#	POWERSHELL CALCULATION OF ISO 8601 WEEK-NUMBERING DATE

#	     http://www.merlyn.demon.co.uk/weekpshl.ps1

#		 Page (c) J R Stockton >= 2012-11-09


# This script is for Microsoft PowerShell v1.0 and higher.  It tests its
# PowerShell functions DTobjToYWDarray and YWDarrayToDTobj, which
# converts between a Datetime object and an array {Y, M, D}. and
# related functions.

# To run a script, the command 'set-executionpolicy remotesigned'
# must have been used in PowerShell.
# Type 'help set-executionpolicy -full' in PowerShell for details.
# Undo with 'set-executionpolicy Default' - I think (Restricted?).
# So far, tested only in my Windows XP sp3 and Windows 7 XP mode;
# something additional is needed for (64-bit) windows 7 -
# must use the Administrator account to change settings
# (or "RunAs Administrator"?).

# Save this page in a suitable directory, and, at a Command Prompt
# with that directory current, enter the command
	#####	powershell .\weekpshl.ps1  Arg1  Arg2   #####
# NOTE : the .\ is necessary
# Arg1 (default 146097) controls the number of days finally tested :
#   146097 days is a full cycle of 400 Gregorian years
# Arg2 (default $null) tests the error route at that day-count
# Testing an earlier version for every day in 400 years took,
# using PowerShell 2.0 :
#   9.2 minutes in my P4/3G PC, using Win XP sp3,
#   3.8 minutes in my 64-bit Windows 7 laptop, 32-bit XP mode.
#   16.4 minutes in my 64-bit Windows 7 laptop, 64-bit native mode.




# ROUNDING NOTES by Chris Warwick

# PowerShell integer rounding is directly inherited from .Net which
# uses so-called 'Rounding half to even' (an implementation of the
# recommended default rounding defined in IEEE 754).

# PowerShell tries to be helpful by expanding the type of intermediate
# results as needed (So [Int]$x = [Int]7 / [Int]2 gives $x = 4 (since
# [Int]7/[Int]2 == 3.5, not 3)) which can be suprising to people who
# have used other languages previously





Param($MaxDays=146097, $BadDay=$null) # FIRST executable statement

"`nISO 8601 Week Numbering`n"

# $Host.Version		# for reference
# $PSVersiontable

Set-StrictMode -Version 2.0

$Zeit = Get-Date ; $ThisYear = $Zeit.Year


Function LZ($N) { $X = "" ; if ($N -le 9) { $X = "0" } ; $X + $N }

Function YMDdate($D) { $D.toString("yyyy-MM-dd") }


Function DTobjToYWDarray($Zeit) {
  $DoWk = +$Zeit.DayofWeek
  if ($DoWk -eq 0) { $DoWk = 7 }		# Mon=1..Sun=7
  $Tijd = $Zeit.AddDays(4 - $DoWk)		# Go to nearest Thursday
  $Week = 1+[Math]::Floor(($Tijd.DayOfYear-1)/7)    # Adjusted seventh
  $Year = $Tijd.Year				# Needed
  $Year, $Week, $DoWk } 	# Return an array [0..2]
# http://ss64.com/ps/syntax-arrays.html



Function YWDarrayToDTobj($YWDarr) {
  $ItIs = Get-Date "01/04/$($YWDarr[0])"
  $DoWk = +$ItIs.DayofWeek
    if ($DoWk -eq 0) { $DoWk = 7 } # Mon=1..Sun=7
  $ItIs = $ItIs.AddDays($YWDarr[1]*7+$YWDarr[2]-$DoWk-7)
  $ItIs }


Function LZ($N) { $X = "" ; if ($N -le 9) { $X = "0" } ; $X + $N }


Function YWDarrayToStr($WNDa) {
  "$($WNDa[0])-W$(LZ($WNDa[1]))-$($WNDa[2])" }


Function StrToYWDarray($Str) {
  $X = $Str -Match "\D*(\d+)-W(\d\d)-(\d).*"
  if ($X) { $X = +$Matches[1], +$Matches[2], +$Matches[3] }
  $X }




$Zeit = Get-Date # "12/31/2012" # Test DTobjToYWDarray once
$WNDa = DTobjToYWDarray($Zeit)
"Provided : $(YMDdate($Zeit))"
"WeekDate : $(YWDarrayToStr($WNDa))"
"Reversed : $(YMDdate(YWDarrayToDTobj($WNDa)))"
$ZZ = StrToYWDarray(YWDarrayToStr($WNDa))
Write "Unstrung : $(YMDdate(YWDarrayToDTobj($ZZ)))"


Write-Host "`n  Input Date  Weekday`t WkNum Date  and back"

ForEach ($Yeer in 2010..2013) {
  ForEach ($Offs in -3..+3) {
    $ItIs = Get-Date "01/01/$Yeer"
    $ItIs = $ItIs.AddDays($Offs)

    $WNDa = DTobjToYWDarray($ItIs)
    $Back = YWDarrayToDTobj($WNDa)

    Write-Host -NoNewline "  $(YMDdate($ItIs))  $($ItIs.DayOfWeek)"
    Write-Host "`t $(YWDarrayToStr($WNDa))  $(YMDdate($Back))" }
  Write-Host "" }



$Zeit = Get-Date
# $MaxDays = 146097

Write-Host "Full test from Monday 2001-01-01, 0 to $MaxDays days :"
Write-Host "  Input Date -> WkNum Date -> Date After" -NoNewline
Write-Host "    Y    W  D <- by counting"
$Y = 2001 ; $W = 1 ; $D = 0
ForEach ($Offs in 0..$MaxDays) {
  $ItIs = Get-Date "01/01/2001"
  $ItIs = $ItIs.AddDays($Offs) ; $Day = $ItIs.day # of month

  # Increment (W53 can only start on 28th or 27th) :
  $D++
  if ($D -gt 7) { $D = 1 ; $W++
    if ( ($W -eq 53) -and ( ($Day -ne 28) -and ($Day -ne 27) ) ) {
      $W = 1 ; $Y++ }
    if ($W -gt 53) { $W = 1 ; $Y++ } }

  $This = YMDdate($ItIs)
  $WNDa = DTobjToYWDarray($ItIs)
  $Wstr = YWDarrayToStr($WNDa)
  $WNDa = StrToYWDarray($Wstr)
  $Twas = YMDdate(YWDarrayToDTobj($WNDa))

  Write-Host -NoNewline `
    "  $This    $Wstr    $Twas    $Y $(LZ($W)) $D`t    $Offs`r"

  If ($This -ne $Twas) { Write-Warning "FAIL, QUIT" ; EXIT }

  If ($Offs -eq $BadDay `
      -or $WNDa[0] -ne $Y -or $WNDa[1] -ne $W -or $WNDa[2] -ne $D ) {
     Write-Host "" ; Write-Warning "FAIL, QUIT" ; EXIT }

  }

$Zeit = (Get-Date) - $Zeit
 "`nFinished OK at $(YMDdate($ItIs)),"  + `
 " time taken: {0:F2} minutes." -f ($Zeit.TotalSeconds/60)


"`nTest Get-Date formats for some dates, to see if weeks are ISO :"

# http://technet.microsoft.com/en-us/library/hh849887.aspx

$Str = Get-Date "12/30/2019" -uFormat %V
Write "Get-Date ""12/30/2019"" -uFormat %V   gives $Str, want 1"

$Str = Get-Date "2101-01-02" -uFormat %V
Write "Get-Date ""2101-01-02"" -uFormat %V   gives $Str, want 52"

$Str = Get-Date "01/02/2101" -uFormat %V
Write "Get-Date ""01/02/2101"" -uFormat %V   gives $Str, want 52"

"END."



# Also test Get-Date "12/31/2007" -uFormat %V
# and Calendar.GetWeekOfYear() for ISO weeks !!

# $ErrorActionPreference = stop

                           #######