Shuffle groups in an AIMP playlist ("*.aimppl4") while preserving the order inside groups.

Shuffle-Groups.ps1

<#
.SYNOPSIS
Shuffle groups in an AIMP playlist ("*.aimppl4")
while preserving the order inside groups.

.PARAMETER inputPath
Input file to be shuffled ("*.aimppl4").

#>

Param (
    [Parameter(Mandatory, HelpMessage="Input file to be shuffled.")]
    [ValidateScript({($_ -Like "*.aimppl4") -And (Test-Path $_ -PathType Leaf)})] 
    [string]$inputPath
)

Set-StrictMode -Version Latest

$lines = Get-Content $inputPath
$contentMarkerLine = $lines |
    Select-String -pattern "`#-----CONTENT-----`#" -SimpleMatch |
    Select-Object -ExpandProperty LineNumber

$groupsList = [System.Collections.ArrayList]@()
$group = [System.Collections.ArrayList]@()

$lines |
    Select-Object -Skip $contentMarkerLine |
    ForEach-Object -Process {
        If ($_.StartsWith("-") -And ($group.Count -gt 0)) {
            [void]$groupsList.Add($group)
            $group = [System.Collections.ArrayList]@()
        }
        [void]$group.Add($_)
    }
[void]$groupsList.Add($group)

Write-Host "Found $($groupsList.Count) groups."

$shuffled =
    ($lines | Select-Object -First $contentMarkerLine) +
    @($groupsList | Sort-Object { Get-Random } | ForEach-Object { $_ })

$shuffled | Set-Content $inputPath -Encoding unicode

Write-Host "Shuffled."