From af6845cc08ae223ad67ebad61559d8264fd3346b Mon Sep 17 00:00:00 2001
From: Jakob Odersky <jakob@odersky.com>
Date: Tue, 13 Feb 2018 15:09:31 -0800
Subject: Initial commit

---
 src/main/scala/DerivedFormats.scala | 55 +++++++++++++++++++++++++++++++++++++
 1 file changed, 55 insertions(+)
 create mode 100644 src/main/scala/DerivedFormats.scala

(limited to 'src/main/scala/DerivedFormats.scala')

diff --git a/src/main/scala/DerivedFormats.scala b/src/main/scala/DerivedFormats.scala
new file mode 100644
index 0000000..6c2396e
--- /dev/null
+++ b/src/main/scala/DerivedFormats.scala
@@ -0,0 +1,55 @@
+import magnolia._
+import spray.json._
+
+import scala.language.experimental.macros
+
+trait JsonFormatDerivation extends DefaultJsonProtocol {
+  type Typeclass[T] = JsonFormat[T]
+
+  def combine[T](ctx: CaseClass[JsonFormat, T]): JsonFormat[T] = new JsonFormat[T] {
+    override def write(value: T): JsValue = {
+      val fields: Seq[(String, JsValue)] = ctx.parameters.map { param =>
+        param.label -> param.typeclass.write(param.dereference(value))
+      }
+      JsObject(fields: _*)
+    }
+    override def read(value: JsValue): T = value match {
+      case obj: JsObject =>
+        ctx.construct { param =>
+          param.typeclass.read(obj.fields(param.label))
+        }
+      case js =>
+        deserializationError(s"Cannot read JSON '$js' as a ${ctx.typeName}")
+    }
+  }
+
+  def dispatch[T](ctx: SealedTrait[JsonFormat, T]): JsonFormat[T] = new JsonFormat[T] {
+    override def write(value: T): JsValue = {
+      ctx.dispatch(value) { sub =>
+        val obj = sub.typeclass.write(sub.cast(value)).asJsObject
+        JsObject((obj.fields ++ Map("type" -> JsString(sub.label))).toSeq: _*)
+      }
+    }
+    override def read(value: JsValue): T = value match {
+      case obj: JsObject if obj.fields.contains("type") =>
+        val fieldName = obj.fields("type").convertTo[String]
+
+        ctx.subtypes.find(_.label == fieldName) match {
+          case Some(tpe) => tpe.typeclass.read(obj)
+          case None =>
+            deserializationError(
+              s"Cannot deserialize JSON to ${ctx.typeName} because type field '${fieldName}' has an unsupported value.")
+        }
+
+      case js =>
+        deserializationError(s"Cannot read JSON '$js' as a ${ctx.typeName}")
+    }
+
+  }
+
+  implicit def gen[T]: JsonFormat[T] = macro Magnolia.gen[T]
+
+}
+object JsonFormatDerivation extends JsonFormatDerivation
+
+trait DerivedFormats extends JsonFormatDerivation
-- 
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