fix(ui): make the queue button say whether the queue is open

It looked identical in both states, so the only way to tell what
pressing it would do was to look at the other side of the window and
infer it -- and for anyone not looking there was nothing to infer from:
no aria-expanded, no aria-controls, no drawn state.

The state is reflected *from the panel* rather than kept beside the
click. This button is not the only thing that opens the queue --
now-playing-view sets the same attribute, because it hides the bar the
button lives in -- so a flag maintained by the click handler would be
right until something else opened the panel and then quietly wrong.
The panel's `open` attribute stays the one fact; a MutationObserver
reflects it.

Refs #26

e2e/specs/queue-toggle-state.spec.ts

@@ -0,0 +1,66 @@
+import { test, expect } from '../support/fixtures.js';
+
+/**
+ * The queue button says whether the queue is open.
+ *
+ * It used to look identical in both states, so the only way to tell
+ * what pressing it would do was to look at the other side of the window
+ * and infer it — and for anyone not looking at all there was nothing to
+ * infer from: no `aria-expanded`, no `aria-controls`, no pressed state.
+ *
+ * The state is reflected *from the panel*, not kept beside the click,
+ * because the button is not the only thing that opens the queue —
+ * `now-playing-view` sets the same attribute, since it hides the bar
+ * this button lives in. A flag maintained by the click handler would be
+ * right until something else opened the panel and then quietly wrong,
+ * which is the second test here.
+ */
+test.describe('the queue toggle', () => {
+  test('reports open and closed, and names what it controls', async ({
+    app,
+  }) => {
+    const toggle = app.locator('#queue-button');
+
+    await expect(toggle).toHaveAttribute('aria-controls', 'queue-panel');
+    await expect(toggle).toHaveAttribute('aria-expanded', 'false');
+
+    await toggle.click();
+    await expect(toggle).toHaveAttribute('aria-expanded', 'true');
+
+    // The state is not only in the accessibility tree: a control that
+    // announces a state it does not draw is half a fix.
+    //
+    // Background rather than colour, because the pointer is still on
+    // the button after the click and `:hover` paints it the same accent
+    // the open state does -- so a colour comparison here passes on the
+    // broken build and proves nothing.
+    const [open, closed] = await toggle.evaluate((el) => {
+      const now = getComputedStyle(el).backgroundColor;
+
+      el.setAttribute('aria-expanded', 'false');
+      const shut = getComputedStyle(el).backgroundColor;
+
+      el.setAttribute('aria-expanded', 'true');
+
+      return [now, shut];
+    });
+
+    expect(open).not.toBe(closed);
+
+    await toggle.click();
+    await expect(toggle).toHaveAttribute('aria-expanded', 'false');
+  });
+
+  test('follows the panel when something else opens it', async ({ app }) => {
+    const toggle = app.locator('#queue-button');
+
+    await expect(toggle).toHaveAttribute('aria-expanded', 'false');
+
+    // Exactly what `now-playing-view`'s queue button does.
+    await app.evaluate(() =>
+      document.getElementById('queue-panel')?.setAttribute('open', ''),
+    );
+
+    await expect(toggle).toHaveAttribute('aria-expanded', 'true');
+  });
+});

frontend/index.css

@@ -207,6 +207,17 @@ body div.sidebar {
         color: var(--yj-accent, #ffd43b);
     }
 
+    /* An open queue is a state this button can be in, and it used to
+       look exactly like the closed one -- so the only way to tell what
+       pressing it would do was to look at the other side of the window
+       and infer it. `aria-expanded` is the same fact for anyone not
+       looking at all, and it points at the panel it controls. */
+    #queue-button[aria-expanded='true'] {
+        color: var(--yj-accent, #ffd43b);
+        background: var(--yj-bg-overlay, #404040);
+        border-radius: 4px;
+    }
+
     #queue-button.drag-over {
         color: var(--yj-accent, #ffd43b);
         outline: 2px dashed var(--yj-accent, #ffd43b);

frontend/index.html

@@ -37,7 +37,8 @@
     <footer class="bottom-bar">
         <now-playing></now-playing>
         <audio-player></audio-player>
-        <button aria-label="Toggle queue" id="queue-button">
+        <button aria-label="Toggle queue" aria-controls="queue-panel" aria-expanded="false"
+            id="queue-button">
             <wa-icon name="list"></wa-icon>
         </button>
     </footer>

frontend/index.ts

@@ -521,6 +521,28 @@ if (queueButton && queuePanel) {
         }
     });
 
+    // The button says whether the panel is open, and it learns that
+    // from the panel rather than from its own click handler.
+    //
+    // It is not the only thing that opens the queue -- `now-playing-view`
+    // sets the same attribute, because it hides the bar this button
+    // lives in -- so a state kept beside the click would be right until
+    // something else opened the panel and then quietly wrong. The panel's
+    // `open` attribute is the one fact; this reflects it.
+    const reflectQueueState = () => {
+        queueButton.setAttribute(
+            'aria-expanded',
+            String(queuePanel.hasAttribute('open')),
+        );
+    };
+
+    new MutationObserver(reflectQueueState).observe(queuePanel, {
+        attributes: true,
+        attributeFilter: ['open'],
+    });
+
+    reflectQueueState();
+
     // ---------------------------------------------------------------
     // Queue button as drop target (when queue panel is closed)
     // ---------------------------------------------------------------