Calculates the total size used by child folders of the specified location

FileUtils.psm1

function Get-TreeLength {
  <#
    .SYNOPSIS
      Calculates the total size used by child folders of the specified location
    .PARAMETER path
      The root path
    .PARAMETER depth
      How many levels deep in the folder structure to go.
      Defaults to 0, displays sizes of all subfolders of path
      The higher the depth value is the slower it will be to fetch the inital
        folder list needs to iterate through more levels
    .EXAMPLE
      Import-Module .\FileUtils -force; Get-TreeLength c:\test-folder
      Returns the size of each folder in c:\test-folder
    .EXAMPLE
      ipmo .\FileUtils -force; Get-TreeLength c:\test-folder -depth 1
      Returns the size of the child folders of the folders inside c:\test-folder
    .EXAMPLE
      ipmo .\FileUtils.psm1 -force; Get-TreeLength c:\test-folder -depth 0 | Export-Csv c:\test-folder-length.csv
      Pipes the output to a csv file
  #>
  [CmdletBinding()]
  param(
    [parameter(position=0, mandatory=$true)]
    [string]$path,

    [ValidateRange(0,2)]
    [int]$depth
  )

  GetFolders $path 0 $depth |
    % {
      New-Object PsObject -Property @{
        "FullName" = $_;
        "length" = GetRobocopyDirSize $_
      }
    }
}

function GetFolders {
  <#
    .SYNOPSIS
    Recursively iterates through folders to match the depth
  #>
  [CmdletBinding()]
  param(
    [parameter(position=0, mandatory=$true)]
    [string]$path,

    [parameter(position=1, mandatory=$true)]
    [int]$currentDepth,

    [parameter(position=2, mandatory=$true)]
    [int]$depth
  )

  Write-Verbose "Fetching child folders of $($path)"
  $currentDepth++
  gci $path |
    ? { $_.PSIsContainer } |
    % {
      if ($currentDepth -gt $depth) {
        Write-Output $_.FullName
      }
      else {
        GetFolders $_.FullName $currentDepth $depth
      }
    }
}

function GetRobocopyDirSize {
  <#
    .SYNOPSIS
    Uses robocopy to determine a dir size, which is much faster than windows
  #>
  [CmdletBinding()]
  param(
    [parameter(position=0, mandatory=$true)]
    [string]$path
  )

  [string]$result = robocopy /b /l /mir $path "c:\8c97b9e1-0f72-428e-9ab2-5017a6353182" /r:0 /w:0 /ns /nc /nfl /ndl /njh /bytes
  if (-not ($lastexitcode -eq 16)) {
    $pos = $result.IndexOf("Bytes : ")
    $start = $pos + 8
    $length = $result.Length
    $end = $length - $start
    $newstring = $result.Substring($start, $end)
    $newstring = $newstring.Trim()

    return [long]$newstring.Split()[0]
  }
  else {
    Write-Error "Cannot access $path"
  }
}

Export-ModuleMember -function Get-TreeLength