Attribute VB_Name = "Module2"
Function calulate_date_next(chktype As String, num_cal As Integer, r_date As Date) As Date
    Dim l As Integer
    Dim dd As Integer
    Dim mm As Integer
    Dim yy As Integer
    Dim sdd As String
    Dim smm As String
    Dim syy As String
    dd = Day(r_date)
    mm = Month(r_date)
    yy = Year(r_date)
    'get exact day in month
    If mm = 1 Or mm = 3 Or mm = 5 Or mm = 7 Or mm = 8 Or mm = 10 Or mm = 12 Then
        l = 31
    ElseIf mm = 4 Or mm = 6 Or mm = 9 Or mm = 11 Then
        l = 30
    ElseIf mm = 2 Then
        If (yy Mod 4 = 0 And yy Mod 100 <> 0) Or yy Mod 400 = 0 Then
            l = 29
        Else
            l = 28
        End If
    End If
    Select Case chktype
        Case "D"
            dd = dd + num_cal
            If dd > l Then
                dd = dd - l
                mm = mm + 1
            End If
            If mm > 12 Then
                mm = mm - 12
                yy = yy + 1
            End If
        Case "W"
            If dd = 15 Then
                dd = 1
                mm = mm + 1
            Else
                dd = 15
            End If
            If mm > 12 Then
                mm = mm - 12
                yy = yy + 1
            End If
        Case "M"
            dd = 1
            mm = mm + num_cal
            If mm > 12 Then
                mm = mm - 12
                yy = yy + 1
            End If
        Case "Y"
            dd = 1
            mm = 1
            yy = yy + 1
    End Select
    sdd = LTrim(Str(dd))
    smm = LTrim(Str(mm))
    syy = LTrim(Str(yy))
    l = Len(sdd)
    If l = 1 Then sdd = "0" + sdd
    l = Len(smm)
    If l = 1 Then smm = "0" + smm
    calulate_date_next = DateSerial(syy, smm, sdd)
End Function

Function calulate_date_bef(chktype As String, num_cal As Integer, r_date As Date) As Date
    Dim l As Integer
    Dim dd As Integer
    Dim mm As Integer
    Dim yy As Integer
    Dim sdd As String
    Dim smm As String
    Dim syy As String

    dd = Day(r_date)
    mm = Month(r_date)
     yy = Year(r_date)
    'get exact day in month
    Select Case mm - 1
    Case 1, 3, 5, 7, 8, 10, 0
        l = 31
    Case 4, 6, 9, 11
        l = 30
    Case 2
        If (yy Mod 4 = 0 And yy Mod 100 <> 0) Or (yy Mod 400) = 0 Then
            l = 29
        Else
            l = 28
        End If
    End Select
    Select Case chktype
        Case "D"
            If dd > num_cal Then
                dd = dd - num_cal
            Else
                dd = dd + l - num_cal
                mm = mm - 1
            End If
            If mm = 0 Then
                mm = 12
                yy = yy - 1
            End If
        Case "W"
            If dd > 15 Then
                dd = 15
            ElseIf dd > 1 Then
                dd = 1
            Else
                dd = 15
                mm = mm - 1
            End If
            If mm = 0 Then
                mm = 12
                yy = yy - 1
            End If
        Case "M"
            dd = 1
            If mm > num_cal Then
                mm = mm - num_cal
            Else
                mm = mm + 12 - num_cal
                yy = yy - 1
            End If
        Case "Y"
            dd = 1
            mm = 1
            yy = yy - 1
    End Select
    sdd = LTrim(Str(dd))
    smm = LTrim(Str(mm))
    syy = LTrim(Str(yy))

    l = Len(sdd)
    If l = 1 Then sdd = "0" + sdd
    l = Len(smm)
    If l = 1 Then smm = "0" + smm

    calulate_date_bef = DateSerial(syy, smm, sdd)
End Function

Function convert_date(d_date As Date) As String
Dim mm As Integer
Dim mm_con As String
    mm = Month(d_date)
    Select Case mm
    Case 1
        mm_con = "มกราคม"
    Case 2
        mm_con = "กุมภาพันธ์"
    Case 3
        mm_con = "มีนาคม"
    Case 4
        mm_con = "เมษายน"
    Case 5
        mm_con = "พฤษภาคม"
    Case 6
        mm_con = "มิถุนายน"
    Case 7
        mm_con = "กรกฎาคม"
    Case 8
        mm_con = "สิงหาคม"
    Case 9
        mm_con = "กันยายน"
    Case 10
        mm_con = "ตุลาคม"
    Case 11
        mm_con = "พฤศจิการยน"
    Case 12
        mm_con = "ธันวาคม"
  End Select
  convert_date = Trim(Str(Day(d_date))) + " " + mm_con + " " + Trim(Str(Year(d_date) + 543))
End Function