How can I associate a file type with a powershell script?

Question

I have a very powershell script that works perfectly and does:

Param(
  [string]$fileName
) 

echo \"Woo I opened $fileName\"

When I run it on

Answer 1

Here's my remix of @Matthieu 's great remix of @Ansgar Weichar's great answer.

Matthieu's is set up for executables, and doesn't work for powershell scripts for the same reasons the OP describes.

Function Set-FileAssociationToPowerShellScript($extension, $pathToScript) {

    # first create a filetype
    $filetype = cmd /c "assoc $extension 2>NUL"
    if ($filetype) {
        # Association already exists: override it
        $filetype = $filetype.Split('=')[1]
        Write-Output "Using filetype $filetype"
    }
    else {
        # Name doesn't exist: create it
        # ".log.1" becomes "log1file"
        $filetype = "$($extension.Replace('.', ''))file"
        Write-Output "Creating filetype $filetype ($extension)"
        cmd /c "assoc $extension=$filetype"
    }
    Write-Output "Associating filetype $filetype ($extension) with $pathToScript.."
    cmd /c "ftype $filetype=powershell.exe -File `"$pathToScript`" `"%1`""
}