Posh-git style powershell prompt

Microsoft.PowerShell_profile.ps1

# IPython-like history search:
Set-PSReadLineKeyHandler -Key UpArrow -Function HistorySearchBackward
Set-PSReadLineKeyHandler -Key DownArrow -Function HistorySearchForward


function Get-BranchName () {
    try {
        $branch = git rev-parse --abbrev-ref HEAD

        if ($branch -eq "HEAD") {
            # we're probably in detached HEAD state
            $tag = git describe --tags --exact-match
            if ($tag) {
                return "($tag)"
            }
            $sha = git rev-parse --short HEAD
            if ($sha) {
                return "($sha...)"
            }
            $isBare = git rev-parse --is-bare-repository
            if ($isBare -eq "true") {
                return "(BARE)"
            }
            # probably an empty repo
            return "(HEAD)"
        }
        # else we're on an actual branch, so print it
        return $branch
    } catch {
        return "(UNKNOWN)"
    }
}

function Get-TrackingStatus () {
    $color = "cyan"
    try {
        $status = git status -sb
        $hasUpstream = $status | Select-String -Pattern  '^## .*(\.\.\.)'
        $gone = $status | Select-String -Pattern '^## .* \[gone\]'

        if ($gone) {
            $str = [char]0x00D7
        } elseif ($hasUpstream) {
            $match = $status | Select-String -Pattern '^## .*\[ahead (\d+)'
            try {
                $aheadNum = $match.Matches.Groups[1]
            } catch {}

            $match = $status | Select-String -Pattern '^## .*behind (\d+)\]'
            try {
                $behindNum = $match.Matches.Groups[1]
            } catch {}

            if ($aheadNum -and $behindNum) {
                $str = "$([char]0x2193)$behindNum $([char]0x2191)$aheadNum"
                $color = "yellow"
            } elseif ($aheadNum) {
                $str = "$([char]0x2191)$aheadNum"
                $color = "green"
            } elseif ($behindNum) {
                $str = "$([char]0x2193)$behindNum"
                $color = "red"
            } else {
                $str = [char]0x2261
            }
        } else {
            $str = "?"
        }
    } catch {
        $str = "?"
    }
    return $str, $color, $status
}

function Write-Status () {
    $branchStr = Get-BranchName
    $trackingStr, $trackingColor, $status = Get-TrackingStatus

    if ($status) {
        $match = $status | Select-String -Pattern '^([MARC][ MD]|D[ RC])'
        $stagedChanges = $match.Matches.Count

        $match = $status | Select-String -Pattern '^([ MARC][MD]| A|[ D][RC])'
        $unstagedChanges = $match.Matches.Count

        $match = $status | Select-String -Pattern '^(D[DU]|A[AU]|U[DAU])'
        $conflicts = $match.Matches.Count

        $match = $status | Select-String -Pattern '^\?\?'
        $untrackedFiles = $match.Matches.Count
    }

    Write-Host " [" -NoNewline -ForegroundColor "gray"

    Write-Host "$branchStr $trackingStr" -NoNewline -ForegroundColor $trackingColor

    if ($stagedChanges) {
        Write-Host " ~$stagedChanges" -NoNewline -ForegroundColor "darkgreen"
        if ($unstagedChanges -or $conflicts -or $untrackedFiles) {
            Write-Host " |" -NoNewline -ForegroundColor "gray"
        }
    }
    if ($unstagedChanges) {
        Write-Host " ~$unstagedChanges" -NoNewline -ForegroundColor "darkred"
    }
    if ($conflicts) {
        Write-Host " !$conflicts" -NoNewline -ForegroundColor "darkred"
    }
    if ($untrackedFiles) {
        Write-Host " ?$untrackedFiles" -NoNewline -ForegroundColor "darkred"
    }

    Write-Host "]" -NoNewline -ForegroundColor "gray"
}

function prompt {
    $base = "PS"
    $path = "$($executionContext.SessionState.Path.CurrentLocation)"
    $userPrompt = "$('>' * ($nestedPromptLevel + 1)) "

    Write-Host "`n$base $path" -NoNewline

    if (git rev-parse --git-dir) {
        Write-Status
    }

    return $userPrompt
}