1 files changed, 83 insertions, 0 deletions
diff --git a/scala/ace/src/main/scala/com/github/jodersky/ace/Framer.scala b/scala/ace/src/main/scala/com/github/jodersky/ace/Framer.scala
new file mode 100644
index 0000000..8546c48
--- /dev/null
+++ b/scala/ace/src/main/scala/com/github/jodersky/ace/Framer.scala
@@ -0,0 +1,83 @@
+package com.github.jodersky.ace
+
+import scala.collection.mutable.ArrayBuffer
+import scala.concurrent.Future
+import scala.concurrent.ExecutionContext.Implicits.global
+
+/** A framer takes bytes (as unsigned integers) and creates frames.
+ *  Note that the input type of this reactive layer is also a sequence of
+ *  integers for performance reasons (i.e. a future will not be created for every byte sent).
+ */
+class Framer extends ReactiveLayer[Seq[Int], Seq[Int]] {
+  import Framer._
+
+  private var state: State = Waiting
+  private val buffer = new ArrayBuffer[Int]
+
+  protected def receive(bytes: Seq[Int]) = bytes foreach receive
+  
+  protected def receive(byte: Int): Unit = {
+
+    state match {
+      case Escaping => {
+        buffer += byte
+        state = Receiving
+      }
+      case Waiting => if (byte == Start) {
+        buffer.clear()
+        state = Receiving
+      }
+      case Receiving => byte match {
+        case Escape => state = Escaping
+        case Start => buffer.clear()
+        case Stop => {
+          state = Waiting
+          if (checksum(buffer.init) == buffer.last)
+            notifyHigher(buffer.init)
+        }
+        case datum => buffer += datum
+      }
+    }
+  }
+
+  def send(data: Seq[Int]): Future[Seq[Int]] = {
+    val buffer = new ArrayBuffer[Int]
+    
+    buffer += Start    
+    data foreach { byte =>
+      byte match {
+        case Start | Stop | Escape => {
+          buffer += Escape
+          buffer += byte
+        }
+        case _ => buffer += byte
+      }
+    }
+    val c = checksum(data)
+    c match {
+        case Start | Stop | Escape => {
+          buffer += Escape
+          buffer += c
+        }
+        case _ => buffer += c
+      }
+    buffer += Stop
+    sendToLower(buffer) map (_ => data)
+  }
+}
+
+object Framer {
+  sealed trait State
+  case object Waiting extends State
+  case object Receiving extends State
+  case object Escaping extends State
+
+  final val Escape = 0x10
+  final val Start = 0x02
+  final val Stop = 0x03
+
+  def checksum(unsignedData: Seq[Int]) = {
+    unsignedData.fold(0)(_ ^ _)
+  }
+
+}
+\ No newline at end of file