package db

import (
	"context"
	"fmt"
	"reflect"

	"gorm.io/gorm/schema"
)

// 必须给结构体（而不是指针）实现此接口。FromString实现为静态方法
type StringDBValuer interface {
	ToString() (string, error)
	FromString(str string) (any, error)
}

type StringSerializer struct {
}

func (StringSerializer) Scan(ctx context.Context, field *schema.Field, dst reflect.Value, dbValue interface{}) error {
	if dbValue == nil {
		fieldValue := reflect.New(field.FieldType)
		field.ReflectValueOf(ctx, dst).Set(fieldValue.Elem())
		return nil
	}

	str := ""
	switch v := dbValue.(type) {
	case []byte:
		str = string(v)
	case string:
		str = v
	default:
		return fmt.Errorf("expected []byte or string, got: %T", dbValue)
	}

	if field.FieldType.Kind() == reflect.Struct {
		val := reflect.Zero(field.FieldType)

		sv, ok := val.Interface().(StringDBValuer)
		if !ok {
			return fmt.Errorf("ref of field type %v is not StringDBValuer", field.FieldType)
		}

		v2, err := sv.FromString(str)
		if err != nil {
			return err
		}

		field.ReflectValueOf(ctx, dst).Set(reflect.ValueOf(v2))
		return nil
	}

	if field.FieldType.Kind() == reflect.Ptr {
		val := reflect.Zero(field.FieldType.Elem())

		sv, ok := val.Interface().(StringDBValuer)
		if !ok {
			return fmt.Errorf("field type %v is not StringDBValuer", field.FieldType)
		}

		v2, err := sv.FromString(str)
		if err != nil {
			return err
		}

		field.ReflectValueOf(ctx, dst).Set(reflect.ValueOf(v2))
		return nil
	}

	return fmt.Errorf("unsupported field type: %v", field.FieldType)
}

func (StringSerializer) Value(ctx context.Context, field *schema.Field, dst reflect.Value, fieldValue interface{}) (interface{}, error) {
	val := reflect.ValueOf(fieldValue)
	if val.Kind() == reflect.Struct {
		sv, ok := val.Interface().(StringDBValuer)
		if !ok {
			return nil, fmt.Errorf("ref of field type %v is not StringDBValuer", field.FieldType)
		}

		return sv.ToString()
	}

	if val.Kind() == reflect.Ptr {
		sv, ok := val.Elem().Interface().(StringDBValuer)
		if !ok {
			return nil, fmt.Errorf("field type %v is not StringDBValuer", field.FieldType)
		}

		return sv.ToString()
	}

	return nil, fmt.Errorf("unsupported field type: %v", field.FieldType)
}

func init() {
	schema.RegisterSerializer("string", StringSerializer{})
}