1 files changed, 72 insertions, 0 deletions
diff --git a/scala/ace/src/main/scala/com/github/jodersky/ace/protocol/LinkLayer.scala b/scala/ace/src/main/scala/com/github/jodersky/ace/protocol/LinkLayer.scala
new file mode 100644
index 0000000..5f8d228
--- /dev/null
+++ b/scala/ace/src/main/scala/com/github/jodersky/ace/protocol/LinkLayer.scala
@@ -0,0 +1,72 @@
+package com.github.jodersky.ace.protocol
+
+import scala.collection.mutable.ArrayBuffer
+import scala.concurrent.Future
+import scala.concurrent.ExecutionContext.Implicits.global
+
+class LinkLayer extends ReactiveLayer[Array[Byte], Packet] {
+  import LinkLayer._
+
+  private var state: State = Waiting
+  private val buffer = new ArrayBuffer[Int]
+
+  def receive(data: Array[Byte]) = for (d <- data) receive(d)
+
+  def receive(data: Byte): Unit = {
+    val unsigned = data & 0xff
+
+    state match {
+      case Escaping => {
+        buffer += unsigned
+        state = Receiving
+      }
+      case Waiting => if (unsigned == Start) {
+        buffer.clear()
+        state = Receiving
+      }
+      case Receiving => unsigned match {
+        case Escape => state = Escaping
+        case Start => buffer.clear()
+        case End => {
+          state = Waiting
+          if (checksum(buffer.init.toArray) == buffer.last)
+            notifyHigher(Packet(buffer.init.toArray))
+        }
+        case datum => buffer += datum
+      }
+    }
+  }
+
+  def write(packet: Packet): Future[Packet] = {
+    val buffer = new ArrayBuffer[Int]
+    buffer += Start
+    packet.data foreach { unsigned =>
+      unsigned match {
+        case Start | End | Escape => {
+          buffer += Escape
+          buffer += unsigned
+        }
+        case _ => buffer += unsigned
+      }
+    }
+    buffer += checksum(packet.data)
+    buffer += End
+    writeToLower(buffer.map(_.toByte).toArray).map(_ => packet)
+  }
+}
+
+object LinkLayer {
+  sealed trait State
+  case object Waiting extends State
+  case object Receiving extends State
+  case object Escaping extends State
+
+  final val Escape = 0x02
+  final val Start = 0x03
+  final val End = 0x10
+
+  def checksum(unsignedData: Seq[Int]) = {
+    unsignedData.fold(0)(_ ^ _)
+  }
+
+}
+\ No newline at end of file