-- Migration 024: server admin role + audit log (Fase 13.1)
--
-- Introduces an orthogonal global role used by the operator-facing /admin area.
-- A `server_admin` is NOT a `collective_member` role — it's a separate gate
-- that lets one user delete/restore collectives, expel members, set default
-- section visibility, and inspect any colective on the instance.
--
-- ── Design notes ────────────────────────────────────────────────────────────
-- * We pick a table (`server_admins`) over a column on `users` because the
--   JWT doesn't need to carry the flag — `is_server_admin()` is a cheap STABLE
--   query and there's no way for an admin to silently keep the role after a
--   `revoke` if the bit lived inside the cached JWT.
-- * `admin_actions` is append-only at the policy level. Only SECURITY DEFINER
--   RPCs (migration 025) ever write to it, so we never declare INSERT/UPDATE/
--   DELETE policies. SELECT is admin-only — even the actor cannot reach back
--   in via PostgREST and rewrite their own history without a superuser shell.
-- * `server_admins.user_id` cascades on user delete: when an admin hard-deletes
--   their own public.users row via the standard `delete_account()` flow, their
--   privilege evaporates. The 'last admin' guard lives in the RPC layer
--   (migration 025), not here — `delete_account()` is intentionally orthogonal.
-- * Bootstrap: see `infra/db-init/10-server-admin-seed.sh`. The seed reads
--   SERVER_ADMIN_EMAIL on FIRST volume init only. For dev (where the volume is
--   long-lived) we additionally seed Ana as admin via supabase/seed.sql.

CREATE TABLE public.server_admins (
    user_id    uuid        PRIMARY KEY REFERENCES public.users(id) ON DELETE CASCADE,
    granted_by uuid        NULL REFERENCES public.users(id) ON DELETE SET NULL,
    granted_at timestamptz NOT NULL DEFAULT now()
);

ALTER TABLE public.server_admins ENABLE ROW LEVEL SECURITY;

-- ── is_server_admin() ───────────────────────────────────────────────────────
-- Declared BEFORE the RLS policy so the policy can call it. The function is
-- SECURITY DEFINER → it bypasses RLS on `server_admins`, which is the only way
-- to break the otherwise-recursive policy ("you can see rows if you ARE in
-- this table" → the inner SELECT triggers the same policy → infinite
-- recursion, observed empirically before this rewrite).
--
-- The default-arg form lets RLS-style call-sites write `is_server_admin()` and
-- get `auth.uid()` for free, matching the shape of `is_admin()` / `is_member()`
-- from migration 003.
CREATE OR REPLACE FUNCTION public.is_server_admin(p_user uuid DEFAULT auth.uid())
RETURNS boolean
LANGUAGE sql
STABLE
SECURITY DEFINER
SET search_path = public, auth
AS $$
    SELECT EXISTS (
        SELECT 1 FROM public.server_admins WHERE user_id = p_user
    );
$$;

COMMENT ON FUNCTION public.is_server_admin(uuid) IS
    'Returns true if the given user (default auth.uid()) is a server admin.';

REVOKE ALL ON FUNCTION public.is_server_admin(uuid) FROM PUBLIC;
GRANT EXECUTE ON FUNCTION public.is_server_admin(uuid) TO anon, authenticated;

-- A user can always read their own row (so the client can compute
-- $isServerAdmin without escalation); other admins can read the full list.
-- The admin branch uses is_server_admin() — NOT an inline EXISTS — to bypass
-- the otherwise-recursive RLS evaluation (see function comment above).
-- No INSERT/UPDATE/DELETE policy — only SECURITY DEFINER RPCs touch this.
CREATE POLICY "select_self_or_admin" ON public.server_admins
    FOR SELECT
    USING (
        user_id = auth.uid()
        OR public.is_server_admin()
    );

-- ── admin_actions ──────────────────────────────────────────────────────────
-- Append-only audit log. Every privileged RPC in migration 025 writes one
-- row before mutating state. `actor_id` is RESTRICT so the audit trail
-- never silently disappears when an admin's user row is removed — the FK
-- forces an explicit decision (delete the actions first, or transfer
-- ownership). Operationally the audit log is intended to outlive admins.

CREATE TABLE public.admin_actions (
    id          uuid        PRIMARY KEY DEFAULT gen_random_uuid(),
    actor_id    uuid        NOT NULL REFERENCES public.users(id) ON DELETE RESTRICT,
    action      text        NOT NULL,
    target_type text        NOT NULL,
    target_id   uuid        NULL,
    payload     jsonb       NOT NULL DEFAULT '{}'::jsonb,
    created_at  timestamptz NOT NULL DEFAULT now()
);

ALTER TABLE public.admin_actions ENABLE ROW LEVEL SECURITY;

-- Only admins can read the log. No write policy: SECURITY DEFINER RPCs only.
CREATE POLICY "select_admin_only" ON public.admin_actions
    FOR SELECT
    USING (public.is_server_admin());

CREATE INDEX admin_actions_actor_idx  ON public.admin_actions (actor_id, created_at DESC);
CREATE INDEX admin_actions_target_idx ON public.admin_actions (target_type, target_id);
CREATE INDEX admin_actions_created_idx ON public.admin_actions (created_at DESC);

COMMENT ON TABLE public.admin_actions IS
    'Append-only audit log of every privileged RPC call. Written exclusively '
    'by SECURITY DEFINER functions in migration 025.';