import AppKit

/// Transparent overlay that accepts a dragged music file
/// (`.mid` / `.midi` for direct MIDI playback, or a Menu Band-
/// authored `.pdf` whose Info dictionary embeds the score's
/// MusicXML) and forwards it to `onDrop`. Installed as a subview
/// of the menubar status item button (and, optionally, the popover
/// content view) so dragging a music file onto Menu Band auto-
/// plays it through the synth — MIDI directly, PDFs after a
/// MusicXML→MIDI round-trip handled by AppDelegate.
final class MidiDropTargetView: NSView {

    var onDrop: ((URL) -> Void)?

    override init(frame frameRect: NSRect) {
        super.init(frame: frameRect)
        registerForDraggedTypes([.fileURL])
    }

    required init?(coder: NSCoder) { fatalError() }

    /// Pass mouse events through so the parent button still gets
    /// its clicks — we only care about drag operations.
    override func hitTest(_ point: NSPoint) -> NSView? { nil }

    override func draggingEntered(_ sender: NSDraggingInfo) -> NSDragOperation {
        return Self.dragURL(from: sender) != nil ? .copy : []
    }

    override func draggingUpdated(_ sender: NSDraggingInfo) -> NSDragOperation {
        return Self.dragURL(from: sender) != nil ? .copy : []
    }

    override func performDragOperation(_ sender: NSDraggingInfo) -> Bool {
        guard let url = Self.dragURL(from: sender) else { return false }
        onDrop?(url)
        return true
    }

    /// Pull the first acceptable music-file URL off the drag
    /// pasteboard. Accepts `.mid`, `.midi`, and `.pdf` — extension
    /// dispatch happens in the `onDrop` handler (AppDelegate
    /// validates the PDF actually carries Menu Band metadata
    /// before kicking off a render).
    private static func dragURL(from sender: NSDraggingInfo) -> URL? {
        let pb = sender.draggingPasteboard
        guard let urls = pb.readObjects(forClasses: [NSURL.self],
                                         options: nil) as? [URL] else {
            return nil
        }
        return urls.first(where: { url in
            let ext = url.pathExtension.lowercased()
            return ext == "mid" || ext == "midi" || ext == "pdf"
        })
    }
}