Enhance bulk booking handling and wagon capacity calculations across services

apps/edr-freight-api/src/modules/train-scheduling/train-capacity.util.spec.ts

@@ -6,6 +6,7 @@ import {
   deriveTrainCapacityFromLocomotive,
   grossWagonWeightTons,
   minLocomotiveLimits,
+  sizePartialOfferWagons,
 } from './train-capacity.util';
 
 describe('train-capacity.util', () => {
@@ -185,4 +186,54 @@ describe('train-capacity.util', () => {
     expect(limits?.maxPullWeightTons).toBe(3500);
     expect(limits?.overageToleranceTons).toBe(20);
   });
+
+  describe('sizePartialOfferWagons', () => {
+    it('sizes a bulk split by the WEIGHT axis when the pull limit binds, not wagon slots', () => {
+      // The 3500T-train scenario: two 1000T bookings boarded gross (each 15 PW2
+      // wagons: 1000 + 378 tare = 1378), leaving 744T of pull weight but plenty
+      // of slots/length. The boundary 1000T booking (15 wagons) must be offered
+      // the largest part 744T can carry: 8 wagons whose tare is 201.6T, hauling
+      // 542.4T of cargo — gross exactly 744.
+      const offer = sizePartialOfferWagons(
+        { wagons: 40, weightTons: 744, lengthMeters: 500 },
+        15,
+        pw2,
+      );
+      expect(offer).toEqual({ wagons: 8, maxCargoTons: 542.4 });
+    });
+
+    it('still sizes by wagon slots when they bind first (legacy behavior)', () => {
+      const offer = sizePartialOfferWagons(
+        { wagons: 3, weightTons: 100000, lengthMeters: 100000 },
+        15,
+        pw2,
+      );
+      expect(offer?.wagons).toBe(3);
+    });
+
+    it('sizes by the LENGTH axis when it binds first', () => {
+      // 60m of train left → 3 PW2 (17.066m) fit, the 4th does not.
+      const offer = sizePartialOfferWagons(
+        { wagons: 40, weightTons: 100000, lengthMeters: 60 },
+        15,
+        pw2,
+      );
+      expect(offer?.wagons).toBe(3);
+    });
+
+    it('never offers all of the booking — a split is a strict subset', () => {
+      const offer = sizePartialOfferWagons(
+        { wagons: 40, weightTons: 100000, lengthMeters: 100000 },
+        15,
+        pw2,
+      );
+      expect(offer?.wagons).toBe(14);
+    });
+
+    it('returns null when not even one part-loaded wagon fits the weight room', () => {
+      expect(
+        sizePartialOfferWagons({ wagons: 5, weightTons: 20, lengthMeters: 500 }, 15, pw2),
+      ).toBeNull();
+    });
+  });
 });