Creates a unique AD DS Username.

New-Username.ps1

<#
.SYNOPSIS
    Creates a new username with AD DS Validation.
.DESCRIPTION
    Create a new username with the following order until a unique Username is found.
    1. First Initial Last Name.
    2. First Initial First Middle Intial Last Name.
    3. Itterates First Name adding Char until a unique Username is found.
.EXAMPLE
    New-Username -FirstName John -LastName Doe
    ---OUTPUT---
    jdoe
.EXAMPLE
    New-Username -FirstName Jane -LastName Doe -MiddleName Ala
    ---OUTPUT---
    jadoe
.NOTES 
    Requires ActiveDirectory Module available with Remote Server Administration Tools.
    RSAT 7SP1: http://www.microsoft.com/en-us/download/details.aspx?id=7887
    RSAT 8:    http://www.microsoft.com/en-us/download/details.aspx?id=28972
    RSAT 8.1:  http://www.microsoft.com/en-us/download/details.aspx?id=39296
.LINK
    http://dotps1.github.io
#>
function New-Username
{
    [CmdletBinding()]
    [OutputType([String])]
    param
    (
        # FirstName, Type String, The first name of the user to be created.
        [Parameter(Mandatory = $true)]
        [String]
        $FirstName,

        # LastName, Type String, the last name of the user to be created.
        [Parameter(Mandatory = $true)]
        [String]
        $LastName,

        # MiddleName, Type String, the middle name of the user to be created.
        [Parameter(Mandatory = $false)]
        [AllowNull()]
        [String]
        $MiddleName
    )

    Begin
    {
        if (-not(Get-Module -Name ActiveDirectory)) 
        {
            try
            {
                Import-Module -Name ActiveDirectory -ErrorAction Stop
            }
            catch
            {
                throw "ActiveDirectory Module is not available on this computer, and this cmdlet cannot be used.  Use Get-Help New-Username -Full and see the .NOTE section for links about RSAT."
            }
        }

        # '|' = Or Operand, '\s' = Spaces, '-' = Hyphens, ''' = Apostrophe,
        [RegEx]$pattern = "\s|-|'"
    }

    Process
    {
        try
        {
            $primaryUsername = ($FirstName.Substring(0,1) + $LastName) -replace $pattern,""
            Get-ADUser -Identity $primaryUsername | Out-Null
        }
        catch
        {
            return $primaryUsername.ToLower()
        }
    
        if (-not([String]::IsNullOrEmpty($MiddleName)))
        {
            try
            {
                $secondaryUsername = ($FirstName.Substring(0,1) + $MiddleName.Substring(0,1) + $LastName) -replace $pattern,""
                Get-ADUser -Identity $secondaryUsername | Out-Null
            }
            catch
            {
                return $secondaryUsername.ToLower()
            }
        }

        foreach ($char in $FirstName.ToCharArray())
        {
            $prefix += $char
            $tertiaryUsername = ($prefix + $LastName) -replace $pattern,""

            if ($tertiaryUsername -eq $primaryUsername)
            {
                continue
            }

            try
            {
                Get-ADUser -Identity $tertiaryUsername | Out-Null
            }
            catch
            {
                return $tertiaryUsername.ToLower()
                break
            }
        }
    }
}