public/Write-WindowsEvent.ps1

function Write-WindowsEvent {
    <#
    .SYNOPSIS
        Workaround for Write-EventLog where -Source often pisses me off
    .DESCRIPTION
        I'm still pissed. I mean,seriously, too busy? More things to rename to Defender something something?
    .PARAMETER LogName
        For now: System or Application. That's it. I'm cheap.
    .PARAMETER EventID
        You guessed it: The event ID number. The default is 1. The value must be within the
        range of 1 to 16,384.
    .PARAMETER Category
        I really don't care about Category, but it's whatever you want (within allowances)
    .PARAMETER Severity
        For now: Information,Warning or Error. The default is Information
    .PARAMETER Source
        And now, for the main event: The event source name. The docs (as of 3/27/2023) show examples that
        clearly imply you can provide any custom name you desire. They show "MyApp". But if you try that
        you'll get punched in the face with something annoying, like:
 
        ```Write-EventLog : The source name "MyApp" does not exist on computer "localhost"```
 
        * So I inserted my bite guard and strapped on the head gear and took the face hit for you.
        * Source: https://learn.microsoft.com/en-us/powershell/module/microsoft.powershell.management/write-eventlog?view=powershell-5.1
    .PARAMETER Message
        Say something. I don't care. You can say 'Hello world!' if it makes you happy.
    .EXAMPLE
        Write-WindowsEvent -EventID 101 -Source "SCORCH" -Message "Runbook FUBAR-TARFU state: Stopped" -Severity "Warning"
    #>

    param (
        [parameter()][string][ValidateSet('System','Application')]$LogName = "Application",
        [parameter()][int][ValidateRange(1,16384)]$EventID = 1,
        [parameter()][int]$Category = 1,
        [parameter()][string][ValidateSet('Information','Warning','Error')]$Severity = 'Information',
        [parameter()][string]$ComputerName = $env:COMPUTERNAME,
        [parameter(Mandatory)][string][ValidateNotNullOrEmpty()]$Source,
        [parameter(Mandatory)][string][ValidateNotNullOrEmpty()]$Message
    )
    $sourceExists = (Get-WmiObject -Class Win32_NTEventLOgFile |
        Select-Object FileName, Sources |
            ForEach-Object -Begin { $hash = @{}} -Process { $hash[$_.FileName] = $_.Sources } -End { $Hash })["Application"] | findstr $Source
    if (-not $SourceExists) {
        $null = New-EventLog -LogName Application -Source $Source
    }
    Write-EventLog -ComputerName $ComputerName -LogName $LogName -Source $Source -EventID $EventID -Message $Message -Category $Category -EntryType $Severity
}