backend/src/legacy-mysql/legacy-mysql.service.ts

import {
  Injectable,
  OnModuleDestroy,
  ServiceUnavailableException,
} from '@nestjs/common';
import { ConfigService } from '@nestjs/config';
import mysql, { Pool, PoolOptions, RowDataPacket } from 'mysql2/promise';

@Injectable()
export class LegacyMysqlService implements OnModuleDestroy {
  private pool: Pool | null = null;

  constructor(private readonly config: ConfigService) {}

  async onModuleDestroy() {
    if (this.pool) {
      await this.pool.end();
      this.pool = null;
    }
  }

  isConfigured(): boolean {
    return Boolean(
      this.config.get<string>('OLD_MYSQL_HOST') &&
        this.config.get<string>('OLD_MYSQL_USER') &&
        this.config.get<string>('OLD_MYSQL_DATABASE'),
    );
  }

  async query<T extends RowDataPacket[]>(
    sql: string,
    params: unknown[] = [],
  ): Promise<T> {
    const pool = this.getPool();
    try {
      const [rows] = await pool.query<T>(sql, params);
      return rows;
    } catch (err) {
      const message = err instanceof Error ? err.message : 'Unknown MySQL error';
      throw new ServiceUnavailableException(
        `Old CMS MySQL query failed: ${message}. Ensure the SSH tunnel is up and OLD_MYSQL_* is set.`,
      );
    }
  }

  private getPool(): Pool {
    if (this.pool) {
      return this.pool;
    }

    if (!this.isConfigured()) {
      throw new ServiceUnavailableException(
        'Old CMS MySQL is not configured. Set OLD_MYSQL_HOST, OLD_MYSQL_USER, OLD_MYSQL_DATABASE (and password/port).',
      );
    }

    const options: PoolOptions = {
      host: this.config.getOrThrow<string>('OLD_MYSQL_HOST'),
      port: Number(this.config.get<string>('OLD_MYSQL_PORT', '3307')),
      user: this.config.getOrThrow<string>('OLD_MYSQL_USER'),
      password: this.config.get<string>('OLD_MYSQL_PASSWORD', ''),
      database: this.config.getOrThrow<string>('OLD_MYSQL_DATABASE'),
      waitForConnections: true,
      connectionLimit: 4,
      namedPlaceholders: false,
    };

    this.pool = mysql.createPool(options);
    return this.pool;
  }
}