# Now-playing helper for the Go agent.
# Reads the current Windows media session via WinRT and emits a compact JSON
# blob on stdout, or `null` when nothing is playing. Compatible with PS5+.
#
# The Go agent shells out to this every few seconds and ships a `media`
# event when the song/state changes.

$ErrorActionPreference = 'SilentlyContinue'

try {
    [Windows.Media.Control.GlobalSystemMediaTransportControlsSessionManager,
     Windows.Media.Control, ContentType=WindowsRuntime] | Out-Null
} catch {
    Write-Output 'null'
    exit 0
}

Add-Type -AssemblyName System.Runtime.WindowsRuntime

$asTaskGeneric = [System.WindowsRuntimeSystemExtensions].GetMethods() |
    Where-Object {
        $_.Name -eq 'AsTask' -and
        $_.GetParameters().Count -eq 1 -and
        $_.GetParameters()[0].ParameterType.Name -eq 'IAsyncOperation`1'
    } | Select-Object -First 1

function Await($op, $resultType) {
    if ($null -eq $op) { return $null }
    $task = $asTaskGeneric.MakeGenericMethod($resultType).Invoke($null, @($op))
    $task.Wait(-1) | Out-Null
    return $task.Result
}

try {
    $mgrType = [Windows.Media.Control.GlobalSystemMediaTransportControlsSessionManager]
    $mgr = Await ($mgrType::RequestAsync()) ($mgrType)
    $session = $mgr.GetCurrentSession()
    if ($null -eq $session) { Write-Output 'null'; exit 0 }

    $infoType = [Windows.Media.Control.GlobalSystemMediaTransportControlsSessionMediaProperties]
    $info = Await ($session.TryGetMediaPropertiesAsync()) ($infoType)
    $pb = $session.GetPlaybackInfo()

    $payload = [pscustomobject]@{
        app    = $session.SourceAppUserModelId
        title  = $info.Title
        artist = $info.Artist
        album  = $info.AlbumTitle
        status = if ($pb) { $pb.PlaybackStatus.ToString() } else { $null }
    }
    $payload | ConvertTo-Json -Compress
} catch {
    Write-Output 'null'
}