PowerShell Parameter Madness

enrol.ps1

# This function takes a user and a course, but it should be possible to specify either argument
# as an ID rather than an instance of the class. 

# Named parameters work fine, but positional parameters don't always parse correctly.
# All the commands at the bottom of this file *should* work.

class User { [int] $Id }
class Course { [int] $Id }

function New-Enrolment {
    [CmdletBinding(SupportsShouldProcess,DefaultParameterSetName='id')]
    param (
        [Parameter(Mandatory,Position=0,ParameterSetName='userid course')]
        [Parameter(Mandatory,Position=0,ParameterSetName='userid courseid')]
        [Parameter(Mandatory,Position=0,ParameterSetName='course|userid')]
        [int]
        $UserId,

        [Parameter(Mandatory,Position=0,ParameterSetName='user course')]
        [Parameter(Mandatory,Position=0,ParameterSetName='user courseid')]
        [Parameter(Mandatory,Position=0,ParameterSetName='course|user')]
        [User]
        $User,

        [Parameter(Mandatory,ValueFromPipeline,ParameterSetName='user|course')]
        [Parameter(Mandatory,ValueFromPipeline,ParameterSetName='user|courseid')]
        [User]
        $PipelineUser,

        [Parameter(Mandatory,Position=1,ParameterSetName='userid course')]
        [Parameter(Mandatory,Position=1,ParameterSetName='user course')]
        [Parameter(Mandatory,Position=0,ParameterSetName='user|course')]
        [Course]
        $Course,

        [Parameter(Mandatory,Position=1,ParameterSetName='user courseid')]
        [Parameter(Mandatory,Position=1,ParameterSetName='userid courseid')]
        [Parameter(Mandatory,Position=0,ParameterSetName='user|courseid')]
        [int]
        $CourseId,

        [Parameter(Mandatory,ValueFromPipeline,ParameterSetName='course|user')]
        [Parameter(Mandatory,ValueFromPipeline,ParameterSetName='course|userid')]
        [Course]
        $PipelineCourse       
    )

    if ($PipelineCourse) {
        $CourseId = $PipelineCourse.Id
    }
    elseif ($Course) {
        $CourseId = $Course.Id
    }

    if ($PipelineUser) {
        $UserId = $PipelineUser.Id
    }
    elseif ($User) {
        $UserId = $User.Id
    }
    write-output "User $UserId`tCourse $CourseId"
}

$user = [User] @{ Id = 1 }
$course = [Course] @{ Id = 2 }

"Named:"

"userid courseid"
New-Enrolment -UserId $user.Id -CourseId $course.Id

"user courseid"
New-Enrolment -User $user -CourseId $course.Id

"userid course"
New-Enrolment -UserId $user.Id -Course $course 

"user course"
New-Enrolment -User $user -Course $course

"user|courseid"
$user | New-Enrolment -CourseId $course.Id

"user|course"
$user | New-Enrolment -Course $course

"course|user"
$course | New-Enrolment -User $user 

"course|userid"
$course | New-Enrolment -UserId $user.id



"`nPositional:"

"userid courseid"
New-Enrolment $user.Id $course.Id

"user courseid"
New-Enrolment $user $course.Id

"userid course"
New-Enrolment $user.Id $course 

"user course"
New-Enrolment $user $course

"user|courseid"
$user | New-Enrolment $course.Id

"user|course"
$user | New-Enrolment $course

"course|user"
$course | New-Enrolment $user 

"course|userid"
$course | New-Enrolment $user.id

I've tried it without dedicated "pipeline" parameters too, but still can't get every combination to work.