force chat messages unread on insert

Author: dnywh

supabase/migrations/20260511061153_force_chat_insert_unread_state.sql

@@ -0,0 +1,81 @@
+-- Chat unread state is server-owned. Authenticated senders can create a
+-- message, but they cannot mark it read during insert.
+
+revoke insert on table public.chat_messages from authenticated;
+
+grant insert (
+  thread_id,
+  sender_id,
+  content
+) on table public.chat_messages to authenticated;
+
+revoke insert on table public.chat_threads from authenticated;
+
+grant insert (
+  listing_id,
+  initiator_id,
+  owner_id
+) on table public.chat_threads to authenticated;
+
+create or replace function private.enforce_chat_message_insert()
+returns trigger
+language plpgsql
+security definer
+set search_path = ''
+as $$
+declare
+  thread_record public.chat_threads%rowtype;
+  jwt_role text;
+begin
+  jwt_role := nullif(current_setting('request.jwt.claim.role', true), '');
+
+  if jwt_role = 'service_role'
+    or ((select auth.uid()) is null and jwt_role is null)
+  then
+    return new;
+  end if;
+
+  new.created_at := timezone('utc'::text, now());
+  new.read_at := null;
+
+  if (select auth.uid()) is null or new.sender_id is distinct from (select auth.uid()) then
+    raise exception 'Users can only send messages as themselves.'
+      using errcode = '42501';
+  end if;
+
+  select *
+  into thread_record
+  from public.chat_threads
+  where id = new.thread_id;
+
+  if thread_record.id is null or (
+    thread_record.initiator_id is distinct from new.sender_id
+    and thread_record.owner_id is distinct from new.sender_id
+  ) then
+    raise exception 'Users can only send messages in their own threads.'
+      using errcode = '42501';
+  end if;
+
+  if new.content is null or trim(both from new.content) = '' then
+    raise exception 'Message content cannot be empty.'
+      using errcode = '23514';
+  end if;
+
+  if (
+    select count(*)
+    from public.chat_messages
+    where sender_id = new.sender_id
+      and created_at >= now() - interval '1 hour'
+  ) >= 10 then
+    raise exception 'Too many messages sent recently.'
+      using errcode = '42501';
+  end if;
+
+  return new;
+end;
+$$;
+
+alter function private.enforce_chat_message_insert() owner to postgres;
+
+revoke all privileges on function private.enforce_chat_message_insert()
+  from anon, authenticated, public;