import AppKit
import Foundation
import UserNotifications

final class NotificationService: NSObject, UNUserNotificationCenterDelegate {
    static let shared = NotificationService()

    private let center = UNUserNotificationCenter.current()
    private var isAuthorized = false

    private override init() {
        super.init()
        center.delegate = self
    }

    func requestAuthorizationIfNeeded() async {
        guard !isAuthorized else { return }
        let granted = (try? await center.requestAuthorization(options: [.alert, .sound, .badge])) ?? false
        isAuthorized = granted
    }

    func handleChanges(_ changes: [BugChange]) async {
        await requestAuthorizationIfNeeded()
        guard isAuthorized else { return }

        let significant = changes
            .filter { $0.type == .newBug || $0.type == .priorityChanged }
            .prefix(3)

        for change in significant {
            deliver(change)
        }

        let statusChanges = changes.filter { $0.type == .statusChanged }
        if statusChanges.count > 1 {
            deliverBatchStatusChange(statusChanges)
        } else if let single = statusChanges.first {
            deliver(single)
        }
    }

    private func deliver(_ change: BugChange) {
        let content = UNMutableNotificationContent()
        switch change.type {
        case .newBug:
            content.title = "New Bug Assigned"
            content.body = "[\(change.bug.priority.rawValue)] \(change.bug.title)"
            content.sound = .default
        case .statusChanged:
            content.title = "Bug Status Changed"
            content.body = "\(change.bug.title) → \(change.bug.status.rawValue)"
        case .priorityChanged:
            content.title = "Bug Priority Changed"
            content.body = "\(change.bug.title) → \(change.bug.priority.rawValue)"
        case .assigneeChanged:
            return
        }

        var userInfo: [String: Any] = ["bugId": change.bug.id]
        if let url = change.bug.feishuURL {
            userInfo["feishuURL"] = url.absoluteString
        }
        content.userInfo = userInfo

        let request = UNNotificationRequest(
            identifier: "bugger-\(change.bug.id)-\(Date().timeIntervalSince1970)",
            content: content,
            trigger: nil
        )
        center.add(request)
    }

    private func deliverBatchStatusChange(_ changes: [BugChange]) {
        let content = UNMutableNotificationContent()
        content.title = "\(changes.count) Bugs Updated"
        content.body = changes.prefix(3).map { "• \($0.bug.title)" }.joined(separator: "\n")
        content.sound = .default

        let request = UNNotificationRequest(
            identifier: "bugger-batch-\(Date().timeIntervalSince1970)",
            content: content,
            trigger: nil
        )
        center.add(request)
    }

    func userNotificationCenter(
        _ center: UNUserNotificationCenter,
        willPresent notification: UNNotification,
        withCompletionHandler completionHandler: @escaping (UNNotificationPresentationOptions) -> Void
    ) {
        completionHandler([.banner, .sound])
    }

    func userNotificationCenter(
        _ center: UNUserNotificationCenter,
        didReceive response: UNNotificationResponse,
        withCompletionHandler completionHandler: @escaping () -> Void
    ) {
        if let urlString = response.notification.request.content.userInfo["feishuURL"] as? String,
           let url = URL(string: urlString) {
            NSWorkspace.shared.open(url)
        }
        completionHandler()
    }
}