Convert a week into a datetime when the year contains 2 times 52 weeks-CodePudding

For my project, I need to convert year, week and day of week in DateTime. For this, I use this link : https://github.com/dotnet/runtime/blob/b41f1c5f2fde25d752d857a54c3af24145060cdd/src/libraries/System.Private.CoreLib/src/System/Globalization/ISOWeek.cs#L102-L139

BUT, in my current case, this solution can't function, for example : 1989-01-01 and 1989-12-31.

This two dates start and finish the last day of week and belong to the 52nd week.

Have you an idea ?

Thanks you :)

CodePudding user response：

Solution :

''' <summary>
''' Convert the <see cref="DateTime"/> object passed as a parameter to the <see cref="DateWeek"/> object (according to ISO 8601)
''' </summary>
''' <param name="value"></param>
''' <returns></returns>
''' <remarks>https://stackoverflow.com/a/1497606/15423682</remarks>
Public Shared Function FromDateTime(value As DateTime) As DateWeek
    ' https://github.com/dotnet/runtime/blob/b41f1c5f2fde25d752d857a54c3af24145060cdd/src/libraries/System.Private.CoreLib/src/System/Globalization/ISOWeek.cs
    ' in current country (FR), first day of week is Monday
    Dim _dayOfWeek As Integer = GetWeekday(value.DayOfWeek)
    If (_dayOfWeek = 0) Then
        _dayOfWeek = 7 ' in .Net, Sunday is 0
    End If

    ' Get the week number for the current value
    Dim week As Integer = CultureInfo.CurrentCulture.Calendar.GetWeekOfYear(
                                    value, CalendarWeekRule.FirstFourDayWeek, DayOfWeek.Monday
                                    )
    Dim year As Integer = value.Year
    ' if the current value is during week 52 and only for first month
    If (week >= 52) Then
        ' In ISO 8601, the first Thurday is in first week.
        ' If the current value is before Thurday, is in previous week

        ' The last week of the year (52 or 53) is the one containing the last Thursday of the year.
        ' It is the last week to have the majority of its days (at least 4) in the year and systematically contains
        ' 28 December. It is also the one whose Sunday is closest to 31 December.

        ' It ends no earlier than 28 December or no later than 3 January (so the 4th day belongs to the first week)
        ' https://fr.wikipedia.org/wiki/ISO_8601#Système_de_numérotation
        If (value.Month = 1 And value.Day < 4) Then
            year -= 1
        End If
    End If

    Return New DateWeek(_dayOfWeek, week, year)
End Function