module Arel
  module Visitors
    class Oracle12 < Arel::Visitors::ToSql
      private

      def visit_Arel_Nodes_SelectStatement o, collector
        # Oracle does not allow LIMIT clause with select for update
        if o.limit && o.lock
          raise ArgumentError, <<-MSG
            'Combination of limit and lock is not supported.
            because generated SQL statements
            `SELECT FOR UPDATE and FETCH FIRST n ROWS` generates ORA-02014.`
          MSG
        end
        super
      end

      def visit_Arel_Nodes_SelectOptions o, collector
        collector = maybe_visit o.offset, collector
        collector = maybe_visit o.limit, collector
        collector = maybe_visit o.lock, collector
      end

      def visit_Arel_Nodes_Limit o, collector
        collector << "FETCH FIRST "
        collector = visit o.expr, collector
        collector << " ROWS ONLY"
      end

      def visit_Arel_Nodes_Offset o, collector
        collector << "OFFSET "
        visit o.expr, collector
        collector << " ROWS"
      end

      def visit_Arel_Nodes_Except o, collector
        collector << "( "
        collector = infix_value o, collector, " MINUS "
        collector << " )"
      end

      def visit_Arel_Nodes_UpdateStatement o, collector
        # Oracle does not allow ORDER BY/LIMIT in UPDATEs.
        if o.orders.any? && o.limit.nil?
          # However, there is no harm in silently eating the ORDER BY clause if no LIMIT has been provided,
          # otherwise let the user deal with the error
          o = o.dup
          o.orders = []
        end

        super
      end

      def visit_Arel_Nodes_BindParam o, collector
        collector.add_bind(o) { |i| ":a#{i}" }
      end
    end
  end
end
