Download multiple parts of an OpenAPI spec

Get-OpenApiDefinition.ps1

using namespace System.Collections.Generic

function Get-OpenApiDefinition {
  <#
	Fetches the OpenAPI definition from the specified URI and for every ref, downloads the relative file to the destination folder. Currently only works with relative refs
	#>
  param (
    #The source
    [Parameter(Mandatory)]
    [Uri]$Uri,
    #The destination path to download all files/folders
    [Parameter(Mandatory)]
    [string]$Destination
  )
  [uri]$baseUri = ((Split-Path -Path $Uri) -replace '\\', '/') + '/'
  $destinationDir = New-Item -ItemType Directory -Path $Destination -Force

  [HashSet[string]]$files = @()
  [Queue[string]]$queue = @()
  $queue.Enqueue($Uri)

  while ($queue.count -ne 0) {
    $UriToDownload = $queue.Dequeue()
    Write-Debug $UriToDownload

    $definition = Invoke-RestMethod -Uri $UriToDownload
    $path = $baseUri.MakeRelative($UriToDownload)
    $outFilePath = Join-Path $destinationDir $path
    $definition | Out-File -FilePath (New-Item -Path $outFilePath -Force)

    foreach ($ref in (Get-Refs -Definition $definition)) {
      $candidateUri = [uri]::new(([uri]$UriToDownload), $ref)
      #If we have not seen the file yet, process it
      if ($files.Add($candidateUri)) {
        $queue.Enqueue($candidateUri)
      }
    }
  }

  return $files
}

function Get-Refs {
  param (
    #The OpenAPI definition
    [string]$Definition
  )

  # Look for $ref in the definition
  $refs = $definition.split("`n") | Select-String -Pattern '\$ref: ["'']?([^"''].+?)#/' | ForEach-Object { $_.Matches.Groups[1].Value }

  # Deduplicate the refs
  $uniqueRefs = $refs | Select-Object -Unique

  return $uniqueRefs
}