add changes

backend/models/GuestSession.js

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+const { v4: uuidv4 } = require('uuid');
+const jwt = require('jsonwebtoken');
+const config = require('../config/config');
+
+module.exports = (sequelize, DataTypes) => {
+  const GuestSession = sequelize.define('GuestSession', {
+    id: {
+      type: DataTypes.CHAR(36),
+      primaryKey: true,
+      defaultValue: () => uuidv4(),
+      allowNull: false,
+      comment: 'UUID primary key'
+    },
+    guestId: {
+      type: DataTypes.STRING(100),
+      allowNull: false,
+      unique: {
+        msg: 'Guest ID already exists'
+      },
+      field: 'guest_id',
+      validate: {
+        notEmpty: {
+          msg: 'Guest ID cannot be empty'
+        }
+      },
+      comment: 'Unique guest identifier'
+    },
+    sessionToken: {
+      type: DataTypes.STRING(500),
+      allowNull: false,
+      unique: {
+        msg: 'Session token already exists'
+      },
+      field: 'session_token',
+      comment: 'JWT session token'
+    },
+    deviceId: {
+      type: DataTypes.STRING(255),
+      allowNull: true,
+      field: 'device_id',
+      comment: 'Device identifier (optional)'
+    },
+    ipAddress: {
+      type: DataTypes.STRING(45),
+      allowNull: true,
+      field: 'ip_address',
+      comment: 'IP address (supports IPv6)'
+    },
+    userAgent: {
+      type: DataTypes.TEXT,
+      allowNull: true,
+      field: 'user_agent',
+      comment: 'Browser user agent string'
+    },
+    quizzesAttempted: {
+      type: DataTypes.INTEGER,
+      allowNull: false,
+      defaultValue: 0,
+      field: 'quizzes_attempted',
+      validate: {
+        min: 0
+      },
+      comment: 'Number of quizzes attempted by guest'
+    },
+    maxQuizzes: {
+      type: DataTypes.INTEGER,
+      allowNull: false,
+      defaultValue: 3,
+      field: 'max_quizzes',
+      validate: {
+        min: 1,
+        max: 100
+      },
+      comment: 'Maximum quizzes allowed for this guest'
+    },
+    expiresAt: {
+      type: DataTypes.DATE,
+      allowNull: false,
+      field: 'expires_at',
+      validate: {
+        isDate: true,
+        isAfter: new Date().toISOString()
+      },
+      comment: 'Session expiration timestamp'
+    },
+    isConverted: {
+      type: DataTypes.BOOLEAN,
+      allowNull: false,
+      defaultValue: false,
+      field: 'is_converted',
+      comment: 'Whether guest converted to registered user'
+    },
+    convertedUserId: {
+      type: DataTypes.CHAR(36),
+      allowNull: true,
+      field: 'converted_user_id',
+      comment: 'User ID if guest converted to registered user'
+    }
+  }, {
+    sequelize,
+    modelName: 'GuestSession',
+    tableName: 'guest_sessions',
+    timestamps: true,
+    underscored: true,
+    indexes: [
+      {
+        unique: true,
+        fields: ['guest_id']
+      },
+      {
+        unique: true,
+        fields: ['session_token']
+      },
+      {
+        fields: ['expires_at']
+      },
+      {
+        fields: ['is_converted']
+      },
+      {
+        fields: ['converted_user_id']
+      },
+      {
+        fields: ['device_id']
+      },
+      {
+        fields: ['created_at']
+      }
+    ]
+  });
+
+  // Static method to generate guest ID
+  GuestSession.generateGuestId = function() {
+    const timestamp = Date.now();
+    const randomStr = Math.random().toString(36).substring(2, 15);
+    return `guest_${timestamp}_${randomStr}`;
+  };
+
+  // Static method to generate session token (JWT)
+  GuestSession.generateToken = function(guestId, sessionId) {
+    const payload = {
+      guestId,
+      sessionId,
+      type: 'guest'
+    };
+
+    return jwt.sign(payload, config.jwt.secret, {
+      expiresIn: config.guest.sessionExpireHours + 'h'
+    });
+  };
+
+  // Static method to verify and decode token
+  GuestSession.verifyToken = function(token) {
+    try {
+      return jwt.verify(token, config.jwt.secret);
+    } catch (error) {
+      throw new Error('Invalid or expired token');
+    }
+  };
+
+  // Static method to create new guest session
+  GuestSession.createSession = async function(options = {}) {
+    const guestId = GuestSession.generateGuestId();
+    const sessionId = uuidv4();
+    const sessionToken = GuestSession.generateToken(guestId, sessionId);
+    
+    const expiryHours = options.expiryHours || config.guest.sessionExpireHours || 24;
+    const expiresAt = new Date(Date.now() + expiryHours * 60 * 60 * 1000);
+
+    const session = await GuestSession.create({
+      id: sessionId,
+      guestId,
+      sessionToken,
+      deviceId: options.deviceId || null,
+      ipAddress: options.ipAddress || null,
+      userAgent: options.userAgent || null,
+      maxQuizzes: options.maxQuizzes || config.guest.maxQuizzes || 3,
+      expiresAt
+    });
+
+    return session;
+  };
+
+  // Instance methods
+  GuestSession.prototype.isExpired = function() {
+    return new Date() > new Date(this.expiresAt);
+  };
+
+  GuestSession.prototype.hasReachedQuizLimit = function() {
+    return this.quizzesAttempted >= this.maxQuizzes;
+  };
+
+  GuestSession.prototype.getRemainingQuizzes = function() {
+    return Math.max(0, this.maxQuizzes - this.quizzesAttempted);
+  };
+
+  GuestSession.prototype.incrementQuizAttempt = async function() {
+    this.quizzesAttempted += 1;
+    await this.save();
+  };
+
+  GuestSession.prototype.extend = async function(hours = 24) {
+    const newExpiry = new Date(Date.now() + hours * 60 * 60 * 1000);
+    this.expiresAt = newExpiry;
+    
+    // Regenerate token with new expiry
+    this.sessionToken = GuestSession.generateToken(this.guestId, this.id);
+    await this.save();
+    
+    return this;
+  };
+
+  GuestSession.prototype.convertToUser = async function(userId) {
+    this.isConverted = true;
+    this.convertedUserId = userId;
+    await this.save();
+  };
+
+  GuestSession.prototype.getSessionInfo = function() {
+    return {
+      guestId: this.guestId,
+      sessionId: this.id,
+      quizzesAttempted: this.quizzesAttempted,
+      maxQuizzes: this.maxQuizzes,
+      remainingQuizzes: this.getRemainingQuizzes(),
+      expiresAt: this.expiresAt,
+      isExpired: this.isExpired(),
+      hasReachedLimit: this.hasReachedQuizLimit(),
+      isConverted: this.isConverted
+    };
+  };
+
+  // Class methods
+  GuestSession.findByGuestId = async function(guestId) {
+    return await this.findOne({
+      where: { guestId }
+    });
+  };
+
+  GuestSession.findByToken = async function(token) {
+    try {
+      const decoded = GuestSession.verifyToken(token);
+      return await this.findOne({
+        where: {
+          guestId: decoded.guestId,
+          id: decoded.sessionId
+        }
+      });
+    } catch (error) {
+      return null;
+    }
+  };
+
+  GuestSession.findActiveSession = async function(guestId) {
+    return await this.findOne({
+      where: {
+        guestId,
+        isConverted: false
+      }
+    });
+  };
+
+  GuestSession.cleanupExpiredSessions = async function() {
+    const expiredCount = await this.destroy({
+      where: {
+        expiresAt: {
+          [sequelize.Sequelize.Op.lt]: new Date()
+        },
+        isConverted: false
+      }
+    });
+    return expiredCount;
+  };
+
+  GuestSession.getActiveGuestCount = async function() {
+    return await this.count({
+      where: {
+        expiresAt: {
+          [sequelize.Sequelize.Op.gt]: new Date()
+        },
+        isConverted: false
+      }
+    });
+  };
+
+  GuestSession.getConversionRate = async function() {
+    const total = await this.count();
+    if (total === 0) return 0;
+
+    const converted = await this.count({
+      where: { isConverted: true }
+    });
+
+    return Math.round((converted / total) * 100);
+  };
+
+  // Hooks
+  GuestSession.beforeValidate((session) => {
+    // Ensure UUID is set
+    if (!session.id) {
+      session.id = uuidv4();
+    }
+
+    // Ensure expiry is in the future (only for new records, not updates)
+    if (session.isNewRecord && session.expiresAt && new Date(session.expiresAt) <= new Date()) {
+      throw new Error('Expiry date must be in the future');
+    }
+  });
+
+  // Define associations
+  GuestSession.associate = function(models) {
+    // GuestSession belongs to a User (if converted)
+    if (models.User) {
+      GuestSession.belongsTo(models.User, {
+        foreignKey: 'convertedUserId',
+        as: 'convertedUser'
+      });
+    }
+
+    // GuestSession has many quiz sessions
+    if (models.QuizSession) {
+      GuestSession.hasMany(models.QuizSession, {
+        foreignKey: 'guestSessionId',
+        as: 'quizSessions'
+      });
+    }
+  };
+
+  return GuestSession;
+};