feat(messages): word diff of the last edit on "(edited)" hover (#144)

Hovering or focusing "(edited)" shows a tooltip with only the most recent
edit as a word diff — removed words struck, added words bold — plus a
+N/−N summary. Clicking still opens the full history viewer. On touch, a
long-press on the label shows the same diff as a popout (a plain tap opens
the viewer; the message's own long-press action sheet is not triggered).

utils/wordDiff.ts is a unit-tested LCS over words that ignores whitespace-
only changes and gives up past 400 words. Only plain-text bodies are
diffed; formatted edits fall back to the viewer.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PPmy3tPq869XDW4njjVaKA

src/app/components/RenderMessageContent.tsx

@@ -26,6 +26,8 @@ import {
   VerificationRequestContent,
   VideoContent,
 } from './message';
+import { DiffToken } from '../utils/wordDiff';
+import { EditDiffContext } from './message/content/EditDiffContext';
 import { UrlPreviewCard, UrlPreviewHolder } from './url-preview';
 import { Image, MediaControl, Video } from './media';
 import { ImageViewer } from './image-viewer';
@@ -74,8 +76,17 @@ type RenderMessageContentProps = {
   onOpenImageViewer?: () => void;
   /** [Gitea #159] The event, for the undecryptable placeholder's reason + retry. */
   mEvent?: MatrixEvent;
+  /** [Gitea #144] Word diff of the last edit, shown on "(edited)" hover. */
+  editDiff?: DiffToken[];
 };
-export function RenderMessageContent({
+export function RenderMessageContent({ editDiff, ...props }: RenderMessageContentProps) {
+  return (
+    <EditDiffContext.Provider value={editDiff}>
+      <RenderMessageContentBody {...props} />
+    </EditDiffContext.Provider>
+  );
+}
+function RenderMessageContentBody({
   displayName,
   msgType,
   ts,
@@ -91,7 +102,7 @@ export function RenderMessageContent({
   eventId,
   onOpenImageViewer,
   mEvent,
-}: RenderMessageContentProps) {
+}: Omit<RenderMessageContentProps, 'editDiff'>) {
   const renderUrlsPreview = (urls: string[]) => {
     // Cap previews per message so a link-dump doesn't spawn dozens of preview
     // fetches + iframes at once. De-dupe first: a message linking the same URL

src/app/components/message/content/EditDiffContext.ts

@@ -0,0 +1,6 @@
+import { createContext, useContext } from 'react';
+import { DiffToken } from '../../../utils/wordDiff';
+
+/** [Gitea #144] Word diff of the message's last edit, for the "(edited)" hover. */
+export const EditDiffContext = createContext<DiffToken[] | undefined>(undefined);
+export const useEditDiff = () => useContext(EditDiffContext);

src/app/components/message/content/FallbackContent.tsx

@@ -1,5 +1,20 @@
-import { Box, Icon, Icons, Text, as, color, config } from 'folds';
-import React from 'react';
+import {
+  Box,
+  Icon,
+  Icons,
+  PopOut,
+  RectCords,
+  Text,
+  Tooltip,
+  TooltipProvider,
+  as,
+  color,
+  config,
+} from 'folds';
+import React, { useEffect, useState } from 'react';
+import { useLongPress } from '../../../hooks/useLongPress';
+import { DiffToken, countChanges } from '../../../utils/wordDiff';
+import { useEditDiff } from './EditDiffContext';
 
 const warningStyle = { color: color.Warning.Main, opacity: config.opacity.P300 };
 const criticalStyle = { color: color.Critical.Main, opacity: config.opacity.P300 };
@@ -66,29 +81,157 @@ export const MessageVerificationRequestContent = as<'div', { children?: never }>
   ),
 );
 
+const editDiffStyle: React.CSSProperties = {
+  maxWidth: '40ch',
+  whiteSpace: 'pre-wrap',
+  overflowWrap: 'anywhere',
+  maxHeight: '12lh',
+  overflow: 'hidden',
+};
+
+/** The last edit as a word diff: removed words struck, added words bold. */
+export function EditDiffBody({ tokens, hint }: { tokens: DiffToken[]; hint: string }) {
+  const { added, removed } = countChanges(tokens);
+  return (
+    <Box direction="Column" gap="100" style={editDiffStyle}>
+      <Text size="T200" priority="300">
+        Last edit
+        {added > 0 && ` · +${added}`}
+        {removed > 0 && ` · −${removed}`}
+      </Text>
+      <Text as="span" size="T300" dir="auto">
+        {tokens.map((t, i) => {
+          if (t.op === 'add')
+            return (
+              <ins key={i} style={{ textDecoration: 'none', fontWeight: 'bold' }}>
+                {t.text}
+              </ins>
+            );
+          if (t.op === 'del')
+            return (
+              <del key={i} style={{ opacity: config.opacity.P300 }}>
+                {t.text}
+              </del>
+            );
+          return <React.Fragment key={i}>{t.text}</React.Fragment>;
+        })}
+      </Text>
+      <Text size="T200" priority="300">
+        {hint}
+      </Text>
+    </Box>
+  );
+}
+
+const editedButtonStyle: React.CSSProperties = {
+  cursor: 'pointer',
+  background: 'none',
+  border: 'none',
+  padding: 0,
+};
+
+/**
+ * "(edited)" label. With an edit-history handler it is a button that opens
+ * the viewer; when the surrounding message also provides a last-edit diff
+ * (see `EditDiffContext`) hover/focus shows it as a tooltip and a touch
+ * long-press shows it as a popout. [Gitea #144]
+ */
 export const MessageEditedContent = as<
   'span',
   { children?: never; onEditHistoryClick?: () => void }
->(({ onEditHistoryClick, ...props }, ref) =>
-  onEditHistoryClick ? (
+>(({ onEditHistoryClick, ...props }, ref) => {
+  const diff = useEditDiff();
+  const [pressAnchor, setPressAnchor] = useState<RectCords | undefined>();
+  const { coarse, handlers, suppressContextMenu } = useLongPress((x, y) => {
+    if (diff) setPressAnchor({ x, y, width: 1, height: 1 });
+  });
+
+  useEffect(() => {
+    if (!pressAnchor) return undefined;
+    const close = () => setPressAnchor(undefined);
+    const t = window.setTimeout(close, 6000);
+    window.addEventListener('touchstart', close, { passive: true });
+    window.addEventListener('scroll', close, { passive: true, capture: true });
+    return () => {
+      window.clearTimeout(t);
+      window.removeEventListener('touchstart', close);
+      window.removeEventListener('scroll', close, { capture: true });
+    };
+  }, [pressAnchor]);
+
+  if (!onEditHistoryClick) {
+    return (
+      <Text as="span" size="T200" priority="300" {...props} ref={ref}>
+        {' (edited)'}
+      </Text>
+    );
+  }
+
+  const button = (tipRef?: React.RefCallback<HTMLElement>) => (
+    <button
+      ref={tipRef}
+      type="button"
+      onClick={() => {
+        if (suppressContextMenu.current) return;
+        onEditHistoryClick();
+      }}
+      onContextMenu={(evt) => {
+        if (suppressContextMenu.current) evt.preventDefault();
+      }}
+      {...handlers}
+      // Keep the message's own long-press (action sheet) from firing too.
+      onTouchStart={(evt) => {
+        evt.stopPropagation();
+        handlers.onTouchStart?.(evt);
+      }}
+      aria-label={diff ? 'View edit history — hover for the last change' : 'View edit history'}
+      style={editedButtonStyle}
+    >
+      <Text as="span" size="T200" priority="300">
+        {' (edited)'}
+      </Text>
+    </button>
+  );
+
+  return (
     <span ref={ref} {...(props as React.HTMLAttributes<HTMLSpanElement>)}>
-      <button
-        type="button"
-        onClick={onEditHistoryClick}
-        aria-label="View edit history"
-        style={{ cursor: 'pointer', background: 'none', border: 'none', padding: 0 }}
-      >
-        <Text as="span" size="T200" priority="300">
-          {' (edited)'}
-        </Text>
-      </button>
+      {diff ? (
+        <TooltipProvider
+          position="Top"
+          align="Start"
+          delay={300}
+          tooltip={
+            <Tooltip>
+              <EditDiffBody
+                tokens={diff}
+                hint={coarse ? 'Tap for full history' : 'Click for full history'}
+              />
+            </Tooltip>
+          }
+        >
+          {(tipRef) => button(tipRef)}
+        </TooltipProvider>
+      ) : (
+        button()
+      )}
+      {diff && pressAnchor && (
+        <PopOut
+          anchor={pressAnchor}
+          position="Top"
+          align="Start"
+          content={
+            <Tooltip>
+              <EditDiffBody
+                tokens={diff}
+                hint={coarse ? 'Tap for full history' : 'Click for full history'}
+              />
+            </Tooltip>
+          }
+        />
+      )}
     </span>
-  ) : (
-    <Text as="span" size="T200" priority="300" {...props} ref={ref}>
-      {' (edited)'}
-    </Text>
-  ),
-);
+  );
+});
 
 type TranslatedStatus = 'downloading' | 'translating' | 'done' | 'error';