-- ============================================================================
-- Cached OpenGraph previews. The edge function `og-preview` writes rows
-- server-side (service-role). Clients read via RLS for any authenticated
-- user. Rows are keyed by URL so hits across conversations deduplicate.
-- ============================================================================
create table public.link_previews (
  url           text primary key,
  title         text,
  description   text,
  image_url     text,
  site_name     text,
  fetched_at    timestamptz not null default now(),
  -- Absence of metadata (404, unreachable, parse failure) still produces a
  -- cache row so we don't spam the fetcher. `ok = false` signals the UI to
  -- hide the preview.
  ok            boolean not null default true,
  error         text
);

create index link_previews_fetched_at_idx on public.link_previews (fetched_at);

alter table public.link_previews enable row level security;

create policy link_previews_select_authenticated on public.link_previews
  for select to authenticated
  using (true);

-- No INSERT/UPDATE policy: writes flow exclusively through the edge function
-- which authenticates with the service-role key.