VTFormat.ps1

#requires -module psreadline
using namespace System.Collections
using namespace System.Collections.Generic
using namespace System.Management.Automation
using namespace System.Management.Automation.Language

#create a hash table of VT codes
# Reverse, underline and reset; the console colors as Name, NameBackground; Markdown theme colors if present, PsReadline theme colors, and out-stream colors
if (-not $host.UI.SupportsVirtualTerminal) {$Script:VTCodes = @{}}
else {
    $esc = [char]0x1b
    ([System.ConsoleColor]).GetEnumNames()     |
        ForEach-Object -Begin  {$Script:VTCodes = [ordered]@{"UnderLine"="$esc[4m";"Reverse"="$esc[7m";"Reset"="$esc[0m"}} -Process {
                                $Script:VTCodes[$_]              = [Microsoft.PowerShell.VTColorUtils]::AsEscapeSequence($_)
                                $Script:VTCodes["$_`Background"] = [Microsoft.PowerShell.VTColorUtils]::AsEscapeSequence($_,$true)
        }
    try {
    (Get-MarkdownOption).psobject.Properties    | Where-Object -Property value -match "^\[\d" |
        ForEach-Object -Process {$Script:VTCodes[$_.name] = $esc+ $_.value}
    }
    catch {Write-Verbose "Markdown not present, continuing"}
    (Get-PSReadLineOption ).psobject.Properties | Where-Object -Property name -like "*color"  |
        ForEach-Object -Process {$Script:VTCodes[($_.name -Replace "color$","")]              = [Microsoft.PowerShell.VTColorUtils]::AsEscapeSequence($_.value)}
    $host.PrivateData.psobject.Properties       | Where-Object -Property  name -like "*color" |
        ForEach-Object -Process {$Script:VTCodes[($_.name -Replace "(Foreground)?color$","")] = [Microsoft.PowerShell.VTColorUtils]::AsEscapeSequence($_.value,[boolean]($_.name -like "*BackgroundColor"))}
}

#completer class for VT codes - returns one of codes in the hash table above
class VTCodeCompleter : IArgumentCompleter {
    [IEnumerable[CompletionResult]] CompleteArgument(
        [string]      $CommandName ,
        [string]      $ParameterName,
        [string]      $WordToComplete,
        [CommandAst]  $CommandAst,
        [IDictionary] $FakeBoundParameters
    )
    {
        $wildcard          = ("*" + $wordToComplete + "*")
        $completionResults = [List[CompletionResult]]::new()
        $Script:VTCodes.keys.where({$_ -like $wildcard }) |
            ForEach-Object {$completionResults.Add([CompletionResult]::new($_))}
        return $completionResults
    }
}

Function Add-VtFormat {
    <#
      .Synopsis
        Adds VT formatting codes to strings, formatting either the whole string, or a matching part of it.
      .Example
        Add-VtFormat "arbitrary color" -vtcode 'DarkBlue', 'CyanBackground'
        Sets the text to be Dark blue on a cyan background.
      .Example
        Add-vtformat "theme color" -VtCode 'Warning'
        Sets the text to a the colour used for warning text.
      .Example
        Add-VtFormat "highlight this not that" -VtCode 'Reverse' -Select "this"
        Highlights just word "this"
      .Example
        $s = select-string -path *.ps1 -SimpleMatch "\s*="
        Add-VtFormat $s.line 'Reverse' -Select $s.Pattern -EscapeFirst
        $S matchinfo object and $S.pattern holds a string which should NOT be treated as a regular
        expression - Select String was told to find the litteral text "\s*=". To ensure that text is
        highlighted , and not look for "space, any number of times, followed by =" -EscapeFirst is needed
      .Example
        Add-VtFormat "highlight this not that" -VtCode 'Reverse' -select  "^.{4}"
        Add-VtFormat "highlight this not that" -VtCode 'Reverse' -select  ".{3}$"
        Add-VtFormat "highlight this not that" -VtCode 'Reverse' -select  "(?<=^.{15}).*"
        Add-VtFormat "highlight this not that" -VtCode 'Reverse' -select  "(?<=^.{15}).{3}"
        Add-VtFormat "highlight this not that" -VtCode 'Reverse' -select  "(?<=^.{15}).*(?=.{5})"
        Add-VtFormat "highlight this not that" -VtCode 'Reverse' -select  ".*(?=.{5})"
        Using regular expressions to select first 4 chars, last 3 , all text after the first 15,
        3 chars after the first 15, from the first 15 to the the last 5, everything up to the last 5.
    #>
    param (
        #The Text to format
        [Parameter(ValueFromPipeline=$true,Mandatory=$true)]
        [string]$Text,
        #One or more VT formatting code name(s) or escape string(s) to apply to the text
        [ArgumentCompleter([VTCodeCompleter])]
        [string[]]$VtCode,
        #Applies the code to only a substring in -Text (by default the whole of text is format)
        [string]$Select,
        #If escapes any characters in -Select which have a special meaning in a regular expression
        [switch]$EscapeFirst
    )
    process {
        if ($DisableVTFormat -or -not $host.UI.SupportsVirtualTerminal) {$text}
        else {
            $codeString = ""
            foreach ($code in $VTcode) {
                if ($code -match "^\e\[\d.*m") {
                    $codeString += $code
                }
                else {
                    $codeString += $Script:VTCodes[$code]
                }
            }
            if ($Select) {
                if ($EscapeFirst) {$Select = [regex]::Escape($Select)}
                $substition = $codeString + '$1' +  $Script:VTCodes["Reset"]
                $text -Replace "($Select)",$substition
            }
            else {
                $codeString + $text + $Script:VTCodes["Reset"]
            }
        }
    }
}