Add PatchSupport trait and tests

1 files changed, 81 insertions, 0 deletions

diff --git a/src/main/scala/xyz/driver/core/rest/PatchSupport.scala b/src/main/scala/xyz/driver/core/rest/PatchSupport.scala
new file mode 100644
index 0000000..5fd9149
--- /dev/null
+++ b/src/main/scala/xyz/driver/core/rest/PatchSupport.scala
@@ -0,0 +1,81 @@
+package xyz.driver.core.rest
+
+import akka.http.javadsl.server.Rejections
+import akka.http.scaladsl.marshallers.sprayjson.SprayJsonSupport
+import akka.http.scaladsl.server.{Directive, Directive1, Directives, Route}
+import spray.json._
+import xyz.driver.core.Id
+
+import scala.concurrent.Future
+
+trait PatchSupport extends Directives with SprayJsonSupport {
+
+  trait PatchRetrievable[T] {
+    def apply(id: Id[T]): Future[Option[T]]
+  }
+
+  protected def mergeObjects(oldObj: JsObject, newObj: JsObject, maxLevels: Option[Int] = None): JsObject = {
+    JsObject(oldObj.fields.map({
+      case (key, oldValue) =>
+        val newValue = newObj.fields.get(key).fold(oldValue)(mergeJsValues(oldValue, _, maxLevels.map(_ - 1)))
+        key -> newValue
+    })(collection.breakOut): _*)
+  }
+
+  protected def mergeJsValues(oldValue: JsValue, newValue: JsValue, maxLevels: Option[Int] = None): JsValue = {
+    def mergeError(typ: String): Nothing =
+      deserializationError(s"Expected $typ value, got $newValue")
+
+    if (maxLevels.exists(_ < 0)) oldValue
+    else {
+      (oldValue, newValue) match {
+        case (_: JsString, newString @ (JsString(_) | JsNull)) => newString
+        case (_: JsString, _)                                  => mergeError("string")
+        case (_: JsNumber, newNumber @ (JsNumber(_) | JsNull)) => newNumber
+        case (_: JsNumber, _)                                  => mergeError("number")
+        case (_: JsBoolean, newBool @ (JsBoolean(_) | JsNull)) => newBool
+        case (_: JsBoolean, _)                                 => mergeError("boolean")
+        case (_: JsArray, newArr @ (JsArray(_) | JsNull))      => newArr
+        case (_: JsArray, _)                                   => mergeError("array")
+        case (oldObj: JsObject, newObj: JsObject)              => mergeObjects(oldObj, newObj)
+        case (_: JsObject, JsNull)                             => JsNull
+        case (_: JsObject, _)                                  => mergeError("object")
+        case (JsNull, _)                                       => newValue
+      }
+    }
+  }
+
+  def as[T](
+      implicit patchable: PatchRetrievable[T],
+      jsonFormat: RootJsonFormat[T]): (PatchRetrievable[T], RootJsonFormat[T]) =
+    (patchable, jsonFormat)
+
+  def patch[T](patchable: (PatchRetrievable[T], RootJsonFormat[T]), id: Id[T]): Directive1[T] = Directive {
+    inner => requestCtx =>
+      import requestCtx.executionContext
+      val retriever                              = patchable._1
+      implicit val jsonFormat: RootJsonFormat[T] = patchable._2
+      Directives.patch {
+        entity(as[JsValue]) { newValue =>
+          onSuccess(retriever(id).map(_.map(_.toJson))) {
+            case Some(oldValue) =>
+              val mergedObj = mergeJsValues(oldValue, newValue)
+              util
+                .Try(mergedObj.convertTo[T])
+                .transform[Route](
+                  mergedT => util.Success(inner(Tuple1(mergedT))), {
+                    case jsonException: DeserializationException =>
+                      util.Success(reject(Rejections.malformedRequestContent(jsonException.getMessage, jsonException)))
+                    case t => util.Failure(t)
+                  }
+                )
+                .get // intentionally re-throw all other errors
+            case None =>
+              reject()
+          }
+        }
+      }(requestCtx)
+  }
+}
+
+object PatchSupport extends PatchSupport