add back btn for mobile view (#1861)

src/app/components/BackRouteHandler.tsx

@@ -0,0 +1,86 @@
+import { ReactNode, useCallback } from 'react';
+import { matchPath, useLocation, useNavigate } from 'react-router-dom';
+import {
+  getDirectPath,
+  getExplorePath,
+  getHomePath,
+  getInboxPath,
+  getSpacePath,
+} from '../pages/pathUtils';
+import { DIRECT_PATH, EXPLORE_PATH, HOME_PATH, INBOX_PATH, SPACE_PATH } from '../pages/paths';
+
+type BackRouteHandlerProps = {
+  children: (onBack: () => void) => ReactNode;
+};
+export function BackRouteHandler({ children }: BackRouteHandlerProps) {
+  const navigate = useNavigate();
+  const location = useLocation();
+
+  const goBack = useCallback(() => {
+    if (
+      matchPath(
+        {
+          path: HOME_PATH,
+          caseSensitive: true,
+          end: false,
+        },
+        location.pathname
+      )
+    ) {
+      navigate(getHomePath());
+      return;
+    }
+    if (
+      matchPath(
+        {
+          path: DIRECT_PATH,
+          caseSensitive: true,
+          end: false,
+        },
+        location.pathname
+      )
+    ) {
+      navigate(getDirectPath());
+      return;
+    }
+    const spaceMatch = matchPath(
+      {
+        path: SPACE_PATH,
+        caseSensitive: true,
+        end: false,
+      },
+      location.pathname
+    );
+    if (spaceMatch?.params.spaceIdOrAlias) {
+      navigate(getSpacePath(spaceMatch.params.spaceIdOrAlias));
+      return;
+    }
+    if (
+      matchPath(
+        {
+          path: EXPLORE_PATH,
+          caseSensitive: true,
+          end: false,
+        },
+        location.pathname
+      )
+    ) {
+      navigate(getExplorePath());
+      return;
+    }
+    if (
+      matchPath(
+        {
+          path: INBOX_PATH,
+          caseSensitive: true,
+          end: false,
+        },
+        location.pathname
+      )
+    ) {
+      navigate(getInboxPath());
+    }
+  }, [navigate, location]);
+
+  return children(goBack);
+}