package db

import (
	"context"
	"database/sql"
	"fmt"
	"strings"
)

// GetDDL 返回表/视图的建表语句。mysql 族走 SHOW CREATE TABLE,sqlite 读 sqlite_master,
// pg/mssql/oracle 用 ListColumns 元数据在 Go 侧拼装 CREATE TABLE。
func GetDDL(ctx context.Context, c ConnReq) (string, error) {
	ctx = reqCtx(ctx)
	if c.Table == "" {
		return "", fmt.Errorf("缺少表名")
	}
	if isRedis(c.Driver) {
		return "", fmt.Errorf("该驱动不支持 DDL 查看")
	}
	// pg/mssql/oracle:复用列元数据拼装,避免再查一次库
	switch {
	case isPostgresFamily(c.Driver), isMSSQL(c.Driver), driverKey(c.Driver) == "oracle":
		cols, err := ListColumns(ctx, c)
		if err != nil {
			return "", err
		}
		return buildDDLFromColumns(c.Driver, c.Table, cols)
	}
	var out string
	err := withDB(c, func(db *sql.DB) error {
		var err error
		switch {
		case isMySQLFamily(c.Driver):
			out, err = getDDLMySQL(ctx, db, c)
		case driverKey(c.Driver) == "sqlite":
			out, err = getDDLSQLite(ctx, db, c.Table)
		default:
			err = unsupportedDriverErr(c)
		}
		return err
	})
	if err != nil {
		return "", err
	}
	return out, nil
}

// getDDLMySQL SHOW CREATE TABLE 第二列即 DDL(列名随对象类型变化:Create Table/Create View)。
func getDDLMySQL(ctx context.Context, dbh *sql.DB, c ConnReq) (string, error) {
	ident := quoteMySQLIdent(c.Table)
	if c.Database != "" {
		ident = quoteMySQLIdent(c.Database) + "." + ident
	}
	rows, err := dbh.QueryContext(ctx, "SHOW CREATE TABLE "+ident)
	if err != nil {
		return "", err
	}
	defer rows.Close()
	if rows.Next() {
		var name string
		var ddl sql.NullString
		if err := rows.Scan(&name, &ddl); err != nil {
			return "", err
		}
		if !ddl.Valid {
			return "", fmt.Errorf("无法读取 %s 的 DDL", c.Table)
		}
		return ddl.String, nil
	}
	if err := rows.Err(); err != nil {
		return "", err
	}
	return "", fmt.Errorf("表 %s 不存在", c.Table)
}

// getDDLSQLite sqlite_master 的 sql 列即建表语句。
func getDDLSQLite(ctx context.Context, dbh *sql.DB, table string) (string, error) {
	var ddl sql.NullString
	err := dbh.QueryRowContext(ctx, `SELECT sql FROM sqlite_master WHERE name = ?`, table).Scan(&ddl)
	if err == sql.ErrNoRows {
		return "", fmt.Errorf("表 %s 不存在", table)
	}
	if err != nil {
		return "", err
	}
	if !ddl.Valid {
		return "", fmt.Errorf("表 %s 无 DDL 记录", table)
	}
	return ddl.String, nil
}

// buildDDLFromColumns 用列元数据拼装 CREATE TABLE(类型直接用 ColumnInfo.Type)。
func buildDDLFromColumns(driver, table string, cols []ColumnInfo) (string, error) {
	if len(cols) == 0 {
		return "", fmt.Errorf("表 %s 不存在或无列", table)
	}
	var pks []string
	for _, col := range cols {
		if col.Key == "PRI" {
			pks = append(pks, quoteIdentFor(driver, col.Name))
		}
	}
	var b strings.Builder
	fmt.Fprintf(&b, "CREATE TABLE %s (\n", quoteTableNameFor(driver, table))
	for i, col := range cols {
		line := "  " + quoteIdentFor(driver, col.Name) + " " + col.Type
		if !col.Nullable {
			line += " NOT NULL"
		}
		// 非最后一列、或后面还有 PRIMARY KEY 子句时需要逗号
		if i < len(cols)-1 || len(pks) > 0 {
			line += ","
		}
		b.WriteString(line + "\n")
	}
	if len(pks) > 0 {
		b.WriteString("  PRIMARY KEY (" + strings.Join(pks, ", ") + ")\n")
	}
	b.WriteString(");\n")
	return b.String(), nil
}