//
//  https://mczachurski.dev
//  Copyright © 2023 Marcin Czachurski and the repository contributors.
//  Licensed under the Apache License 2.0.
//

import Foundation
import SwiftData
import PixelfedKit
import ClientKit
import ServicesKit
import Nuke
import OSLog
import EnvironmentKit
import Semaphore
import UserNotifications

/// Service responsible for managing notifications.
@MainActor
public class NotificationsService {
    public static let shared = NotificationsService()
    private init() { }
    
    private let semaphore = AsyncSemaphore(value: 1)
    
    public func newNotificationsHasBeenAdded(for account: AccountModel, modelContext: ModelContext) async -> Bool {
        await semaphore.wait()
        defer { semaphore.signal() }
        
        guard let accessToken = account.accessToken else {
            return false
        }
     
        // Get maximimum downloaded stauts id.
        guard let lastSeenNotificationId = self.getLastSeenNotificationId(accountId: account.id, modelContext: modelContext)  else {
            return false
        }
        
        let client = PixelfedClient(baseURL: account.serverUrl).getAuthenticated(token: accessToken)
        
        do {
            let linkableNotifications = try await client.notifications(minId: lastSeenNotificationId, limit: 5)
            return linkableNotifications.data.first(where: { $0.id != lastSeenNotificationId }) != nil
        } catch {
            ErrorService.shared.handle(error, message: "notifications.error.loadingNotificationsFailed")
            return false
        }
    }
    
    public func amountOfNewNotifications(for account: AccountModel, modelContext: ModelContext) async -> Int {
        await semaphore.wait()
        defer { semaphore.signal() }
        
        guard let accessToken = account.accessToken else {
            return 0
        }
                
        // Get maximimum downloaded stauts id.
        guard let lastSeenNotificationId = self.getLastSeenNotificationId(accountId: account.id, modelContext: modelContext)  else {
            return 0
        }
        
        let client = PixelfedClient(baseURL: account.serverUrl).getAuthenticated(token: accessToken)
        var notifications: [PixelfedKit.Notification] = []
        var newestNotificationId = lastSeenNotificationId
        
        // There can be more then 80 newest notifications, that's why we have to sometimes send more then one request.
        while true {
            do {
                let downloadedNotifications = try await client.notifications(minId: newestNotificationId, limit: 80)
                
                guard let firstNotification = downloadedNotifications.data.first else {
                    break
                }
                
                let visibleNotifications = downloadedNotifications.data.filter({ $0.id != lastSeenNotificationId })

                notifications.append(contentsOf: visibleNotifications)
                newestNotificationId = firstNotification.id
            } catch {
                ErrorService.shared.handle(error, message: "global.error.errorDuringDownloadingNewStatuses")
                break
            }
        }
        
        // Return number of new notifications not visible yet on the timeline.
        return notifications.count
    }
    
    /// Function sets application badge counts when notifications (and badge) are enabled.
    public func setBadgeCount(_ count: Int) async throws {
        let center = UNUserNotificationCenter.current()
        let settings = await center.notificationSettings()
        
        guard (settings.authorizationStatus == .authorized) || (settings.authorizationStatus == .provisional) else { return }

        if settings.badgeSetting == .enabled {
            try await center.setBadgeCount(count)
        }
    }
    
    private func getLastSeenNotificationId(accountId: String, modelContext: ModelContext) -> String? {
        let accountData = AccountDataHandler.shared.getAccountData(accountId: accountId, modelContext: modelContext)
        return accountData?.lastSeenNotificationId
    }
}