1 files changed, 104 insertions, 0 deletions
diff --git a/core-rest/src/main/scala/xyz/driver/core/rest/PatchDirectives.scala b/core-rest/src/main/scala/xyz/driver/core/rest/PatchDirectives.scala
new file mode 100644
index 0000000..f33bf9d
--- /dev/null
+++ b/core-rest/src/main/scala/xyz/driver/core/rest/PatchDirectives.scala
@@ -0,0 +1,104 @@
+package xyz.driver.core.rest
+
+import akka.http.javadsl.server.Rejections
+import akka.http.scaladsl.marshallers.sprayjson.SprayJsonSupport
+import akka.http.scaladsl.model.{ContentTypeRange, HttpCharsets, MediaType}
+import akka.http.scaladsl.server._
+import akka.http.scaladsl.unmarshalling.{FromEntityUnmarshaller, Unmarshaller}
+import spray.json._
+
+import scala.concurrent.Future
+import scala.util.{Failure, Success, Try}
+
+trait PatchDirectives extends Directives with SprayJsonSupport {
+
+  /** Media type for patches to JSON values, as specified in [[https://tools.ietf.org/html/rfc7396 RFC 7396]]. */
+  val `application/merge-patch+json`: MediaType.WithFixedCharset =
+    MediaType.applicationWithFixedCharset("merge-patch+json", HttpCharsets.`UTF-8`)
+
+  /** Wraps a JSON value that represents a patch.
+    * The patch must given in the format specified in [[https://tools.ietf.org/html/rfc7396 RFC 7396]]. */
+  case class PatchValue(value: JsValue) {
+
+    /** Applies this patch to a given original JSON value. In other words, merges the original with this "diff". */
+    def applyTo(original: JsValue): JsValue = mergeJsValues(original, value)
+  }
+
+  /** Witness that the given patch may be applied to an original domain value.
+    * @tparam A type of the domain value
+    * @param patch the patch that may be applied to a domain value
+    * @param format a JSON format that enables serialization and deserialization of a domain value */
+  case class Patchable[A](patch: PatchValue, format: RootJsonFormat[A]) {
+
+    /** Applies the patch to a given domain object. The result will be a combination
+      * of the original value, updates with the fields specified in this witness' patch. */
+    def applyTo(original: A): A = {
+      val serialized   = format.write(original)
+      val merged       = patch.applyTo(serialized)
+      val deserialized = format.read(merged)
+      deserialized
+    }
+  }
+
+  implicit def patchValueUnmarshaller: FromEntityUnmarshaller[PatchValue] =
+    Unmarshaller.byteStringUnmarshaller
+      .andThen(sprayJsValueByteStringUnmarshaller)
+      .forContentTypes(ContentTypeRange(`application/merge-patch+json`))
+      .map(js => PatchValue(js))
+
+  implicit def patchableUnmarshaller[A](
+      implicit patchUnmarshaller: FromEntityUnmarshaller[PatchValue],
+      format: RootJsonFormat[A]): FromEntityUnmarshaller[Patchable[A]] = {
+    patchUnmarshaller.map(patch => Patchable[A](patch, format))
+  }
+
+  protected def mergeObjects(oldObj: JsObject, newObj: JsObject, maxLevels: Option[Int] = None): JsObject = {
+    JsObject((oldObj.fields.keys ++ newObj.fields.keys).map({ key =>
+      val oldValue = oldObj.fields.getOrElse(key, JsNull)
+      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 mergePatch[T](patchable: Patchable[T], retrieve: => Future[Option[T]]): Directive1[T] =
+    Directive { inner => requestCtx =>
+      onSuccess(retrieve)({
+        case Some(oldT) =>
+          Try(patchable.applyTo(oldT))
+            .transform[Route](
+              mergedT => scala.util.Success(inner(Tuple1(mergedT))), {
+                case jsonException: DeserializationException =>
+                  Success(reject(Rejections.malformedRequestContent(jsonException.getMessage, jsonException)))
+                case t => Failure(t)
+              }
+            )
+            .get // intentionally re-throw all other errors
+        case None => reject()
+      })(requestCtx)
+    }
+}
+
+object PatchDirectives extends PatchDirectives