import type { RateAppliesTo, RateTrigger, RateUnit } from './rate.entity';

/**
 * Which rate units make sense for a given rate shape. The weighting basis is
 * driven by the *type* of thing being billed — a container leg bills per
 * container, bulk freight per ton, an intercity move can be per-km, a
 * cancellation is a flat/per-invoice fee, and overweight is always per excess
 * ton. This keeps the rate table dynamic yet non-conflicting: the admin can
 * only pick a unit the pricing engine knows how to apply.
 *
 * Returned lists are ordered with the most natural/default unit first.
 */
export function allowedRateUnits(input: {
  appliesTo: RateAppliesTo;
  trigger: RateTrigger;
}): RateUnit[] {
  const { appliesTo, trigger } = input;

  // Surcharges (Applies to = Other) are governed by their trigger.
  if (appliesTo === 'OTHER') {
    switch (trigger) {
      case 'OVERWEIGHT':
        // Overweight always bills the excess tonnage — per ton, nothing else.
        return ['PER_TON'];
      case 'REEFER':
      case 'HAZARDOUS':
        // Scale with the freight shape: per container for boxes, per ton for bulk.
        return ['PER_CONTAINER', 'PER_TON'];
      case 'DEMURRAGE':
        return ['PER_CONTAINER', 'PER_TON'];
      case 'WITH_RETURN':
        // Container-only empty-return service — bills per returned container.
        return ['PER_CONTAINER', 'FLAT'];
      case 'CANCELLATION':
        return ['FLAT', 'PER_INVOICE'];
      case 'CUSTOMS_CLEARANCE':
        // Flat per clearance (ONE_TIME contract) / per shipment request (GENERAL).
        return ['FLAT'];
      case 'CONSOLIDATION':
        return ['PER_CONTAINER', 'FLAT'];
      case 'SHIPPING_LINE':
      case 'PIL_EXTRA_FEE':
        return ['PER_CONTAINER', 'FLAT'];
      default:
        return ['FLAT', 'PER_TON', 'PER_CONTAINER'];
    }
  }

  // Base freight + first/last mile scale with the cargo type.
  switch (appliesTo) {
    case 'CONTAINER':
      return ['PER_CONTAINER', 'PER_WAGON'];
    case 'BULK':
      return ['PER_TON', 'PER_WAGON'];
    case 'INTERCITY':
      return ['PER_CONTAINER', 'PER_TON', 'PER_WAGON', 'PER_KM'];
    case 'FIRST_MILE':
    case 'LAST_MILE':
      return ['PER_CONTAINER', 'PER_TON', 'PER_KM', 'FLAT'];
    default:
      return ['FLAT'];
  }
}

/** The default (first / most natural) unit for a rate shape. */
export function defaultRateUnit(input: { appliesTo: RateAppliesTo; trigger: RateTrigger }): RateUnit {
  return allowedRateUnits(input)[0];
}

/** True when `unit` is a valid weighting basis for the given rate shape. */
export function isRateUnitAllowed(input: {
  appliesTo: RateAppliesTo;
  trigger: RateTrigger;
  unit: RateUnit;
}): boolean {
  return allowedRateUnits(input).includes(input.unit);
}