feat(renderer): drag-to-reorder tabs (dnd-kit)

src/renderer/components/layout/TabBar.tsx

@@ -1,12 +1,92 @@
 import { X } from 'lucide-react';
-import { useFileStore } from '@/stores/file-store';
+import {
+  DndContext,
+  PointerSensor,
+  useSensor,
+  useSensors,
+  closestCenter,
+  type DragEndEvent,
+} from '@dnd-kit/core';
+import {
+  SortableContext,
+  horizontalListSortingStrategy,
+  useSortable,
+} from '@dnd-kit/sortable';
+import { CSS } from '@dnd-kit/utilities';
+import { useFileStore, type OpenTab } from '@/stores/file-store';
 import { cn } from '@/lib/utils';
 
+function SortableTab({
+  tab,
+  isActive,
+  onSelect,
+  onClose,
+}: {
+  tab: OpenTab;
+  isActive: boolean;
+  onSelect: (id: string) => void;
+  onClose: (id: string) => void;
+}) {
+  const { attributes, listeners, setNodeRef, transform, transition, isDragging } = useSortable({
+    id: tab.id,
+  });
+
+  const style = {
+    transform: CSS.Transform.toString(transform),
+    transition,
+    opacity: isDragging ? 0.5 : 1,
+  };
+
+  return (
+    <div
+      ref={setNodeRef}
+      style={style}
+      {...attributes}
+      {...listeners}
+      role="tab"
+      aria-selected={isActive}
+      aria-current={isActive ? 'page' : undefined}
+      data-testid={`tab-${tab.id}`}
+      className={cn(
+        'group flex h-full cursor-pointer select-none items-center gap-1 border-r border-border px-3 text-xs transition-colors',
+        isActive
+          ? 'bg-accent text-accent-foreground'
+          : 'text-muted-foreground hover:bg-muted/50 hover:text-foreground'
+      )}
+      onClick={() => onSelect(tab.id)}
+    >
+      {tab.dirty && (
+        <span
+          className="h-1.5 w-1.5 shrink-0 rounded-full bg-primary"
+          aria-label="Unsaved changes"
+        />
+      )}
+      <span className="max-w-[120px] truncate">{tab.title}</span>
+      <button
+        aria-label={`Close ${tab.title}`}
+        className="ml-1 flex h-4 w-4 shrink-0 items-center justify-center rounded opacity-0 group-hover:opacity-100 hover:bg-muted-foreground/20 transition-opacity"
+        onPointerDown={(e) => e.stopPropagation()}
+        onClick={(e) => {
+          e.stopPropagation();
+          onClose(tab.id);
+        }}
+      >
+        <X className="h-3 w-3" />
+      </button>
+    </div>
+  );
+}
+
 export function TabBar() {
   const openTabs = useFileStore((s) => s.openTabs);
   const activeTabId = useFileStore((s) => s.activeTabId);
   const setActiveTab = useFileStore((s) => s.setActiveTab);
   const closeTab = useFileStore((s) => s.closeTab);
+  const reorderTabs = useFileStore((s) => s.reorderTabs);
+
+  // Require a small drag distance before activating — so a click on the tab
+  // body still triggers `onClick` (dnd-kit's PointerSensor default is 0).
+  const sensors = useSensors(useSensor(PointerSensor, { activationConstraint: { distance: 6 } }));
 
   if (openTabs.length === 0) {
     return (
@@ -16,43 +96,32 @@ export function TabBar() {
     );
   }
 
+  function handleDragEnd(e: DragEndEvent) {
+    const { active, over } = e;
+    if (!over || active.id === over.id) return;
+    const fromIndex = openTabs.findIndex((t) => t.id === active.id);
+    const toIndex = openTabs.findIndex((t) => t.id === over.id);
+    if (fromIndex === -1 || toIndex === -1) return;
+    reorderTabs(fromIndex, toIndex);
+  }
+
   return (
     <div className="flex h-9 items-center border-b border-border bg-card/20 overflow-x-auto">
-      <div className="flex h-full items-center px-1">
-        {openTabs.map((tab) => {
-          const isActive = tab.id === activeTabId;
-          return (
-            <div
-              key={tab.id}
-              role="tab"
-              aria-selected={isActive}
-              aria-current={isActive ? 'page' : undefined}
-              className={cn(
-                'group flex h-full cursor-pointer items-center gap-1 border-r border-border px-3 text-xs transition-colors',
-                isActive
-                  ? 'bg-accent text-accent-foreground'
-                  : 'text-muted-foreground hover:bg-muted/50 hover:text-foreground'
-              )}
-              onClick={() => setActiveTab(tab.id)}
-            >
-              {tab.dirty && (
-                <span className="h-1.5 w-1.5 shrink-0 rounded-full bg-primary" aria-label="Unsaved changes" />
-              )}
-              <span className="truncate max-w-[120px]">{tab.title}</span>
-              <button
-                aria-label={`Close ${tab.title}`}
-                className="ml-1 flex h-4 w-4 shrink-0 items-center justify-center rounded opacity-0 group-hover:opacity-100 hover:bg-muted-foreground/20 transition-opacity"
-                onClick={(e) => {
-                  e.stopPropagation();
-                  closeTab(tab.id);
-                }}
-              >
-                <X className="h-3 w-3" />
-              </button>
-            </div>
-          );
-        })}
-      </div>
+      <DndContext sensors={sensors} collisionDetection={closestCenter} onDragEnd={handleDragEnd}>
+        <SortableContext items={openTabs.map((t) => t.id)} strategy={horizontalListSortingStrategy}>
+          <div className="flex h-full items-center px-1">
+            {openTabs.map((tab) => (
+              <SortableTab
+                key={tab.id}
+                tab={tab}
+                isActive={tab.id === activeTabId}
+                onSelect={setActiveTab}
+                onClose={closeTab}
+              />
+            ))}
+          </div>
+        </SortableContext>
+      </DndContext>
     </div>
   );
 }

tests/component/layout/TabBar.test.tsx

@@ -90,4 +90,27 @@ describe('TabBar', () => {
     const dirtyDot = screen.getByLabelText('Unsaved changes');
     expect(dirtyDot).toBeInTheDocument();
   });
+
+  it('reorders tabs when reorderTabs is called (drag end handler integration)', () => {
+    useFileStore.setState({
+      openTabs: [
+        { id: '/tmp/a.md', path: '/tmp/a.md', title: 'a.md', dirty: false },
+        { id: '/tmp/b.md', path: '/tmp/b.md', title: 'b.md', dirty: false },
+        { id: '/tmp/c.md', path: '/tmp/c.md', title: 'c.md', dirty: false },
+      ],
+      activeTabId: '/tmp/a.md',
+    });
+    render(<TabBar />);
+    // Initial DOM order
+    const initialOrder = screen.getAllByRole('tab').map((el) => el.getAttribute('data-testid'));
+    expect(initialOrder).toEqual(['tab-/tmp/a.md', 'tab-/tmp/b.md', 'tab-/tmp/c.md']);
+
+    // Simulate what dnd-kit's onDragEnd would do: move a.md (idx 0) to idx 2
+    act(() => {
+      useFileStore.getState().reorderTabs(0, 2);
+    });
+
+    const newOrder = screen.getAllByRole('tab').map((el) => el.getAttribute('data-testid'));
+    expect(newOrder).toEqual(['tab-/tmp/b.md', 'tab-/tmp/c.md', 'tab-/tmp/a.md']);
+  });
 });