Small cmdlet to download and install the syzygy tablebases from lichess.org

DownloadSyzygyTablebases.ps1

function Get-Tablebases
{
    [CmdletBinding()]
    param (
        [int]
        [ValidateScript({ $_ -ge 3 },ErrorMessage = "'{0}' is not a valid number of pieces")]
        [Parameter(HelpMessage = "The maximum number of pieces whose tablebases you want to download.")]
        $MaxPieces = 7,
        [string]
        [ValidateScript({ Test-Path -Path $_ -PathType Container }, ErrorMessage = "Cannot find install path '{0}' because it does not exist.")]
        $InstallPath
    )
    
    begin
    {
        Write-Verbose -Message "Retrieving tablebase download URLs for up to $MaxPieces pieces."
        Invoke-RestMethod -Uri "https://syzygy-tables.info/download.txt?source=lichess&max-pieces=${MaxPieces}" | ForEach-Object { $_ -split "`n" } | ForEach-Object -Begin { 
            [uri]$downloadLink = [uri]$null
            $index = 0
        } -Process {
            if ([uri]::TryCreate($_, [System.UriKind]::Absolute, [ref]$downloadLink))
            {
                [pscustomobject]@{
                    Uri   = $downloadLink
                    Index = $index
                }
                $index++
            }
        } | Set-Variable -Name TablebaseDownloadUris -Scope Script

        Write-Verbose -Message "Retrieved $($TablebaseDownloadUris.Count) tablebase download URLs."
    }
    
    process
    {
        Write-Verbose -Message 'Starting download of tablebases.'

        if (Get-Command -Name ForEach-Object | Where-Object { $_.Parameters.ContainsKey('Parallel') })
        {
            $TablebaseDownloadUris | ForEach-Object -ThrottleLimit $env:NUMBER_OF_PROCESSORS -Parallel {
                $outFile = Join-Path -Path $using:InstallPath -ChildPath ($_.Uri.Segments[-1])
                Write-Progress -Activity 'Downloading tablebases' -Status "$($_.Uri)" -PercentComplete(100 * $_.Index / $($using:TablebaseDownloadUris).Count)
                Invoke-RestMethod -Uri $_.Uri -OutFile $outFile
            }
        }
        else
        {
            $client = New-Object -TypeName System.Net.WebClient
            $downloadTasks = $(
                foreach ($downloadLink in $TablebaseDownloadUris)
                {
                    $outFile = Join-Path -Path $InstallPath -ChildPath $($downloadLink.Uri.Segments[-1])
                    Write-Progress -Activity 'Queuing tablebase downloads' -Status "$outFile" -Id 0 -PercentComplete $([System.Math]::Round(100 * $downloadLink.Index / $TablebaseDownloadUris.Count))
                    $client.DownloadFileTaskAsync(($downloadLink.Uri), $outFile) | Write-Output
                }
            )

            Write-Verbose -Message 'Waiting for all downloads to complete.'
            $completedDownloads = 0
            while ($completedDownloads -lt $downloadTasks.Count)
            {
                $completedDownloads = $downloadTasks | Where-Object { $_.IsCompleted } | Measure-Object | Select-Object -ExpandProperty Count
                Write-Progress -Activity 'Downloading tablebases' -Status "$completedDownloads of $($downloadTasks.Count) downloads completed" -PercentComplete $([System.Math]::Round(100 * $completedDownloads / $downloadTasks.Count)) -CurrentOperation
                Start-Sleep -Seconds 1
            }
        }
    }
    
    end
    {
        Write-Verbose -Message 'Tablebase download process completed.'
    }
}