io.circe.generic.extras.decoding.EnumerationDecoder.scala Maven / Gradle / Ivy
package io.circe.generic.extras.decoding
import io.circe.{ Decoder, DecodingFailure, HCursor }
import shapeless.{ :+:, CNil, Coproduct, HNil, Inl, Inr, LabelledGeneric, Witness }
import shapeless.labelled.{ field, FieldType }
abstract class EnumerationDecoder[A] extends Decoder[A]
final object EnumerationDecoder {
implicit val decodeEnumerationCNil: EnumerationDecoder[CNil] = new EnumerationDecoder[CNil] {
def apply(c: HCursor): Decoder.Result[CNil] = Left(DecodingFailure("Enumeration", c.history))
}
implicit def decodeEnumerationCCons[K <: Symbol, V, R <: Coproduct](
implicit
wit: Witness.Aux[K],
gv: LabelledGeneric.Aux[V, HNil],
dr: EnumerationDecoder[R]
): EnumerationDecoder[FieldType[K, V] :+: R] = new EnumerationDecoder[FieldType[K, V] :+: R] {
def apply(c: HCursor): Decoder.Result[FieldType[K, V] :+: R] =
c.as[String] match {
case Right(s) if s == wit.value.name => Right(Inl(field[K](gv.from(HNil))))
case Right(_) => dr.apply(c).right.map(Inr(_))
case Left(err) => Left(DecodingFailure("Enumeration", c.history))
}
}
implicit def decodeEnumeration[A, Repr <: Coproduct](
implicit
gen: LabelledGeneric.Aux[A, Repr],
rr: EnumerationDecoder[Repr]
): EnumerationDecoder[A] =
new EnumerationDecoder[A] {
def apply(c: HCursor): Decoder.Result[A] = rr(c).right.map(gen.from)
}
}