init

client/lib/features/writing/models/writing_record.dart

@@ -0,0 +1,96 @@
+/// 写作完成记录模型
+class WritingRecord {
+  final String id;
+  final String taskId;
+  final String taskTitle;
+  final String taskDescription;
+  final String content;
+  final int wordCount;
+  final int timeUsed; // 使用的时间（秒）
+  final int score;
+  final DateTime completedAt;
+  final Map<String, dynamic>? feedback;
+
+  const WritingRecord({
+    required this.id,
+    required this.taskId,
+    required this.taskTitle,
+    required this.taskDescription,
+    required this.content,
+    required this.wordCount,
+    required this.timeUsed,
+    required this.score,
+    required this.completedAt,
+    this.feedback,
+  });
+
+  Map<String, dynamic> toJson() {
+    return {
+      'id': id,
+      'taskId': taskId,
+      'taskTitle': taskTitle,
+      'taskDescription': taskDescription,
+      'content': content,
+      'wordCount': wordCount,
+      'timeUsed': timeUsed,
+      'score': score,
+      'completedAt': completedAt.toIso8601String(),
+      'feedback': feedback,
+    };
+  }
+
+  factory WritingRecord.fromJson(Map<String, dynamic> json) {
+    return WritingRecord(
+      id: json['id'],
+      taskId: json['taskId'],
+      taskTitle: json['taskTitle'],
+      taskDescription: json['taskDescription'],
+      content: json['content'],
+      wordCount: json['wordCount'],
+      timeUsed: json['timeUsed'],
+      score: json['score'],
+      completedAt: DateTime.parse(json['completedAt']),
+      feedback: json['feedback'],
+    );
+  }
+
+  WritingRecord copyWith({
+    String? id,
+    String? taskId,
+    String? taskTitle,
+    String? taskDescription,
+    String? content,
+    int? wordCount,
+    int? timeUsed,
+    int? score,
+    DateTime? completedAt,
+    Map<String, dynamic>? feedback,
+  }) {
+    return WritingRecord(
+      id: id ?? this.id,
+      taskId: taskId ?? this.taskId,
+      taskTitle: taskTitle ?? this.taskTitle,
+      taskDescription: taskDescription ?? this.taskDescription,
+      content: content ?? this.content,
+      wordCount: wordCount ?? this.wordCount,
+      timeUsed: timeUsed ?? this.timeUsed,
+      score: score ?? this.score,
+      completedAt: completedAt ?? this.completedAt,
+      feedback: feedback ?? this.feedback,
+    );
+  }
+
+  String get formattedDate {
+    return '${completedAt.year}-${completedAt.month.toString().padLeft(2, '0')}-${completedAt.day.toString().padLeft(2, '0')}';
+  }
+
+  String get formattedTime {
+    final minutes = timeUsed ~/ 60;
+    final seconds = timeUsed % 60;
+    return '${minutes}分${seconds}秒';
+  }
+
+  String get scoreText {
+    return '${score}分';
+  }
+}

client/lib/features/writing/models/writing_stats.dart

@@ -0,0 +1,238 @@
+class WritingStats {
+  final String userId;
+  final int totalTasks;
+  final int completedTasks;
+  final int totalWords;
+  final int totalTimeSpent; // 秒
+  final double averageScore;
+  final Map<String, int> taskTypeStats;
+  final Map<String, int> difficultyStats;
+  final List<WritingProgressData> progressData;
+  final WritingSkillAnalysis skillAnalysis;
+  final DateTime lastUpdated;
+
+  const WritingStats({
+    required this.userId,
+    required this.totalTasks,
+    required this.completedTasks,
+    required this.totalWords,
+    required this.totalTimeSpent,
+    required this.averageScore,
+    required this.taskTypeStats,
+    required this.difficultyStats,
+    required this.progressData,
+    required this.skillAnalysis,
+    required this.lastUpdated,
+  });
+
+  double get completionRate => totalTasks > 0 ? (completedTasks / totalTasks) * 100 : 0;
+  
+  double get averageWordsPerTask => completedTasks > 0 ? totalWords / completedTasks : 0;
+  
+  double get averageTimePerTask => completedTasks > 0 ? totalTimeSpent / completedTasks : 0;
+
+  factory WritingStats.fromJson(Map<String, dynamic> json) {
+    final userIdVal = json['userId'];
+    final totalTasksVal = json['totalTasks'] ?? json['total_submissions'];
+    final completedTasksVal = json['completedTasks'] ?? json['completed_submissions'];
+    final totalWordsVal = json['totalWords'] ?? json['total_word_count'];
+    final totalTimeSpentVal = json['totalTimeSpent'] ?? json['total_time_spent'];
+    final averageScoreVal = json['averageScore'] ?? json['average_score'];
+    final difficultyStatsVal = json['difficultyStats'] ?? json['difficulty_stats'] ?? {};
+    final progressDataVal = json['progressData'] ?? [];
+    final skillAnalysisVal = json['skillAnalysis'];
+    final lastUpdatedVal = json['lastUpdated'];
+
+    final stats = WritingStats(
+      userId: userIdVal?.toString() ?? '',
+      totalTasks: _asInt(totalTasksVal),
+      completedTasks: _asInt(completedTasksVal),
+      totalWords: _asInt(totalWordsVal),
+      totalTimeSpent: _asInt(totalTimeSpentVal),
+      averageScore: _asDouble(averageScoreVal),
+      taskTypeStats: Map<String, int>.from(json['taskTypeStats'] ?? {}),
+      difficultyStats: Map<String, int>.from(difficultyStatsVal),
+      progressData: (progressDataVal is List)
+          ? progressDataVal
+              .map((e) => WritingProgressData.fromJson(Map<String, dynamic>.from(e)))
+              .toList()
+          : <WritingProgressData>[],
+      skillAnalysis: skillAnalysisVal is Map<String, dynamic>
+          ? WritingSkillAnalysis.fromJson(skillAnalysisVal)
+          : WritingSkillAnalysis(
+              criteriaScores: {
+                'grammar': _normalize01(_asDouble(json['average_grammar_score'])),
+                'coherence': _normalize01(_asDouble(json['average_coherence_score'])),
+                'vocab': _normalize01(_asDouble(json['average_vocab_score'])),
+              },
+              errorCounts: {},
+              strengths: const [],
+              weaknesses: const [],
+              recommendations: const [],
+              improvementRate: 0.0,
+              lastAnalyzed: DateTime.now(),
+            ),
+      lastUpdated: lastUpdatedVal is String
+          ? DateTime.parse(lastUpdatedVal)
+          : DateTime.now(),
+    );
+
+    return stats;
+  }
+
+  Map<String, dynamic> toJson() {
+    return {
+      'userId': userId,
+      'totalTasks': totalTasks,
+      'completedTasks': completedTasks,
+      'totalWords': totalWords,
+      'totalTimeSpent': totalTimeSpent,
+      'averageScore': averageScore,
+      'taskTypeStats': taskTypeStats,
+      'difficultyStats': difficultyStats,
+      'progressData': progressData.map((e) => e.toJson()).toList(),
+      'skillAnalysis': skillAnalysis.toJson(),
+      'lastUpdated': lastUpdated.toIso8601String(),
+    };
+  }
+
+  WritingStats copyWith({
+    String? userId,
+    int? totalTasks,
+    int? completedTasks,
+    int? totalWords,
+    int? totalTimeSpent,
+    double? averageScore,
+    Map<String, int>? taskTypeStats,
+    Map<String, int>? difficultyStats,
+    List<WritingProgressData>? progressData,
+    WritingSkillAnalysis? skillAnalysis,
+    DateTime? lastUpdated,
+  }) {
+    return WritingStats(
+      userId: userId ?? this.userId,
+      totalTasks: totalTasks ?? this.totalTasks,
+      completedTasks: completedTasks ?? this.completedTasks,
+      totalWords: totalWords ?? this.totalWords,
+      totalTimeSpent: totalTimeSpent ?? this.totalTimeSpent,
+      averageScore: averageScore ?? this.averageScore,
+      taskTypeStats: taskTypeStats ?? this.taskTypeStats,
+      difficultyStats: difficultyStats ?? this.difficultyStats,
+      progressData: progressData ?? this.progressData,
+      skillAnalysis: skillAnalysis ?? this.skillAnalysis,
+      lastUpdated: lastUpdated ?? this.lastUpdated,
+    );
+  }
+}
+
+class WritingProgressData {
+  final DateTime date;
+  final double score;
+  final int wordCount;
+  final int timeSpent;
+  final String taskType;
+  final String difficulty;
+
+  const WritingProgressData({
+    required this.date,
+    required this.score,
+    required this.wordCount,
+    required this.timeSpent,
+    required this.taskType,
+    required this.difficulty,
+  });
+
+  factory WritingProgressData.fromJson(Map<String, dynamic> json) {
+    return WritingProgressData(
+      date: DateTime.parse(json['date'] as String),
+      score: (json['score'] as num).toDouble(),
+      wordCount: json['wordCount'] as int,
+      timeSpent: json['timeSpent'] as int,
+      taskType: json['taskType'] as String,
+      difficulty: json['difficulty'] as String,
+    );
+  }
+
+  Map<String, dynamic> toJson() {
+    return {
+      'date': date.toIso8601String(),
+      'score': score,
+      'wordCount': wordCount,
+      'timeSpent': timeSpent,
+      'taskType': taskType,
+      'difficulty': difficulty,
+    };
+  }
+}
+
+class WritingSkillAnalysis {
+  final Map<String, double> criteriaScores;
+  final Map<String, int> errorCounts;
+  final List<String> strengths;
+  final List<String> weaknesses;
+  final List<String> recommendations;
+  final double improvementRate;
+  final DateTime lastAnalyzed;
+
+  const WritingSkillAnalysis({
+    required this.criteriaScores,
+    required this.errorCounts,
+    required this.strengths,
+    required this.weaknesses,
+    required this.recommendations,
+    required this.improvementRate,
+    required this.lastAnalyzed,
+  });
+
+  factory WritingSkillAnalysis.fromJson(Map<String, dynamic> json) {
+    return WritingSkillAnalysis(
+      criteriaScores: Map<String, double>.from(
+        (json['criteriaScores'] as Map<String, dynamic>).map(
+          (k, v) => MapEntry(k, (v as num).toDouble()),
+        ),
+      ),
+      errorCounts: Map<String, int>.from(json['errorCounts'] ?? {}),
+      strengths: List<String>.from(json['strengths'] ?? []),
+      weaknesses: List<String>.from(json['weaknesses'] ?? []),
+      recommendations: List<String>.from(json['recommendations'] ?? []),
+      improvementRate: (json['improvementRate'] as num).toDouble(),
+      lastAnalyzed: DateTime.parse(json['lastAnalyzed'] as String),
+    );
+  }
+
+  Map<String, dynamic> toJson() {
+    return {
+      'criteriaScores': criteriaScores,
+      'errorCounts': errorCounts,
+      'strengths': strengths,
+      'weaknesses': weaknesses,
+      'recommendations': recommendations,
+      'improvementRate': improvementRate,
+      'lastAnalyzed': lastAnalyzed.toIso8601String(),
+    };
+  }
+}
+
+int _asInt(dynamic v) {
+  if (v == null) return 0;
+  if (v is int) return v;
+  if (v is num) return v.toInt();
+  if (v is String) {
+    final parsed = double.tryParse(v);
+    return parsed?.toInt() ?? int.tryParse(v) ?? 0;
+  }
+  return 0;
+}
+
+double _asDouble(dynamic v) {
+  if (v == null) return 0.0;
+  if (v is double) return v;
+  if (v is num) return v.toDouble();
+  if (v is String) return double.tryParse(v) ?? 0.0;
+  return 0.0;
+}
+
+double _normalize01(double v) {
+  if (v <= 1.0) return v;
+  return v / 100.0;
+}

client/lib/features/writing/models/writing_submission.dart

@@ -0,0 +1,408 @@
+import 'writing_task.dart';
+
+class WritingSubmission {
+  final String id;
+  final String taskId;
+  final String userId;
+  final String content;
+  final int wordCount;
+  final int timeSpent; // 秒
+  final WritingStatus status;
+  final DateTime submittedAt;
+  final WritingFeedback? feedback;
+  final WritingScore? score;
+
+  const WritingSubmission({
+    required this.id,
+    required this.taskId,
+    required this.userId,
+    required this.content,
+    required this.wordCount,
+    required this.timeSpent,
+    required this.status,
+    required this.submittedAt,
+    this.feedback,
+    this.score,
+  });
+
+  factory WritingSubmission.fromJson(Map<String, dynamic> json) {
+    return WritingSubmission(
+      id: json['id'] as String,
+      taskId: json['taskId'] as String,
+      userId: json['userId'] as String,
+      content: json['content'] as String,
+      wordCount: json['wordCount'] as int,
+      timeSpent: json['timeSpent'] as int,
+      status: WritingStatus.values.firstWhere(
+        (e) => e.name == json['status'],
+        orElse: () => WritingStatus.draft,
+      ),
+      submittedAt: DateTime.parse(json['submittedAt'] as String),
+      feedback: json['feedback'] != null 
+          ? WritingFeedback.fromJson(json['feedback'] as Map<String, dynamic>)
+          : null,
+      score: json['score'] != null 
+          ? WritingScore.fromJson(json['score'] as Map<String, dynamic>)
+          : null,
+    );
+  }
+
+  Map<String, dynamic> toJson() {
+    return {
+      'id': id,
+      'taskId': taskId,
+      'userId': userId,
+      'content': content,
+      'wordCount': wordCount,
+      'timeSpent': timeSpent,
+      'status': status.name,
+      'submittedAt': submittedAt.toIso8601String(),
+      'feedback': feedback?.toJson(),
+      'score': score?.toJson(),
+    };
+  }
+
+  WritingSubmission copyWith({
+    String? id,
+    String? taskId,
+    String? userId,
+    String? content,
+    int? wordCount,
+    int? timeSpent,
+    WritingStatus? status,
+    DateTime? submittedAt,
+    WritingFeedback? feedback,
+    WritingScore? score,
+  }) {
+    return WritingSubmission(
+      id: id ?? this.id,
+      taskId: taskId ?? this.taskId,
+      userId: userId ?? this.userId,
+      content: content ?? this.content,
+      wordCount: wordCount ?? this.wordCount,
+      timeSpent: timeSpent ?? this.timeSpent,
+      status: status ?? this.status,
+      submittedAt: submittedAt ?? this.submittedAt,
+      feedback: feedback ?? this.feedback,
+      score: score ?? this.score,
+    );
+  }
+}
+
+class WritingFeedback {
+  final String id;
+  final String submissionId;
+  final String overallComment;
+  final List<WritingCriteriaFeedback> criteriaFeedbacks;
+  final List<WritingError> errors;
+  final List<WritingSuggestion> suggestions;
+  final DateTime createdAt;
+
+  const WritingFeedback({
+    required this.id,
+    required this.submissionId,
+    required this.overallComment,
+    required this.criteriaFeedbacks,
+    required this.errors,
+    required this.suggestions,
+    required this.createdAt,
+  });
+
+  factory WritingFeedback.fromJson(Map<String, dynamic> json) {
+    return WritingFeedback(
+      id: json['id'] as String,
+      submissionId: json['submissionId'] as String,
+      overallComment: json['overallComment'] as String,
+      criteriaFeedbacks: (json['criteriaFeedbacks'] as List<dynamic>)
+          .map((e) => WritingCriteriaFeedback.fromJson(e as Map<String, dynamic>))
+          .toList(),
+      errors: (json['errors'] as List<dynamic>)
+          .map((e) => WritingError.fromJson(e as Map<String, dynamic>))
+          .toList(),
+      suggestions: (json['suggestions'] as List<dynamic>)
+          .map((e) => WritingSuggestion.fromJson(e as Map<String, dynamic>))
+          .toList(),
+      createdAt: DateTime.parse(json['createdAt'] as String),
+    );
+  }
+
+  Map<String, dynamic> toJson() {
+    return {
+      'id': id,
+      'submissionId': submissionId,
+      'overallComment': overallComment,
+      'criteriaFeedbacks': criteriaFeedbacks.map((e) => e.toJson()).toList(),
+      'errors': errors.map((e) => e.toJson()).toList(),
+      'suggestions': suggestions.map((e) => e.toJson()).toList(),
+      'createdAt': createdAt.toIso8601String(),
+    };
+  }
+}
+
+class WritingScore {
+  final String id;
+  final String submissionId;
+  final double totalScore;
+  final double maxScore;
+  final Map<WritingCriteria, double> criteriaScores;
+  final String grade;
+  final DateTime createdAt;
+
+  const WritingScore({
+    required this.id,
+    required this.submissionId,
+    required this.totalScore,
+    required this.maxScore,
+    required this.criteriaScores,
+    required this.grade,
+    required this.createdAt,
+  });
+
+  double get percentage => (totalScore / maxScore) * 100;
+
+  factory WritingScore.fromJson(Map<String, dynamic> json) {
+    return WritingScore(
+      id: json['id'] as String,
+      submissionId: json['submissionId'] as String,
+      totalScore: (json['totalScore'] as num).toDouble(),
+      maxScore: (json['maxScore'] as num).toDouble(),
+      criteriaScores: Map<WritingCriteria, double>.fromEntries(
+        (json['criteriaScores'] as Map<String, dynamic>).entries.map(
+          (e) => MapEntry(
+            WritingCriteria.values.firstWhere((c) => c.name == e.key),
+            (e.value as num).toDouble(),
+          ),
+        ),
+      ),
+      grade: json['grade'] as String,
+      createdAt: DateTime.parse(json['createdAt'] as String),
+    );
+  }
+
+  Map<String, dynamic> toJson() {
+    return {
+      'id': id,
+      'submissionId': submissionId,
+      'totalScore': totalScore,
+      'maxScore': maxScore,
+      'criteriaScores': Map<String, dynamic>.fromEntries(
+        criteriaScores.entries.map(
+          (e) => MapEntry(e.key.name, e.value),
+        ),
+      ),
+      'grade': grade,
+      'createdAt': createdAt.toIso8601String(),
+    };
+  }
+}
+
+class WritingCriteriaFeedback {
+  final WritingCriteria criteria;
+  final double score;
+  final double maxScore;
+  final String comment;
+  final List<String> strengths;
+  final List<String> improvements;
+
+  const WritingCriteriaFeedback({
+    required this.criteria,
+    required this.score,
+    required this.maxScore,
+    required this.comment,
+    required this.strengths,
+    required this.improvements,
+  });
+
+  factory WritingCriteriaFeedback.fromJson(Map<String, dynamic> json) {
+    return WritingCriteriaFeedback(
+      criteria: WritingCriteria.values.firstWhere(
+        (e) => e.name == json['criteria'],
+      ),
+      score: (json['score'] as num).toDouble(),
+      maxScore: (json['maxScore'] as num).toDouble(),
+      comment: json['comment'] as String,
+      strengths: List<String>.from(json['strengths'] ?? []),
+      improvements: List<String>.from(json['improvements'] ?? []),
+    );
+  }
+
+  Map<String, dynamic> toJson() {
+    return {
+      'criteria': criteria.name,
+      'score': score,
+      'maxScore': maxScore,
+      'comment': comment,
+      'strengths': strengths,
+      'improvements': improvements,
+    };
+  }
+}
+
+class WritingError {
+  final WritingErrorType type;
+  final String description;
+  final String originalText;
+  final String? suggestedText;
+  final int startPosition;
+  final int endPosition;
+  final String explanation;
+
+  const WritingError({
+    required this.type,
+    required this.description,
+    required this.originalText,
+    this.suggestedText,
+    required this.startPosition,
+    required this.endPosition,
+    required this.explanation,
+  });
+
+  factory WritingError.fromJson(Map<String, dynamic> json) {
+    return WritingError(
+      type: WritingErrorType.values.firstWhere(
+        (e) => e.name == json['type'],
+      ),
+      description: json['description'] as String,
+      originalText: json['originalText'] as String,
+      suggestedText: json['suggestedText'] as String?,
+      startPosition: json['startPosition'] as int,
+      endPosition: json['endPosition'] as int,
+      explanation: json['explanation'] as String,
+    );
+  }
+
+  Map<String, dynamic> toJson() {
+    return {
+      'type': type.name,
+      'description': description,
+      'originalText': originalText,
+      'suggestedText': suggestedText,
+      'startPosition': startPosition,
+      'endPosition': endPosition,
+      'explanation': explanation,
+    };
+  }
+}
+
+class WritingSuggestion {
+  final WritingSuggestionType type;
+  final String title;
+  final String description;
+  final String? example;
+  final int? position;
+
+  const WritingSuggestion({
+    required this.type,
+    required this.title,
+    required this.description,
+    this.example,
+    this.position,
+  });
+
+  factory WritingSuggestion.fromJson(Map<String, dynamic> json) {
+    return WritingSuggestion(
+      type: WritingSuggestionType.values.firstWhere(
+        (e) => e.name == json['type'],
+      ),
+      title: json['title'] as String,
+      description: json['description'] as String,
+      example: json['example'] as String?,
+      position: json['position'] as int?,
+    );
+  }
+
+  Map<String, dynamic> toJson() {
+    return {
+      'type': type.name,
+      'title': title,
+      'description': description,
+      'example': example,
+      'position': position,
+    };
+  }
+}
+
+enum WritingStatus {
+  draft,
+  submitted,
+  grading,
+  graded,
+  revised,
+}
+
+enum WritingCriteria {
+  content,
+  organization,
+  vocabulary,
+  grammar,
+  mechanics,
+}
+
+enum WritingErrorType {
+  grammar,
+  spelling,
+  punctuation,
+  vocabulary,
+  structure,
+  style,
+}
+
+enum WritingSuggestionType {
+  improvement,
+  enhancement,
+  alternative,
+  clarification,
+}
+
+extension WritingStatusExtension on WritingStatus {
+  String get displayName {
+    switch (this) {
+      case WritingStatus.draft:
+        return '草稿';
+      case WritingStatus.submitted:
+        return '已提交';
+      case WritingStatus.grading:
+        return '评分中';
+      case WritingStatus.graded:
+        return '已评分';
+      case WritingStatus.revised:
+        return '已修改';
+    }
+  }
+}
+
+extension WritingCriteriaExtension on WritingCriteria {
+  String get displayName {
+    switch (this) {
+      case WritingCriteria.content:
+        return '内容';
+      case WritingCriteria.organization:
+        return '结构';
+      case WritingCriteria.vocabulary:
+        return '词汇';
+      case WritingCriteria.grammar:
+        return '语法';
+      case WritingCriteria.mechanics:
+        return '拼写标点';
+    }
+  }
+}
+
+extension WritingErrorTypeExtension on WritingErrorType {
+  String get displayName {
+    switch (this) {
+      case WritingErrorType.grammar:
+        return '语法错误';
+      case WritingErrorType.spelling:
+        return '拼写错误';
+      case WritingErrorType.punctuation:
+        return '标点错误';
+      case WritingErrorType.vocabulary:
+        return '词汇错误';
+      case WritingErrorType.structure:
+        return '结构错误';
+      case WritingErrorType.style:
+        return '风格问题';
+    }
+  }
+}

client/lib/features/writing/models/writing_task.dart

@@ -0,0 +1,267 @@
+class WritingTask {
+  final String id;
+  final String title;
+  final String description;
+  final WritingType type;
+  final WritingDifficulty difficulty;
+  final int timeLimit; // 分钟
+  final int wordLimit;
+  final List<String> keywords;
+  final List<String> requirements;
+  final String? prompt;
+  final String? imageUrl;
+  final ExamType? examType; // 考试类型
+  final DateTime createdAt;
+  final DateTime? updatedAt;
+
+  const WritingTask({
+    required this.id,
+    required this.title,
+    required this.description,
+    required this.type,
+    required this.difficulty,
+    required this.timeLimit,
+    required this.wordLimit,
+    required this.keywords,
+    required this.requirements,
+    this.prompt,
+    this.imageUrl,
+    this.examType,
+    required this.createdAt,
+    this.updatedAt,
+  });
+
+  factory WritingTask.fromJson(Map<String, dynamic> json) {
+    final idVal = json['id'] ?? json['prompt_id'];
+    final typeVal = json['type'];
+    final difficultyVal = json['difficulty'];
+    final timeLimitVal = json['timeLimit'] ?? json['time_limit'];
+    final wordLimitVal = json['wordLimit'] ?? json['word_limit'];
+    final examTypeVal = json['examType'] ?? json['exam_type'];
+    final createdAtVal = json['createdAt'] ?? json['created_at'];
+    final updatedAtVal = json['updatedAt'] ?? json['updated_at'];
+
+    return WritingTask(
+      id: (idVal ?? '').toString(),
+      title: (json['title'] ?? '').toString(),
+      description: (json['description'] ?? '').toString(),
+      type: typeVal is String
+          ? WritingType.values.firstWhere(
+              (e) => e.name == typeVal,
+              orElse: () => WritingType.essay,
+            )
+          : WritingType.essay,
+      difficulty: difficultyVal is String
+          ? WritingDifficulty.values.firstWhere(
+              (e) => e.name == difficultyVal,
+              orElse: () => WritingDifficulty.intermediate,
+            )
+          : WritingDifficulty.intermediate,
+      timeLimit: _asInt(timeLimitVal),
+      wordLimit: _asInt(wordLimitVal),
+      keywords: List<String>.from(json['keywords'] ?? []),
+      requirements: List<String>.from(json['requirements'] ?? []),
+      prompt: json['prompt'] as String?,
+      imageUrl: json['imageUrl'] as String?,
+      examType: examTypeVal is String
+          ? ExamType.values.firstWhere(
+              (e) => e.name == examTypeVal,
+              orElse: () => ExamType.cet,
+            )
+          : null,
+      createdAt: _parseDate(createdAtVal),
+      updatedAt: updatedAtVal != null ? _parseDate(updatedAtVal) : null,
+    );
+  }
+
+  Map<String, dynamic> toJson() {
+    return {
+      'id': id,
+      'title': title,
+      'description': description,
+      'type': type.name,
+      'difficulty': difficulty.name,
+      'timeLimit': timeLimit,
+      'wordLimit': wordLimit,
+      'keywords': keywords,
+      'requirements': requirements,
+      'prompt': prompt,
+      'imageUrl': imageUrl,
+      'examType': examType?.name,
+      'createdAt': createdAt.toIso8601String(),
+      'updatedAt': updatedAt?.toIso8601String(),
+    };
+  }
+
+  WritingTask copyWith({
+    String? id,
+    String? title,
+    String? description,
+    WritingType? type,
+    WritingDifficulty? difficulty,
+    int? timeLimit,
+    int? wordLimit,
+    List<String>? keywords,
+    List<String>? requirements,
+    String? prompt,
+    String? imageUrl,
+    ExamType? examType,
+    DateTime? createdAt,
+    DateTime? updatedAt,
+  }) {
+    return WritingTask(
+      id: id ?? this.id,
+      title: title ?? this.title,
+      description: description ?? this.description,
+      type: type ?? this.type,
+      difficulty: difficulty ?? this.difficulty,
+      timeLimit: timeLimit ?? this.timeLimit,
+      wordLimit: wordLimit ?? this.wordLimit,
+      keywords: keywords ?? this.keywords,
+      requirements: requirements ?? this.requirements,
+      prompt: prompt ?? this.prompt,
+      imageUrl: imageUrl ?? this.imageUrl,
+      examType: examType ?? this.examType,
+      createdAt: createdAt ?? this.createdAt,
+      updatedAt: updatedAt ?? this.updatedAt,
+    );
+  }
+}
+
+enum WritingType {
+  essay,
+  letter,
+  email,
+  report,
+  story,
+  review,
+  article,
+  diary,
+  description,
+  argument,
+}
+
+enum WritingDifficulty {
+  beginner,
+  elementary,
+  intermediate,
+  upperIntermediate,
+  advanced,
+}
+
+extension WritingTypeExtension on WritingType {
+  String get displayName {
+    switch (this) {
+      case WritingType.essay:
+        return '议论文';
+      case WritingType.letter:
+        return '书信';
+      case WritingType.email:
+        return '邮件';
+      case WritingType.report:
+        return '报告';
+      case WritingType.story:
+        return '故事';
+      case WritingType.review:
+        return '评论';
+      case WritingType.article:
+        return '文章';
+      case WritingType.diary:
+        return '日记';
+      case WritingType.description:
+        return '描述文';
+      case WritingType.argument:
+        return '辩论文';
+    }
+  }
+}
+
+extension WritingDifficultyExtension on WritingDifficulty {
+  String get displayName {
+    switch (this) {
+      case WritingDifficulty.beginner:
+        return '初级';
+      case WritingDifficulty.elementary:
+        return '基础';
+      case WritingDifficulty.intermediate:
+        return '中级';
+      case WritingDifficulty.upperIntermediate:
+        return '中高级';
+      case WritingDifficulty.advanced:
+        return '高级';
+    }
+  }
+
+  int get level {
+    switch (this) {
+      case WritingDifficulty.beginner:
+        return 1;
+      case WritingDifficulty.elementary:
+        return 2;
+      case WritingDifficulty.intermediate:
+        return 3;
+      case WritingDifficulty.upperIntermediate:
+        return 4;
+      case WritingDifficulty.advanced:
+        return 5;
+    }
+  }
+}
+
+enum ExamType {
+  cet,      // 四六级
+  kaoyan,   // 考研
+  toefl,    // 托福
+  ielts,    // 雅思
+}
+
+extension ExamTypeExtension on ExamType {
+  String get displayName {
+    switch (this) {
+      case ExamType.cet:
+        return '四六级';
+      case ExamType.kaoyan:
+        return '考研';
+      case ExamType.toefl:
+        return '托福';
+      case ExamType.ielts:
+        return '雅思';
+    }
+  }
+
+  String get description {
+    switch (this) {
+      case ExamType.cet:
+        return '大学英语四六级考试写作';
+      case ExamType.kaoyan:
+        return '研究生入学考试英语写作';
+      case ExamType.toefl:
+        return 'TOEFL托福考试写作';
+      case ExamType.ielts:
+        return 'IELTS雅思考试写作';
+    }
+  }
+}
+
+int _asInt(dynamic v) {
+  if (v == null) return 0;
+  if (v is int) return v;
+  if (v is num) return v.toInt();
+  if (v is String) {
+    final parsed = double.tryParse(v);
+    return parsed?.toInt() ?? int.tryParse(v) ?? 0;
+  }
+  return 0;
+}
+
+DateTime _parseDate(dynamic v) {
+  if (v is String) {
+    try {
+      return DateTime.parse(v);
+    } catch (_) {}
+  }
+  if (v is int) {
+    return DateTime.fromMillisecondsSinceEpoch(v);
+  }
+  return DateTime.now();
+}