Add ability to view alt text by clicking the ALT badge in web UI (#32058)

app/javascript/mastodon/components/alt_text_badge.tsx

@@ -0,0 +1,67 @@
+import { useState, useCallback, useRef } from 'react';
+
+import { FormattedMessage } from 'react-intl';
+
+import Overlay from 'react-overlays/Overlay';
+import type {
+  OffsetValue,
+  UsePopperOptions,
+} from 'react-overlays/esm/usePopper';
+
+const offset = [0, 4] as OffsetValue;
+const popperConfig = { strategy: 'fixed' } as UsePopperOptions;
+
+export const AltTextBadge: React.FC<{
+  description: string;
+}> = ({ description }) => {
+  const anchorRef = useRef<HTMLButtonElement>(null);
+  const [open, setOpen] = useState(false);
+
+  const handleClick = useCallback(() => {
+    setOpen((v) => !v);
+  }, [setOpen]);
+
+  const handleClose = useCallback(() => {
+    setOpen(false);
+  }, [setOpen]);
+
+  return (
+    <>
+      <button
+        ref={anchorRef}
+        className='media-gallery__alt__label'
+        onClick={handleClick}
+      >
+        ALT
+      </button>
+
+      <Overlay
+        rootClose
+        onHide={handleClose}
+        show={open}
+        target={anchorRef.current}
+        placement='top-end'
+        flip
+        offset={offset}
+        popperConfig={popperConfig}
+      >
+        {({ props }) => (
+          <div {...props} className='hover-card-controller'>
+            <div
+              className='media-gallery__alt__popover dropdown-animation'
+              role='tooltip'
+            >
+              <h4>
+                <FormattedMessage
+                  id='alt_text_badge.title'
+                  defaultMessage='Alt text'
+                />
+              </h4>
+              <p>{description}</p>
+            </div>
+          </div>
+        )}
+      </Overlay>
+    </>
+  );
+};

app/javascript/mastodon/components/media_gallery.jsx

@@ -10,6 +10,7 @@ import ImmutablePropTypes from 'react-immutable-proptypes';
 
 import { debounce } from 'lodash';
 
+import { AltTextBadge } from 'mastodon/components/alt_text_badge';
 import { Blurhash } from 'mastodon/components/blurhash';
 import { formatTime } from 'mastodon/features/video';
 
@@ -97,7 +98,7 @@ class Item extends PureComponent {
     }
 
     if (attachment.get('description')?.length > 0) {
-      badges.push(<span key='alt' className='media-gallery__alt__label'>ALT</span>);
+      badges.push(<AltTextBadge key='alt' description={attachment.get('description')} />);
     }
 
     const description = attachment.getIn(['translation', 'description']) || attachment.get('description');
@@ -156,9 +157,9 @@ class Item extends PureComponent {
       const duration = attachment.getIn(['meta', 'original', 'duration']);
 
       if (attachment.get('type') === 'gifv') {
-        badges.push(<span key='gif' className='media-gallery__gifv__label'>GIF</span>);
+        badges.push(<span key='gif' className='media-gallery__alt__label media-gallery__alt__label--non-interactive'>GIF</span>);
       } else {
-        badges.push(<span key='video' className='media-gallery__gifv__label'>{formatTime(Math.floor(duration))}</span>);
+        badges.push(<span key='video' className='media-gallery__alt__label media-gallery__alt__label--non-interactive'>{formatTime(Math.floor(duration))}</span>);
       }
 
       thumbnail = (