trip-planner/internal/routing/graph_test.go

package routing

import (
	"fmt"
	"testing"
)

func TestFindRouteMaxTransfers(t *testing.T) {
	graph := NewGraph()

	// Create 6 stations: s1, s2, s3, s4, s5, s6
	for i := 0; i < 6; i++ {
		graph.AddNode(&Node{ID: fmt.Sprintf("s%d", i+1), Type: NodeTypeStation, Name: fmt.Sprintf("Station %d", i+1), CityCode: "c1"})
	}

	// Add direct edge s1 -> s6 (0 transfers)
	graph.AddEdge(&Edge{
		From:       graph.Nodes()[0], // s1
		To:         graph.Nodes()[5], // s6
		Kind:       EdgeKindReal,
		Duration:   3600,
		Transport:  "train",
		TransportType: TransportTypeTrain,
		IsTransfer: false,
	})

	// Add chain edges s1->s2->s3->s4->s5->s6 (each is a transfer edge)
	for i := 0; i < 5; i++ {
		graph.AddEdge(&Edge{
			From:       graph.Nodes()[i],
			To:         graph.Nodes()[i+1],
			Kind:       EdgeKindReal,
			Duration:   1000,
			Transport:  "train",
			TransportType: TransportTypeTrain,
			IsTransfer: true,
		})
	}

	// Test with MaxTransfers=0: should only find the direct route (0 transfers)
	opts0 := SearchOptions{MaxTransfers: 0}
	results0 := graph.FindRoutesPareto("s1", "s6", opts0)
	t.Logf("MaxTransfers=0: found %d route(s)", len(results0))
	for _, r := range results0 {
		t.Logf("  Route: duration=%d, transfers=%d", r.TotalDuration, r.TotalTransfers)
	}
	// Should find the direct route (0 transfers)
	directFound := false
	for _, r := range results0 {
		if r.TotalTransfers == 0 {
			directFound = true
			break
		}
	}
	if !directFound {
		t.Error("expected direct route (0 transfers) with MaxTransfers=0")
		return
	}

	// Test with MaxTransfers=1: should find direct route + 1-transfer route if any
	opts1 := SearchOptions{MaxTransfers: 1}
	results1 := graph.FindRoutesPareto("s1", "s6", opts1)
	t.Logf("MaxTransfers=1: found %d route(s)", len(results1))
	for _, r := range results1 {
		t.Logf("  Route: duration=%d, transfers=%d", r.TotalDuration, r.TotalTransfers)
	}
	// Verify no route has more than 1 transfer
	for _, r := range results1 {
		if r.TotalTransfers > 1 {
			t.Errorf("route with MaxTransfers=1 has %d transfers, expected <= 1", r.TotalTransfers)
		}
	}

	// Test with MaxTransfers=2: should find more routes
	opts2 := SearchOptions{MaxTransfers: 2}
	results2 := graph.FindRoutesPareto("s1", "s6", opts2)
	t.Logf("MaxTransfers=2: found %d route(s)", len(results2))
	for _, r := range results2 {
		t.Logf("  Route: duration=%d, transfers=%d", r.TotalDuration, r.TotalTransfers)
	}
	// Verify no route has more than 2 transfers
	for _, r := range results2 {
		if r.TotalTransfers > 2 {
			t.Errorf("route with MaxTransfers=2 has %d transfers, expected <= 2", r.TotalTransfers)
		}
	}
}

// TestLazyExpansionDepthLimit tests that BFS stops expanding when transfer depth exceeds MaxTransfers.
func TestLazyExpansionDepthLimit(t *testing.T) {
	graph := NewGraph()

	// Create 7 stations: s1, s2, s3, s4, s5, s6, s7
	for i := 0; i < 7; i++ {
		graph.AddNode(&Node{ID: fmt.Sprintf("s%d", i+1), Type: NodeTypeStation, Name: fmt.Sprintf("Station %d", i+1), CityCode: "c1"})
	}

	// Add chain of transfer edges s1->s2->s3->s4->s5->s6->s7
	for i := 0; i < 6; i++ {
		graph.AddEdge(&Edge{
			From:       graph.Nodes()[i],
			To:         graph.Nodes()[i+1],
			Kind:       EdgeKindReal,
			Duration:   100,
			Transport:  "train",
			TransportType: TransportTypeTrain,
			IsTransfer: true,
		})
	}

	// Test with MaxTransfers=2: should only find routes with <= 2 transfers
	opts2 := SearchOptions{MaxTransfers: 2}
	results2 := graph.FindRoute("s1", "s7", opts2)
	if results2 != nil {
		t.Logf("MaxTransfers=2: found route with %d transfers", results2.TotalTransfers)
		for _, leg := range results2.Legs {
			t.Logf("  Leg: %s -> %s (isTransfer=%v)", leg.From.Name, leg.To.Name, leg.IsTransfer)
		}
		// With MaxTransfers=2, a chain of 6 transfers (s1->...->s7) should not be found
		if results2.TotalTransfers > 2 {
			t.Errorf("expected <= 2 transfers with MaxTransfers=2, got %d", results2.TotalTransfers)
		}
	}

	// Test with MaxTransfers=5: should allow routes with up to 5 transfers
	opts5 := SearchOptions{MaxTransfers: 5}
	results5 := graph.FindRoute("s1", "s7", opts5)
	if results5 != nil {
		t.Logf("MaxTransfers=5: found route with %d transfers", results5.TotalTransfers)
		if results5.TotalTransfers > 5 {
			t.Errorf("expected <= 5 transfers with MaxTransfers=5, got %d", results5.TotalTransfers)
		}
	} else {
		t.Log("MaxTransfers=5: no route found (linear chain may still exceed limit)")
	}

	// Test with MaxTransfers=0: should only find direct routes (no transfers)
	opts0 := SearchOptions{MaxTransfers: 0}
	results0 := graph.FindRoute("s1", "s7", opts0)
	if results0 != nil {
		t.Logf("MaxTransfers=0: found route with %d transfers", results0.TotalTransfers)
		for _, leg := range results0.Legs {
			t.Logf("  Leg: %s -> %s (isTransfer=%v)", leg.From.Name, leg.To.Name, leg.IsTransfer)
		}
		if results0.TotalTransfers != 0 {
			t.Errorf("expected 0 transfers with MaxTransfers=0, got %d", results0.TotalTransfers)
		}
	} else {
		t.Log("MaxTransfers=0: no direct route s1->s7 found (only chain edges exist)")
	}
}