const { QueryInterface } = require('sequelize');
const fs = require('fs').promises;
const path = require('path');

/**
 * Simple migration runner for Sequelize
 * Checks which migrations have been run and executes pending ones
 */
class MigrationRunner {
  constructor(sequelize) {
    this.sequelize = sequelize;
    this.migrationsPath = path.join(__dirname);
  }

  async ensureMigrationsTable() {
    const queryInterface = this.sequelize.getQueryInterface();
    
    // Check if migrations table exists
    const [results] = await this.sequelize.query(`
      SELECT EXISTS (
        SELECT FROM information_schema.tables 
        WHERE table_schema = 'public' 
        AND table_name = 'SequelizeMeta'
      );
    `);

    if (!results[0].exists) {
      // Create migrations table
      await queryInterface.createTable('SequelizeMeta', {
        name: {
          type: require('sequelize').DataTypes.STRING,
          allowNull: false,
          primaryKey: true
        }
      });
    }
  }

  async getExecutedMigrations() {
    await this.ensureMigrationsTable();
    
    const [results] = await this.sequelize.query(
      'SELECT name FROM "SequelizeMeta" ORDER BY name'
    );
    
    return results.map(row => row.name);
  }

  async getAllMigrations() {
    const files = await fs.readdir(this.migrationsPath);
    return files
      .filter(file => file.endsWith('.js') && file !== 'runner.js')
      .sort();
  }

  async runMigrations() {
    const executed = await this.getExecutedMigrations();
    const allMigrations = await this.getAllMigrations();
    const pending = allMigrations.filter(m => !executed.includes(m));

    if (pending.length === 0) {
      console.log('No pending migrations');
      return;
    }

    console.log(`Running ${pending.length} pending migration(s)...`);

    for (const migrationFile of pending) {
      const migration = require(path.join(this.migrationsPath, migrationFile));
      
      if (!migration.up || typeof migration.up !== 'function') {
        throw new Error(`Migration ${migrationFile} does not export an 'up' function`);
      }

      const queryInterface = this.sequelize.getQueryInterface();
      const transaction = await this.sequelize.transaction();

      try {
        console.log(`Running migration: ${migrationFile}`);
        await migration.up(queryInterface, this.sequelize.constructor);
        
        // Record migration as executed
        await this.sequelize.query(
          `INSERT INTO "SequelizeMeta" (name) VALUES (:name)`,
          {
            replacements: { name: migrationFile },
            transaction
          }
        );

        await transaction.commit();
        console.log(`Completed migration: ${migrationFile}`);
      } catch (error) {
        await transaction.rollback();
        throw new Error(`Migration ${migrationFile} failed: ${error.message}`);
      }
    }

    console.log('All migrations completed successfully');
  }
}

module.exports = MigrationRunner;