added gridstack

src/main/java/com/example/components/GridStackItem.java

@@ -0,0 +1,86 @@
+package com.example.components;
+
+import com.vaadin.flow.component.Component;
+import com.vaadin.flow.component.html.Div;
+
+import java.util.UUID;
+
+/**
+ * A single cell inside a {@link GridStackLayout}. Position/size are written as
+ * {@code gs-*} attributes, which is how gridstack.js reads a widget's initial
+ * placement when {@code makeWidget} converts it client-side (see grid-stack.ts).
+ */
+public class GridStackItem extends Div {
+
+    private final Div content = new Div();
+
+    public GridStackItem(Component... content) {
+        this(UUID.randomUUID().toString(), 0, 0, 4, 3, content);
+    }
+
+    public GridStackItem(String id, int x, int y, int w, int h, Component... content) {
+        addClassName("grid-stack-item");
+        getElement().setAttribute("gs-id", id);
+        getElement().setAttribute("gs-x", String.valueOf(x));
+        getElement().setAttribute("gs-y", String.valueOf(y));
+        getElement().setAttribute("gs-w", String.valueOf(w));
+        getElement().setAttribute("gs-h", String.valueOf(h));
+
+        this.content.addClassName("grid-stack-item-content");
+        add(this.content);
+        this.content.add(content);
+    }
+
+    public void add(Component... components) {
+        content.add(components);
+    }
+
+    public void removeAll() {
+        content.removeAll();
+    }
+
+    public String getItemId() {
+        return getElement().getAttribute("gs-id");
+    }
+
+    public GridStackItem setResizable(boolean resizable) {
+        setBooleanAttribute("gs-no-resize", !resizable);
+        return this;
+    }
+
+    public GridStackItem setMovable(boolean movable) {
+        setBooleanAttribute("gs-no-move", !movable);
+        return this;
+    }
+
+    /** Writes an explicit "true" (gridstack reads this via its own
+     *  {@code Utils.toBool}) or removes the attribute — avoids relying on
+     *  Vaadin's HTML5 empty-string boolean-attribute convention, which
+     *  gridstack's own boolean parsing does not document matching. */
+    private void setBooleanAttribute(String name, boolean value) {
+        if (value) {
+            getElement().setAttribute(name, "true");
+        } else {
+            getElement().removeAttribute(name);
+        }
+    }
+
+    public GridStackItem setMinSize(int minWidth, int minHeight) {
+        getElement().setAttribute("gs-min-w", String.valueOf(minWidth));
+        getElement().setAttribute("gs-min-h", String.valueOf(minHeight));
+        return this;
+    }
+
+    public GridStackItem setPosition(int x, int y, int w, int h) {
+        getElement().setAttribute("gs-x", String.valueOf(x));
+        getElement().setAttribute("gs-y", String.valueOf(y));
+        getElement().setAttribute("gs-w", String.valueOf(w));
+        getElement().setAttribute("gs-h", String.valueOf(h));
+        return this;
+    }
+
+    /** Snapshot of a widget's grid placement, as reported by the client after a
+     *  drag/resize (see {@link GridStackLayout#onLayoutChange(String)}). */
+    public record Position(String id, int x, int y, int w, int h) {
+    }
+}