//
//  NotificationsPrefsView.swift
//  Tusker
//
//  Created by Shadowfacts on 4/6/24.
//  Copyright © 2024 Shadowfacts. All rights reserved.
//

import SwiftUI
import UserNotifications
import UserAccounts
import PushNotifications
import TuskerComponents

struct NotificationsPrefsView: View {
    @State private var error: NotificationsSetupError?
    @State private var isSetup = AsyncToggle.Mode.off
    @State private var pushProxyRegistration: PushProxyRegistration?
    @ObservedObject private var userAccounts = UserAccountsManager.shared
    
    var body: some View {
        List {
            enableSection
            if isSetup == .on,
               let pushProxyRegistration {
                accountsSection(pushProxyRegistration: pushProxyRegistration)
            }
        }
        .listStyle(.insetGrouped)
        .appGroupedListBackground(container: PreferencesNavigationController.self)
        .navigationTitle("Notifications")
    }
    
    private var enableSection: some View {
        Section {
            AsyncToggle("Push Notifications", mode: $isSetup, onChange: isSetupChanged(newValue:))
        }
        .appGroupedListRowBackground()
        .alertWithData("An Error Occurred", data: $error) { error in
            Button("OK") {}
        } message: { error in
            Text(error.localizedDescription)
        }
        .task { @MainActor in
            pushProxyRegistration = PushManager.shared.proxyRegistration
            isSetup = pushProxyRegistration != nil ? .on : .off
            if !UIApplication.shared.isRegisteredForRemoteNotifications {
                _ = await registerForRemoteNotifications()
            }
        }
    }
    
    private func accountsSection(pushProxyRegistration: PushProxyRegistration) -> some View {
        Section {
            ForEach(userAccounts.accounts) { account in
                PushInstanceSettingsView(account: account, pushProxyRegistration: pushProxyRegistration)
            }
        }
        .appGroupedListRowBackground()
    }
    
    private func isSetupChanged(newValue: Bool) async -> Bool {
        if newValue {
            return await startRegistration()
        } else {
            return await unregister()
        }
    }
    
    private func startRegistration() async -> Bool {
        let authorized: Bool
        do {
            // TODO: support .providesAppNotificationSettings
            authorized = try await UNUserNotificationCenter.current().requestAuthorization(options: [.alert])
        } catch {
            self.error = .requestingAuthorization(error)
            return false
        }
        guard authorized else {
            return false
        }
        return await registerForRemoteNotifications()
    }
    
    private func registerForRemoteNotifications() async -> Bool {
        do {
            pushProxyRegistration = try await PushManager.shared.register()
            return true
        } catch {
            self.error = .registering(error)
            return false
        }
    }
    
    private func unregister() async -> Bool {
        do {
            try await PushManager.shared.unregister()
            pushProxyRegistration = nil
            for subscription in PushManager.shared.subscriptions {
                if let account = UserAccountsManager.shared.getAccount(id: subscription.accountID) {
                    let mastodonController = MastodonController.getForAccount(account)
                    do {
                        try await mastodonController.deletePushSubscription()
                        PushManager.shared.removeSubscription(account: account)
                        PushManager.logger.debug("Push subscription removed on \(account.instanceURL)")
                        // this is a bit of a hack. the PushInstanceSettingsViews need to know to update
                        // their @State variables after we remove the subscription
                        NotificationCenter.default.post(name: .pushSubscriptionRemoved, object: account.id)
                    } catch {
                        PushManager.logger.error("Erroring removing push subscription: \(String(describing: error))")
                    }
                }
            }
            return true
        } catch {
            self.error = .unregistering(error)
            return false
        }
    }
}

private enum NotificationsSetupError: LocalizedError {
    case requestingAuthorization(any Error)
    case registering(any Error)
    case unregistering(any Error)
    
    var errorDescription: String? {
        switch self {
        case .requestingAuthorization(let error):
            "Notifications authorization request failed: \(error.localizedDescription)"
        case .registering(let error):
            "Registration failed: \(error.localizedDescription)"
        case .unregistering(let error):
            "Deactivation failed: \(error.localizedDescription)"
        }
    }
}

extension Notification.Name {
    static let pushSubscriptionRemoved = Notification.Name("Tusker.pushSubscriptionRemoved")
}