Add a class for drawing hilbert curves

app/src/main/java/ch/nuth/zhaw/exbox/HilbertServer.java

@@ -0,0 +1,40 @@
+package ch.nuth.zhaw.exbox;
+
+/**
+ * Provides the functionality to draw hilbert curves.
+ */
+public class HilbertServer implements CommandExecutor {
+    @Override
+    public String execute(String command) {
+        int depth = Integer.parseInt(command);
+        Turtle turtle = Turtle.instance();
+        double dist = 0.8 / (Math.pow(2, depth + 1) - 1);
+        turtle.reset(0.1, 0.1);
+        hilbert(turtle, depth, dist, -90);
+        return turtle.getTrace();
+    }
+
+    private void hilbert(Turtle turtle, int depth, double dist, double angle) {
+        if (depth > 0) {
+            turtle.turn(-angle);
+            hilbert(turtle, depth - 1, dist, -angle);
+            turtle.move(dist);
+            turtle.turn(angle);
+            hilbert(turtle, depth - 1, dist, angle);
+            turtle.move(dist);
+            hilbert(turtle, depth - 1, dist, angle);
+            turtle.turn(angle);
+            turtle.move(dist);
+            hilbert(turtle, depth - 1, dist, -angle);
+            turtle.turn(-angle);
+        } else {
+            turtle.turn(-angle);
+            turtle.move(dist);
+            turtle.turn(angle);
+            turtle.move(dist);
+            turtle.turn(angle);
+            turtle.move(dist);
+            turtle.turn(-angle);
+        }
+    }
+}