phrase
            ParenthesizedExpression.Rule = "(" + Expression + ")"
            ProximityExpression.Rule = "<" + ProximityList + ">"
            MakePlusRule(ProximityList, Term)

            MarkTransient(PrimaryExpression, Expression, ProximityExpression, ParenthesizedExpression, BinaryOp)
            MarkPunctuation("<", ">", "(", ")")
            RegisterOperators(10, "or", "|")
            RegisterOperators(20, "and", "&", "-")
            RegisterOperators(20, ImpliedAnd)
            'Register brace pairs to improve error reporting
            RegisterBracePair("(", ")")
            RegisterBracePair("<", ">")
            'Do not report ImpliedAnd as expected symbol - it is not really a symbol
            Me.AddToNoReportGroup(ImpliedAnd)
            'also do not report braces as expected
            Me.AddToNoReportGroup("(", ")", "<", ">")

            LanguageFlags = LanguageFlags Or LanguageFlags.CanRunSample
        End Sub

        'Creates extended identifier terminal that allows international characters
        ' Following the pattern used for c# identifier terminal in TerminalFactory.CreateCSharpIdentifier method;
        Private Function CreateTerm(ByVal name As String) As IdentifierTerminal
            Dim term As New IdentifierTerminal(name, "!@#$%^*_'.?-", "!@#$%^*_'.?0123456789")
            'Ul
            'Ll
            'Lt
            'Lm
            'Lo
            'Nl
            'Nd
            'Pc
            'Mc
            'Mn
            'Cf
            term.CharCategories.AddRange(New Globalization.UnicodeCategory() {Globalization.UnicodeCategory.UppercaseLetter, Globalization.UnicodeCategory.LowercaseLetter, Globalization.UnicodeCategory.TitlecaseLetter, Globalization.UnicodeCategory.ModifierLetter, Globalization.UnicodeCategory.OtherLetter, Globalization.UnicodeCategory.LetterNumber, _
             Globalization.UnicodeCategory.DecimalDigitNumber, Globalization.UnicodeCategory.ConnectorPunctuation, Globalization.UnicodeCategory.SpacingCombiningMark, Globalization.UnicodeCategory.NonSpacingMark, Globalization.UnicodeCategory.Format})
            'StartCharCategories are the same
            term.StartCharCategories.AddRange(term.CharCategories)
            Return term
        End Function

        Public Overrides Function RunSample(ByVal parseTree As ParseTree) As String
            Dim sql = ConvertQuery(parseTree.Root)
            Return sql
        End Function


        Public Enum TermType
            Inflectional = 1
            Thesaurus = 2
            Exact = 3
        End Enum
        Public Shared Function ConvertQuery(ByVal node As ParseTreeNode) As String
            Return ConvertQuery(node, TermType.Inflectional)
        End Function

        Private Shared Function ConvertQuery(ByVal node As ParseTreeNode, ByVal type As TermType) As String
            Dim result As String = ""
            ' Note that some NonTerminals don't actually get into the AST tree, 
            ' because of some Irony's optimizations - punctuation stripping and 
            ' transient nodes elimination. For example, ParenthesizedExpression - parentheses 
            ' symbols get stripped off as punctuation, and child expression node 
            ' (parenthesized content) replaces the parent ParenthesizedExpression node
            Select Case node.Term.Name
                Case "BinaryExpression"
                    Dim opSym As String = String.Empty
                    Dim op As String = node.ChildNodes(1).FindTokenAndGetText().ToLower()
                    Dim sqlOp As String = ""
                    Select Case op
                        Case "", "&", "and"
                            sqlOp = " AND "
                            type = TermType.Inflectional
                            Exit Select
                        Case "-"
                            sqlOp = " AND NOT "
                            Exit Select
                        Case "|", "or"
                            sqlOp = " OR "
                            Exit Select
                    End Select
                    'switch
                    result = "(" & ConvertQuery(node.ChildNodes(0), type) & sqlOp & ConvertQuery(node.ChildNodes(2), type) & ")"
                    Exit Select

                Case "PrimaryExpression"
                    result = "(" & ConvertQuery(node.ChildNodes(0), type) & ")"
                    Exit Select

                Case "ProximityList"
                    Dim tmp As String() = New String(node.ChildNodes.Count - 1) {}
                    type = TermType.Exact
                    For i As Integer = 0 To node.ChildNodes.Count - 1
                        tmp(i) = ConvertQuery(node.ChildNodes(i), type)
                    Next
                    result = "(" & String.Join(" NEAR ", tmp) & ")"
                    type = TermType.Inflectional
                    Exit Select

                Case "Phrase"
                    result = """"c + node.Token.ValueString + """"c
                    Exit Select

                Case "ThesaurusExpression"
                    result = " FORMSOF (THESAURUS, " + node.ChildNodes(1).Token.ValueString & ") "
                    Exit Select

                Case "ExactExpression"
                    result = " """ + node.ChildNodes(1).Token.ValueString & """ "
                    Exit Select

                Case "Term"
                    Select Case type
                        Case TermType.Inflectional
                            result = node.Token.ValueString
                            If result.EndsWith("*") Then
                                result = """" & result & """"
                            Else
                                result = " FORMSOF (INFLECTIONAL, " & result & ") "
                            End If
                            Exit Select
                        Case TermType.Exact
                            result = node.Token.ValueString

                            Exit Select
                    End Select
                    Exit Select
                Case Else

                    ' This should never happen, even if input string is garbage
                    Throw New ApplicationException("Converter failed: unexpected term: " & Convert.ToString(node.Term.Name) & ". Please investigate.")

            End Select
            Return result
        End Function
       

    End Class