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

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

    $commandElements = $commandAst.CommandElements
    $command = @(
        'downtools'
        for ($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) {
        'downtools' {
            [CompletionResult]::new('-h', 'h', [CompletionResultType]::ParameterName, 'Print help information')
            [CompletionResult]::new('--help', 'help', [CompletionResultType]::ParameterName, 'Print help information')
            [CompletionResult]::new('-V', 'V', [CompletionResultType]::ParameterName, 'Print version information')
            [CompletionResult]::new('--version', 'version', [CompletionResultType]::ParameterName, 'Print version information')
            [CompletionResult]::new('print-path', 'print-path', [CompletionResultType]::ParameterValue, 'Prints the path to the directory to walk')
            [CompletionResult]::new('move', 'move', [CompletionResultType]::ParameterValue, 'move the maching files to destination')
            [CompletionResult]::new('hlink', 'hlink', [CompletionResultType]::ParameterValue, 'hardlink')
            [CompletionResult]::new('copy', 'copy', [CompletionResultType]::ParameterValue, 'copy')
            [CompletionResult]::new('help', 'help', [CompletionResultType]::ParameterValue, 'Print this message or the help of the given subcommand(s)')
            break
        }
        'downtools;print-path' {
            [CompletionResult]::new('-s', 's', [CompletionResultType]::ParameterName, 'the source dir to find the files')
            [CompletionResult]::new('--source-dir', 'source-dir', [CompletionResultType]::ParameterName, 'the source dir to find the files')
            [CompletionResult]::new('-d', 'd', [CompletionResultType]::ParameterName, 'the target dir to put matched files')
            [CompletionResult]::new('--dest-dir', 'dest-dir', [CompletionResultType]::ParameterName, 'the target dir to put matched files')
            [CompletionResult]::new('-p', 'p', [CompletionResultType]::ParameterName, 'the regex pattern to filter the files')
            [CompletionResult]::new('--pattern', 'pattern', [CompletionResultType]::ParameterName, 'the regex pattern to filter the files')
            [CompletionResult]::new('-c', 'c', [CompletionResultType]::ParameterName, 'if it is present, the pattern will be case insensitive')
            [CompletionResult]::new('--case-insensitive', 'case-insensitive', [CompletionResultType]::ParameterName, 'if it is present, the pattern will be case insensitive')
            [CompletionResult]::new('-h', 'h', [CompletionResultType]::ParameterName, 'Print help information')
            [CompletionResult]::new('--help', 'help', [CompletionResultType]::ParameterName, 'Print help information')
            break
        }
        'downtools;move' {
            [CompletionResult]::new('-s', 's', [CompletionResultType]::ParameterName, 'the source dir to find the files')
            [CompletionResult]::new('--source-dir', 'source-dir', [CompletionResultType]::ParameterName, 'the source dir to find the files')
            [CompletionResult]::new('-d', 'd', [CompletionResultType]::ParameterName, 'the target dir to put matched files')
            [CompletionResult]::new('--dest-dir', 'dest-dir', [CompletionResultType]::ParameterName, 'the target dir to put matched files')
            [CompletionResult]::new('-p', 'p', [CompletionResultType]::ParameterName, 'the regex pattern to filter the files')
            [CompletionResult]::new('--pattern', 'pattern', [CompletionResultType]::ParameterName, 'the regex pattern to filter the files')
            [CompletionResult]::new('-c', 'c', [CompletionResultType]::ParameterName, 'if it is present, the pattern will be case insensitive')
            [CompletionResult]::new('--case-insensitive', 'case-insensitive', [CompletionResultType]::ParameterName, 'if it is present, the pattern will be case insensitive')
            [CompletionResult]::new('-h', 'h', [CompletionResultType]::ParameterName, 'Print help information')
            [CompletionResult]::new('--help', 'help', [CompletionResultType]::ParameterName, 'Print help information')
            break
        }
        'downtools;hlink' {
            [CompletionResult]::new('-s', 's', [CompletionResultType]::ParameterName, 'the source dir to find the files')
            [CompletionResult]::new('--source-dir', 'source-dir', [CompletionResultType]::ParameterName, 'the source dir to find the files')
            [CompletionResult]::new('-d', 'd', [CompletionResultType]::ParameterName, 'the target dir to put matched files')
            [CompletionResult]::new('--dest-dir', 'dest-dir', [CompletionResultType]::ParameterName, 'the target dir to put matched files')
            [CompletionResult]::new('-p', 'p', [CompletionResultType]::ParameterName, 'the regex pattern to filter the files')
            [CompletionResult]::new('--pattern', 'pattern', [CompletionResultType]::ParameterName, 'the regex pattern to filter the files')
            [CompletionResult]::new('-c', 'c', [CompletionResultType]::ParameterName, 'if it is present, the pattern will be case insensitive')
            [CompletionResult]::new('--case-insensitive', 'case-insensitive', [CompletionResultType]::ParameterName, 'if it is present, the pattern will be case insensitive')
            [CompletionResult]::new('-h', 'h', [CompletionResultType]::ParameterName, 'Print help information')
            [CompletionResult]::new('--help', 'help', [CompletionResultType]::ParameterName, 'Print help information')
            break
        }
        'downtools;copy' {
            [CompletionResult]::new('-s', 's', [CompletionResultType]::ParameterName, 'the source dir to find the files')
            [CompletionResult]::new('--source-dir', 'source-dir', [CompletionResultType]::ParameterName, 'the source dir to find the files')
            [CompletionResult]::new('-d', 'd', [CompletionResultType]::ParameterName, 'the target dir to put matched files')
            [CompletionResult]::new('--dest-dir', 'dest-dir', [CompletionResultType]::ParameterName, 'the target dir to put matched files')
            [CompletionResult]::new('-p', 'p', [CompletionResultType]::ParameterName, 'the regex pattern to filter the files')
            [CompletionResult]::new('--pattern', 'pattern', [CompletionResultType]::ParameterName, 'the regex pattern to filter the files')
            [CompletionResult]::new('-c', 'c', [CompletionResultType]::ParameterName, 'if it is present, the pattern will be case insensitive')
            [CompletionResult]::new('--case-insensitive', 'case-insensitive', [CompletionResultType]::ParameterName, 'if it is present, the pattern will be case insensitive')
            [CompletionResult]::new('-h', 'h', [CompletionResultType]::ParameterName, 'Print help information')
            [CompletionResult]::new('--help', 'help', [CompletionResultType]::ParameterName, 'Print help information')
            break
        }
        'downtools;help' {
            [CompletionResult]::new('print-path', 'print-path', [CompletionResultType]::ParameterValue, 'Prints the path to the directory to walk')
            [CompletionResult]::new('move', 'move', [CompletionResultType]::ParameterValue, 'move the maching files to destination')
            [CompletionResult]::new('hlink', 'hlink', [CompletionResultType]::ParameterValue, 'hardlink')
            [CompletionResult]::new('copy', 'copy', [CompletionResultType]::ParameterValue, 'copy')
            [CompletionResult]::new('help', 'help', [CompletionResultType]::ParameterValue, 'Print this message or the help of the given subcommand(s)')
            break
        }
        'downtools;help;print-path' {
            break
        }
        'downtools;help;move' {
            break
        }
        'downtools;help;hlink' {
            break
        }
        'downtools;help;copy' {
            break
        }
        'downtools;help;help' {
            break
        }
    })

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