From c5fe23594f66225eb18bf4e67472cd80023eb448 Mon Sep 17 00:00:00 2001
From: Jakob Odersky <jakob@odersky.com>
Date: Thu, 8 Mar 2018 16:53:44 -0800
Subject: Refactor build to use sbt-crossproject

---
 shared/src/main/scala/DerivedFormats.scala | 108 +++++++++++++++++++++++++++++
 1 file changed, 108 insertions(+)
 create mode 100644 shared/src/main/scala/DerivedFormats.scala

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

diff --git a/shared/src/main/scala/DerivedFormats.scala b/shared/src/main/scala/DerivedFormats.scala
new file mode 100644
index 0000000..d0cac38
--- /dev/null
+++ b/shared/src/main/scala/DerivedFormats.scala
@@ -0,0 +1,108 @@
+package spray.json
+
+import magnolia._
+
+import scala.language.experimental.macros
+
+/** Mixin that enables derivation of JSON formats for any product
+  * (case classes) or coproduct (sealed traits) types. */
+trait DerivedFormats { self: BasicFormats =>
+  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 =>
+          if (ctx.isObject) {
+            ctx.rawConstruct(Seq.empty)
+          } else {
+            ctx.construct { param =>
+              param.typeclass.read(obj.fields(param.label))
+            }
+          }
+        case js =>
+          deserializationError(
+            s"Cannot read JSON '$js' as a ${ctx.typeName.full}")
+      }
+    }
+
+  def dispatch[T](ctx: SealedTrait[JsonFormat, T]): JsonFormat[T] = {
+    val typeFieldName = ctx.annotations
+      .collectFirst {
+        case g: gadt => g.typeFieldName
+      }
+      .getOrElse("type")
+
+    new JsonFormat[T] {
+      override def write(value: T): JsValue = ctx.dispatch(value) { sub =>
+        sub.typeclass.write(sub.cast(value)) match {
+          case obj: JsObject =>
+            JsObject(
+              (Map(typeFieldName -> JsString(sub.typeName.short)) ++
+                obj.fields).toSeq: _*)
+          case js => js
+        }
+      }
+
+      override def read(js: JsValue): T = {
+        val typeName: String = js match {
+          case obj: JsObject if obj.fields.contains(typeFieldName) =>
+            obj.fields(typeFieldName).convertTo[String]
+          case JsString(str) =>
+            str
+          case _ =>
+            deserializationError(
+              s"Cannot deserialize JSON to ${ctx.typeName.full} " +
+                "because serialized type cannot be determined.")
+        }
+
+        ctx.subtypes.find(_.typeName.short == typeName) match {
+          case Some(tpe) => tpe.typeclass.read(js)
+          case None =>
+            deserializationError(
+              s"Cannot deserialize JSON to ${ctx.typeName.full} " +
+                s"because type '${typeName}' is unsupported.")
+        }
+      }
+    }
+  }
+
+  def jsonFormat[T]: RootJsonFormat[T] =
+    macro DerivedFormatMacros.derivedFormat[T]
+
+}
+object DerivedFormats extends DerivedFormats with DefaultJsonProtocol
+
+trait ImplicitDerivedFormats extends DerivedFormats { self: BasicFormats =>
+  implicit def implicitJsonFormat[T]: RootJsonFormat[T] =
+    macro DerivedFormatMacros.derivedFormat[T]
+}
+object ImplicitDerivedFormats
+    extends ImplicitDerivedFormats
+    with DefaultJsonProtocol
+
+object DerivedFormatMacros {
+  import scala.reflect.macros.whitebox._
+
+  /** Utility that converts a magnolia-generated JsonFormat to a RootJsonFormat. */
+  def derivedFormat[T: c.WeakTypeTag](c: Context): c.Tree = {
+    import c.universe._
+    val tpe = weakTypeOf[T].typeSymbol.asType
+    val sprayPkg = c.mirror.staticPackage("spray.json")
+    val valName = TermName(c.freshName("format"))
+    q"""{
+      val $valName = ${Magnolia.gen[T](c)}
+      new $sprayPkg.RootJsonFormat[$tpe] {
+        def write(value: $tpe) = $valName.write(value)
+        def read(value: $sprayPkg.JsValue) = $valName.read(value)
+      }
+    }"""
+  }
+}
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