fix_trailing_ws.ps1

using namespace System.Text.RegularExpressions

param([string[]]$extensions = 'ps1')

function Get-FileEncoding
{
    [CmdletBinding()]
    param (
     [Parameter(Mandatory = $True, ValueFromPipelineByPropertyName = $True)] [string]$Path
    )
 
    [byte[]]$byte = get-content -Encoding byte -ReadCount 4 -TotalCount 4 -Path $Path
 
    if ( $byte[0] -eq 0xef -and $byte[1] -eq 0xbb -and $byte[2] -eq 0xbf ) { Write-Output 'UTF8' }
    elseif ($byte[0] -eq 0xfe -and $byte[1] -eq 0xff) { Write-Output 'Unicode' }
    elseif ($byte[0] -eq 0 -and $byte[1] -eq 0 -and $byte[2] -eq 0xfe -and $byte[3] -eq 0xff) { Write-Output 'UTF32' }
    elseif ($byte[0] -eq 0x2b -and $byte[1] -eq 0x2f -and $byte[2] -eq 0x76) { Write-Output 'UTF7'}
    else { Write-Output 'ASCII' }
}

function CheckFix($orig, $new)
{
    $origContent = Get-Content -Encoding byte $orig
    $newContent = Get-Content -Encoding byte $new

    if ($origContent.Length -lt $newContent.Length)
    {
        Write-Error "Unexpected - original is shorter: $orig"
        return $false
    }

    $newI = 0
    $oldI = 0
    while ($newI -lt $newContent.Length)
    {
        $o = $origContent[$oldI] 
        $n = $newContent[$newI]
        while ($o -ne $n -and ($o -eq 32 -or $o -eq 9))
        {
            $oldI += 1
            $o = $origContent[$oldI] 
        }

        if ($o -ne $n)
        {
            $msg = "file $orig differs, encoding messed up somehow`n" + 
                   ($origContent[($oldI-6)..($oldI+9)] | fhx | Out-String) + 
                   ($newContent[($newI-6)..($newI+9)] | fhx | Out-String) 
            Write-Error $msg
            return $false
        }

        $oldI += 1
        $newI += 1
    }

    return $true
}

function FixWhiteSpace
{
    param(
        [Parameter(Mandatory, ValueFromPipelineByPropertyName, ValueFromPipeline)]
        [Alias('PSPath')]
        [string] $LiteralPath
    )

    begin {
        $trailingWhiteSpace  = [Regex]::new('(?m)[ \t]+\r?$', [RegexOptions]::Compiled)
        $tempFile = New-TemporaryFile
    }

    process {
        try {
            $LiteralPath = (Resolve-Path $LiteralPath).ProviderPath
            if (Test-path -PathType Leaf $LiteralPath) {
                $Encoding = Get-FileEncoding $LiteralPath
                $content = Get-Content -Raw -LiteralPath $LiteralPath
                if ($null -ne $content) {
                    $trimmedContent = $trailingWhiteSpace.Replace($content, "`r")
                    if ($trimmedContent -ne $content) {
                        # Set-Content fails for some reason with 'Set-Content : Stream was not readable.'
                        [io.file]::WriteAllText($tempFile, $trimmedContent, [Text.Encoding]::$Encoding)
                        if (CheckFix $LiteralPath $tempFile)
                        {
                            mv $tempFile $LiteralPath -Force
                        }
                        Write-Verbose "Updated '$LiteralPath' with encoding $Encoding"
                        #Get-Item $LiteralPath
                    }
                }
            }
        }
        catch {
            Write-Error -Message $_.Exception.Message -TargetObject $LiteralPath
        }
    }
}

$extensionRegex = ($extensions -join '$|') + '$'
(git ls-tree -r --name-only --full-name HEAD) -match $extensionRegex | Get-ChildItem | FixWhiteSpace -Verbose