import 'pipeline/question_pipeline.dart';
import 'question_service.dart';
import 'question_source_mix.dart';
import 'question_source_preferences.dart';
import 'question_source_preferences_db.dart';
import 'questions_db.dart';

/// Ratio-aware entry point for topping up a user's unanswered question queue.
class QuestionDispatcher {
  QuestionDispatcher({
    required QuestionsDb questionsDb,
    required QuestionService questionService,
    required QuestionPipeline questionPipeline,
    required QuestionSourcePreferencesDb preferencesDb,
    this.maxQueuedQuestions = 3,
  })  : _questionsDb = questionsDb,
        _questionService = questionService,
        _questionPipeline = questionPipeline,
        _preferencesDb = preferencesDb;

  final QuestionsDb _questionsDb;
  final QuestionService _questionService;
  final QuestionPipeline _questionPipeline;
  final QuestionSourcePreferencesDb _preferencesDb;
  final int maxQueuedQuestions;

  /// Maximum maintenance passes before giving up on an empty queue.
  static const int _maxQueueAttempts = 6;

  /// Ensures at least one enabled-source question exists; returns mix-ordered head.
  Future<Map<String, dynamic>?> dispatchNextQuestion(String firebaseUid) async {
    await _questionsDb.ensureUserExists(firebaseUid);

    var rows = await _listEnabledUnansweredOrdered(firebaseUid);
    for (var attempt = 0;
        rows.isEmpty && attempt < _maxQueueAttempts;
        attempt++) {
      await _runQueueMaintenance(firebaseUid);
      rows = await _listEnabledUnansweredOrdered(firebaseUid);
    }

    if (rows.isEmpty) {
      return null;
    }
    return _toClientPayload(rows.first, rows.length);
  }

  /// Unanswered questions for enabled sources only, ordered by configured mix.
  ///
  /// Runs [_runQueueMaintenance] in a loop until at least one question is ready
  /// or [_maxQueueAttempts] are exhausted.  This ensures spelling enqueue,
  /// catalog seeding, and pipeline-state setup all complete before returning.
  Future<List<Map<String, dynamic>>> listPanelQuestions(
    String firebaseUid,
  ) async {
    await _questionsDb.ensureUserExists(firebaseUid);

    var rows = await _listEnabledUnansweredOrdered(firebaseUid);
    for (var attempt = 0;
        rows.isEmpty && attempt < _maxQueueAttempts;
        attempt++) {
      await _runQueueMaintenance(firebaseUid);
      rows = await _listEnabledUnansweredOrdered(firebaseUid);
    }

    return rows
        .map((Map<String, dynamic> row) => _toClientPayload(row, rows.length))
        .toList(growable: false);
  }

  /// Counts the number of unanswered questions that belong to enabled sources.
  Future<int> countEnabledUnansweredQuestions(String firebaseUid) async {
    final List<ResolvedQuestionSourcePreference> prefs =
        await _preferencesDb.getResolved(firebaseUid);
    final Map<String, int> mix = QuestionSourceMix.effectiveMixFromResolved(prefs);
    final Set<String> allowed = _enabledSourceIds(prefs)
        .where((String id) => (mix[id] ?? 0) > 0)
        .toSet();
    return _questionsDb.countUnansweredForAllowedSources(firebaseUid, allowed);
  }

  /// Next unanswered enabled-source question after an answer.
  Future<Map<String, dynamic>?> nextQuestionAfterAnswer({
    required String firebaseUid,
    required Map<String, dynamic> answeredQuestion,
  }) async {
    var rows = await _listEnabledUnansweredOrdered(firebaseUid);
    if (rows.isEmpty) {
      return dispatchNextQuestion(firebaseUid);
    }

    final List<ResolvedQuestionSourcePreference> prefs =
        await _preferencesDb.getResolved(firebaseUid);
    final Map<String, int> mix = QuestionSourceMix.effectiveMixFromResolved(prefs);
    final Map<String, int> delivered =
        await _questionsDb.countDeliveredBySourceId(firebaseUid);
    final Set<String> allowed = _enabledSourceIds(prefs)
        .where((String id) => (mix[id] ?? 0) > 0)
        .toSet();
    final Map<String, dynamic>? row = await _questionsDb.findHeadUnansweredForMix(
      firebaseUid,
      effectiveMixPercent: mix,
      deliveredCounts: delivered,
      afterAnsweringSourceId:
          QuestionsDb.resolveSourceId(answeredQuestion),
      allowedSourceIds: allowed,
    );
    if (row == null) {
      return dispatchNextQuestion(firebaseUid);
    }
    return _toClientPayload(row, rows.length);
  }

  /// Next unanswered enabled-source question after deferring a question.
  Future<Map<String, dynamic>?> nextQuestionAfterDefer({
    required String firebaseUid,
    required String deferredQuestionId,
  }) async {
    final List<Map<String, dynamic>> rows =
        await _listEnabledUnansweredOrdered(firebaseUid);
    if (rows.isEmpty) {
      return dispatchNextQuestion(firebaseUid);
    }
    for (final Map<String, dynamic> row in rows) {
      if (row['id'] != deferredQuestionId) {
        return _toClientPayload(row, rows.length);
      }
    }
    return _toClientPayload(rows.first, rows.length);
  }

  /// Fills the queue up to [maxQueuedQuestions] using mix-sequential source picks.
  Future<void> topUpQueue(String firebaseUid) async {
    await _questionsDb.ensureUserExists(firebaseUid);

    while (true) {
      final int enabledQueued =
          (await _listEnabledUnansweredOrdered(firebaseUid)).length;
      if (enabledQueued >= maxQueuedQuestions) {
        return;
      }
      if (!await _enqueueOneFromMix(firebaseUid)) {
        return;
      }
    }
  }

  /// Runs both mix-based enqueue and spelling-specific maintenance in one pass.
  ///
  /// Both helpers are idempotent (spelling checks for an existing unanswered
  /// word-quiz before creating a new one), so calling this in a loop is safe.
  Future<void> _runQueueMaintenance(String firebaseUid) async {
    if (!await _enqueueOneFromMix(firebaseUid)) {
      await _ensureSpellingQuestionWhenNeeded(firebaseUid);
    }
  }

  Future<bool> _enqueueOneFromMix(String firebaseUid) async {
    final List<ResolvedQuestionSourcePreference> prefs =
        await _preferencesDb.getResolved(firebaseUid);
    final Map<String, int> mix = QuestionSourceMix.effectiveMixFromResolved(prefs);
    if (mix.isEmpty) {
      return false;
    }

    final Map<String, int> delivered =
        await _questionsDb.countDeliveredBySourceId(firebaseUid);
    final String primary = QuestionSourceMix.pickNextSourceId(
      effectiveMixPercent: mix,
      deliveredCounts: delivered,
    );
    final List<String> order = _sourceTryOrderForEnqueue(
      prefs: prefs,
      primarySourceId: primary,
    ).where((String id) => (mix[id] ?? 0) > 0).toList(growable: false);

    final int? marketBatchCap = _marketBatchCapForMix(prefs);

    for (final String sourceId in order) {
      final bool added = await _produceFromSource(
        firebaseUid,
        sourceId,
        marketBatchCap: marketBatchCap,
      );
      if (added) {
        return true;
      }
    }
    return false;
  }

  Future<List<Map<String, dynamic>>> _listEnabledUnansweredOrdered(
    String firebaseUid,
  ) async {
    final List<ResolvedQuestionSourcePreference> prefs =
        await _preferencesDb.getResolved(firebaseUid);
    final Map<String, int> mix = QuestionSourceMix.effectiveMixFromResolved(prefs);
    // Only include sources that are both enabled and have a non-zero mix share.
    // A source with enabled=true but ratio=0 should not serve questions.
    final Set<String> allowed = _enabledSourceIds(prefs)
        .where((String id) => (mix[id] ?? 0) > 0)
        .toSet();
    if (allowed.isEmpty) {
      return <Map<String, dynamic>>[];
    }
    return _questionsDb.listUnansweredOrderedForMix(
      firebaseUid,
      effectiveMixPercent: mix,
      allowedSourceIds: allowed,
    );
  }

  Set<String> _enabledSourceIds(
    List<ResolvedQuestionSourcePreference> prefs,
  ) {
    return prefs
        .where(
          (ResolvedQuestionSourcePreference s) =>
              s.enabled && !s.comingSoon,
        )
        .map((ResolvedQuestionSourcePreference s) => s.id)
        .toSet();
  }

  List<String> _sourceTryOrderForEnqueue({
    required List<ResolvedQuestionSourcePreference> prefs,
    required String primarySourceId,
  }) {
    final List<ResolvedQuestionSourcePreference> enabled = prefs
        .where(
          (ResolvedQuestionSourcePreference s) =>
              s.enabled && !s.comingSoon,
        )
        .toList(growable: false);
    final List<String> rest = enabled
        .map((ResolvedQuestionSourcePreference s) => s.id)
        .where((String id) => id != primarySourceId)
        .toList()
      ..sort(
        (
          String a,
          String b,
        ) {
          final int ratioA = enabled
              .firstWhere((ResolvedQuestionSourcePreference s) => s.id == a)
              .ratio;
          final int ratioB = enabled
              .firstWhere((ResolvedQuestionSourcePreference s) => s.id == b)
              .ratio;
          return ratioB.compareTo(ratioA);
        },
      );
    return <String>[primarySourceId, ...rest];
  }

  /// Last-resort spelling enqueue when mix dispatch did not produce a row.
  Future<void> _ensureSpellingQuestionWhenNeeded(String firebaseUid) async {
    final List<ResolvedQuestionSourcePreference> prefs =
        await _preferencesDb.getResolved(firebaseUid);
    if (!QuestionSourcePreferences.isEnabled(prefs, 'spelling')) {
      return;
    }
    await _questionPipeline.maintainSpellingForUser(firebaseUid);
  }

  Future<bool> _produceFromSource(
    String firebaseUid,
    String sourceId, {
    int? marketBatchCap,
  }) async {
    if (!await _isSourceEnabled(firebaseUid, sourceId)) {
      return false;
    }
    final int before =
        (await _listEnabledUnansweredOrdered(firebaseUid)).length;
    switch (sourceId) {
      case 'market_history':
        await _questionService.tryEnqueueMarketQuestions(
          firebaseUid,
          maxCreates: marketBatchCap,
        );
      case 'spelling':
        await _questionPipeline.maintainSpellingForUser(firebaseUid);
      default:
        return false;
    }
    final int after =
        (await _listEnabledUnansweredOrdered(firebaseUid)).length;
    return after > before;
  }

  Future<bool> _isSourceEnabled(String firebaseUid, String sourceId) async {
    final List<ResolvedQuestionSourcePreference> prefs =
        await _preferencesDb.getResolved(firebaseUid);
    return QuestionSourcePreferences.isEnabled(prefs, sourceId);
  }

  int? _marketBatchCapForMix(List<ResolvedQuestionSourcePreference> prefs) {
    if (!QuestionSourcePreferences.isEnabled(prefs, 'market_history') ||
        !QuestionSourcePreferences.isEnabled(prefs, 'spelling')) {
      return null;
    }
    final Map<String, int> mix = QuestionSourcePreferences.effectiveMix(prefs);
    final int spellingShare = mix['spelling'] ?? 0;
    if (spellingShare <= 0) {
      return null;
    }
    return 1;
  }

  Map<String, dynamic> _toClientPayload(
    Map<String, dynamic> row,
    int unansweredCount,
  ) {
    return _questionsDb.toClientPayload(
      row,
      unansweredCount: unansweredCount,
    );
  }
}