import 'question_source_preferences.dart';
import 'questions_db.dart';

/// Picks the next question source to match configured mix percentages over time.
abstract final class QuestionSourceMix {
  /// Source id with the largest deficit vs configured effective mix (sequential balance).
  static String pickNextSourceId({
    required Map<String, int> effectiveMixPercent,
    required Map<String, int> deliveredCounts,
  }) {
    if (effectiveMixPercent.isEmpty) {
      return 'market_history';
    }

    final int totalDelivered =
        deliveredCounts.values.fold<int>(0, (int a, int b) => a + b);
    if (totalDelivered == 0) {
      return effectiveMixPercent.entries
          .reduce(
            (
              MapEntry<String, int> a,
              MapEntry<String, int> b,
            ) =>
                a.value >= b.value ? a : b,
          )
          .key;
    }

    String? pick;
    var maxDeficit = double.negativeInfinity;
    for (final MapEntry<String, int> entry in effectiveMixPercent.entries) {
      final double target = entry.value / 100.0;
      final double actual =
          (deliveredCounts[entry.key] ?? 0) / totalDelivered;
      final double deficit = target - actual;
      if (deficit > maxDeficit) {
        maxDeficit = deficit;
        pick = entry.key;
      }
    }
    return pick ?? effectiveMixPercent.keys.first;
  }

  static Map<String, int> effectiveMixFromResolved(
    List<ResolvedQuestionSourcePreference> prefs,
  ) {
    return QuestionSourcePreferences.effectiveMix(prefs);
  }

  /// Orders unanswered rows so [preferredSourceId] is shown first (stable FIFO within source).
  static List<Map<String, dynamic>> orderUnansweredByPreferredSource(
    List<Map<String, dynamic>> rows, {
    required String preferredSourceId,
  }) {
    if (rows.length <= 1) {
      return rows;
    }

    final List<Map<String, dynamic>> preferred = <Map<String, dynamic>>[];
    final List<Map<String, dynamic>> rest = <Map<String, dynamic>>[];
    for (final Map<String, dynamic> row in rows) {
      if (QuestionsDb.resolveSourceId(row) == preferredSourceId) {
        preferred.add(row);
      } else {
        rest.add(row);
      }
    }
    return <Map<String, dynamic>>[...preferred, ...rest];
  }
}