feat: AtCoderレーティング情報の取得機能を追加し、レート表示を改善

refactor: 不要なインポートを削除
fix: 表示用レートの計算ロジックを修正

Author: yuubinnkyoku

lib/main.dart

@@ -3,7 +3,6 @@ import 'package:flutter/material.dart';
 import 'package:dynamic_color/dynamic_color.dart';
 import 'package:google_fonts/google_fonts.dart';
 import 'package:provider/provider.dart';
-import 'package:animations/animations.dart';
 import 'screens/problem_detail_screen.dart';
 import 'screens/editor_screen.dart';
 import 'screens/settings_screen.dart';

lib/models/atcoder_rating_info.dart

@@ -0,0 +1,9 @@
+class AtcoderRatingInfo {
+  final int latestRating;
+  final int contestCount;
+
+  const AtcoderRatingInfo({
+    required this.latestRating,
+    required this.contestCount,
+  });
+}

lib/models/contest.dart

@@ -69,11 +69,11 @@ class Contest {
     final hours = durationMin ~/ 60;
     final minutes = durationMin % 60;
       if (hours == 0) {
-      return '${minutes}分';
+      return '$minutes分';
     } else if (minutes == 0) {
-      return '${hours}時間';
+      return '$hours時間';
     } else {
-      return '${hours}時間${minutes}分';
+      return '$hours時間$minutes分';
     }
   }
 }

lib/screens/problem_detail_screen.dart

@@ -1,7 +1,6 @@
 import 'package:flutter/material.dart';
 import 'package:flutter/services.dart';
 import 'dart:developer' as developer;
-import 'package:google_fonts/google_fonts.dart';
 import 'package:provider/provider.dart';
 import '../models/problem.dart';
 import '../services/atcoder_service.dart';

lib/screens/recommend_screen.dart

@@ -3,6 +3,8 @@ import 'package:shared_preferences/shared_preferences.dart';
 import '../models/problem_difficulty.dart';
 import '../services/atcoder_service.dart';
 import 'problem_detail_screen.dart';
+import '../utils/atcoder_colors.dart';
+import '../utils/rating_utils.dart';
 
 class RecommendScreen extends StatefulWidget {
   const RecommendScreen({super.key});
@@ -20,7 +22,7 @@ class _RecommendScreenState extends State<RecommendScreen> {
   bool _isLoading = false;
   String? _errorMessage;
   String? _savedUsername; // 設定済みユーザー名
-  int? _currentRating; // 取得したレート
+  int? _currentRating; // 取得したレート（表示用: 最新レート）
 
   // AtCoder カラー判定
   Color _ratingColor(int rating) {
@@ -62,6 +64,43 @@ class _RecommendScreenState extends State<RecommendScreen> {
     );
   }
 
+  // Difficulty 表示用バッジ（補正後diffで表示。色も補正後ベース）
+  Widget _difficultyBadge(int? difficulty) {
+    int? mappedInt;
+    if (difficulty != null) {
+      final mapped = difficulty <= 400
+          ? RatingUtils.mapRating(difficulty)
+          : difficulty.toDouble();
+      mappedInt = mapped.round();
+    }
+    final color = (mappedInt != null)
+        ? atcoderRatingToColor(mappedInt)
+        : const Color(0xFF808080);
+    return Container(
+      padding: const EdgeInsets.symmetric(horizontal: 10, vertical: 4),
+      decoration: BoxDecoration(
+        color: color.withOpacity(0.12),
+        border: Border.all(color: color, width: 1),
+        borderRadius: BorderRadius.circular(999),
+      ),
+      child: Row(
+        mainAxisSize: MainAxisSize.min,
+        children: [
+          Icon(Icons.bolt, size: 14, color: color),
+          const SizedBox(width: 6),
+          Text(
+            mappedInt?.toString() ?? 'N/A',
+            style: TextStyle(
+              color: color,
+              fontSize: 14,
+              fontWeight: FontWeight.w700,
+            ),
+          ),
+        ],
+      ),
+    );
+  }
+
   @override
   void initState() {
     super.initState();
@@ -131,31 +170,44 @@ class _RecommendScreenState extends State<RecommendScreen> {
         throw Exception('ユーザー名を入力してください');
       }
 
-      final rating = await _atcoderService.fetchAtCoderRate(username);
-      if (rating == null) {
+      final ratingInfo = await _atcoderService.fetchAtcoderRatingInfo(username);
+      if (ratingInfo == null) {
         throw Exception('ユーザーが見つからないか、レーティングがありません');
       }
 
       // レートを保存してUIに表示
       if (mounted) {
         setState(() {
-          _currentRating = rating;
+          _currentRating = ratingInfo.latestRating;
         });
       }
 
       final allProblems = await _atcoderService.fetchProblemDifficulties();
+      // TrueRating を計算（数式(10)）
+      final trueRating = RatingUtils.trueRating(
+        rating: ratingInfo.latestRating,
+        contests: ratingInfo.contestCount,
+      );
 
       final recommended = allProblems.entries.where((entry) {
         final difficulty = entry.value.difficulty;
-        return difficulty != null &&
-            difficulty >= rating + lowerDelta &&
-            difficulty <= rating + upperDelta;
+        if (difficulty == null) return false;
+        // 400 以下の diff は mapRating で補正（比較用のみ）
+        final mappedDiff = difficulty <= 400
+            ? RatingUtils.mapRating(difficulty)
+            : difficulty.toDouble();
+        return mappedDiff >= trueRating + lowerDelta &&
+            mappedDiff <= trueRating + upperDelta;
       }).toList();
 
       // 自分のレートに近い順に並べ替え（差の絶対値の昇順）
       recommended.sort((a, b) {
-        final da = (a.value.difficulty! - rating).abs();
-        final db = (b.value.difficulty! - rating).abs();
+        final ad = a.value.difficulty!;
+        final bd = b.value.difficulty!;
+        final mad = ad <= 400 ? RatingUtils.mapRating(ad) : ad.toDouble();
+        final mbd = bd <= 400 ? RatingUtils.mapRating(bd) : bd.toDouble();
+        final da = (mad - trueRating).abs();
+        final db = (mbd - trueRating).abs();
         final cmp = da.compareTo(db);
         if (cmp != 0) return cmp;
         // 差が同じ場合は難易度の昇順で安定化
@@ -275,13 +327,18 @@ class _RecommendScreenState extends State<RecommendScreen> {
                   itemCount: _recommendedProblems.length,
                   itemBuilder: (context, index) {
                     final problem = _recommendedProblems[index];
+                    final diff = problem.value.difficulty;
                     return ListTile(
                       title: Text(problem.key),
-                      subtitle: Text(
-                          'Difficulty: ${problem.value.difficulty ?? "なし"}'),
-                      trailing: const Icon(Icons.open_in_new),
+                      trailing: Row(
+                        mainAxisSize: MainAxisSize.min,
+                        children: [
+                          _difficultyBadge(diff),
+                          const SizedBox(width: 8),
+                          const Icon(Icons.open_in_new),
+                        ],
+                      ),
                       onTap: () {
-                        // 問題詳細へ遷移（WebView連携と同様にIDからページを開く）
                         Navigator.push(
                           context,
                           MaterialPageRoute(

lib/services/atcoder_service.dart

@@ -3,6 +3,7 @@ import 'package:http/http.dart' as http;
 import 'package:html/parser.dart' as parser;
 import 'package:html/dom.dart';
 import '../models/atcoder_user_history.dart';
+import '../models/atcoder_rating_info.dart';
 import '../models/problem.dart';
 import '../models/problem_difficulty.dart';
 import 'dart:developer' as developer;
@@ -26,6 +27,28 @@ class AtCoderService {
     }
   }
 
+  Future<AtcoderRatingInfo?> fetchAtcoderRatingInfo(String name) async {
+    final url = Uri.parse('https://atcoder.jp/users/$name/history/json');
+    final response = await http.get(url);
+
+    if (response.statusCode == 200) {
+      final List<dynamic> data = jsonDecode(response.body);
+      if (data.isEmpty) {
+        return null;
+      }
+      final history =
+          data.map((item) => AtCoderUserHistory.fromJson(item)).toList();
+      if (history.isEmpty) return null;
+      history.sort((a, b) => b.endTime.compareTo(a.endTime));
+      final latest = history.first.newRating;
+      // Count only rated contests
+      final ratedCount = history.where((h) => h.isRated).length;
+      return AtcoderRatingInfo(latestRating: latest, contestCount: ratedCount);
+    } else {
+      throw Exception('Failed to load user history');
+    }
+  }
+
   Future<Map<String, ProblemDifficulty>> fetchProblemDifficulties() async {
     final url =
         Uri.parse('https://kenkoooo.com/atcoder/resources/problem-models.json');

lib/utils/rating_utils.dart

@@ -0,0 +1,60 @@
+import 'dart:math' as math;
+
+/// Rating utilities implementing AtCoder-like supplemental formulas.
+///
+/// Formulas (from user's spec):
+/// mapRating(r) = r                       if r > 400
+///              = 400 / exp((400 - r)/400) if r <= 400
+///
+/// F(n) = sqrt(sum_{i=1..n} 0.81^i) / (sum_{i=1..n} 0.9^i)
+/// f(n) = (F(n) - F(infty)) / (F(1) - F(infty)) * 1200
+///
+/// TrueRating = mapRating(Rating - f(n))
+class RatingUtils {
+  RatingUtils._();
+
+  /// Maps ratings (or difficulties) below or equal to 400
+  /// to a positive scale per the provided exponential mapping.
+  /// Returns a double to keep precision; callers can round if needed.
+  static double mapRating(num r) {
+    final rr = r.toDouble();
+    if (rr > 400.0) return rr;
+    return 400.0 / math.exp((400.0 - rr) / 400.0);
+  }
+
+  /// Computes F(n) using closed-form geometric sums.
+  /// sum_{i=1..n} a^i = a * (1 - a^n) / (1 - a)
+  static double _F(int n) {
+    if (n <= 0) return 0.0;
+    const a1 = 0.81; // 0.9^2
+    const a2 = 0.9;
+    final sum1 = a1 * (1 - math.pow(a1, n)) / (1 - a1);
+    final sum2 = a2 * (1 - math.pow(a2, n)) / (1 - a2);
+    return math.sqrt(sum1) / sum2;
+  }
+
+  /// F(infty) using closed-form limits of geometric sums.
+  static double _FInf() {
+    const a1 = 0.81;
+    const a2 = 0.9;
+    final sum1Inf = a1 / (1 - a1);
+    final sum2Inf = a2 / (1 - a2);
+    return math.sqrt(sum1Inf) / sum2Inf;
+  }
+
+  /// f(n) per the provided formula.
+  static double f(int n) {
+    if (n <= 0) return 1200.0; // safe fallback; not expected in practice
+    final fn = _F(n);
+    final finf = _FInf();
+    final f1 = _F(1);
+    // Avoid division by a tiny number; clamp if needed
+    final denom = (f1 - finf).abs() < 1e-12 ? 1e-12 : (f1 - finf);
+    return ((fn - finf) / denom) * 1200.0;
+  }
+
+  /// Computes TrueRating = mapRating(Rating - f(n)).
+  static double trueRating({required num rating, required int contests}) {
+    return mapRating(rating - f(contests));
+  }
+}

test/widget_test.dart

@@ -1,4 +1,3 @@
-import 'package:flutter/material.dart';
 import 'package:flutter_test/flutter_test.dart';
 import 'package:provider/provider.dart';
 import 'package:shojin_app/main.dart';