param(
    [string]$ExternalRelativePath = "node_modules"
)
$ErrorActionPreference = "Stop"
function Get-RelativeDirectoryPath([string]$BaseDirectory, [string]$TargetDirectory)
{
    $basePath = [System.IO.Path]::GetFullPath($BaseDirectory)
    $targetPath = [System.IO.Path]::GetFullPath($TargetDirectory)
    if ([System.IO.Path]::GetPathRoot($basePath) -ne [System.IO.Path]::GetPathRoot($targetPath))
    {
        throw "Relative symbolic links require the source and target to be on the same drive"
    }
    $separator = [string][System.IO.Path]::DirectorySeparatorChar
    if (-not $basePath.EndsWith($separator))
    {
        $basePath += $separator
    }
    $baseUri = [System.Uri]::new($basePath)
    $targetUri = [System.Uri]::new($targetPath)
    return [System.Uri]::UnescapeDataString($baseUri.MakeRelativeUri($targetUri).ToString()).Replace("/", $separator)
}
$projectDir = [System.IO.Path]::GetFullPath((Join-Path $PSScriptRoot ".."))
$frontendDir = Join-Path $projectDir "frontend"
$externalDir = [System.IO.Path]::GetFullPath((Join-Path $projectDir $ExternalRelativePath))
$linkPath = Join-Path $frontendDir "node_modules"
New-Item -ItemType Directory -Force -Path $externalDir | Out-Null
$linkTarget = Get-RelativeDirectoryPath $frontendDir $externalDir
$item = Get-Item -LiteralPath $linkPath -Force -ErrorAction SilentlyContinue
if ($null -ne $item)
{
    if (($item.Attributes -band [System.IO.FileAttributes]::ReparsePoint) -eq 0)
    {
        throw "A real directory already exists at $linkPath; move or remove it before creating the symbolic link"
    }
    Remove-Item -LiteralPath $linkPath -Force
}
Push-Location $frontendDir
try
{
    $command = 'mklink /D "node_modules" "{0}"' -f $linkTarget
    & $env:ComSpec /d /c $command
    if ($LASTEXITCODE -ne 0)
    {
        throw "mklink failed with exit code $LASTEXITCODE"
    }
}
finally
{
    Pop-Location
}
Write-Host "node_modules -> $linkTarget"
Write-Host "physical directory: $externalDir"