handle multiple selection with shift

src/main/java/ovh/gasser/newshapes/Selection.java

@@ -2,23 +2,30 @@ package ovh.gasser.newshapes;
 
 import ovh.gasser.newshapes.attributes.SelectionAttributes;
 import ovh.gasser.newshapes.shapes.Shape;
+import ovh.gasser.newshapes.util.Streamable;
 
-public class Selection {
+import java.util.ArrayList;
+import java.util.Iterator;
+import java.util.List;
 
-    private final SelectionAttributes attributes;
-    public final Shape shape;
+public class Selection implements Streamable<Shape> {
+    private final List<Shape> selectedShapes = new ArrayList<>();
 
-    public Selection(final Shape shape, boolean selected) {
-        this(shape);
-        attributes.selected = selected;
+    @Override
+    public Iterator<Shape> iterator() {
+        return selectedShapes.iterator();
     }
 
-    private Selection(final Shape shape) {
-        attributes = (SelectionAttributes) shape.getAttributes(SelectionAttributes.ID);
-        this.shape = shape;
+    public void clear() {
+        for (Shape shape : selectedShapes) {
+            shape.addAttributes(new SelectionAttributes(false));
+        }
+
+        selectedShapes.clear();
     }
 
-    public void unselect() {
-        attributes.selected = false;
+    public void add(Shape s) {
+        selectedShapes.add(s);
+        s.addAttributes(new SelectionAttributes(true));
     }
 }