1 files changed, 69 insertions, 0 deletions
diff --git a/pointedthing.go b/pointedthing.go
new file mode 100644
index 0000000..c73130f
--- /dev/null
+++ b/pointedthing.go
@@ -0,0 +1,69 @@
+package mt
+
+import (
+	"fmt"
+	"io"
+)
+
+type PointedThing interface {
+	pt()
+}
+
+func (*PointedNode) pt() {}
+func (*PointedAO) pt()   {}
+
+type PointedNode struct {
+	Under, Above [3]int16
+}
+
+func PointedSameNode(pos [3]int16) PointedThing {
+	return &PointedNode{pos, pos}
+}
+
+type PointedAO struct {
+	ID AOID
+}
+
+func writePointedThing(w io.Writer, pt PointedThing) error {
+	buf := make([]byte, 2)
+	buf[0] = 0
+	switch pt.(type) {
+	case nil:
+		buf[1] = 0
+	case *PointedNode:
+		buf[1] = 1
+	case *PointedAO:
+		buf[1] = 2
+	default:
+		panic(pt)
+	}
+	if _, err := w.Write(buf); err != nil {
+		return err
+	}
+	if pt == nil {
+		return nil
+	}
+	return serialize(w, pt)
+}
+
+func readPointedThing(r io.Reader) (PointedThing, error) {
+	buf := make([]byte, 2)
+	if _, err := io.ReadFull(r, buf); err != nil {
+		return nil, err
+	}
+	if buf[0] != 0 {
+		return nil, fmt.Errorf("unsupported PointedThing version: %d", buf[0])
+	}
+	var pt PointedThing
+	switch buf[1] {
+	case 0:
+		return nil, nil
+	case 1:
+		pt = new(PointedNode)
+	case 2:
+		pt = new(PointedAO)
+	case 3:
+		return nil, fmt.Errorf("invalid PointedThing type: %d", buf[1])
+	}
+	return pt, deserialize(r, pt)
+}