life-helper/app/lib/domain/recommend/recommend_variant.dart

import '../models/habit.dart';

class CheckInContext {
  final String? location;
  final String? condition;
  const CheckInContext({this.location, this.condition});
}

enum RecommendReason { exactMatch, partial, fallbackMinimum, fallbackFirst }

class VariantPick {
  final HabitDoseVariantModel variant;
  final int score;
  final RecommendReason reason;
  const VariantPick(this.variant, this.score, this.reason);
}

/// fn-recommend-variant: returns best variant for current context.
/// O(N). Pure function. Returns null if habit has no variants.
VariantPick? recommendVariant(HabitModel habit, CheckInContext ctx) {
  final variants = habit.doseVariants;
  if (variants.isEmpty) return null;

  final scored = variants
      .map((v) => MapEntry(v, _scoreVariant(v, ctx)))
      .toList();

  // Stable sort: score desc, then sortOrder asc.
  scored.sort((a, b) {
    final byScore = b.value.compareTo(a.value);
    if (byScore != 0) return byScore;
    return a.key.sortOrder.compareTo(b.key.sortOrder);
  });

  final best = scored.first;
  if (best.value > 0) {
    final reason =
        best.value >= 4 ? RecommendReason.exactMatch : RecommendReason.partial;
    return VariantPick(best.key, best.value, reason);
  }

  // Fallback: first is_minimum variant (by sortOrder).
  final minimum = variants
      .where((v) => v.isMinimum)
      .fold<HabitDoseVariantModel?>(null,
          (a, v) => a == null || v.sortOrder < a.sortOrder ? v : a);
  if (minimum != null) {
    return VariantPick(minimum, 0, RecommendReason.fallbackMinimum);
  }
  // No is_minimum — fall back to first by sortOrder.
  final first = [...variants]..sort((a, b) => a.sortOrder.compareTo(b.sortOrder));
  return VariantPick(first.first, 0, RecommendReason.fallbackFirst);
}

int _scoreVariant(HabitDoseVariantModel v, CheckInContext ctx) {
  var s = 0;
  if (ctx.location != null && v.contextTags.contains(ctx.location)) {
    s += 2;
  }
  if (ctx.condition != null && v.conditionTags.contains(ctx.condition)) {
    s += 2;
  }
  if (v.isMinimum && ctx.condition == '나쁨') {
    s += 1;
  }
  return s;
}