import AppKit
import Foundation

if CommandLine.arguments.count != 3 {
    print("Must have 2 args")
    exit(1)
}

let wallpaperDir = CommandLine.arguments[1]
let interval: TimeInterval = Double(CommandLine.arguments[2]) ?? 30.0

let workspace = NSWorkspace.shared
let imageExtensions: Set<String> = ["jpg", "jpeg", "png", "heic", "tiff", "gif", "bmp"]

func images() -> [URL] {
    let dir = URL(fileURLWithPath: wallpaperDir, isDirectory: true)
    let entries = (try? FileManager.default.contentsOfDirectory(
        at: dir, includingPropertiesForKeys: nil)) ?? []
    return entries.filter { imageExtensions.contains($0.pathExtension.lowercased()) }
}

var current: URL?

// setDesktopImageURL only touches the current Space (all displays).
func apply(_ url: URL?) {
    guard let url else { return }
    for screen in NSScreen.screens {
        try? workspace.setDesktopImageURL(url, for: screen, options: [:])
    }
}

func advance() {
    let imgs = images()
    guard !imgs.isEmpty else { return }
    let pool = imgs.count > 1 ? imgs.filter { $0 != current } : imgs
    current = pool.randomElement()
    apply(current)
}

// Whenever you switch Space, repaint it to the current image.
workspace.notificationCenter.addObserver(
    forName: NSWorkspace.activeSpaceDidChangeNotification,
    object: nil, queue: .main
) { _ in apply(current) }

advance()
Timer.scheduledTimer(withTimeInterval: interval, repeats: true) { _ in advance() }

let app = NSApplication.shared
app.setActivationPolicy(.accessory)   // no Dock icon
app.run()