Function New-SPOSubsite {
    <#
        .SYNOPSIS
        Creates a new subsite under the specified site with the specified parameters.
        .DESCRIPTION
        Creates a new subsite under the specified site with the specified parameters.
        .PARAMETER SiteUrl
        The URL of the site where the subsite belongs, can be a root level site collection or a subsite.
        .PARAMETER SubsiteUrl
        The short URL of the new subsite.
        .PARAMETER Title
        The subsite title.
        .PARAMETER Template
        Template is an enumeration, your choices are either Project or Team.
        .PARAMETER SamePermissions
        A boolean parameter that specifies if the subsite is going to use the same permissions as the parent. $false=broken, $true=inherit
        .PARAMETER Description
        An optional site description.
        .EXAMPLE
        Create a new project subsite from the root of a site collection with inherited permissions
        New-OISubsite -SiteUrl "https://tenant.sharepoint.com/teams/eric" -SubsiteUrl "ProjectX" -Title "Secret Project X" -Template Project -SamePermissions $true -Description "This is a project space"
        .EXAMPLE
        Create a new team subsite with broken permissions inheritance
        New-OISubsite -SiteUrl "https://tenant.sharepoint.com/teams/eric/operations" -SubsiteUrl "DevOps" -Title "DevOps Team Site" -Template Team -SamePermissions $false
        .NOTES
        Mainly used as part of New-Plant provisioning, but could be used to create a subsite in any site collection.
        Created since there is no New-SPOWeb commandlet.
    #>
    Param(
        [Parameter(Mandatory=$true,HelpMessage="The URL of the site collection",Position=0)][ValidateNotNull()]
        [string]$SiteUrl,

        [Parameter(Mandatory=$true,HelpMessage="The short URL of the subsite",Position=1)][ValidateNotNull()]
        [string]$SubsiteUrl,

        [Parameter(Mandatory=$true,HelpMessage="The site title",Position=2)][ValidateNotNull()]
        [string]$Title,

        [Parameter(Mandatory=$true,HelpMessage="The template to use, Project or Team",Position=3)][ValidateSet("Project","Team")]
        [string]$Template,

        [Parameter(Mandatory=$true,HelpMessage="Use Same Permissions As Parent Site",Position=4)]
        [boolean]$SamePermissions,

        [Parameter(Mandatory=$false,HelpMessage="Site description",Position=5)]
        [string]$Description

    )
    begin{
        $tmplt = ""

        If($Template -eq "Team"){
            $tmplt = "STS#0"
        }
        Else {
            $tmplt = "PROJECTSITE#0"
        }

        $subsite = $SiteUrl+"/"+$SubsiteUrl
        write-host "Creating subsite $subsite"
    }
    process{
        $context = New-Object Microsoft.SharePoint.Client.ClientContext($SiteUrl)
        $context.Credentials = New-Object Microsoft.SharePoint.Client.SharePointOnlineCredentials($credential.UserName, $credential.Password)

        #Create SubSite
        $wci = New-Object Microsoft.SharePoint.Client.WebCreationInformation
        $wci.WebTemplate = $tmplt
        if ($Description.Length -gt 0){
            $wci.Description = $Description
        }
        $wci.UseSamePermissionsAsParentSite = $SamePermissions
        $wci.Title = $Title
        $wci.Url = $SubsiteUrl
        $wci.Language = "1033"

        $SubWeb = $context.Web.Webs.Add($wci)
        $context.ExecuteQuery()

        if($SamePermissions -eq $false){
            try{
                #Check to see if this is a root site collection that was passed
                Get-SPOSite -Identity $SiteUrl
            }
            catch {
               #If here we are working with a subsite
               Write-Host "Oops, it looks like we're dealing with a subsite, I can handle that" -ForegroundColor Yellow
               #reconstruct the SiteUrl parameter
               $SiteUrl = "https://tenant.sharepoint.com/"+$SiteUrl.Split("/")[3]+"/"+$SiteUrl.Split("/")[4]
            }
            finally{
                $ownerGroup = "$Title Owners"
                $memberGroup = "$Title Members"
                $visitorGroup = "$Title Visitors"
                Write-Host "Hang tight, creating groups, updating ownership and adjusting permissions"
                New-SPOSiteGroup -Site $SiteUrl -Group $ownerGroup -PermissionLevels "Read" | Out-Null
                #Updating the group owner does not work from PowerShell, using the new Set-GroupOwner function
                Set-GroupOwner -SiteUrl $SiteUrl -GroupToUpdate $ownerGroup.ToString() -GroupOwner $ownerGroup.ToString()
                New-SPOSiteGroup -Site $SiteUrl -Group $memberGroup -PermissionLevels "Read" | Out-Null
                Set-GroupOwner -SiteUrl $SiteUrl -GroupToUpdate $memberGroup.ToString() -GroupOwner $ownerGroup.ToString()
                New-SPOSiteGroup -Site $SiteUrl -Group $visitorGroup -PermissionLevels "Read" | Out-Null
                Set-GroupOwner -SiteUrl $SiteUrl -GroupToUpdate $visitorGroup.ToString() -GroupOwner $ownerGroup.ToString()
                Set-PermissionsOnSite -Url $subsite -GroupName $ownerGroup -Roletype "Full Control"
                Set-PermissionsOnSite -Url $subsite -GroupName $memberGroup -Roletype "Contribute"
                Set-PermissionsOnSite -Url $subsite -GroupName $visitorGroup -Roletype "Read"
                Set-DefaultSiteGroups -SiteUrl $subsite -VisitorGroup $visitorGroup -MemberGroup $memberGroup -OwnerGroup $ownerGroup
            }
        }
    }
    end {
        $context.Dispose()
        Write-Host -ForegroundColor Green "Subsite $subsite created successfully!"
    }
}

#Add references to SharePoint client assemblies and authenticate to Office 365 site
Add-Type -Path "C:Program FilesCommon FilesMicrosoft SharedWeb Server Extensions16ISAPIMicrosoft.SharePoint.Client.dll"
Add-Type -Path "C:Program FilesCommon FilesMicrosoft SharedWeb Server Extensions16ISAPIMicrosoft.SharePoint.Client.Publishing.dll"
Add-Type -Path "C:Program FilesCommon FilesMicrosoft SharedWeb Server Extensions16ISAPIMicrosoft.SharePoint.Client.Runtime.dll"
$Username = Read-Host -Prompt "Please enter your username"
$Password = Read-Host -Prompt "Please enter your password" -AsSecureString
$Site = "https://site.sharepoint.com"
$Context = New-Object Microsoft.SharePoint.Client.ClientContext($Site)
$Creds = New-Object Microsoft.SharePoint.Client.SharePointOnlineCredentials($Username,$Password)
$Context.Credentials = $Creds


#Create SubSite
$WCI = New-Object Microsoft.SharePoint.Client.WebCreationInformation
$WCI.WebTemplate = "STS#0"
$WCI.Description = "SubSite"
$WCI.Title = "SubSite"
$WCI.Url = "SubSite"
$WCI.Language = "1033"
$SubWeb = $Context.Web.Webs.Add($WCI)
$Context.ExecuteQuery()