1 package io.circe
2 
3 import cats.data.{Validated, ValidatedNel}
4 import cats.syntax.either._
5 
6 trait ValidatingDecoder[A] extends Decoder[A] {
7   override def apply(cursor: HCursor): Decoder.Result[A] = decodeValidating(cursor).toEither.leftMap(_.head)
8 
9   override def decodeAccumulating(cursor: HCursor): Decoder.AccumulatingResult[A] = decodeValidating(cursor)
10 
11   def decodeValidating(cursor: HCursor): Decoder.AccumulatingResult[A]
12 }
13 
14 object ValidatingDecoder {
15   def instance[A](f: HCursor => Decoder.AccumulatingResult[A]): ValidatingDecoder[A] =
16     new ValidatingDecoder[A] {
17       override def decodeValidating(cursor: HCursor): Decoder.AccumulatingResult[A] = f(cursor)
18     }
19 
20   def lift[A, B](decoder: Decoder[A])(validate: A => ValidatedNel[String, B]): ValidatingDecoder[B] =
21     ValidatingDecoder.instance { cursor =>
22       Validated
23         .fromEither(decoder(cursor))
24         .toValidatedNel
25         .andThen(liftDecodingFailures[A, B](validate, cursor))
26     }
27 
28   private def liftDecodingFailures[A, B](
29       validate: A => ValidatedNel[String, B],
30       cursor: HCursor
31   ): A => ValidatedNel[DecodingFailure, B] = validate.andThen(_.leftMap(_.map(DecodingFailure(_, cursor.history))))
32 
33   def apply[A]: ApplyBuilder[A] = new ApplyBuilder[A]
34 
35   final class ApplyBuilder[A] {
36     def apply[B](validate: A => ValidatedNel[String, B])(implicit decoder: Decoder[A]): ValidatingDecoder[B] =
37       lift(decoder)(validate)
38   }
39 }