using namespace System.Management.Automation
using namespace System.Management.Automation.Language

Register-ArgumentCompleter -Native -CommandName 'chgrp' -ScriptBlock {
    param($wordToComplete, $commandAst, $cursorPosition)

    $commandElements = $commandAst.CommandElements
    $command = @(
        'chgrp'
        for ($i = 1; $i -lt $commandElements.Count; $i++) {
            $element = $commandElements[$i]
            if ($element -isnot [StringConstantExpressionAst] -or
                $element.StringConstantType -ne [StringConstantType]::BareWord -or
                $element.Value.StartsWith('-') -or
                $element.Value -eq $wordToComplete) {
                break
        }
        $element.Value
    }) -join ';'

    $completions = @(switch ($command) {
        'chgrp' {
            [CompletionResult]::new('-c', 'c', [CompletionResultType]::ParameterName, 'report only when a change is made')
            [CompletionResult]::new('--changes', 'changes', [CompletionResultType]::ParameterName, 'report only when a change is made')
            [CompletionResult]::new('-v', 'v', [CompletionResultType]::ParameterName, 'output a diagnostic for every file processed')
            [CompletionResult]::new('--verbose', 'verbose', [CompletionResultType]::ParameterName, 'output a diagnostic for every file processed')
            [CompletionResult]::new('-R', 'R', [CompletionResultType]::ParameterName, 'operate on files and directories recursively')
            [CompletionResult]::new('--recursive', 'recursive', [CompletionResultType]::ParameterName, 'operate on files and directories recursively')
            [CompletionResult]::new('-H', 'H', [CompletionResultType]::ParameterName, 'if a command line argument is a symbolic link to a directory, traverse it')
            [CompletionResult]::new('-L', 'L', [CompletionResultType]::ParameterName, 'traverse every symbolic link encountered in a directory')
            [CompletionResult]::new('-P', 'P', [CompletionResultType]::ParameterName, 'do not traverse any symbolic links (default)')
            [CompletionResult]::new('-s', 's', [CompletionResultType]::ParameterName, 'do not cross filesystem boundaries (requires recursive)')
            [CompletionResult]::new('--same-filesystem', 'same-filesystem', [CompletionResultType]::ParameterName, 'do not cross filesystem boundaries (requires recursive)')
            [CompletionResult]::new('-h', 'h', [CompletionResultType]::ParameterName, 'Print help')
            [CompletionResult]::new('--help', 'help', [CompletionResultType]::ParameterName, 'Print help')
            [CompletionResult]::new('-V', 'V', [CompletionResultType]::ParameterName, 'Print version')
            [CompletionResult]::new('--version', 'version', [CompletionResultType]::ParameterName, 'Print version')
            break
        }
    })

    $completions.Where{ $_.CompletionText -like "$wordToComplete*" } |
        Sort-Object -Property ListItemText
}