feat: compare two page versions (#2385)

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

@@ -1291,5 +1291,11 @@
   "{{count}} rows deleted_one": "1 row deleted",
   "{{count}} rows deleted_other": "{{count}} rows deleted",
   "{{count}} selected_one": "1 selected",
-  "{{count}} selected_other": "{{count}} selected"
+  "{{count}} selected_other": "{{count}} selected",
+  "Compare": "Compare",
+  "Compare versions": "Compare versions",
+  "Select version from {{date}}": "Select version from {{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/atoms/history-atoms.ts

@@ -6,4 +6,13 @@ export const activeHistoryPrevIdAtom = atom<string>("");
 export const highlightChangesAtom = atom<boolean>(true);
 
 export type DiffCounts = { added: number; deleted: number; total: number };
-export const diffCountsAtom = atom<DiffCounts | null>(null);
+export const diffCountsAtom = atom<DiffCounts | null>(
+  null as DiffCounts | null,
+);
+
+export type ComparePair = { newerId: string; olderId: string };
+export const compareModeAtom = atom<boolean>(false);
+export const compareSelectionAtom = atom<string[]>([]);
+export const comparePairAtom = atom<ComparePair | null>(
+  null as ComparePair | null,
+);

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

@@ -1,7 +1,7 @@
 .history {
-  display: block;
+  display: flex;
+  align-items: center;
   width: 100%;
-  padding: var(--mantine-spacing-md);
   color: light-dark(var(--mantine-color-black), var(--mantine-color-dark-0));
 
   @mixin hover {
@@ -12,6 +12,28 @@
   }
 }
 
+.historyButton {
+  flex: 1;
+  min-width: 0;
+  color: inherit;
+}
+
+.compareCheckbox {
+  padding-left: var(--mantine-spacing-xs);
+}
+
+.itemMenu {
+  opacity: 0;
+  margin-right: var(--mantine-spacing-xs);
+}
+
+.history:hover .itemMenu,
+.history:focus-within .itemMenu,
+.history.active .itemMenu,
+.itemMenu[aria-expanded="true"] {
+  opacity: 1;
+}
+
 .historyEditor {
   :global(.ProseMirror) {
     padding: 0 !important;
@@ -77,3 +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-editor.tsx

@@ -170,7 +170,6 @@ export function HistoryEditor({
     }
 
     const total = addedCount + deletedCount;
-    // @ts-ignore
     setDiffCounts({ added: addedCount, deleted: deletedCount, total });
 
     editor.setOptions({

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

@@ -1,10 +1,21 @@
-import { Text, Group, UnstyledButton, Avatar, Tooltip } from "@mantine/core";
+import {
+  Text,
+  Group,
+  UnstyledButton,
+  Avatar,
+  Tooltip,
+  ActionIcon,
+  Checkbox,
+  Menu,
+} from "@mantine/core";
+import { IconDots } from "@tabler/icons-react";
 import { CustomAvatar } from "@/components/ui/custom-avatar.tsx";
 import { formattedDate } from "@/lib/time";
 import classes from "./css/history.module.css";
 import clsx from "clsx";
 import { IPageHistory } from "@/features/page-history/types/page.types";
 import { memo, useCallback } from "react";
+import { useTranslation } from "react-i18next";
 
 const MAX_VISIBLE_AVATARS = 5;
 
@@ -15,6 +26,13 @@ interface HistoryItemProps {
   onHover?: (id: string, index: number) => void;
   onHoverEnd?: () => void;
   isActive: boolean;
+  compareMode: boolean;
+  isChecked: boolean;
+  isCheckboxDisabled: boolean;
+  canCompare: boolean;
+  onToggleCompare: (id: string) => void;
+  onStartCompare: (id: string) => void;
+  onRestore?: (id: string, index: number) => void;
 }
 
 const HistoryItem = memo(function HistoryItem({
@@ -24,10 +42,24 @@ const HistoryItem = memo(function HistoryItem({
   onHover,
   onHoverEnd,
   isActive,
+  compareMode,
+  isChecked,
+  isCheckboxDisabled,
+  canCompare,
+  onToggleCompare,
+  onStartCompare,
+  onRestore,
 }: HistoryItemProps) {
+  const { t } = useTranslation();
+  const date = formattedDate(new Date(historyItem.createdAt));
+
   const handleClick = useCallback(() => {
-    onSelect(historyItem.id, index);
-  }, [onSelect, historyItem.id, index]);
+    if (compareMode) {
+      onToggleCompare(historyItem.id);
+    } else {
+      onSelect(historyItem.id, index);
+    }
+  }, [compareMode, onToggleCompare, onSelect, historyItem.id, index]);
 
   const handleMouseEnter = useCallback(() => {
     onHover?.(historyItem.id, index);
@@ -37,63 +69,115 @@ const HistoryItem = memo(function HistoryItem({
   const hasContributors = contributors && contributors.length > 0;
 
   return (
-    <UnstyledButton
-      p="xs"
-      onClick={handleClick}
+    <div
+      className={clsx(classes.history, { [classes.active]: isActive })}
       onMouseEnter={handleMouseEnter}
       onMouseLeave={onHoverEnd}
-      className={clsx(classes.history, { [classes.active]: isActive })}
     >
-      <Text size="sm">{formattedDate(new Date(historyItem.createdAt))}</Text>
+      {compareMode && (
+        <Checkbox
+          size="xs"
+          className={classes.compareCheckbox}
+          checked={isChecked}
+          disabled={isCheckboxDisabled}
+          onChange={() => onToggleCompare(historyItem.id)}
+          aria-label={t("Select version from {{date}}", { date })}
+        />
+      )}
 
-      <Group gap={6} wrap="nowrap" mt={4}>
-        {hasContributors ? (
-          <>
-            <Tooltip.Group openDelay={300} closeDelay={100}>
-              <Avatar.Group spacing={8}>
-                {contributors.slice(0, MAX_VISIBLE_AVATARS).map((contributor) => (
-                  <Tooltip key={contributor.id} label={contributor.name} withArrow>
-                    <CustomAvatar
-                      size="sm"
-                      avatarUrl={contributor.avatarUrl}
-                      name={contributor.name}
-                    />
-                  </Tooltip>
-                ))}
-                {contributors.length > MAX_VISIBLE_AVATARS && (
-                  <Tooltip
-                    withArrow
-                    label={contributors.slice(MAX_VISIBLE_AVATARS).map((c) => (
-                      <div key={c.id}>{c.name}</div>
+      <UnstyledButton
+        p="xs"
+        onClick={handleClick}
+        className={classes.historyButton}
+      >
+        <Text size="sm">{date}</Text>
+
+        <Group gap={6} wrap="nowrap" mt={4}>
+          {hasContributors ? (
+            <>
+              <Tooltip.Group openDelay={300} closeDelay={100}>
+                <Avatar.Group spacing={8}>
+                  {contributors
+                    .slice(0, MAX_VISIBLE_AVATARS)
+                    .map((contributor) => (
+                      <Tooltip
+                        key={contributor.id}
+                        label={contributor.name}
+                        withArrow
+                      >
+                        <CustomAvatar
+                          size="sm"
+                          avatarUrl={contributor.avatarUrl}
+                          name={contributor.name}
+                        />
+                      </Tooltip>
                     ))}
-                  >
-                    <Avatar size="sm" color="gray">
-                      +{contributors.length - MAX_VISIBLE_AVATARS}
-                    </Avatar>
-                  </Tooltip>
-                )}
-              </Avatar.Group>
-            </Tooltip.Group>
-            {contributors.length === 1 && (
+                  {contributors.length > MAX_VISIBLE_AVATARS && (
+                    <Tooltip
+                      withArrow
+                      label={contributors
+                        .slice(MAX_VISIBLE_AVATARS)
+                        .map((c) => (
+                          <div key={c.id}>{c.name}</div>
+                        ))}
+                    >
+                      <Avatar size="sm" color="gray">
+                        +{contributors.length - MAX_VISIBLE_AVATARS}
+                      </Avatar>
+                    </Tooltip>
+                  )}
+                </Avatar.Group>
+              </Tooltip.Group>
+              {contributors.length === 1 && (
+                <Text size="sm" c="dimmed" lineClamp={1}>
+                  {contributors[0].name}
+                </Text>
+              )}
+            </>
+          ) : (
+            <>
+              <CustomAvatar
+                size="sm"
+                avatarUrl={historyItem.lastUpdatedBy?.avatarUrl}
+                name={historyItem.lastUpdatedBy?.name}
+              />
               <Text size="sm" c="dimmed" lineClamp={1}>
-                {contributors[0].name}
+                {historyItem.lastUpdatedBy?.name}
               </Text>
+            </>
+          )}
+        </Group>
+      </UnstyledButton>
+
+      {!compareMode && (
+        <Menu shadow="md" width={180} position="bottom-end">
+          <Menu.Target>
+            <ActionIcon
+              variant="subtle"
+              color="gray"
+              className={classes.itemMenu}
+              aria-label={t("Version actions for {{date}}", { date })}
+              onClick={(e) => e.stopPropagation()}
+            >
+              <IconDots size={18} />
+            </ActionIcon>
+          </Menu.Target>
+          <Menu.Dropdown>
+            <Menu.Item
+              disabled={!canCompare}
+              onClick={() => onStartCompare(historyItem.id)}
+            >
+              {t("Compare")}
+            </Menu.Item>
+            {onRestore && (
+              <Menu.Item onClick={() => onRestore(historyItem.id, index)}>
+                {t("Restore")}
+              </Menu.Item>
             )}
-          </>
-        ) : (
-          <>
-            <CustomAvatar
-              size="sm"
-              avatarUrl={historyItem.lastUpdatedBy?.avatarUrl}
-              name={historyItem.lastUpdatedBy?.name}
-            />
-            <Text size="sm" c="dimmed" lineClamp={1}>
-              {historyItem.lastUpdatedBy?.name}
-            </Text>
-          </>
-        )}
-      </Group>
-    </UnstyledButton>
+          </Menu.Dropdown>
+        </Menu>
+      )}
+    </div>
   );
 });
 

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

@@ -6,8 +6,12 @@ import HistoryItem from "@/features/page-history/components/history-item";
 import {
   activeHistoryIdAtom,
   activeHistoryPrevIdAtom,
+  compareModeAtom,
+  comparePairAtom,
+  compareSelectionAtom,
   historyAtoms,
 } from "@/features/page-history/atoms/history-atoms";
+import { resolveComparePair } from "@/features/page-history/utils/resolve-compare-pair";
 import { useAtom, useSetAtom } from "jotai";
 import { useCallback, useEffect, useMemo, useRef } from "react";
 import {
@@ -32,6 +36,9 @@ function HistoryList({ pageId }: Props) {
   const [activeHistoryId, setActiveHistoryId] = useAtom(activeHistoryIdAtom);
   const setActiveHistoryPrevId = useSetAtom(activeHistoryPrevIdAtom);
   const setHistoryModalOpen = useSetAtom(historyAtoms);
+  const [compareMode, setCompareMode] = useAtom(compareModeAtom);
+  const [compareSelection, setCompareSelection] = useAtom(compareSelectionAtom);
+  const setComparePair = useSetAtom(comparePairAtom);
 
   const {
     data: pageHistoryData,
@@ -79,10 +86,58 @@ function HistoryList({ pageId }: Props) {
 
   const handleSelect = useCallback(
     (id: string, index: number) => {
+      setComparePair(null);
       setActiveHistoryId(id);
       setActiveHistoryPrevId(historyItems[index + 1]?.id ?? "");
     },
-    [historyItems, setActiveHistoryId, setActiveHistoryPrevId],
+    [historyItems, setActiveHistoryId, setActiveHistoryPrevId, setComparePair],
+  );
+
+  const handleToggleCompare = useCallback(
+    (id: string) => {
+      setCompareSelection((prev) => {
+        if (prev.includes(id)) return prev.filter((item) => item !== id);
+        if (prev.length >= 2) return prev;
+        return [...prev, id];
+      });
+    },
+    [setCompareSelection],
+  );
+
+  const handleStartCompare = useCallback(
+    (id: string) => {
+      setComparePair(null);
+      setCompareMode(true);
+      setCompareSelection([id]);
+    },
+    [setComparePair, setCompareMode, setCompareSelection],
+  );
+
+  const handleCancelCompare = useCallback(() => {
+    setCompareMode(false);
+    setCompareSelection([]);
+  }, [setCompareMode, setCompareSelection]);
+
+  const handleConfirmCompare = useCallback(() => {
+    const pair = resolveComparePair(historyItems, compareSelection);
+    if (!pair) return;
+    setComparePair(pair);
+    setCompareMode(false);
+    setCompareSelection([]);
+  }, [
+    historyItems,
+    compareSelection,
+    setComparePair,
+    setCompareMode,
+    setCompareSelection,
+  ]);
+
+  const handleRestoreItem = useCallback(
+    (id: string, index: number) => {
+      handleSelect(id, index);
+      confirmRestore(id);
+    },
+    [handleSelect, confirmRestore],
   );
 
   useEffect(() => {
@@ -138,6 +193,16 @@ function HistoryList({ pageId }: Props) {
             onHover={handleHover}
             onHoverEnd={clearPrefetchTimeout}
             isActive={historyItem.id === activeHistoryId}
+            compareMode={compareMode}
+            isChecked={compareSelection.includes(historyItem.id)}
+            isCheckboxDisabled={
+              !compareSelection.includes(historyItem.id) &&
+              compareSelection.length >= 2
+            }
+            canCompare={historyItems.length >= 2}
+            onToggleCompare={handleToggleCompare}
+            onStartCompare={handleStartCompare}
+            onRestore={canRestore ? handleRestoreItem : undefined}
           />
         ))}
         {hasNextPage && <div ref={loadMoreRef} style={{ height: 1 }} />}
@@ -148,22 +213,44 @@ function HistoryList({ pageId }: Props) {
         )}
       </ScrollArea>
 
-      {canRestore && (
+      {compareMode ? (
         <>
           <Divider />
           <Group p="xs" wrap="nowrap">
             <Button
               variant="default"
               size="compact-md"
-              onClick={() => setHistoryModalOpen(false)}
+              onClick={handleCancelCompare}
             >
               {t("Cancel")}
             </Button>
-            <Button size="compact-md" onClick={confirmRestore}>
-              {t("Restore")}
+            <Button
+              size="compact-md"
+              disabled={compareSelection.length !== 2}
+              onClick={handleConfirmCompare}
+            >
+              {t("Compare")}
             </Button>
           </Group>
         </>
+      ) : (
+        canRestore && (
+          <>
+            <Divider />
+            <Group p="xs" wrap="nowrap">
+              <Button
+                variant="default"
+                size="compact-md"
+                onClick={() => setHistoryModalOpen(false)}
+              >
+                {t("Cancel")}
+              </Button>
+              <Button size="compact-md" onClick={() => confirmRestore()}>
+                {t("Restore")}
+              </Button>
+            </Group>
+          </>
+        )
       )}
     </div>
   );

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 && (
+          <Group
+            justify="space-between"
+            wrap="nowrap"
+            px="md"
+            py={4}
+            className={classes.compareBanner}
+          >
+            <Text size="sm" fw={500} lineClamp={1}>
+              {compareLabel ?? t("Compare versions")}
+            </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-modal-mobile.tsx

@@ -166,7 +166,7 @@ export default function HistoryModalMobile({ pageId, pageTitle }: Props) {
           <Button variant="default" onClick={() => setHistoryModalOpen(false)}>
             {t("Cancel")}
           </Button>
-          <Button onClick={confirmRestore}>{t("Restore")}</Button>
+          <Button onClick={() => confirmRestore()}>{t("Restore")}</Button>
         </Group>
       )}
 

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 prevHistoryId = useAtomValue(activeHistoryPrevIdAtom);
+  const activeId = useAtomValue(activeHistoryIdAtom);
+  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 <></>;

apps/client/src/features/page-history/hooks/use-history-reset.ts

@@ -3,22 +3,45 @@ import { useEffect } from "react";
 import {
   activeHistoryIdAtom,
   activeHistoryPrevIdAtom,
+  compareModeAtom,
+  comparePairAtom,
+  compareSelectionAtom,
   diffCountsAtom,
 } from "@/features/page-history/atoms/history-atoms";
 
 /**
  * Resets history state when pageId changes.
- * Clears active selection and diff counts.
+ * Clears active selection, diff counts, and compare state.
+ * Compare state also resets on unmount so reopening the modal starts clean.
  */
 export function useHistoryReset(pageId: string) {
   const [, setActiveHistoryId] = useAtom(activeHistoryIdAtom);
   const [, setActiveHistoryPrevId] = useAtom(activeHistoryPrevIdAtom);
   const [, setDiffCounts] = useAtom(diffCountsAtom);
+  const [, setCompareMode] = useAtom(compareModeAtom);
+  const [, setCompareSelection] = useAtom(compareSelectionAtom);
+  const [, setComparePair] = useAtom(comparePairAtom);
 
   useEffect(() => {
+    const resetCompare = () => {
+      setCompareMode(false);
+      setCompareSelection([]);
+      setComparePair(null);
+    };
+
     setActiveHistoryId("");
     setActiveHistoryPrevId("");
-    // @ts-ignore
     setDiffCounts(null);
-  }, [pageId, setActiveHistoryId, setActiveHistoryPrevId, setDiffCounts]);
+    resetCompare();
+
+    return resetCompare;
+  }, [
+    pageId,
+    setActiveHistoryId,
+    setActiveHistoryPrevId,
+    setDiffCounts,
+    setCompareMode,
+    setCompareSelection,
+    setComparePair,
+  ]);
 }

apps/client/src/features/page-history/hooks/use-history-restore.tsx

@@ -1,4 +1,4 @@
-import { useAtom, useAtomValue, useSetAtom } from "jotai";
+import { useAtomValue, useSetAtom } from "jotai";
 import { useCallback } from "react";
 import { useTranslation } from "react-i18next";
 import { Text } from "@mantine/core";
@@ -9,7 +9,8 @@ import {
   activeHistoryIdAtom,
   historyAtoms,
 } from "@/features/page-history/atoms/history-atoms";
-import { usePageHistoryQuery } from "@/features/page-history/queries/page-history-query";
+import { fetchPageHistory } from "@/features/page-history/queries/page-history-query";
+import { IPageHistory } from "@/features/page-history/types/page.types";
 import {
   pageEditorAtom,
   titleEditorAtom,
@@ -25,8 +26,6 @@ export function useHistoryRestore() {
   const { t } = useTranslation();
 
   const activeHistoryId = useAtomValue(activeHistoryIdAtom);
-  const { data: activeHistoryData } = usePageHistoryQuery(activeHistoryId);
-
   const mainEditor = useAtomValue(pageEditorAtom);
   const mainEditorTitle = useAtomValue(titleEditorAtom);
   const setHistoryModalOpen = useSetAtom(historyAtoms);
@@ -40,47 +39,66 @@ export function useHistoryRestore() {
     SpaceCaslSubject.Page,
   );
 
-  const handleRestore = useCallback(() => {
-    if (!activeHistoryData) return;
-    if (
-      !mainEditor ||
-      mainEditor.isDestroyed ||
-      !mainEditorTitle ||
-      mainEditorTitle.isDestroyed
-    ) {
-      return;
-    }
+  const handleRestore = useCallback(
+    async (historyId: string) => {
+      let historyData: IPageHistory;
+      try {
+        historyData = await fetchPageHistory(historyId);
+      } catch {
+        notifications.show({
+          message: t("Error fetching page data."),
+          color: "red",
+        });
+        return;
+      }
 
-    mainEditorTitle
-      .chain()
-      .clearContent()
-      .setContent(activeHistoryData.title, { emitUpdate: true })
-      .run();
+      if (
+        !mainEditor ||
+        mainEditor.isDestroyed ||
+        !mainEditorTitle ||
+        mainEditorTitle.isDestroyed
+      ) {
+        return;
+      }
 
-    mainEditor
-      .chain()
-      .clearContent()
-      .setContent(activeHistoryData.content)
-      .run();
+      mainEditorTitle
+        .chain()
+        .clearContent()
+        .setContent(historyData.title, { emitUpdate: true })
+        .run();
 
-    setHistoryModalOpen(false);
-    notifications.show({ message: t("Successfully restored") });
-  }, [activeHistoryData, mainEditor, mainEditorTitle, setHistoryModalOpen, t]);
+      mainEditor
+        .chain()
+        .clearContent()
+        .setContent(historyData.content)
+        .run();
 
-  const confirmRestore = useCallback(() => {
-    modals.openConfirmModal({
-      title: t("Please confirm your action"),
-      children: (
-        <Text size="sm">
-          {t(
-            "Are you sure you want to restore this version? Any changes not versioned will be lost.",
-          )}
-        </Text>
-      ),
-      labels: { confirm: t("Confirm"), cancel: t("Cancel") },
-      onConfirm: handleRestore,
-    });
-  }, [t, handleRestore]);
+      setHistoryModalOpen(false);
+      notifications.show({ message: t("Successfully restored") });
+    },
+    [mainEditor, mainEditorTitle, setHistoryModalOpen, t],
+  );
+
+  const confirmRestore = useCallback(
+    (historyId?: string) => {
+      const targetId = historyId ?? activeHistoryId;
+      if (!targetId) return;
+
+      modals.openConfirmModal({
+        title: t("Please confirm your action"),
+        children: (
+          <Text size="sm">
+            {t(
+              "Are you sure you want to restore this version? Any changes not versioned will be lost.",
+            )}
+          </Text>
+        ),
+        labels: { confirm: t("Confirm"), cancel: t("Cancel") },
+        onConfirm: () => handleRestore(targetId),
+      });
+    },
+    [t, handleRestore, activeHistoryId],
+  );
 
   return { canRestore, confirmRestore };
 }

apps/client/src/features/page-history/queries/page-history-query.ts

@@ -23,6 +23,14 @@ export function prefetchPageHistory(historyId: string) {
   });
 }
 
+export function fetchPageHistory(historyId: string): Promise<IPageHistory> {
+  return queryClient.fetchQuery({
+    queryKey: ["page-history", historyId],
+    queryFn: () => getPageHistoryById(historyId),
+    staleTime: HISTORY_STALE_TIME,
+  });
+}
+
 export function usePageHistoryListQuery(
   pageId: string,
 ): UseInfiniteQueryResult<InfiniteData<IPagination<IPageHistory>, unknown>> {

apps/client/src/features/page-history/utils/resolve-compare-pair.test.ts

@@ -0,0 +1,32 @@
+import { describe, expect, it } from "vitest";
+import { resolveComparePair } from "./resolve-compare-pair";
+
+// list is newest-first, matching usePageHistoryListQuery order
+const items = [{ id: "v3" }, { id: "v2" }, { id: "v1" }];
+
+describe("resolveComparePair", () => {
+  it("orders newer before older regardless of selection order", () => {
+    expect(resolveComparePair(items, ["v1", "v3"])).toEqual({
+      newerId: "v3",
+      olderId: "v1",
+    });
+    expect(resolveComparePair(items, ["v3", "v1"])).toEqual({
+      newerId: "v3",
+      olderId: "v1",
+    });
+  });
+
+  it("returns null unless exactly two versions are selected", () => {
+    expect(resolveComparePair(items, [])).toBeNull();
+    expect(resolveComparePair(items, ["v1"])).toBeNull();
+    expect(resolveComparePair(items, ["v1", "v2", "v3"])).toBeNull();
+  });
+
+  it("returns null when a selected id is not in the list", () => {
+    expect(resolveComparePair(items, ["v1", "missing"])).toBeNull();
+  });
+
+  it("returns null when the same id is selected twice", () => {
+    expect(resolveComparePair(items, ["v2", "v2"])).toBeNull();
+  });
+});

apps/client/src/features/page-history/utils/resolve-compare-pair.ts

@@ -0,0 +1,18 @@
+import { ComparePair } from "@/features/page-history/atoms/history-atoms";
+
+/**
+ * Resolves which of the two selected versions is newer using their position
+ * in the history list (list is newest-first: lower index = newer).
+ */
+export function resolveComparePair(
+  historyItems: { id: string }[],
+  selection: string[],
+): ComparePair | null {
+  if (selection.length !== 2) return null;
+  const indexA = historyItems.findIndex((item) => item.id === selection[0]);
+  const indexB = historyItems.findIndex((item) => item.id === selection[1]);
+  if (indexA === -1 || indexB === -1 || indexA === indexB) return null;
+  return indexA < indexB
+    ? { newerId: selection[0], olderId: selection[1] }
+    : { newerId: selection[1], olderId: selection[0] };
+}