import Foundation
import UserNotifications

/// 周期性指标提醒的本地通知调度。
/// 同一 `metricId` 在 iOS 通知中心展开成 N 条 weekly-repeats 通知,id 形如
/// `kangkang.reminder.<metricId>.w<weekday>`,方便按 weekday 单独 cancel。
///
/// 数据存 SwiftData `MetricReminder`;本服务只负责系统通知中心的同步,
/// 不写 SwiftData。两边写入的协调由调用方负责。
enum ReminderService {

    static let idPrefix = "kangkang.reminder."

    enum AuthState: String {
        case granted, denied, notDetermined, provisional
    }

    // MARK: - authorization

    static func currentAuthState() async -> AuthState {
        let settings = await UNUserNotificationCenter.current().notificationSettings()
        switch settings.authorizationStatus {
        case .authorized:        return .granted
        case .denied:            return .denied
        case .provisional:       return .provisional
        case .ephemeral:         return .granted
        case .notDetermined:     return .notDetermined
        @unknown default:        return .notDetermined
        }
    }

    /// 申请通知权限。已 granted/denied 时直接返回当前状态。
    @discardableResult
    static func requestAuthorization() async -> AuthState {
        let center = UNUserNotificationCenter.current()
        let settings = await center.notificationSettings()
        if settings.authorizationStatus != .notDetermined {
            return await currentAuthState()
        }
        do {
            let granted = try await center.requestAuthorization(options: [.alert, .sound, .badge])
            return granted ? .granted : .denied
        } catch {
            return .denied
        }
    }

    // MARK: - upsert / cancel

    /// 取消该 metric 在通知中心所有 pending 通知,再按当前 enabled/时间/weekdays 重排。
    /// 调用方在 `MetricReminder` save 之后调用。
    static func sync(_ reminder: MetricReminder) async {
        cancel(metricId: reminder.metricId)
        guard reminder.enabled, !reminder.weekdays.isEmpty else { return }

        let center = UNUserNotificationCenter.current()
        let content = UNMutableNotificationContent()
        content.title = "该测\(reminder.displayName)了"
        content.body = "在「+ 新建 → 指标记录 → \(reminder.displayName)」记录一次"
        content.sound = .default
        content.threadIdentifier = "kangkang.reminder.\(reminder.metricId)"

        for weekday in reminder.weekdays {
            var comps = DateComponents()
            comps.hour = reminder.hour
            comps.minute = reminder.minute
            comps.weekday = weekday
            let trigger = UNCalendarNotificationTrigger(dateMatching: comps, repeats: true)
            let id = identifier(metricId: reminder.metricId, weekday: weekday)
            let request = UNNotificationRequest(identifier: id,
                                                content: content,
                                                trigger: trigger)
            try? await center.add(request)
        }
    }

    /// 取消某个 metric 的所有 pending 通知(7 个 weekday 一并取消,不漏)。
    static func cancel(metricId: String) {
        let center = UNUserNotificationCenter.current()
        let ids = (1...7).map { identifier(metricId: metricId, weekday: $0) }
        center.removePendingNotificationRequests(withIdentifiers: ids)
    }

    /// 全清。Me Tab 一键关闭所有提醒时用。
    static func cancelAll() {
        UNUserNotificationCenter.current().removeAllPendingNotificationRequests()
    }

    // MARK: - helpers

    private static func identifier(metricId: String, weekday: Int) -> String {
        "\(idPrefix)\(metricId).w\(weekday)"
    }
}