package migrate

import (
	"context"
	"fmt"

	"github.com/gogf/gf/v2/database/gdb"
)

// ============================== 数据库连接 ==============================

// openConn 按 DSN 动态建立连接并探活
//
// 通过 gdb.New 注册独立命名节点，不触碰 config.yaml 中的默认连接
func openConn(ctx context.Context, node string, dsn DSN) (gdb.DB, error) {
	link, err := buildLink(dsn)
	if err != nil {
		return nil, err
	}
	db, err := gdb.New(gdb.ConfigNode{
		Name: node,
		Type: dsn.Type,
		Link: link,
	})
	if err != nil {
		return nil, fmt.Errorf("连接 %s 库失败: %v", node, err)
	}
	if _, err = db.Query(ctx, "SELECT 1"); err != nil {
		return nil, fmt.Errorf("%s 库探活失败: %v", node, err)
	}
	return db, nil
}

// ensureDatabase 目标库不存在时先创建
//
// MySQL、PostgreSQL、SQL Server 经维护库建库；Oracle 与 SQLite 无需预建
func ensureDatabase(ctx context.Context, dsn DSN) error {
	var maintainDB, createSQL, checkSQL string
	switch dsn.Type {
	case "mysql":
		maintainDB, checkSQL = "", "SELECT SCHEMA_NAME FROM information_schema.SCHEMATA WHERE SCHEMA_NAME = ?"
		createSQL = "CREATE DATABASE `" + dsn.Database + "` CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci"
	case "pgsql":
		maintainDB, checkSQL = "postgres", "SELECT 1 FROM pg_database WHERE datname = ?"
		createSQL = `CREATE DATABASE "` + dsn.Database + `"`
	case "mssql":
		maintainDB, checkSQL = "master", "SELECT 1 FROM sys.databases WHERE name = ?"
		createSQL = "CREATE DATABASE [" + dsn.Database + "]"
	default:
		return nil // oracle/sqlite 无需预建
	}
	checkDSN := dsn
	checkDSN.Database = maintainDB
	link, err := buildLink(checkDSN)
	if err != nil {
		return err
	}
	maintain, err := gdb.New(gdb.ConfigNode{Name: "migrate_maintain", Type: dsn.Type, Link: link})
	if err != nil {
		return fmt.Errorf("连接 %s 维护库失败: %v", dsn.Type, err)
	}
	defer maintain.Close(ctx)
	row, err := maintain.Query(ctx, checkSQL, dsn.Database)
	if err != nil {
		return fmt.Errorf("检查目标库是否存在失败: %v", err)
	}
	if len(row) > 0 {
		return nil // 已存在
	}
	if _, err = maintain.Exec(ctx, createSQL); err != nil {
		return fmt.Errorf("创建目标库 %s 失败: %v", dsn.Database, err)
	}
	return nil
}

// buildLink 将 DSN 转换为 gdb link 串
//
// 各方言按驱动约定格式组装，对齐配置示例
func buildLink(dsn DSN) (string, error) {
	switch dsn.Type {
	case "mysql":
		return fmt.Sprintf("%s:%s@tcp(%s:%s)/%s?charset=utf8mb4&parseTime=true&loc=Local",
			dsn.Username, dsn.Password, dsn.Host, dsn.Port, dsn.Database), nil
	case "pgsql":
		return fmt.Sprintf("%s:%s@tcp(%s:%s)/%s?sslmode=disable",
			dsn.Username, dsn.Password, dsn.Host, dsn.Port, dsn.Database), nil
	case "mssql":
		return fmt.Sprintf("%s:%s@tcp(%s:%s)/%s?encrypt=disable",
			dsn.Username, dsn.Password, dsn.Host, dsn.Port, dsn.Database), nil
	case "oracle":
		return fmt.Sprintf("%s:%s@tcp(%s:%s)/%s",
			dsn.Username, dsn.Password, dsn.Host, dsn.Port, dsn.Database), nil
	case "sqlite":
		if dsn.Database == "" {
			return "", fmt.Errorf("sqlite 需以 -src-database/-dst-database 指定数据库文件路径")
		}
		return fmt.Sprintf("sqlite::@file(%s)", dsn.Database), nil
	}
	return "", fmt.Errorf("不支持的数据库类型: %s", dsn.Type)
}

// tableExists 判断目标库中同名表是否已存在
func tableExists(ctx context.Context, db gdb.DB, table string) (bool, error) {
	tables, err := db.Tables(ctx)
	if err != nil {
		return false, err
	}
	for _, t := range tables {
		if t == table {
			return true, nil
		}
	}
	return false, nil
}