/**
 * SQL mirror of `bookingCargoTons()` (train-scheduling/train-capacity.util.ts).
 *
 * Three storage conventions share `bookings.cargo_total_weight_vgm`:
 *  - BULK PER_TON  — the column holds tons.
 *  - BULK PER_ITEM — the column holds an ITEM COUNT; the tons are in
 *    `bulk_total_weight_tons`.
 *  - CONTAINER     — the portal wizard captures VGM per line, not per booking,
 *    and sends 0 (portal NewBookingPage: "containers carry NO weight at the
 *    wizard"). The tons live in `booking_container.total_vgm_tons`. The
 *    backoffice wizard does store a booking-level total, so both shapes exist
 *    in the same table.
 *
 * Hence NULLIF on both columns: a plain
 * `COALESCE(bulk_total_weight_tons, cargo_total_weight_vgm)` stops at the
 * portal's 0 — COALESCE falls through on NULL, never on 0 — and every
 * portal-created container booking reads as 0 tons in exports and reports.
 */
export function bookingTonsSql(alias = 'b'): string {
  return `COALESCE(
    NULLIF(${alias}.bulk_total_weight_tons, 0),
    NULLIF(${alias}.cargo_total_weight_vgm, 0),
    (SELECT SUM(bc.total_vgm_tons) FROM freight.booking_container bc
      WHERE bc.booking_id = ${alias}.id AND bc.deleted_at IS NULL),
    0)`;
}