LocalDateTimeCodec.scala

import java.time.{Instant, ZoneId, LocalDateTime}

import io.circe.{Encoder, Decoder}

import io.circe.syntax._

trait LocalDateTimeCodec {
  val UTC = ZoneId.of("UTC")

  implicit val dateTimeEncoder: Encoder[LocalDateTime] = Encoder.instance(
    dt => dt.atZone(UTC).toInstant.toEpochMilli.asJson
  )

  implicit val dateTimeDecoder: Decoder[LocalDateTime] = Decoder.instance { cursor =>
    for {
      millis <- cursor.as[Long]
    } yield LocalDateTime.ofInstant(Instant.ofEpochMilli(millis), UTC)
  }
}