/**
 * Migration: Add Database Indexes for Performance Optimization
 * 
 * This migration adds indexes to improve query performance for:
 * - QuizSession: userId, guestSessionId, categoryId, status, createdAt
 * - QuizSessionQuestion: quizSessionId, questionId
 * 
 * Note: Other models (User, Question, Category, GuestSession, QuizAnswer, UserBookmark) 
 * already have indexes defined in their models.
 */

module.exports = {
  up: async (queryInterface, Sequelize) => {
    console.log('Adding performance indexes...');
    
    try {
      // QuizSession indexes
      await queryInterface.addIndex('quiz_sessions', ['user_id'], {
        name: 'idx_quiz_sessions_user_id'
      });
      
      await queryInterface.addIndex('quiz_sessions', ['guest_session_id'], {
        name: 'idx_quiz_sessions_guest_session_id'
      });
      
      await queryInterface.addIndex('quiz_sessions', ['category_id'], {
        name: 'idx_quiz_sessions_category_id'
      });
      
      await queryInterface.addIndex('quiz_sessions', ['status'], {
        name: 'idx_quiz_sessions_status'
      });
      
      await queryInterface.addIndex('quiz_sessions', ['created_at'], {
        name: 'idx_quiz_sessions_created_at'
      });
      
      // Composite indexes for common queries
      await queryInterface.addIndex('quiz_sessions', ['user_id', 'created_at'], {
        name: 'idx_quiz_sessions_user_created'
      });
      
      await queryInterface.addIndex('quiz_sessions', ['guest_session_id', 'created_at'], {
        name: 'idx_quiz_sessions_guest_created'
      });
      
      await queryInterface.addIndex('quiz_sessions', ['category_id', 'status'], {
        name: 'idx_quiz_sessions_category_status'
      });
      
      // QuizSessionQuestion indexes
      await queryInterface.addIndex('quiz_session_questions', ['quiz_session_id'], {
        name: 'idx_quiz_session_questions_session_id'
      });
      
      await queryInterface.addIndex('quiz_session_questions', ['question_id'], {
        name: 'idx_quiz_session_questions_question_id'
      });
      
      await queryInterface.addIndex('quiz_session_questions', ['quiz_session_id', 'question_order'], {
        name: 'idx_quiz_session_questions_session_order'
      });
      
      // Unique constraint to prevent duplicate questions in same session
      await queryInterface.addIndex('quiz_session_questions', ['quiz_session_id', 'question_id'], {
        name: 'idx_quiz_session_questions_session_question_unique',
        unique: true
      });
      
      console.log('✅ Performance indexes added successfully');
      
    } catch (error) {
      console.error('❌ Error adding indexes:', error);
      throw error;
    }
  },

  down: async (queryInterface, Sequelize) => {
    console.log('Removing performance indexes...');
    
    try {
      // Remove QuizSession indexes
      await queryInterface.removeIndex('quiz_sessions', 'idx_quiz_sessions_user_id');
      await queryInterface.removeIndex('quiz_sessions', 'idx_quiz_sessions_guest_session_id');
      await queryInterface.removeIndex('quiz_sessions', 'idx_quiz_sessions_category_id');
      await queryInterface.removeIndex('quiz_sessions', 'idx_quiz_sessions_status');
      await queryInterface.removeIndex('quiz_sessions', 'idx_quiz_sessions_created_at');
      await queryInterface.removeIndex('quiz_sessions', 'idx_quiz_sessions_user_created');
      await queryInterface.removeIndex('quiz_sessions', 'idx_quiz_sessions_guest_created');
      await queryInterface.removeIndex('quiz_sessions', 'idx_quiz_sessions_category_status');
      
      // Remove QuizSessionQuestion indexes
      await queryInterface.removeIndex('quiz_session_questions', 'idx_quiz_session_questions_session_id');
      await queryInterface.removeIndex('quiz_session_questions', 'idx_quiz_session_questions_question_id');
      await queryInterface.removeIndex('quiz_session_questions', 'idx_quiz_session_questions_session_order');
      await queryInterface.removeIndex('quiz_session_questions', 'idx_quiz_session_questions_session_question_unique');
      
      console.log('✅ Performance indexes removed successfully');
      
    } catch (error) {
      console.error('❌ Error removing indexes:', error);
      throw error;
    }
  }
};