add changes

frontend/src/app/core/models/category.model.ts

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+/**
+ * Category Interface
+ * Represents a quiz category
+ */
+export interface Category {
+  id: string;
+  name: string;
+  slug: string;
+  description: string;
+  icon?: string;
+  color?: string;
+  questionCount: number;
+  displayOrder?: number;
+  isActive: boolean;
+  guestAccessible: boolean;
+  createdAt: string;
+  updatedAt: string;
+}
+
+/**
+ * Category Detail with Stats
+ */
+export interface CategoryDetail extends Category {
+  questionPreview?: QuestionPreview[];
+  stats?: CategoryStats;
+}
+
+/**
+ * Category Statistics
+ */
+export interface CategoryStats {
+  totalQuestions: number;
+  questionsByDifficulty: {
+    easy: number;
+    medium: number;
+    hard: number;
+  };
+  totalAttempts: number;
+  totalCorrect: number;
+  averageAccuracy: number;
+}
+
+/**
+ * Question Preview (limited info)
+ */
+export interface QuestionPreview {
+  id: string;
+  questionText: string;
+  questionType: QuestionType;
+  difficulty: Difficulty;
+  points: number;
+  accuracy?: number;
+}
+
+/**
+ * Question Types
+ */
+export type QuestionType = 'multiple_choice' | 'true_false' | 'written';
+
+/**
+ * Difficulty Levels
+ */
+export type Difficulty = 'easy' | 'medium' | 'hard';
+
+/**
+ * Category Create/Update Request
+ */
+export interface CategoryFormData {
+  name: string;
+  slug?: string;
+  description: string;
+  icon?: string;
+  color?: string;
+  displayOrder?: number;
+  guestAccessible: boolean;
+}

frontend/src/app/core/models/dashboard.model.ts

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+import { User } from './user.model';
+import { QuizSession } from './quiz.model';
+
+/**
+ * User Dashboard Response
+ */
+export interface UserDashboard {
+  success: boolean;
+  totalQuizzes: number;
+  totalQuestionsAnswered: number;
+  overallAccuracy: number;
+  currentStreak: number;
+  longestStreak: number;
+  averageScore: number;
+  recentQuizzes: QuizSession[];
+  categoryPerformance: CategoryPerformance[];
+  achievements?: Achievement[];
+}
+
+/**
+ * Category Performance
+ */
+export interface CategoryPerformance {
+  categoryId: string;
+  categoryName: string;
+  quizzesTaken: number;
+  averageScore: number;
+  accuracy: number;
+}
+
+/**
+ * User Quiz History
+ */
+export interface QuizHistoryResponse {
+  success: boolean;
+  sessions: QuizSession[];
+  pagination: PaginationInfo;
+}
+
+/**
+ * Pagination Info
+ */
+export interface PaginationInfo {
+  currentPage: number;
+  totalPages: number;
+  totalItems: number;
+  itemsPerPage: number;
+}
+
+/**
+ * Achievement
+ */
+export interface Achievement {
+  id: string;
+  name: string;
+  description: string;
+  icon: string;
+  earnedAt?: string;
+  progress?: number;
+  maxProgress?: number;
+}
+
+/**
+ * User Profile Update Request
+ */
+export interface UserProfileUpdate {
+  username?: string;
+  email?: string;
+  currentPassword?: string;
+  newPassword?: string;
+}
+
+/**
+ * Bookmark
+ */
+export interface Bookmark {
+  id: string;
+  userId: string;
+  questionId: string;
+  question?: any; // Will use Question type
+  createdAt: string;
+}
+
+/**
+ * Bookmarks Response
+ */
+export interface BookmarksResponse {
+  success: boolean;
+  bookmarks: any[]; // Will contain Question objects
+}
+
+/**
+ * Admin Statistics
+ */
+export interface AdminStatistics {
+  totalUsers: number;
+  activeUsers: number;
+  totalQuizSessions: number;
+  totalQuestions: number;
+  totalCategories: number;
+  mostPopularCategories: PopularCategory[];
+  averageQuizScore: number;
+  userGrowth: UserGrowthData[];
+}
+
+/**
+ * Popular Category
+ */
+export interface PopularCategory {
+  categoryId: string;
+  categoryName: string;
+  quizzesTaken: number;
+}
+
+/**
+ * User Growth Data
+ */
+export interface UserGrowthData {
+  date: string;
+  count: number;
+}
+
+/**
+ * Admin Users List Response
+ */
+export interface AdminUsersResponse {
+  success: boolean;
+  users: User[];
+  pagination: PaginationInfo;
+}
+
+/**
+ * Admin User Details
+ */
+export interface AdminUserDetails extends User {
+  quizHistory?: QuizSession[];
+  activityTimeline?: ActivityEvent[];
+}
+
+/**
+ * Activity Event
+ */
+export interface ActivityEvent {
+  id: string;
+  type: 'quiz_completed' | 'achievement_earned' | 'profile_updated';
+  description: string;
+  timestamp: string;
+}

frontend/src/app/core/models/guest.model.ts

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+/**
+ * Guest Session Interface
+ * Represents a temporary guest user session
+ */
+export interface GuestSession {
+  guestId: string;
+  sessionToken: string;
+  deviceId?: string;
+  quizzesTaken: number;
+  maxQuizzes: number;
+  remainingQuizzes: number;
+  expiresAt: string;
+  isConverted: boolean;
+  convertedUserId?: string;
+  createdAt: string;
+  updatedAt: string;
+}
+
+/**
+ * Guest Session Start Response
+ */
+export interface GuestSessionStartResponse {
+  success: boolean;
+  sessionToken: string;
+  guestId: string;
+  expiresAt: string;
+  maxQuizzes: number;
+  message?: string;
+}
+
+/**
+ * Guest Quiz Limit Response
+ */
+export interface GuestQuizLimitResponse {
+  success: boolean;
+  remainingQuizzes: number;
+  maxQuizzes: number;
+  quizzesTaken: number;
+  expiresAt: string;
+  upgradePrompt?: string;
+}
+
+/**
+ * Guest to User Conversion Request
+ */
+export interface GuestConversionRequest {
+  guestSessionId: string;
+  username: string;
+  email: string;
+  password: string;
+}
+
+/**
+ * Guest Settings (Admin)
+ */
+export interface GuestSettings {
+  id: string;
+  guestAccessEnabled: boolean;
+  maxQuizzesPerDay: number;
+  maxQuestionsPerQuiz: number;
+  sessionExpiryHours: number;
+  upgradePromptMessage: string;
+  createdAt: string;
+  updatedAt: string;
+}
+
+/**
+ * Guest Analytics (Admin)
+ */
+export interface GuestAnalytics {
+  totalGuestSessions: number;
+  activeGuestSessions: number;
+  guestToUserConversionRate: number;
+  averageQuizzesPerGuest: number;
+  totalGuestQuizzes: number;
+  conversionFunnel?: {
+    totalSessions: number;
+    startedQuiz: number;
+    completedQuiz: number;
+    converted: number;
+  };
+}
+
+/**
+ * Guest Quiz Limit
+ * Tracks remaining quiz attempts for guest
+ */
+export interface GuestLimit {
+  maxQuizzes: number;
+  quizzesTaken: number;
+  quizzesRemaining: number;
+  expiresAt?: string;
+}
+
+/**
+ * Guest State (for signal management)
+ */
+export interface GuestState {
+  session: GuestSession | null;
+  isGuest: boolean;
+  isLoading: boolean;
+  error: string | null;
+  quizLimit: GuestLimit | null;
+}

frontend/src/app/core/models/index.ts

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+/**
+ * API Response Wrapper
+ */
+export interface ApiResponse<T> {
+  success: boolean;
+  data?: T;
+  message?: string;
+  error?: string;
+}
+
+/**
+ * API Error Response
+ */
+export interface ApiError {
+  message: string;
+  error?: string;
+  statusCode?: number;
+  timestamp?: string;
+}
+
+/**
+ * HTTP Error
+ */
+export interface HttpError {
+  status: number;
+  statusText: string;
+  message: string;
+  error?: any;
+}
+
+/**
+ * Loading State
+ */
+export interface LoadingState {
+  isLoading: boolean;
+  message?: string;
+}
+
+/**
+ * Toast Notification
+ */
+export interface ToastNotification {
+  id?: string;
+  type: 'success' | 'error' | 'warning' | 'info';
+  message: string;
+  duration?: number;
+  action?: ToastAction;
+}
+
+/**
+ * Toast Action
+ */
+export interface ToastAction {
+  label: string;
+  callback: () => void;
+}
+
+/**
+ * Sort Options
+ */
+export interface SortOptions {
+  sortBy: string;
+  sortOrder: 'asc' | 'desc';
+}
+
+/**
+ * Filter Options
+ */
+export interface FilterOptions {
+  [key: string]: any;
+}
+
+/**
+ * Search Options
+ */
+export interface SearchOptions {
+  query: string;
+  filters?: FilterOptions;
+  sort?: SortOptions;
+  page?: number;
+  limit?: number;
+}
+
+// Export all models
+export * from './user.model';
+export * from './category.model';
+export * from './question.model';
+export * from './quiz.model';
+export * from './guest.model';
+export * from './dashboard.model';

frontend/src/app/core/models/question.model.ts

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+import { QuestionType, Difficulty } from './category.model';
+
+/**
+ * Question Interface
+ * Represents a quiz question
+ */
+export interface Question {
+  id: string;
+  questionText: string;
+  questionType: QuestionType;
+  difficulty: Difficulty;
+  categoryId: string;
+  categoryName?: string;
+  options?: string[]; // For multiple choice
+  correctAnswer: string | string[];
+  explanation: string;
+  points: number;
+  timeLimit?: number; // in seconds
+  tags?: string[];
+  keywords?: string[];
+  isActive: boolean;
+  isPublic: boolean;
+  timesAttempted?: number;
+  timesCorrect?: number;
+  accuracy?: number;
+  createdBy?: string;
+  createdAt: string;
+  updatedAt: string;
+}
+
+/**
+ * Question Create/Update Request
+ */
+export interface QuestionFormData {
+  questionText: string;
+  questionType: QuestionType;
+  difficulty: Difficulty;
+  categoryId: string;
+  options?: string[];
+  correctAnswer: string | string[];
+  explanation: string;
+  points?: number;
+  timeLimit?: number;
+  tags?: string[];
+  keywords?: string[];
+  isPublic: boolean;
+  isGuestAccessible: boolean;
+}
+
+/**
+ * Question Search Filters
+ */
+export interface QuestionSearchFilters {
+  q?: string; // search query
+  category?: string;
+  difficulty?: Difficulty;
+  questionType?: QuestionType;
+  isPublic?: boolean;
+  page?: number;
+  limit?: number;
+}
+
+/**
+ * Question Search Response
+ */
+export interface QuestionSearchResponse {
+  results: Question[];
+  totalCount: number;
+  page: number;
+  limit: number;
+}

frontend/src/app/core/models/quiz.model.ts

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+import { Question } from './question.model';
+
+/**
+ * Quiz Session Interface
+ * Represents an active or completed quiz session
+ */
+export interface QuizSession {
+  id: string;
+  userId?: string;
+  guestSessionId?: string;
+  categoryId: string;
+  categoryName?: string;
+  quizType: QuizType;
+  difficulty: string;
+  totalQuestions: number;
+  currentQuestionIndex: number;
+  score: number;
+  correctAnswers: number;
+  incorrectAnswers: number;
+  skippedAnswers: number;
+  status: QuizStatus;
+  startedAt: string;
+  completedAt?: string;
+  timeSpent?: number; // in seconds
+  isPassed?: boolean;
+  passingScore?: number;
+}
+
+/**
+ * Quiz Types
+ */
+export type QuizType = 'practice' | 'timed' | 'exam';
+
+/**
+ * Quiz Status
+ */
+export type QuizStatus = 'in_progress' | 'completed' | 'abandoned';
+
+/**
+ * Quiz Start Request
+ */
+export interface QuizStartRequest {
+  categoryId: string;
+  questionCount: number;
+  difficulty?: string; // 'easy', 'medium', 'hard', 'mixed'
+  quizType?: QuizType;
+}
+
+/**
+ * Quiz Start Response
+ */
+export interface QuizStartResponse {
+  success: boolean;
+  sessionId: string;
+  questions: Question[];
+  totalQuestions: number;
+  message?: string;
+}
+
+/**
+ * Quiz Answer Submission
+ */
+export interface QuizAnswerSubmission {
+  questionId: string;
+  answer: string | string[];
+  quizSessionId: string;
+  timeSpent?: number;
+}
+
+/**
+ * Quiz Answer Response
+ */
+export interface QuizAnswerResponse {
+  success: boolean;
+  isCorrect: boolean;
+  correctAnswer: string | string[];
+  explanation: string;
+  points: number;
+  score: number;
+  message?: string;
+}
+
+/**
+ * Quiz Results
+ */
+export interface QuizResults {
+  success: boolean;
+  score: number;
+  totalQuestions: number;
+  correctAnswers: number;
+  incorrectAnswers: number;
+  skippedAnswers: number;
+  percentage: number;
+  timeSpent: number;
+  isPassed: boolean;
+  performanceMessage: string;
+  questions: QuizQuestionResult[];
+}
+
+/**
+ * Quiz Question Result
+ */
+export interface QuizQuestionResult {
+  questionId: string;
+  questionText: string;
+  questionType: string;
+  userAnswer: string | string[];
+  correctAnswer: string | string[];
+  isCorrect: boolean;
+  explanation: string;
+  points: number;
+  timeSpent?: number;
+}
+
+/**
+ * Quiz Session State (for signal management)
+ */
+export interface QuizSessionState {
+  session: QuizSession | null;
+  questions: Question[];
+  currentQuestionIndex: number;
+  answers: Map<string, QuizAnswerResponse>;
+  isLoading: boolean;
+  error: string | null;
+}
+
+/**
+ * Quiz Review Response
+ */
+export interface QuizReviewResponse {
+  success: boolean;
+  session: QuizSession;
+  questions: QuizQuestionResult[];
+}

frontend/src/app/core/models/user.model.ts

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+/**
+ * User Interface
+ * Represents a registered user in the system
+ */
+export interface User {
+  id: string;
+  username: string;
+  email: string;
+  role: 'user' | 'admin';
+  isActive: boolean;
+  totalQuizzesTaken?: number;
+  totalQuestionsAnswered?: number;
+  totalCorrectAnswers?: number;
+  currentStreak?: number;
+  longestStreak?: number;
+  averageScore?: number;
+  createdAt: string;
+  updatedAt: string;
+}
+
+/**
+ * User Registration Request
+ */
+export interface UserRegistration {
+  username: string;
+  email: string;
+  password: string;
+  guestSessionId?: string;
+}
+
+/**
+ * User Login Request
+ */
+export interface UserLogin {
+  email: string;
+  password: string;
+}
+
+/**
+ * Auth Response
+ */
+export interface AuthResponse {
+  success: boolean;
+  token: string;
+  user: User;
+  message?: string;
+  migratedStats?: {
+    quizzesTaken: number;
+    score: number;
+  };
+}
+
+/**
+ * Auth State (for signal management)
+ */
+export interface AuthState {
+  user: User | null;
+  isAuthenticated: boolean;
+  isLoading: boolean;
+  error: string | null;
+}