package dbx

import (
	"context"
	"fmt"
	"strings"
	"time"

	"gorm.io/driver/mysql"
	"gorm.io/gorm"
)

func GetMySQLDB(cfg *DBConfig, dbName string) *gorm.DB {
	db, err := getMySQLInstance(cfg, dbName)
	if err != nil {
		panic("failed to connect to MySQL database: " + err.Error())
	}
	return db
}

func getMySQLInstance(cfg *DBConfig, dbName string) (*gorm.DB, error) {
	targetDSN := fmt.Sprintf("%s:%s@tcp(%s:%s)/%s?charset=utf8mb4&parseTime=True&loc=Local",
		cfg.User, cfg.Password, cfg.Host, cfg.Port, dbName)

	// 先尝试直接连接目标库
	if db, err := gorm.Open(mysql.Open(targetDSN), &gorm.Config{}); err == nil {
		return db, nil
	}

	// 以不指定数据库的 DSN 连接（用于创建数据库）
	adminDSN := fmt.Sprintf("%s:%s@tcp(%s:%s)/?charset=utf8mb4&parseTime=True&loc=Local",
		cfg.User, cfg.Password, cfg.Host, cfg.Port)
	adminDB, err := gorm.Open(mysql.Open(adminDSN), &gorm.Config{})
	if err != nil {
		return nil, fmt.Errorf("connect admin mysql failed: %w", err)
	}
	// 关闭底层连接
	if sqlDB, e := adminDB.DB(); e == nil {
		defer sqlDB.Close()
	}

	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
	defer cancel()

	// 检查是否存在（使用 INFORMATION_SCHEMA）
	var count int64
	checkSQL := "SELECT count(*) FROM INFORMATION_SCHEMA.SCHEMATA WHERE SCHEMA_NAME = ?"
	if err := adminDB.WithContext(ctx).Raw(checkSQL, dbName).Scan(&count).Error; err != nil {
		return nil, fmt.Errorf("check mysql database existence failed: %w", err)
	}
	if count == 0 {
		ident := escapeMySQLIdentifier(dbName)
		createSQL := fmt.Sprintf("CREATE DATABASE %s DEFAULT CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci", ident)
		if err := adminDB.WithContext(ctx).Exec(createSQL).Error; err != nil {
			return nil, fmt.Errorf("create mysql database %s failed: %w", dbName, err)
		}
	}

	// 重试连接目标数据库
	db2, err := gorm.Open(mysql.Open(targetDSN), &gorm.Config{})
	if err != nil {
		return nil, fmt.Errorf("connect mysql target after create failed: %w", err)
	}
	return db2, nil
}

// 辅助：安全转义 MySQL 标识符（用反引号并把 ` 替换为 “）
func escapeMySQLIdentifier(s string) string {
	s = strings.ReplaceAll(s, "`", "``")
	return "`" + s + "`"
}