Imports System

Imports System.Data

Imports System.Data.DataSetExtensions

Imports System.Linq

Imports System.Xml

Public Module Module1

    Private customers As DataTable = New DataTable("Customers")

    Public Sub Main()       

        If IO.File.Exists("data.xml") Then

            customers.ReadXml("data.xml")

        Else

            customers.Columns.AddRange({New DataColumn("ID", GetType(UInt32)), New DataColumn("Name"), New DataColumn("Date of Birth", GetType(DateTime))})

        End If

        Menu_Main()

    End Sub

    Private Sub Menu_Main()

        Console.WriteLine("Main Menu")

        Console.WriteLine("1) Find Customer")

        Console.WriteLine("2) Add Customer")

        Console.WriteLine()

        Dim input As UInteger = 0

        Do

            Console.Write("Selection: ")

            If Not UInteger.TryParse(Console.ReadLine, input) OrElse (input <> 1 AndAlso input <> 2) Then

                Console.WriteLine("Please enter a valid number that is either 1 or 2.")

            End If

        Loop Until input = 1 OrElse input = 2

        If input = 1 Then

            Menu_Find()

        Else

            Menu_Add()

        End If

    End Sub

    Private Sub Menu_Find()

        Console.WriteLine("Find Customer Menu")

        Console.WriteLine("Type the customer's name and hit enter to search. Or enter the value '1' to go back to the main menu.")

        Console.WriteLine()

        Dim input As String = Console.ReadLine

        If input <> "1" Then

            Dim rows = From customer In customers.AsEnumerable() Where customer.Field(Of String)("Name").Equals(input, StringComparer.OrdinalIgnoreCase) Select customer

                Console.WriteLine("Name - Date of Birth")

                For Each customer As DataRow In rows

                Console.WriteLine(customer.Field(Of String)("Name") & " - " & customer.Field(Of DateTime)("Date of Birth").ToShortDateString())

            Next

            Console.WriteLine("End of results. Press enter to go back to the main menu.")

            Console.ReadLine()

        End If

        Menu_Main()

    End Sub

    Private Sub Menu_Add()

        Console.WriteLine("Add Customer Menu")

        Console.WriteLine("Type the customer's name and hit enter. Or enter the value '1' to go back to the main menu.")

        Console.WriteLine()

        Dim input As String = Console.ReadLine

        If input <> "1" Then

            Dim dob As DateTime = Nothing

            Dim dobInput As String = String.Empty

            Do

                Console.WriteLine("Type the customer's date of birth and hit enter. Or enter the value '1' to go back to the main menu.")

                Console.WriteLine()

                dobInput = Console.ReadLine

                If dobInput <> "1" AndAlso Not DateTime.TryParse(dobInput, dob) Then

                    Console.WriteLine("Please enter a valid date.")

                End If

            Loop Until dob <> Nothing OrElse dobInput = "1"

            If dobInput <> "1" Then

                customers.Rows.Add({customers.Rows.Count, input, dob})

                customers.WriteXml("data.xml")

                Console.WriteLine("Customer added. Press enter to go back to the main menu.")

                Console.ReadLine()

            End If

        End If

        Menu_Main()

    End Sub

End Module