doormile_backend/internal/routing/dropforleg_test.go

package routing

import (
	"testing"

	"doormile/internal/legs"
)

// Where a rider's leg actually ends.
//
// The bug these tests exist to prevent, found while testing the base-handover
// flow with a bulk sheet of intercity orders: the sequencer read
// pickupbookings.deliverylatitude for every active assignment, with no idea
// whether the parcel was hub-routed. For a Coimbatore → Chennai booking that
// told the route optimizer the rider was riding 430 km to the receiver, when
// the rider's real next stop is a base a few kilometres away.
//
// Wrong on its own — a 430 km "stop" is not a stop anyone makes — and worse in
// company: one such destination in a rider's set drags the ordering of every
// genuine local stop beside it, because the solver is optimising a journey
// nobody is going to make.

// Coimbatore pickup, and the local base a rider hands parcels to.
const (
	pickPin                = "641025"
	pickLat, pickLng       = 11.0168, 76.9558
	baseLat, baseLng       = 11.0272, 76.9905
	localPin               = "641004"
	localLat, localLng     = 11.029, 76.993
	chennaiPin             = "600001"
	chennaiLat, chennaiLng = 13.091, 80.285
)

func TestDropForLeg(t *testing.T) {
	cases := []struct {
		name             string
		deliveryPin      string
		dLat, dLng       float64
		baseLat, baseLng float64
		wantLat, wantLng float64
		wantOK           bool
		why              string
	}{
		{
			name:        "a hyperlocal parcel ends at the receiver",
			deliveryPin: localPin, dLat: localLat, dLng: localLng,
			baseLat: baseLat, baseLng: baseLng,
			wantLat: localLat, wantLng: localLng, wantOK: true,
			why: "same postal area — the collecting rider carries it all the way",
		},
		{
			name:        "an intercity parcel ends at the base, not in Chennai",
			deliveryPin: chennaiPin, dLat: chennaiLat, dLng: chennaiLng,
			baseLat: baseLat, baseLng: baseLng,
			wantLat: baseLat, wantLng: baseLng, wantOK: true,
			why: "this is the whole fix — the rider rides to the base",
		},
		{
			name:        "a nearby but different postal area still ends at the base",
			deliveryPin: "642001", dLat: 10.658, dLng: 77.008,
			baseLat: baseLat, baseLng: baseLng,
			wantLat: baseLat, wantLng: baseLng, wantOK: true,
			why: "Pollachi is 40km away; the prefix rule decides, not the distance",
		},
		{
			name:        "no pincode and a short hop still ends at the receiver",
			deliveryPin: "", dLat: 11.05, dLng: 77.01,
			baseLat: baseLat, baseLng: baseLng,
			wantLat: 11.05, wantLng: 77.01, wantOK: true,
			why: "the distance fallback puts it inside 30km",
		},
		{
			name:        "no pincode and a long haul ends at the base",
			deliveryPin: "", dLat: chennaiLat, dLng: chennaiLng,
			baseLat: baseLat, baseLng: baseLng,
			wantLat: baseLat, wantLng: baseLng, wantOK: true,
			why: "the distance fallback puts it far outside 30km",
		},
	}

	for _, tc := range cases {
		t.Run(tc.name, func(t *testing.T) {
			lat, lng, ok := dropForLeg(pickPin, tc.deliveryPin,
				pickLat, pickLng, tc.dLat, tc.dLng, tc.baseLat, tc.baseLng)
			if ok != tc.wantOK {
				t.Fatalf("ok = %v, want %v — %s", ok, tc.wantOK, tc.why)
			}
			if lat != tc.wantLat || lng != tc.wantLng {
				t.Errorf("drop = (%v, %v), want (%v, %v) — %s", lat, lng, tc.wantLat, tc.wantLng, tc.why)
			}
		})
	}
}

func TestDropForLegNeverSendsARiderInterstate(t *testing.T) {
	// The regression guard, stated as the thing that actually matters rather
	// than as a coordinate comparison: whatever the destination, the drop the
	// sequencer is given must be somewhere a rider can plausibly ride to.
	for _, d := range []struct {
		name     string
		pin      string
		lat, lng float64
	}{
		{"Chennai", "600001", 13.091, 80.285},
		{"Hyderabad", "500081", 17.44, 78.3489},
		{"Bengaluru", "560066", 12.9698, 77.75},
		{"Madurai", "625001", 9.9195, 78.119},
	} {
		t.Run(d.name, func(t *testing.T) {
			lat, lng, ok := dropForLeg(pickPin, d.pin, pickLat, pickLng, d.lat, d.lng, baseLat, baseLng)
			if !ok {
				t.Fatal("a stop with a usable base must still be sequenced")
			}
			if lat == d.lat && lng == d.lng {
				t.Fatalf("%s was passed to the optimizer as the rider's own drop", d.name)
			}
			if km := legs.HaversineKM(pickLat, pickLng, lat, lng); km > 50 {
				t.Errorf("drop is %.0f km from the pickup — no rider is making that leg", km)
			}
		})
	}
}

func TestDropForLegSkipsAHubRoutedStopWithNoBase(t *testing.T) {
	// Falling back to the receiver here would be the original bug wearing a
	// different hat: better to leave one stop unsequenced than to skew the
	// ordering of every other stop the rider is carrying.
	_, _, ok := dropForLeg(pickPin, chennaiPin, pickLat, pickLng, chennaiLat, chennaiLng, 0, 0)
	if ok {
		t.Error("a hub-routed stop with no base coordinates must be left out, not pointed at the receiver")
	}
}

func TestDropForLegKeepsAHyperlocalStopWithNoBase(t *testing.T) {
	// A hyperlocal parcel never needed a base, so a missing one is irrelevant
	// to it and must not cost the rider a stop.
	lat, lng, ok := dropForLeg(pickPin, localPin, pickLat, pickLng, localLat, localLng, 0, 0)
	if !ok || lat != localLat || lng != localLng {
		t.Errorf("hyperlocal stop = (%v, %v, %v), want the receiver and ok", lat, lng, ok)
	}
}