Add convenience methods to work with Tags: `taggedWith` wrapper and a proxy JSON format (#147)

* Add convenience methods to work with Tags: `tagged` wrapper and a proxy JSON format

3 files changed, 28 insertions, 2 deletions

diff --git a/src/main/scala/xyz/driver/core/core.scala b/src/main/scala/xyz/driver/core/core.scala
index be19f0f..14e1b10 100644
--- a/src/main/scala/xyz/driver/core/core.scala
+++ b/src/main/scala/xyz/driver/core/core.scala
@@ -25,6 +25,10 @@ package object core {
 
   object tagging {
     private[core] trait Tagged[+V, +Tag]
+
+    implicit class Taggable[V <: Any](val v: V) extends AnyVal {
+      def tagged[Tag]: V @@ Tag = v.asInstanceOf[V @@ Tag]
+    }
   }
   type @@[+V, +Tag] = V with tagging.Tagged[V, Tag]
 
diff --git a/src/main/scala/xyz/driver/core/json.scala b/src/main/scala/xyz/driver/core/json.scala
index 06a8837..e7efce6 100644
--- a/src/main/scala/xyz/driver/core/json.scala
+++ b/src/main/scala/xyz/driver/core/json.scala
@@ -34,16 +34,24 @@ object json {
     }
   }
 
-  implicit def idFormat[T] = new RootJsonFormat[Id[T]] {
+  implicit def idFormat[T]: JsonFormat[Id[T]] = new JsonFormat[Id[T]] {
     def write(id: Id[T]) = JsString(id.value)
 
-    def read(value: JsValue) = value match {
+    def read(value: JsValue): Id[T] = value match {
       case JsString(id) if Try(UUID.fromString(id)).isSuccess => Id[T](id.toLowerCase)
       case JsString(id)                                       => Id[T](id)
       case _                                                  => throw DeserializationException("Id expects string")
     }
   }
 
+  implicit def taggedFormat[F, T](implicit underlying: JsonFormat[F]): JsonFormat[F @@ T] = new JsonFormat[F @@ T] {
+    import tagging._
+
+    override def write(obj: F @@ T): JsValue = underlying.write(obj)
+
+    override def read(json: JsValue): F @@ T = underlying.read(json).tagged[T]
+  }
+
   def NameInPath[T]: PathMatcher1[Name[T]] = new PathMatcher1[Name[T]] {
     def apply(path: Path) = path match {
       case Path.Segment(segment, tail) => Matched(tail, Tuple1(Name[T](segment)))
diff --git a/src/test/scala/xyz/driver/core/JsonTest.scala b/src/test/scala/xyz/driver/core/JsonTest.scala
index 7e8dba2..b845a44 100644
--- a/src/test/scala/xyz/driver/core/JsonTest.scala
+++ b/src/test/scala/xyz/driver/core/JsonTest.scala
@@ -13,6 +13,7 @@ import spray.json._
 import xyz.driver.core.TestTypes.CustomGADT
 import xyz.driver.core.domain.{Email, PhoneNumber}
 import xyz.driver.core.json.enumeratum.HasJsonFormat
+import xyz.driver.core.tagging.Taggable
 import xyz.driver.core.time.TimeOfDay
 
 import scala.collection.immutable.IndexedSeq
@@ -31,6 +32,19 @@ class JsonTest extends FlatSpec with Matchers {
     parsedId should be(referenceId)
   }
 
+  "Json format for @@" should "read and write correct JSON" in {
+    trait Irrelevant
+    val reference = Id[JsonTest]("SomeID").tagged[Irrelevant]
+
+    val format = json.taggedFormat[Id[JsonTest], Irrelevant]
+
+    val writtenJson = format.write(reference)
+    writtenJson shouldBe JsString("SomeID")
+
+    val parsedId: Id[JsonTest] @@ Irrelevant = format.read(writtenJson)
+    parsedId shouldBe reference
+  }
+
   "Json format for Name" should "read and write correct JSON" in {
 
     val referenceName = Name[String]("Homer")