import 'dart:async';
import 'dart:developer';

import 'package:app_settings/app_settings.dart';
import 'package:flutter/material.dart';
import 'package:flutter_bloc/flutter_bloc.dart';

import '../session/session_manager.dart';
import '../state/app/modules/app_modules.dart';
import '../state/app/modules/capabilities/bloc/capabilities_cubit.dart';
import '../state/app/modules/settings/bloc/settings_cubit.dart';
import '../storage/notification_settings.dart';
import '../widget/confirm_dialog.dart';
import 'push_registration.dart';

const _talkExplanation =
    'Damit du keine neuen Nachrichten im Talk verpasst, fragen wir dich '
    'gleich nach der Erlaubnis für Benachrichtigungen. Bitte akzeptiere '
    'sie, um Push-Nachrichten zu erhalten.';
const _talkDeclinedNote =
    'Ohne die Berechtigung erhältst du keine Benachrichtigungen bei neuen '
    'Talk-Nachrichten. Du kannst sie jederzeit in den Systemeinstellungen '
    'deines Geräts nachträglich aktivieren.';
const _parentLetterExplanation =
    'Damit du keine Elternbriefe der Schule verpasst, fragen wir dich gleich '
    'nach der Erlaubnis für Benachrichtigungen. Bitte akzeptiere sie, um '
    'Push-Nachrichten zu erhalten.';
const _parentLetterDeclinedNote =
    'Ohne die Berechtigung erhältst du keine Benachrichtigungen bei neuen '
    'Elternbriefen. Du kannst sie jederzeit in den Systemeinstellungen deines '
    'Geräts nachträglich aktivieren.';

/// The occasions with a guided notification-permission flow. Each runs at
/// most once per install, guarded by its own flag in [NotificationSettings].
enum _PermissionPrompt {
  talkVisit(_talkExplanation, _talkDeclinedNote),
  guardianLogin(
    _parentLetterExplanation,
    _parentLetterDeclinedNote,
    module: Modules.parentLetters,
    spentOnDisplay: true,
  ),
  parentLettersVisit(
    _parentLetterExplanation,
    _parentLetterDeclinedNote,
    module: Modules.parentLetters,
  );

  const _PermissionPrompt(
    this.explanation,
    this.declinedNote, {
    this.module,
    this.spentOnDisplay = false,
  });

  final String explanation;
  final String declinedNote;

  /// Only sessions that have this module are asked.
  final Modules? module;

  /// Spends the one-shot as soon as the explanation is displayed, so a
  /// dismissed dialog does not come back on every app start.
  final bool spentOnDisplay;

  bool wasShown(NotificationSettings settings) => switch (this) {
    talkVisit => settings.talkPermissionPromptShown,
    guardianLogin => settings.guardianLoginPromptShown,
    parentLettersVisit => settings.parentLettersPromptShown,
  };

  void markShown(NotificationSettings settings) {
    switch (this) {
      case talkVisit:
        settings.talkPermissionPromptShown = true;
      case guardianLogin:
        settings.guardianLoginPromptShown = true;
      case parentLettersVisit:
        settings.parentLettersPromptShown = true;
    }
  }
}

/// Shows the one-time notification-permission flow on the first Talk visit.
///
/// The OS prompt is deliberately kept out of the cold-start path (younger users
/// decline it reflexively before ever seeing why they'd want it). Instead, the
/// first time Talk is opened we explain the request, then trigger the OS prompt,
/// and — if declined — offer a shortcut to the system settings.
///
/// Runs at most once per install (guarded by `talkPermissionPromptShown`).
Future<void> maybePromptTalkNotifications(BuildContext context) =>
    _maybePrompt(context, _PermissionPrompt.talkVisit);

/// Accounts that receive parent letters never reach the Talk flow, so they
/// are asked once right after signing in.
Future<void> maybePromptGuardianLoginNotifications(BuildContext context) =>
    _maybePrompt(context, _PermissionPrompt.guardianLogin);

/// Second chance with context: explains the request once more on the first
/// visit of the parent letters when the permission is still missing.
Future<void> maybePromptParentLetterNotifications(BuildContext context) =>
    _maybePrompt(context, _PermissionPrompt.parentLettersVisit);

bool _promptInFlight = false;

Future<void> _maybePrompt(
  BuildContext context,
  _PermissionPrompt prompt,
) async {
  final module = prompt.module;
  if (module != null &&
      !AppModule.isAvailableFor(module, SessionManager().current)) {
    return;
  }

  final settings = context.read<SettingsCubit>();
  final notificationSettings = settings.val().notificationSettings;

  // Already handled once, or the user opted out of push entirely.
  if (prompt.wasShown(notificationSettings)) return;
  if (!notificationSettings.enabled) return;

  // Capabilities may still be loading on a fresh cold start; retry on the next
  // occasion instead of burning the one-shot flag.
  if (!context.read<CapabilitiesCubit>().canReceivePushNotifications) return;

  if (_promptInFlight) return;
  _promptInFlight = true;
  try {
    // Users who already granted the permission: register silently and mark the
    // prompt as handled without showing any dialog.
    if (await PushRegistration.isOsPermissionGranted()) {
      prompt.markShown(settings.val(write: true).notificationSettings);
      unawaited(PushRegistration().register());
      return;
    }

    if (!context.mounted) return;

    if (prompt.spentOnDisplay) {
      prompt.markShown(settings.val(write: true).notificationSettings);
    }
    await showDialog<void>(
      context: context,
      builder: ConfirmDialog(
        icon: Icons.notifications_active_outlined,
        title: 'Benachrichtigungen aktivieren',
        content: prompt.explanation,
        confirmButton: 'Weiter',
        cancelButton: null,
        onConfirm: () =>
            unawaited(_requestPermission(context, settings, prompt)),
      ).build,
    );
  } finally {
    _promptInFlight = false;
  }
}

Future<void> _requestPermission(
  BuildContext context,
  SettingsCubit settings,
  _PermissionPrompt prompt,
) async {
  final granted = await PushRegistration.requestOsPermission();

  // Mark handled regardless of the outcome — the user can re-enable later via
  // the system settings; we don't want to prompt again on the next occasion.
  prompt.markShown(settings.val(write: true).notificationSettings);

  if (granted) {
    unawaited(PushRegistration().register());
    return;
  }

  log('Push: notification permission declined on ${prompt.name}');

  if (!context.mounted) return;

  ConfirmDialog(
    icon: Icons.notifications_off_outlined,
    title: 'Benachrichtigungen deaktiviert',
    content: prompt.declinedNote,
    confirmButton: 'Einstellungen öffnen',
    cancelButton: 'Später',
    onConfirm: () =>
        AppSettings.openAppSettings(type: AppSettingsType.notification),
  ).asDialog(context);
}