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apps/desktop/src/lib/useMessageReads.ts

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+import { listPeerReadsForMessages, markMessagesRead } from '@chat-app/shared/chat';
+import { useCallback, useEffect, useMemo, useState } from 'react';
+
+import { supabase } from './supabase';
+
+// Tracks which of our own messages the peer has read. For groups this would
+// return a per-message Map<userId, readAt>; M1 is DM-focused so we just return
+// a Set of message ids read by the single peer.
+export function useMessageReads(
+  messageIds: string[],
+  peerUserId: string | undefined,
+): { peerReadSet: Set<string>; refresh: () => Promise<void> } {
+  const idsKey = useMemo(() => messageIds.join(','), [messageIds]);
+  const [peerReadSet, setPeerReadSet] = useState<Set<string>>(new Set());
+
+  const refresh = useCallback(async () => {
+    if (!peerUserId || messageIds.length === 0) {
+      setPeerReadSet(new Set());
+      return;
+    }
+    try {
+      const s = await listPeerReadsForMessages(supabase, messageIds, peerUserId);
+      setPeerReadSet(s);
+    } catch (err: unknown) {
+      console.error('listPeerReadsForMessages failed', err);
+    }
+    // eslint-disable-next-line react-hooks/exhaustive-deps
+  }, [peerUserId, idsKey]);
+
+  useEffect(() => {
+    void refresh();
+    if (!peerUserId) return;
+    const channel = supabase
+      .channel('reads:' + peerUserId)
+      .on(
+        'postgres_changes',
+        {
+          event: 'INSERT',
+          schema: 'public',
+          table: 'message_reads',
+          filter: 'user_id=eq.' + peerUserId,
+        },
+        () => {
+          void refresh();
+        },
+      )
+      .subscribe();
+    return () => {
+      void supabase.removeChannel(channel);
+    };
+  }, [peerUserId, refresh]);
+
+  return { peerReadSet, refresh };
+}
+
+// Mark a batch of messages as read. Caller uses this when they arrive while
+// the conversation is actively being viewed.
+export async function markRead(messageIds: string[]): Promise<void> {
+  await markMessagesRead(supabase, messageIds);
+}