function Get-FirstFreeIP {
    [CmdletBinding(DefaultParameterSetName="ByID")]
    param (
        [parameter(
            Mandatory=$true,
            ValueFromPipeline=$true,
            ValueFromPipelineByPropertyName=$true,
            Position=0,
            ParameterSetName="ByCIDR"
        )]
        [ValidateScript({[ipaddress] $_.Split("/")[0] -and $_.Split("/")[1] -match "\d{1,2}"})]
        [ValidateNotNullOrEmpty()]
        [string]
        $CIDR,
        [parameter(
            Mandatory=$true,
            ValueFromPipeline=$true,
            ValueFromPipelineByPropertyName=$true,
            Position=0,
            ParameterSetName="ByID"
        )]
        [ValidateNotNullOrEmpty()]
        [int]
        $Id,
        [parameter(
            Mandatory=$false,
            ValueFromPipeline=$true,
            ValueFromPipelineByPropertyName=$true,
            Position=0,
            ParameterSetName="BySubnetObject"
        )]
        [ValidateNotNullOrEmpty()]
        [PS.IPAM.Subnetwork]
        $SubnetObject
    )
    process {
        $_params = @{
            Controller = [PS.IPAM.controllers]::subnets
            Method     = "GET"
        }
        switch ($PSCmdlet.ParameterSetName) {
            "ByID"      { $_subnetId = $Id; break }
            "ByCIDR"    {
                $_subnetId = (Get-Subnet -CIDR $CIDR).id
                if (!$_subnetId) { throw "Cannot find subnet!" }
                break
            }
            "BySubnetObject" { $_subnetId = $SubnetObject.Id; break }
        }
        $_identifiers = @($_subnetId,"first_free")
        $_params.Add("Identifiers",$_identifiers)

        return Invoke-Request @_params | Select-Object @{n="Ip";e={$_}}
    }
}
Export-ModuleMember -Function Get-FirstFreeIP