ZIO learning - custom encoding/decoding / published by https://github.com/dacr/code-examples-manager #fccee49f-5fbe-4f91-bc78-366369f04294/374c50dd7a5be7a7817fb9c558ba41fbc5a0d263

zio-learning-json-4-custom-codec.sc

// summary : ZIO learning - custom encoding/decoding
// keywords : scala, zio, learning, json, pure-functional, @testable
// publish : gist
// authors : David Crosson
// license : Apache NON-AI License Version 2.0 (https://raw.githubusercontent.com/non-ai-licenses/non-ai-licenses/main/NON-AI-APACHE2)
// id : fccee49f-5fbe-4f91-bc78-366369f04294
// created-on : 2022-01-22T08:12:30.292458847Z
// managed-by : https://github.com/dacr/code-examples-manager
// run-with : scala-cli $file

// ---------------------
//> using scala "3.4.2"
//> using dep "dev.zio::zio:2.0.13"
//> using dep "dev.zio::zio-test:2.0.13"
//> using dep "dev.zio::zio-json:0.5.0"
// ---------------------

import zio.*
import zio.json.*
import zio.json.ast.*
import zio.json.ast.Json.*
import zio.json.internal.{RetractReader, Write}
import zio.test.*
import zio.test.Assertion.*

import java.nio.file.Path

case class Something(
  field1: Int,
  field2: Boolean,
  attributes: Map[String, Json]
)

object Something:
  // implicit val encoder: JsonEncoder[Something] = DeriveJsonEncoder.gen
  implicit val encoder: JsonEncoder[Something] = JsonEncoder[Json].contramap { something =>
    val obj =
      Obj("_field1" -> Num(something.field1), "_field2" -> Bool(something.field2))
        .merge(Obj(something.attributes.toArray*))
    obj
  }

  // implicit val decoder: JsonDecoder[Something] = DeriveJsonDecoder.gen
  implicit val decoder: JsonDecoder[Something] = JsonDecoder[Obj].map { obj =>
    val (fieldsTuples, attributesTuples) = obj.fields.partition { case (key, _) => key.startsWith("_") }

    val fields = fieldsTuples.toMap
    val field1 = fields.get("_field1").flatMap(_.as[Int].toOption).get     // TODO to enhance of course
    val field2 = fields.get("_field2").flatMap(_.as[Boolean].toOption).get // TODO to enhance of course

    Something(field1 = field1, field2 = field2, attributes = attributesTuples.toMap)
  }

object JsonTests extends ZIOSpecDefault:
  def spec = suite("more complex json encoding/decoding")(
    test("using data custom encoder/decoder approach") {
      val json =
        """{
          |  "_field1" : 42,
          |  "_field2" : true,
          |  "attr1" : 424,
          |  "attr2" : "a value"
          |}""".stripMargin
      for {
        obj       <- ZIO.fromEither(json.fromJson)
        something <- ZIO.fromEither(obj.as[Something])
      } yield assertTrue(something.attributes.get("attr1") == Some(Num(424))) &&
        assertTrue(something.toJsonPretty == json)
    }
  )

JsonTests.main(Array.empty)