Add hover cards in web UI (#30754)

Co-authored-by: Renaud Chaput <renchap@gmail.com>

app/javascript/hooks/useLinks.ts

@@ -0,0 +1,61 @@
+import { useCallback } from 'react';
+
+import { useHistory } from 'react-router-dom';
+
+import { openURL } from 'mastodon/actions/search';
+import { useAppDispatch } from 'mastodon/store';
+
+const isMentionClick = (element: HTMLAnchorElement) =>
+  element.classList.contains('mention');
+
+const isHashtagClick = (element: HTMLAnchorElement) =>
+  element.textContent?.[0] === '#' ||
+  element.previousSibling?.textContent?.endsWith('#');
+
+export const useLinks = () => {
+  const history = useHistory();
+  const dispatch = useAppDispatch();
+
+  const handleHashtagClick = useCallback(
+    (element: HTMLAnchorElement) => {
+      const { textContent } = element;
+
+      if (!textContent) return;
+
+      history.push(`/tags/${textContent.replace(/^#/, '')}`);
+    },
+    [history],
+  );
+
+  const handleMentionClick = useCallback(
+    (element: HTMLAnchorElement) => {
+      dispatch(
+        openURL(element.href, history, () => {
+          window.location.href = element.href;
+        }),
+      );
+    },
+    [dispatch, history],
+  );
+
+  const handleClick = useCallback(
+    (e: React.MouseEvent) => {
+      const target = (e.target as HTMLElement).closest('a');
+
+      if (!target || e.button !== 0 || e.ctrlKey || e.metaKey) {
+        return;
+      }
+
+      if (isMentionClick(target)) {
+        e.preventDefault();
+        handleMentionClick(target);
+      } else if (isHashtagClick(target)) {
+        e.preventDefault();
+        handleHashtagClick(target);
+      }
+    },
+    [handleMentionClick, handleHashtagClick],
+  );
+
+  return handleClick;
+};