Clear-WindowsInstallerPatchInfo; cleanly/safely remove files from c:\windows\installer

Clear-WindowsInstallerPatchInfo.ps1

#based on 
# - http://blogs.msdn.com/b/heaths/archive/2007/01/31/how-to-safely-delete-orphaned-patches.aspx 
# - http://www.bryanvine.com/2015/06/powershell-script-cleaning-up.html
# - https://p0w3rsh3ll.wordpress.com/2012/01/10/working-with-the-windowsinstaller-installer-object/

clear-host

function Get-WindowsInstallerPatchInfo {
    [CmdletBinding()]
    Param ()
    
    $msi = New-Object -ComObject 'WindowsInstaller.Installer'
    
    <# didn't need this; all "methods" were actually properties
    $msi | Add-Member -Name 'InvokeMethod' -MemberType ScriptMethod -Value {
        $type = $this.GetType();
        $index = $args.Count -1 ;
        $methodargs=$args[1..$index]
        $type.invokeMember($args[0],[System.Reflection.BindingFlags]::InvokeMethod,$null,$this,$methodargs)

    }
    #>

    $msi | Add-Member -Name 'GetProperty' -MemberType ScriptMethod -Value {
        $type = $this.gettype();
        $index = $args.count -1 ;
        $methodargs=$args[1..$index]
        $type.invokeMember($args[0],[System.Reflection.BindingFlags]::GetProperty,$null,$this,$methodargs)
    }

    $products = $msi.GetProperty('Products')
    if ($products) {
        Write-Verbose "Product Count: $($products.Count)"  
        foreach ($productCode in $products) {
            Write-Verbose "Product: $productCode" 
            $patches = $msi.GetProperty('Patches',$productCode)
            if ($patches) {
                foreach ($patchCode in $patches) {
                    Write-Verbose "Patch: $patchCode" 
                    $location = $msi.GetProperty('PatchInfo', $patchCode, 'LocalPackage')
                    Write-Verbose "Location: $location" 
                    if ($location) {
                        (New-Object -TypeName 'PSObject' -Property @{
                            ProductCode = $productCode
                            PatchCode = $patchCode
                            Location = $location 
                        })
                    }
                }
            }
        }
    }
}

function Clear-WindowsInstallerPatchInfo {
    [CmdletBinding()]
    Param ()

    [string]$installDir = Join-Path -Path $env:windir -ChildPath 'Installer'

    [PSObject[]]$installerInfo = Get-WindowsInstallerPatchInfo -Verbose

    [string[]]$itemsOfInterest = $installerInfo | select-Object -ExpandProperty 'location'
    [string[]]$guidsOfInterest = @($installerInfo | select-Object -ExpandProperty 'productCode') + @($installerInfo | select-Object -ExpandProperty 'patchCode')

    [PSObject[]]$pathsAndActions = Get-ChildItem -Path $installDir -Recurse | Select-Object -ExpandProperty 'FullName' | ForEach-Object {
        [bool]$keepPath = if ($_ -in $itemsOfInterest) {
            $true
        } else {
            [string[]]$guids = [Regex]::Matches($_,'\{[0-9A-F]{8}\-([0-9A-F]{4}\-){3}[0-9A-F]{12}\}') | Select-Object -ExpandProperty value
            if ($guids | Where-Object {$_ -in $guidsOfInterest}) {
                $true
            } else {
                $false
            }
        }
        (New-Object -TypeName 'PSObject' -Property @{
            Path = $_
            Keep = $keepPath
        })
    }

    $pathsAndActions | ForEach-Object {
        if ($_.Keep) {
            Write-Verbose "Keep $($_.Path)"
        } else {
            Write-Verbose "Remove $($_.Path)"        
            Remove-Item -Path $_.Path -Recurse -Force
        }
    }
}

Clear-WindowsInstallerPatchInfo -Verbose