JsonInstances.scala

package json

import java.time.format.{DateTimeFormatter, DateTimeParseException}
import java.time.{Instant, LocalDateTime, ZoneId, ZonedDateTime}

import cats.data.Xor
import io.circe.{Decoder, DecodingFailure, HCursor}

object JsonInstances {
  /** f.ex. 'Europe/Vienna' */
  implicit val zoneId: Decoder[ZoneId] = Decoder.instance { cursor ⇒
    for {
      string ← cursor.as[String]
      zoneId ← wrap(Xor.catchOnly[RuntimeException] {
                ZoneId.of(string)
              }, cursor)
    } yield zoneId
  }

  /** This assume ISO8601 formatted times, so it is not imported automatically */
  object alaCarte {
    final private val iso8601formatter = DateTimeFormatter.ISO_ZONED_DATE_TIME

    implicit val decodeIso8601LocalDateTime: Decoder[LocalDateTime] = Decoder.instance { cursor ⇒
      for {
        string   ← cursor.as[String]
        datetime ← wrap(Xor.catchOnly[DateTimeParseException] {
          iso8601formatter.parse(string)
        }, cursor)
      } yield LocalDateTime.from(datetime)
    }

    implicit val decodeIso8601ZonedDateTime: Decoder[ZonedDateTime] = Decoder.instance { cursor ⇒
      for {
        string   ← cursor.as[String]
        datetime ← wrap(Xor.catchOnly[DateTimeParseException] {
          iso8601formatter.parse(string)
        }, cursor)
      } yield ZonedDateTime.from(datetime)
    }

    implicit val decodeIso8601Instant: Decoder[Instant] = Decoder.instance { cursor ⇒
      for {
        string   ← cursor.as[String]
        datetime ← wrap(Xor.catchOnly[DateTimeParseException] {
                     iso8601formatter.parse(string)
                   }, cursor)
      } yield Instant.from(datetime)
    }
  }

  private def wrap[L <: RuntimeException, R](xor: Xor[L, R], cursor: HCursor) =
    xor.leftMap(t ⇒ DecodingFailure(t.getMessage, cursor.history))
}