3 files changed, 99 insertions, 1 deletions
diff --git a/src/main/scala/xyz/driver/core/json.scala b/src/main/scala/xyz/driver/core/json.scala
index 66cae52..277543b 100644
--- a/src/main/scala/xyz/driver/core/json.scala
+++ b/src/main/scala/xyz/driver/core/json.scala
@@ -107,4 +107,52 @@ object json {
       case _               => deserializationError(s"Expected number as ${typeOf[T].getClass.getName}, but got " + json)
     }
   }
+
+  class GadtJsonFormat[T: TypeTag](typeField: String,
+                                   typeValue: PartialFunction[T, String],
+                                   jsonFormat: PartialFunction[String, JsonFormat[_ <: T]])
+      extends RootJsonFormat[T] {
+
+    def write(value: T): JsValue = {
+
+      val valueType = typeValue.applyOrElse(value, { v: T =>
+        deserializationError(s"No Value type for this type of ${typeOf[T].getClass.getName}: " + v)
+      })
+
+      val valueFormat =
+        jsonFormat.applyOrElse(valueType, { f: String =>
+          deserializationError(s"No Json format for this type of $valueType")
+        })
+
+      valueFormat.asInstanceOf[JsonFormat[T]].write(value) match {
+        case JsObject(fields) => JsObject(fields ++ Map(typeField -> JsString(valueType)))
+        case _                => serializationError(s"${typeOf[T].getClass.getName} serialized not to a JSON object")
+      }
+    }
+
+    def read(json: JsValue): T = json match {
+      case JsObject(fields) =>
+        val valueJson = JsObject(fields.filterNot(_._1 == typeField))
+        fields(typeField) match {
+          case JsString(valueType) =>
+            val valueFormat = jsonFormat.applyOrElse(valueType, { t: String =>
+              deserializationError(s"Unknown ${typeOf[T].getClass.getName} type ${fields(typeField)}")
+            })
+            valueFormat.read(valueJson)
+          case _ =>
+            deserializationError(s"Unknown ${typeOf[T].getClass.getName} type ${fields(typeField)}")
+        }
+      case _ =>
+        deserializationError(s"Expected Json Object as ${typeOf[T].getClass.getName}, but got " + json)
+    }
+  }
+
+  object GadtJsonFormat {
+
+    def create[T: TypeTag](typeField: String)(typeValue: PartialFunction[T, String])(
+            jsonFormat: PartialFunction[String, JsonFormat[_ <: T]]) = {
+
+      new GadtJsonFormat[T](typeField, typeValue, jsonFormat)
+    }
+  }
 }
diff --git a/src/test/scala/xyz/driver/core/JsonTest.scala b/src/test/scala/xyz/driver/core/JsonTest.scala
index c113c59..eb8d5d8 100644
--- a/src/test/scala/xyz/driver/core/JsonTest.scala
+++ b/src/test/scala/xyz/driver/core/JsonTest.scala
@@ -1,9 +1,11 @@
 package xyz.driver.core
 
 import org.scalatest.{FlatSpec, Matchers}
-import xyz.driver.core.json.{EnumJsonFormat, ValueClassFormat}
+import xyz.driver.core.json.{EnumJsonFormat, GadtJsonFormat, ValueClassFormat}
 import xyz.driver.core.revision.Revision
 import xyz.driver.core.time.provider.SystemTimeProvider
+import spray.json._
+import xyz.driver.core.TestTypes.CustomGADT
 
 class JsonTest extends FlatSpec with Matchers {
 
@@ -98,4 +100,38 @@ class JsonTest extends FlatSpec with Matchers {
     parsedValue1 should be(referenceValue1)
     parsedValue2 should be(referenceValue2)
   }
+
+  "Json format for classes GADT" should "read and write correct JSON" in {
+
+    import CustomGADT._
+    import DefaultJsonProtocol._
+    implicit val case1Format = jsonFormat1(GadtCase1)
+    implicit val case2Format = jsonFormat1(GadtCase2)
+    implicit val case3Format = jsonFormat1(GadtCase3)
+
+    val format = GadtJsonFormat.create[CustomGADT]("gadtTypeField") {
+      case t1: CustomGADT.GadtCase1 => "case1"
+      case t2: CustomGADT.GadtCase2 => "case2"
+      case t3: CustomGADT.GadtCase3 => "case3"
+    } {
+      case "case1" => case1Format
+      case "case2" => case2Format
+      case "case3" => case3Format
+    }
+
+    val referenceValue1 = CustomGADT.GadtCase1("4")
+    val referenceValue2 = CustomGADT.GadtCase2("Hi!")
+
+    val writtenJson1 = format.write(referenceValue1)
+    writtenJson1 should be("{\n \"field\": \"4\",\n\"gadtTypeField\": \"case1\"\n}".parseJson)
+
+    val writtenJson2 = format.write(referenceValue2)
+    writtenJson2 should be("{\"field\":\"Hi!\",\"gadtTypeField\":\"case2\"}".parseJson)
+
+    val parsedValue1 = format.read(writtenJson1)
+    val parsedValue2 = format.read(writtenJson2)
+
+    parsedValue1 should be(referenceValue1)
+    parsedValue2 should be(referenceValue2)
+  }
 }
diff --git a/src/test/scala/xyz/driver/core/TestTypes.scala b/src/test/scala/xyz/driver/core/TestTypes.scala
new file mode 100644
index 0000000..bb25deb
--- /dev/null
+++ b/src/test/scala/xyz/driver/core/TestTypes.scala
@@ -0,0 +1,14 @@
+package xyz.driver.core
+
+object TestTypes {
+
+  sealed trait CustomGADT {
+    val field: String
+  }
+
+  object CustomGADT {
+    final case class GadtCase1(field: String) extends CustomGADT
+    final case class GadtCase2(field: String) extends CustomGADT
+    final case class GadtCase3(field: String) extends CustomGADT
+  }
+}