package dts

import (
	"database/sql"
	"database/sql/driver"
	"encoding/json"
)

// NullString represents a string that may be null.
// NullString implements the [Scanner] interface so
// it can be used as a scan destination:
//
//	var s NullString
//	err := db.QueryRow("SELECT name FROM foo WHERE id=?", id).Scan(&s)
//	...
//	if s.Valid {
//	   // use s.String
//	} else {
//	   // NULL value
//	}
type NullString struct {
	String string
	Valid  bool // Valid is true if String is not NULL
}

// Scan implements the Scanner interface.
func (ns *NullString) Scan(value any) error {
	if value == nil {
		ns.String, ns.Valid = "", false
		return nil
	}
	ss := new(sql.NullString)
	err := ss.Scan(value)
	ns.String = ss.String
	ns.Valid = ss.Valid
	return err
}

// Value implements the driver Valuer interface.
func (ns NullString) Value() (driver.Value, error) {
	if !ns.Valid {
		return nil, nil
	}
	return ns.String, nil
}

func (ns NullString) MarshalJSON() ([]byte, error) {
	if ns.Valid {
		return json.Marshal(ns.String)
	}
	return json.Marshal(nil)
}

func (ns *NullString) UnmarshalJSON(b []byte) error {
	if string(b) == "null" {
		ns.Valid = false
		return nil
	}
	err := json.Unmarshal(b, &ns.String)
	ns.Valid = err == nil
	return err
}