How to get a result from a function - powershell

Question

I'm trying to write a function to calculate either a full ISO date (yyyy-W-d, where W is the ISO week number), or just the ISO week number by itself. My function is based on this.
I have 2 problems with my code. One is that I do not know how extract either of the results I am after as written above. The other problem is that the second parameter doesn't show when I try to call the function.
This is my current code.
Function Get-ISODate {
Param(
[datetime]$Date = (Get-Date),
[bool]$LongFormat
)
$DayOfWeek = $Date.DayOfWeek
If ($DayOfWeek -match "[1-3]") {$Date.AddDays(3)}
$Year = $Date.Year
$Week = $(Get-Culture).Calendar.GetWeekOfYear(($Date),[System.Globalization.CalendarWeekRule]::FirstFourDayWeek, [DayOfWeek]::Monday)
$Day = $Date.Day
If ($LongFormat)
{
Get-ISODate = $Year + '-W' + $Week + '-' + $Day
}
Else
{
Get-ISODate = 'W' + $Week
}
}
My expected results would be,
Get-ISOWeek returns W16, which is the current ISO week at this time of writing.
Get-ISOWeek -LongFormat $true returns 2021-W16-1
Get-ISOWeek -Date '2000-1-1' returns W52
Get-ISOWeek -Date '2000-1-1' -LongFormat $true returns 1999-W52-6
I'm using this link to verifiy my results with regards to the week calculation.

Answer 1

You can read about switch paramenter here.
What Mathias meant is to literally remove Get-ISODate =
The function should look like this:
Function Get-ISODate {
Param(
[datetime]$Date = (Get-Date),
[switch]$LongFormat
)
$DayOfWeek = $Date.DayOfWeek
If ($DayOfWeek -match "[1-3]") {$Date.AddDays(3)}
$Year = $Date.Year
$Week = $(Get-Culture).Calendar.GetWeekOfYear(($Date),[System.Globalization.CalendarWeekRule]::FirstFourDayWeek, [DayOfWeek]::Monday)
$Day = $Date.Day
If ($LongFormat.IsPresent)
{
return "$Year-W$Week-$Day"
}
'W' + $Week
}
# Testing the function
PS /~> Get-IsoDate
W16
PS /~> Get-IsoDate -LongFormat
2021-W16-19

Answer 2

Got this working. Please note that the main issue was that I was trying to call the function incorrectly with "Get-ISOWeek". Monday morning.
I also added .value__ to Day for $Day to get the number instead of the day as "Monday" etc.
Function Get-ISODate {
Param(
[datetime]$Date = (Get-Date),
[bool]$LongFormat
)
$DayOfWeek = $Date.DayOfWeek
If ($DayOfWeek -match "[1-3]") {$Date.AddDays(3)}
$Year = $Date.Year
$Week = $(Get-Culture).Calendar.GetWeekOfYear(($Date),[System.Globalization.CalendarWeekRule]::FirstFourDayWeek, [DayOfWeek]::Monday)
$Day = $Date.DayOfWeek.value__
If ($LongFormat -eq $true)
{
"$Year-W$Week-$Day"
}
Else
{
"W$Week"
}
}
Edit: I realised after posting this, the year was sometimes wrong according to the week number and day of the week. So here is my new version. I have checked the dates here.
Function Get-ISODate {
Param(
[datetime]$Date = (Get-Date),
[switch]$LongFormat
)
[int]$Year = $Date.Year
[int]$Month = $Date.Month
[int]$Day = $Date.DayOfWeek.value__
If ($Day -eq 0) {$Day = 7}
If ($Day -ge 1 -and $Day -le 3) {$Date = $Date.AddDays(3)}
$Week = (Get-Culture).Calendar.GetWeekOfYear($Date, 'FirstFourDayWeek', 'Monday')
Switch ($Week)
{
52 {If ($Day -ge 5 -and $Day -le 7 -and $Month -ne 12) {$Year = $Year - 1} ; Break}
53 {If ($Day -ge 5 -and $Day -le 7 -and $Month -ne 12) {$Year = $Year - 1} ; Break}
1 {If ($Month -eq 12) {$Year = $Year + 1} ; Break}
}
$Week = $Week.ToString('00')
If ($LongFormat.IsPresent)
{
"$Year-W$Week-$Day"
}
Else
{
"W$Week"
}
}