feat(client): compare two page history versions in history view

apps/client/public/locales/en-US/translation.json

@@ -1293,5 +1293,7 @@
   "Compare": "Compare",
   "Compare versions": "Compare versions",
   "Select version from {{date}}": "Select version from {{date}}",
-  "Version actions for {{date}}": "Version actions for {{date}}"
+  "Version actions for {{date}}": "Version actions for {{date}}",
+  "Comparing {{newer}} and {{older}}": "Comparing {{newer}} and {{older}}",
+  "Exit compare": "Exit compare"
 }

apps/client/src/features/page-history/components/css/history.module.css

@@ -99,3 +99,8 @@
   flex: 1;
   padding: rem(16px) rem(40px);
 }
+
+.compareBanner {
+  border-bottom: rem(1px) solid
+    light-dark(var(--mantine-color-gray-3), var(--mantine-color-dark-4));
+}

apps/client/src/features/page-history/components/history-modal-body.tsx

@@ -1,5 +1,6 @@
 import {
   ActionIcon,
+  CloseButton,
   Group,
   Paper,
   ScrollArea,
@@ -12,17 +13,20 @@ import { useAtom, useAtomValue } from "jotai";
 import {
   activeHistoryIdAtom,
   activeHistoryPrevIdAtom,
+  comparePairAtom,
   diffCountsAtom,
   highlightChangesAtom,
 } from "@/features/page-history/atoms/history-atoms";
 import HistoryView from "@/features/page-history/components/history-view";
-import { useRef } from "react";
+import { useMemo, useRef } from "react";
 import { IconChevronUp, IconChevronDown } from "@tabler/icons-react";
 import { useTranslation } from "react-i18next";
 import {
   useDiffNavigation,
   useHistoryReset,
 } from "@/features/page-history/hooks";
+import { usePageHistoryListQuery } from "@/features/page-history/queries/page-history-query";
+import { formattedDate } from "@/lib/time";
 
 interface Props {
   pageId: string;
@@ -36,6 +40,28 @@ export default function HistoryModalBody({ pageId }: Props) {
   const activeHistoryPrevId = useAtomValue(activeHistoryPrevIdAtom);
   const [highlightChanges, setHighlightChanges] = useAtom(highlightChangesAtom);
   const diffCounts = useAtomValue(diffCountsAtom);
+  const [comparePair, setComparePair] = useAtom(comparePairAtom);
+
+  const { data: pageHistoryData } = usePageHistoryListQuery(pageId);
+  const historyItems = useMemo(
+    () => pageHistoryData?.pages.flatMap((page) => page.items) ?? [],
+    [pageHistoryData],
+  );
+
+  const compareLabel = useMemo(() => {
+    if (!comparePair) return null;
+    const newerItem = historyItems.find(
+      (item) => item.id === comparePair.newerId,
+    );
+    const olderItem = historyItems.find(
+      (item) => item.id === comparePair.olderId,
+    );
+    if (!newerItem || !olderItem) return null;
+    return t("Comparing {{newer}} and {{older}}", {
+      newer: formattedDate(new Date(newerItem.createdAt)),
+      older: formattedDate(new Date(olderItem.createdAt)),
+    });
+  }, [comparePair, historyItems, t]);
 
   useHistoryReset(pageId);
   const { currentChangeIndex, handlePrevChange, handleNextChange } =
@@ -50,6 +76,25 @@ export default function HistoryModalBody({ pageId }: Props) {
       </nav>
 
       <div style={{ position: "relative", flex: 1 }}>
+        {comparePair && compareLabel && (
+          <Group
+            justify="space-between"
+            wrap="nowrap"
+            px="md"
+            py={4}
+            className={classes.compareBanner}
+          >
+            <Text size="sm" fw={500} lineClamp={1}>
+              {compareLabel}
+            </Text>
+            <CloseButton
+              size="sm"
+              aria-label={t("Exit compare")}
+              onClick={() => setComparePair(null)}
+            />
+          </Group>
+        )}
+
         <ScrollArea
           h={650}
           w="100%"
@@ -57,11 +102,18 @@ export default function HistoryModalBody({ pageId }: Props) {
           viewportRef={scrollViewportRef}
         >
           <div className={classes.sidebarRightSection}>
-            {activeHistoryId && <HistoryView />}
+            {comparePair ? (
+              <HistoryView
+                historyId={comparePair.newerId}
+                prevHistoryId={comparePair.olderId}
+              />
+            ) : (
+              activeHistoryId && <HistoryView />
+            )}
           </div>
         </ScrollArea>
 
-        {activeHistoryId && activeHistoryPrevId && (
+        {(comparePair || (activeHistoryId && activeHistoryPrevId)) && (
           <Paper
             shadow="md"
             radius="xl"

apps/client/src/features/page-history/components/history-view.tsx

@@ -7,21 +7,29 @@ import {
   activeHistoryPrevIdAtom,
 } from "@/features/page-history/atoms/history-atoms";
 
-function HistoryView() {
+interface Props {
+  historyId?: string;
+  prevHistoryId?: string;
+}
+
+function HistoryView({ historyId, prevHistoryId }: Props) {
   const { t } = useTranslation();
-  const historyId = useAtomValue(activeHistoryIdAtom);
+  const activeId = useAtomValue(activeHistoryIdAtom);
-  const prevHistoryId = useAtomValue(activeHistoryPrevIdAtom);
+  const activePrevId = useAtomValue(activeHistoryPrevIdAtom);
+
+  const resolvedId = historyId ?? activeId;
+  const resolvedPrevId = prevHistoryId ?? activePrevId;
 
   const {
     data,
     isLoading: isLoadingCurrent,
     isError: isErrorCurrent,
-  } = usePageHistoryQuery(historyId);
+  } = usePageHistoryQuery(resolvedId);
   const {
     data: prevData,
     isLoading: isLoadingPrev,
     isError: isErrorPrev,
-  } = usePageHistoryQuery(prevHistoryId);
+  } = usePageHistoryQuery(resolvedPrevId);
 
   if (isLoadingCurrent || isLoadingPrev) {
     return <></>;