-- One-shot: run in Supabase Dashboard → SQL Editor **after** schemas/alter_users_rc_bigint.sql
-- (requires `users.rc` bigint so large balances support small debits/credits).
-- Atomically debits RC from supply user id 1, credits the buyer, inserts `transactions`.
-- SECURITY DEFINER avoids RLS/trigger edge cases on direct `users` updates from the API.

create or replace function public.purchase_rc(p_buyer_id bigint, p_amount bigint)
returns jsonb
language plpgsql
security definer
set search_path = public
as $$
declare
  v_supply bigint := 1;
begin
  if p_buyer_id is null or p_buyer_id < 1 then
    raise exception 'invalid_buyer';
  end if;
  if p_amount is null or p_amount <= 0 then
    raise exception 'invalid_amount';
  end if;

  -- Same account: net balance must stay the same; only log for audit.
  if p_buyer_id = v_supply then
    insert into public.transactions ("from", "to", amount, remarks)
    values (v_supply, v_supply, p_amount, 'purchase');
    return (
      select to_jsonb(t)
      from (
        select id, username, cc, rc, created_at, last_logged_at
        from public.users
        where id = p_buyer_id
      ) t
    );
  end if;

  update public.users
  set rc = coalesce(rc, 0) - p_amount
  where id = v_supply
    and coalesce(rc, 0) >= p_amount;
  if not found then
    raise exception 'insufficient_supply';
  end if;

  update public.users
  set rc = coalesce(rc, 0) + p_amount
  where id = p_buyer_id;
  if not found then
    raise exception 'buyer_not_found';
  end if;

  insert into public.transactions ("from", "to", amount, remarks)
  values (v_supply, p_buyer_id, p_amount, 'purchase');

  return (
    select to_jsonb(t)
    from (
      select id, username, cc, rc, created_at, last_logged_at
      from public.users
      where id = p_buyer_id
    ) t
  );
end;
$$;

revoke all on function public.purchase_rc(bigint, bigint) from public;
grant execute on function public.purchase_rc(bigint, bigint) to service_role;