Imports System.IO
Module Module1
    Sub Main()
        Dim choice As String
        Do 'Validates choice so the user can only choose 1 or 2 repeating if neither are chose
            Console.Write("1. Sign in " & vbCrLf & "2. Register " & vbCrLf & "Choose: ") : choice = Console.ReadLine 'vbcrlf puts it on a new line
        Loop While choice <> "1" And choice <> "2"
        If choice = "1" Then
            If signIn() = True Then 'Calls the function sign in
                Console.WriteLine("Welcome!")
            End If
        Else
            Register() 'Calls the sub procedure register
            Console.WriteLine("Registered!")
        End If
        Console.ReadLine()
    End Sub

    Function signIn()
        Dim username, password, readPass As String 'Read in password from a individual file
        Dim finish As Boolean = False 'End states for each loop
        Do While finish = False
            Do While readPass = Nothing 'Loops until username is acceptable
                Console.Write("Enter your username: ") : username = Console.ReadLine
                readPass = ReadFrom(username) 'Uses function to read in the file with the username as its path
                If readPass = Nothing Then
                    Console.WriteLine("Please enter a valid username")
                End If
            Loop
            Console.Write("Enter your password: ") : password = Console.ReadLine
            If readPass = password Then 'Checks if password in file equals users inputted password
                finish = True
            Else
                finish = False
                Console.WriteLine("Please enter a valid password")
            End If
        Loop
        Return finish
    End Function

    Sub Register()
        Dim Iage As Integer
        Dim name, age, username, password As String
        Do
            Console.Write("Please enter your first name: ") : name = Console.ReadLine
        Loop While name.Length < 4  'Loops until there name is more than 4 characters
        Try
            Console.Write("please enter your age: ") : Iage = Console.ReadLine 'Gets there age as Iage so it can be checked if its an integer if it doesnt work it calls sub main and program restarts
        Catch ex As Exception
            Console.WriteLine("Not an age!") : Console.ReadLine()
            Main()
        End Try
        age = Iage 'Sets iage to a string
        username = name.Substring(0, 3) & age 'gets first 3 characters of name and adds age
        Console.WriteLine("Your username is: " & username)
        Console.Write("Please input a password: ") : password = Console.ReadLine
        Create(username) 'Calls the create procedure
        WriteTo(username, password) 'calls the writeto procedure
    End Sub

    Sub WriteTo(ByRef FilePath As String, Message As String)
        Using Writet As New StreamWriter(FilePath) 'Writes to file in bin with username as title
            Writet.WriteLine(Message)
        End Using
    End Sub
    Function ReadFrom(ByVal FilePath As String)
        Dim message As String
        Try
            Using ReadFr As New StreamReader(FilePath) 'trys to read the message from the file
                message = ReadFr.ReadLine
            End Using
        Catch ex As Exception
            message = Nothing ' if there is no message an error will happen so it sets message = to nothing and allows the program to carry on
        End Try
        Return message 'returns the message
    End Function
    Sub Create(ByRef username As String) 'Creates text document in bin with username as title
        Dim filepath As String = username
        If Not System.IO.File.Exists(filepath) Then 'Checks if document already exists
            System.IO.File.Create(filepath).Dispose() 'Creates a new file
        End If
    End Sub
End Module