Introduction

This script selects a file based on a date string that is part of the filename. Once the date has been determined, the script tries to find out whether this file is the latest of the week that the date belongs to. The first part of the script generates some sample files and the second part filters out the correct files and copies them into the export folder.

Figure 1: The Orange County Great Park from a helium balloon

The script uses a regular expression to parse the date and hashtables for grouping the files weeks based on the parsed date.

Set-StrictMode -Version "latest"
$DebugPreference = "Continue"

Remove-Item -Path "E:\Archive" -Recurse -Force


New-Item -Path "E:\Archive\Export\Final" -Type "Directory"

$FinalFolder = "E:\Archive\Export\Final"
$ArchiveFolder = "E:\Archive\Export\"

function CreateArchiveFile($Prefix, $Date, $ArchiveFolder)
{
    $FileName = "{0}{1:yyyyMMdd}.txt" -f $Prefix, $Date
    Write-Debug "Debug $FileName"
    $FilePath = Join-Path -Path $ArchiveFolder -ChildPath $FileName
    New-Item -Path $FilePath -Type "File"
}

#Create Archive Files
$Today = Get-Date
$TwoMonthsAgo = $Today.AddMonths(-2)
$CurrentDay = $TwoMonthsAgo
while($CurrentDay -le $Today.AddDays(-1))
{
    CreateArchiveFile -Prefix "ExportPrevious" -Date $CurrentDay -ArchiveFolder $ArchiveFolder
    $CurrentDay = $CurrentDay.AddDays(1)
}
CreateArchiveFile -Prefix "ExportCurrent" -Date $CurrentDay -ArchiveFolder $ArchiveFolder


$Files = Get-ChildItem -Path $ArchiveFolder

$WeeklyFileTable = @{}

function ParseDateFromFileName($FileName)
{
    $FileName -match '^(?<PREFIX>ExportPrevious|ExportCurrent)(?<YEAR>\d{4})(?<MONTH>\d{2})(?<DAY>\d{2}).txt$' | Out-Null
    $Date = New-Object -TypeName "System.DateTime" -ArgumentList $matches.YEAR, $matches.MONTH, $matches.DAY, 0, 0, 0, 0
    return $Date
}

function CopyWeeklyFiles($FileTable, $Destination)
{
    $FileTable.GetEnumerator() | ForEach-Object { Write-Debug ($_.Value.FullName);Copy-Item -Path ($_.Value.Fullname) -Destination $Destination -Force }

}

function GetNextSaturday($CurrentDay)
{
    $LastSaturdayTable = @{"Saturday"=0; "Friday"=1; "Thursday"=2; "Wednesday" = 3; "Tuesday" = 4; "Monday"=5; "Sunday" = 6}
    $DaysToNextSaturday = $LastSaturdayTable[($CurrentDay.DayOfWeek).ToString()]
    $NextSaturday = $CurrentDay.AddDays($DaysToNextSaturday)
    return $NextSaturday
}

foreach($file in $files)
{
    Write-Debug $file.Fullname
    #ParseFileDate String -> DateTime
    $Date = ParseDateFromFileName -FileName $file.name 
    $NextSaturday = GetNextSaturday -CurrentDay $Date
    
    if($WeeklyFileTable[$NextSaturday] -ne $Null)
    {
        $LatestFile = $WeeklyFileTable[$NextSaturday]
        $LatestFileDate = ParseDateFromFileName -FileName $LatestFile.name
        if($Date -gt $LatestFileDate)
        {
            $WeeklyFileTable[$NextSaturday] = $file
        }
    }
    else
    {
        $WeeklyFileTable[$NextSaturday] = $file
    }
    $NextSaturday
}

$WeeklyFileTable


CopyWeeklyFiles -FileTable $WeeklyFileTable -Destination $FinalFolder

Ausblick

I actually needed to write this function as part of a .NET C# project, but I used PowerShell to prototype the algorithm. The .NET C# version will be published in the next blog post. Stay tuned!