Powerline Prompt Builder

Add-Prompt.ps1

function Add-Prompt {
<#
.SYNOPSIS
Builds a powerline-style prompt from segments
.DESCRIPTION
This command is used to build a prompt from existing segments, and automagically will figure out the colors for the 
separators as necessary. You can insert additional colors into your string with ANSI escape sequences (don't use reset)
#>
    [CmdletBinding()]
    param (
        #The additional prompt segment to add
        [Parameter(ValueFromPipeline)][String]$InputObject,
        #The separator to use. Defaults to Powerline Separator.
        [String]$Separator = [char]0xe0b0,
        #The name of a background color if not specified a random color will be chosen
        [String]$Background,
        #The name of a foreground color. If not specified this function will automatically choose based on background
        [String]$Foreground
    )

    begin {
        #Set some "constants"
        if ($psedition -eq 'core') {
            $ansiesc = "`e"
        } else {
            $ansiesc = [char]0x1b
        }
        $resetcolor = "$ansiesc[39;49m"
        $fgcode = "$ansiesc[38;2;"
        $bgcode = "$ansiesc[48;2;"

        function Test-IsLightColor ([Drawing.Color]$Color) {
            #https://stackoverflow.com/a/36888120/5511129
            [double]$luma = ((0.299 * $Color.R) + (0.587 * $Color.G) + (0.114 * $Color.B)) / 255
            $luma -gt 0.5
        }
    }

    process {
        if ($Background) {
            $bgColorItem = $Background
        } else {
            $bgColorItem = (Get-Random (([Drawing.Color] | Get-Member -static).where{$_.membertype -eq 'property'}.name))
        }
        $bgColor = [Drawing.Color]::$bgColorItem
        write-host -fore Green "$bgColorItem Light: $(Test-IsLightColor $bgColor) "
        if ($bgColor) {
            if ($Foreground) {
                $fgColor = [Drawing.Color]::$Foreground
            } else {
                if (Test-IsLightColor $bgColor) {
                    $fgColor = [Drawing.Color]::Black
                } else {
                    $fgColor = [Drawing.Color]::White
                }
            }

            $bgColorCode = "$bgcode{0};{1};{2}m" -f
                $bgColor.r,
                $bgColor.g,
                $bgcolor.b
            $separatorColorCode = "$fgcode{0};{1};{2}m" -f
                $bgColor.r,
                $bgColor.g,
                $bgcolor.b
            $fgColorCode = "$fgcode{0};{1};{2}m" -f
                $fgColor.r,
                $fgColor.g,
                $fgColor.b
        } else {
            $bgColorCode = $resetColor
        }

        #This is used later to strip off the characters
        [String]$PSPromptEnd = "${resetcolor}${separatorColorCode}${Separator}${resetcolor}"

        [String]$PSPromptSegment = "${bgColorCode}${fgColorCode}${InputObject}${PSPromptEnd}"
        if (-not $GLOBAL:MyPSPrompt) {
            $GLOBAL:MyPSPrompt = $PSPromptSegment
        } else {
            #Strip the leading separator so we can replace it with one of the proper background lead-in. We leave the 
            #foreground as-is since it is the same color as the background was previously.
            $GLOBAL:MyPSPrompt = $GLOBAL:MyPSPrompt.SubString(0,($GLOBAL:MyPSPrompt.length-$GLOBAL:MyPSPromptEnd.length))
            
            $GLOBAL:MyPSPrompt += "${resetcolor}$($GLOBAL:MyPSPromptLastSeparatorFG)${bgColorCode}${Separator}${resetcolor}${$bgColorCode}"
            $GLOBAL:MyPSPrompt += $PSPromptSegment
        }
        Write-Host -fore green $inputobject
        $GLOBAL:MyPSPromptLastSeparatorFG = $separatorColorCode
        $GLOBAL:MyPSPromptEnd = $PSPromptEnd
    }
}