如何编写抽象类的circe解码器

import io.circe._
import io.circe.parser._
import io.circe.generic.semiauto._

abstract class AbstractClass

case class ConcreteClassA(fieldA: String) extends AbstractClass
case class ConcreteClassB(fieldB: Int) extends AbstractClass

object AbstractClass {
  implicit val decoder: Decoder[AbstractClass] = Decoder.instance { c =>
    // 根据JSON字段类型进行解码
    c.downField("type").as[String].flatMap {
      case "A" => c.as[ConcreteClassA]
      case "B" => c.as[ConcreteClassB]
      case _ => Left(DecodingFailure("Invalid type", c.history))
    }
  }
}

// 示例JSON数据
val json = """
{
  "type": "A",
  "fieldA": "valueA"
}
"""

// 解码JSON数据为抽象类实例
val result = decode[AbstractClass](json)

result match {
  case Right(obj) => println(obj)
  case Left(error) => println(error.getMessage)
}