Allow an object to alter its behavior when its internal state changes. The object will appear to change its class.

CeilingFan.ps1

<#
    Allow an object to alter its behavior when its internal state changes.
    The object will appear to change its class.

    The State pattern puts each branch of the conditional in a separate class.

    This lets you treat the object's state as an object in its own right
    that can vary independently from other objects
#>

class CeilingFanState {
    Change([CeilingFan] $ceilingFan) {
        throw "not implemented"
    }
}

class CeilingFanOff : CeilingFanState {
    Change([CeilingFan] $context) {
        $context.State = [CeilingFanLow]::new()
        "Change state from Off to Low." | Out-Host
    }
}

class CeilingFanLow: CeilingFanState {
    Change([CeilingFan] $context) {
        $context.State = [CeilingFanMedium]::new()
        "Change state from Low to Medium." | Out-Host
    }
}

class CeilingFanMedium: CeilingFanState {
    Change([CeilingFan] $context) {
        $context.State = [CeilingFanHigh]::new()
        "Change state from Medium to High." | Out-Host
    }
}

class CeilingFanHigh: CeilingFanState {
    Change([CeilingFan] $context) {
        $context.State = [CeilingFanLow]::new()
        "Change state from High to Off." | Out-Host
    }
}

class CeilingFan {

    $State

    CeilingFan ([CeilingFanState] $state) { $this.State = $state }

    Pull() { $this.State.Change($this) }
}

$ceilingFan = [CeilingFan]::new([CeilingFanOff]::new())

$ceilingFan.Pull()
$ceilingFan.Pull()
$ceilingFan.Pull()
$ceilingFan.Pull()