import Foundation
import Observation
#if canImport(UserNotifications)
import UserNotifications
#endif

/// Surfaces download events two ways: a macOS Notification Center alert (works when
/// the app is backgrounded; one-time permission prompt) AND an in-app banner via the
/// observable `lastBanner` (always set, even when notifications are denied or
/// unavailable — e.g. a non-bundled test run). Posting is a no-op when
/// `notifyDownloads` is off.
@Observable
@MainActor
public final class NotificationsService {
    public static let shared = NotificationsService()
    public init() {}

    @ObservationIgnored private var authorized = false
    @ObservationIgnored private var asked = false
    /// Most recent in-app banner message (the UI shows + auto-clears it).
    public private(set) var lastBanner: String?
    public func clearBanner() { lastBanner = nil }

    /// In-app toast only — always shown, independent of `notifyDownloads`.
    public func showBanner(_ message: String) { lastBanner = message }

    /// Ask once for Notification Center permission (the in-app banner needs none).
    public func requestAuthorizationIfNeeded() {
        #if canImport(UserNotifications)
        guard !asked else { return }
        asked = true
        UNUserNotificationCenter.current().requestAuthorization(options: [.alert, .sound]) { [weak self] ok, _ in
            Task { @MainActor in self?.authorized = ok }
        }
        #endif
    }

    /// Post a notification (+ banner). Gated by the `notifyDownloads` setting.
    public func post(title: String, body: String = "") {
        guard SettingsStore.load().notifyDownloads else { return }
        lastBanner = body.isEmpty ? title : "\(title) — \(body)"
        #if canImport(UserNotifications)
        guard authorized else { return }
        let content = UNMutableNotificationContent()
        content.title = title
        if !body.isEmpty { content.body = body }
        content.sound = .default
        UNUserNotificationCenter.current().add(
            UNNotificationRequest(identifier: UUID().uuidString, content: content, trigger: nil))
        #endif
    }
}