import { createPool, type Pool } from 'mysql2/promise';
import type { OnModuleDestroy } from '@nestjs/common';

import type { MysqlRuntimeConfig } from '../../config/src/runtime-config';
import type { DependencyHealthDto } from '../../http-contracts/src/health.dto';

/** 固定的只读元数据查询，用于验证服务端版本、库名和会话字符口径。 */
export const MYSQL_HEALTH_QUERY = `SELECT
  VERSION() AS version,
  DATABASE() AS databaseName,
  @@character_set_database AS charset,
  @@collation_database AS collation,
  @@session.time_zone AS timezone`;

interface MysqlQueryPort {
  query(sql: string): Promise<[unknown, unknown]>;
  end(): Promise<void>;
}

interface MysqlMetadataRow {
  version: string;
  databaseName: string;
  charset: string;
  collation: string;
  timezone: string;
}

/** MySQL 健康客户端只校验元数据，不读取表数据或执行写入。 */
export class MysqlHealthClient implements OnModuleDestroy {
  constructor(
    private readonly client: MysqlQueryPort,
    private readonly expectedDatabase: string,
  ) {}

  async check(): Promise<DependencyHealthDto> {
    const [rows] = await this.client.query(MYSQL_HEALTH_QUERY);
    const row = (rows as unknown as MysqlMetadataRow[])[0];
    if (!row) throw new Error('MySQL 未返回元数据');
    const versionMatch = /^(5\.7\.\d+)(?:[-+].*)?$/.exec(row.version ?? '');
    if (!versionMatch) {
      throw new Error('MySQL 5.7.x 版本要求未满足');
    }
    if (row.databaseName !== this.expectedDatabase) {
      throw new Error(`MySQL 健康检查必须连接 ${this.expectedDatabase}`);
    }
    if (row.charset !== 'utf8mb4') throw new Error('MySQL 字符集必须为 utf8mb4');
    if (row.collation !== 'utf8mb4_general_ci') {
      throw new Error('MySQL 排序规则必须为 utf8mb4_general_ci');
    }
    if (row.timezone !== '+08:00') throw new Error('MySQL 会话时区必须为 +08:00');

    return {
      status: 'healthy',
      detail: `MySQL ${versionMatch[1]} / ${row.databaseName} / ${row.timezone}`,
    };
  }

  async close(): Promise<void> {
    await this.client.end();
  }

  async onModuleDestroy(): Promise<void> {
    await this.close();
  }
}

/** 创建最多两个连接的只读健康池，并显式应用 MySQL 5.7.x 会话时区。 */
export function createMysqlHealthClient(config: MysqlRuntimeConfig): MysqlHealthClient {
  const pool: Pool = createPool({
    host: config.host,
    port: config.port,
    database: config.database,
    user: config.username,
    password: config.password,
    charset: config.charset,
    timezone: config.timezone,
    connectionLimit: 2,
    enableKeepAlive: false,
  });
  return new MysqlHealthClient(pool, config.database);
}