import 'dart:math';

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

/// Picks the next question source randomly matching configured mix percentages.
abstract final class QuestionSourceMix {
  /// Source id selected using weighted random selection based on configured mix ratios.
  static String pickNextSourceId({
    required Map<String, int> effectiveMixPercent,
    required Map<String, int> deliveredCounts,
    Random? random,
  }) {
    if (effectiveMixPercent.isEmpty) {
      return 'market_history';
    }

    final int totalWeight =
        effectiveMixPercent.values.fold<int>(0, (int a, int b) => a + b);
    if (totalWeight <= 0) {
      return effectiveMixPercent.keys.first;
    }

    // If one source has 100% of the active weight, bypass the random roll completely.
    for (final MapEntry<String, int> entry in effectiveMixPercent.entries) {
      if (entry.value == totalWeight) {
        return entry.key;
      }
    }

    final Random rng = random ?? Random();
    var roll = rng.nextInt(totalWeight);
    for (final MapEntry<String, int> entry in effectiveMixPercent.entries) {
      roll -= entry.value;
      if (roll < 0) {
        return entry.key;
      }
    }
    return 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];
  }
}