import AppKit
import ShotdeckCore

@MainActor
enum Sharing {
    /// Presents the AirDrop picker for `fileURL`, anchored to `view`.
    /// Throws `ShotdeckError.airDropUnavailable` when the service cannot be created,
    /// `canPerform` is false, or `view` is not in a visible window (a detached view
    /// never produces an on-screen sheet).
    static func airDrop(fileURL: URL, from view: NSView) throws {
        guard let service = NSSharingService(named: .sendViaAirDrop),
              service.canPerform(withItems: [fileURL]) else {
            throw ShotdeckError.airDropUnavailable
        }
        // Presenting from a detached NSView (no window) yields a sheet that never appears.
        guard let window = view.window, window.isVisible else {
            throw ShotdeckError.airDropUnavailable
        }

        NSApp.activate()
        window.makeKeyAndOrderFront(nil)

        service.subject = fileURL.lastPathComponent
        let session = AirDropSession(service: service, window: window, view: view)
        AirDropSession.keepAlive(session)
        service.delegate = session
        service.perform(withItems: [fileURL])
    }
}

/// Retains the sharing service for the life of the picker and supplies the real
/// on-screen window as the sheet parent. `NSSharingService.delegate` is weak.
@MainActor
private final class AirDropSession: NSObject, NSSharingServiceDelegate {
    static var live: [AirDropSession] = []

    let service: NSSharingService
    let window: NSWindow
    let view: NSView

    init(service: NSSharingService, window: NSWindow, view: NSView) {
        self.service = service
        self.window = window
        self.view = view
    }

    static func keepAlive(_ session: AirDropSession) {
        live.append(session)
    }

    private func drop() {
        Self.live.removeAll { $0 === self }
    }

    func sharingService(
        _ sharingService: NSSharingService,
        sourceWindowForShareItems items: [Any],
        sharingContentScope: UnsafeMutablePointer<NSSharingService.SharingContentScope>
    ) -> NSWindow? {
        sharingContentScope.pointee = .item
        return window
    }

    func sharingService(
        _ sharingService: NSSharingService,
        sourceFrameOnScreenForShareItem item: Any
    ) -> NSRect {
        let inWindow = view.convert(view.bounds, to: nil)
        return window.convertToScreen(inWindow)
    }

    func sharingService(_ sharingService: NSSharingService, didShareItems items: [Any]) {
        drop()
    }

    func sharingService(
        _ sharingService: NSSharingService,
        didFailToShareItems items: [Any],
        error: any Error
    ) {
        drop()
    }
}