Avoid duplicate Bulk-New-ADUser Creation via a csv file - windows

Question

I have some modifications for this script. UserID is normally a user’s first name followed by their last name.
What I need to do is to compare the proxy address & SAMAccountName attribute associated with each Username before it create.
So I mean lets say Jack Sparrow , if jsparrow already in use then script will try as jasparrow (first and second letter of firstname) and in use jasparrow as well , will be jacsparrow and so on. I want to avoid duplicate usernames.
2-I decided that it would be better to make 'fun' passwords that use the first two letters of the FirstName , day/month , first two letters of the Lastname. The end result is that users get a password like "Ja1009Sp".
Firstname,LastName,Department,Manager,MobilePhone
Jack,Sparrow,IT,jsmith,1 88 635 5254-0551
John Smith,Sparrow,Finance,jsmith,188 635 5254-0554
Script :
Import-Module ActiveDirectory
$UserList = Import-CSV -Path C:\Temp\CreateUsers.csv
$targetOU='OU=usersOU,DC=My,DC=Domain,DC=org'
$upnDomain='sec.local'
foreach($Person in $UserList){
$useritems=#{
GivenName=$Person.Firstname
Surname=$Person.LastName
Department=$Person.Department
AccountPassword=ConvertTo-SecureString -String $Person.Password -AsPlainText -force
ChangePasswordAtLogon=$false
Enabled=$true
DisplayName="$($Person.Firstname) $($Person.Lastname)"
Manager=$Person.Manager
MobilePhone=$Person.MobilePhone
Name="$($Person.Firstname) $($Person.Lastname)"
SamAccountName="$($Person.Firstname+$Person.LastName.Substring(0,1))"
UserPrincipalName="$($Person.FirstName+$Person.LastName.Substring(0,1))#$upnDomain"
Company="Contoso"
}
New-ADUser #useritems -Path $targetOU
}

Answer 1

Try something like this.. I don't have AD available atm. to test the Get-ADUser-query used to look for existing account so it might need some tuning.
foreach ($Person in $UserList) {
#Reset counters
$i = 1
$n = 1
do {
if($i -le $person.Firstname.Length) {
$user = "$($Person.Firstname.Substring(0,$i)+$Person.LastName)"
$i++
} else {
#All combinations in use, adding number
$user = "$($Person.Firstname.Substring(0,1)+$Person.LastName+$n)"
$n++
}
} while ((Get-ADUser -Filter "(samAccountName -eq '$user') -or (proxyaddresses -like '$user*')"))
#Result username
#$user
#$useritems = #{
#.....
#SamAccountName=$user
#UserPrincipalName="$user#$upnDomain"
#....
#}
}
If all combinations are in use including jacksparrow, it tries jsparrow1 ++ until it finds a free number.
The password can be generated using:
$Password = "{0}{1}{2}" -f $Person.Firstname.Substring(0,2), (Get-Date).ToString("ddMM"), $Person.Lastname.Substring(0,2)