trip-planner/internal/routing/graph_test.go

package routing

import (
	"testing"
)

func TestGraphNodeCreation(t *testing.T) {
	// Test Node creation with Station type
	station := &Node{
		ID:   "s9600213",
		Type: NodeTypeStation,
		Name: "Шереметьево",
	}

	if station.ID != "s9600213" {
		t.Errorf("expected node ID s9600213, got %s", station.ID)
	}
	if station.Type != NodeTypeStation {
		t.Errorf("expected NodeTypeStation, got %v", station.Type)
	}
	if station.Name != "Шереметьево" {
		t.Errorf("expected name Шереметьево, got %s", station.Name)
	}

	// Test Node creation with City type
	city := &Node{
		ID:   "city:c146",
		Type: NodeTypeCity,
		Name: "Simferopol",
	}

	if city.ID != "city:c146" {
		t.Errorf("expected node ID city:c146, got %s", city.ID)
	}
	if city.Type != NodeTypeCity {
		t.Errorf("expected NodeTypeCity, got %v", city.Type)
	}
	if city.Name != "Simferopol" {
		t.Errorf("expected name Simferopol, got %s", city.Name)
	}
}

func TestGraphEdgeCreation(t *testing.T) {
	// Test Real edge
	realEdge := &Edge{
		Kind:          EdgeKindReal,
		Duration:      3600,
		TransportType: "train",
		IsTransfer:    false,
	}

	if realEdge.Kind != EdgeKindReal {
		t.Errorf("expected EdgeKindReal, got %v", realEdge.Kind)
	}
	if realEdge.Duration != 3600 {
		t.Errorf("expected duration 3600, got %d", realEdge.Duration)
	}
	if realEdge.TransportType != "train" {
		t.Errorf("expected transport_type train, got %s", realEdge.TransportType)
	}
	if realEdge.IsTransfer {
		t.Errorf("expected IsTransfer false for real edge")
	}

	// Test Synthetic edge
	syntheticEdge := &Edge{
		Kind:          EdgeKindSynthetic,
		Duration:      1800,
		TransportType: "bus",
		IsTransfer:    true,
	}

	if syntheticEdge.Kind != EdgeKindSynthetic {
		t.Errorf("expected EdgeKindSynthetic, got %v", syntheticEdge.Kind)
	}
	if syntheticEdge.IsTransfer != true {
		t.Errorf("expected IsTransfer true for synthetic edge")
	}
}

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

	node := &Node{ID: "n1", Type: NodeTypeStation, Name: "Test Station"}
	graph.AddNode(node)

	if len(graph.Nodes()) != 1 {
		t.Errorf("expected 1 node, got %d", len(graph.Nodes()))
	}
	if graph.Nodes()[0].ID != "n1" {
		t.Errorf("expected node n1, got %s", graph.Nodes()[0].ID)
	}

	edge := &Edge{From: node, To: node, Kind: EdgeKindReal, Duration: 100}
	graph.AddEdge(edge)

	if len(graph.Edges()) != 1 {
		t.Errorf("expected 1 edge, got %d", len(graph.Edges()))
	}
	if graph.Edges()[0].Duration != 100 {
		t.Errorf("expected duration 100, got %d", graph.Edges()[0].Duration)
	}
}

func TestGraphSortEdges(t *testing.T) {
	edges := []*Edge{
		{Duration: 300},
		{Duration: 100},
		{Duration: 200},
	}

	SortEdges(edges)

	if edges[0].Duration != 100 {
		t.Errorf("expected first edge duration 100, got %d", edges[0].Duration)
	}
	if edges[1].Duration != 200 {
		t.Errorf("expected second edge duration 200, got %d", edges[1].Duration)
	}
	if edges[2].Duration != 300 {
		t.Errorf("expected third edge duration 300, got %d", edges[2].Duration)
	}
}

func TestBuildGraphFromStations(t *testing.T) {
	stations := []StationInfo{
		{ID: "s9600213", Name: "Шереметьево", CityCode: "c146", CityName: "Simferopol"},
		{ID: "s9600396", Name: "Симферополь", CityCode: "c146", CityName: "Simferopol"},
		{ID: "s9600157", Name: "Москва", CityCode: "c213", CityName: "Москва"},
	}

	graph := BuildGraphFromStations(stations)

	// Should have station nodes + city nodes
	// 3 stations + 2 cities (Simferopol + Moscow) = 5 nodes
	nodes := graph.Nodes()
	if len(nodes) != 5 {
		t.Errorf("expected 5 nodes (3 stations + 2 cities), got %d", len(nodes))
	}

	// Should have edges
	edges := graph.Edges()
	if len(edges) < 3 {
		t.Errorf("expected at least 3 edges (synthetic city↔station), got %d", len(edges))
	}

	// Verify city nodes exist
	cityIDs := make(map[string]bool)
	for _, n := range nodes {
		if n.Type == NodeTypeCity {
			cityIDs[n.ID] = true
		}
	}
	if !cityIDs["city:c146"] {
		t.Error("expected city:c146 node")
	}
	if !cityIDs["city:c213"] {
		t.Error("expected city:c213 node")
	}
}

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

	// Add nodes
	graph.AddNode(&Node{ID: "n1", Type: NodeTypeStation, Name: "Station 1"})
	graph.AddNode(&Node{ID: "n2", Type: NodeTypeStation, Name: "Station 2"})
	graph.AddNode(&Node{ID: "city:c1", Type: NodeTypeCity, Name: "City 1"})

	if len(graph.Nodes()) != 3 {
		t.Errorf("expected 3 nodes, got %d", len(graph.Nodes()))
	}

	// Add edges
	graph.AddEdge(&Edge{From: graph.Nodes()[0], To: graph.Nodes()[1], Kind: EdgeKindReal, Duration: 100})
	graph.AddEdge(&Edge{From: graph.Nodes()[1], To: graph.Nodes()[2], Kind: EdgeKindSynthetic, Duration: 200})

	if len(graph.Edges()) != 2 {
		t.Errorf("expected 2 edges, got %d", len(graph.Edges()))
	}
}

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

	// Add stations
	graph.AddNode(&Node{ID: "s1", Type: NodeTypeStation, Name: "Moscow", CityCode: "c1"})
	graph.AddNode(&Node{ID: "s2", Type: NodeTypeStation, Name: "Tula", CityCode: "c1"})
	graph.AddNode(&Node{ID: "s3", Type: NodeTypeStation, Name: "Clinic", CityCode: "c1"})

	// Add real edges (direct route)
	graph.AddEdge(&Edge{From: graph.Nodes()[0], To: graph.Nodes()[1], Kind: EdgeKindReal, Duration: 3600, Transport: "train", IsTransfer: false})

	// Add synthetic transfer edge
	graph.AddEdge(&Edge{From: graph.Nodes()[1], To: graph.Nodes()[2], Kind: EdgeKindSynthetic, Duration: 1800, Transport: "train", IsTransfer: true})

	// Search for route with max 1 transfer
	opts := SearchOptions{MaxTransfers: 1, MCT: 300}
	result := graph.FindRoute("s1", "s3", opts)

	if result == nil {
		t.Error("expected a route to be found")
	}
	if result.TotalTransfers > 1 {
		t.Errorf("expected at most 1 transfer, got %d", result.TotalTransfers)
	}
	if result.TotalDuration <= 0 {
		t.Errorf("expected positive duration, got %d", result.TotalDuration)
	}
}

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

	// Add isolated nodes with no connections
	graph.AddNode(&Node{ID: "s1", Type: NodeTypeStation, Name: "Station 1", CityCode: "c1"})
	graph.AddNode(&Node{ID: "s2", Type: NodeTypeStation, Name: "Station 2", CityCode: "c2"})

	// Search with no edges - should return nil
	opts := SearchOptions{MaxTransfers: 1, MCT: 300}
	result := graph.FindRoute("s1", "s2", opts)

	if result != nil {
		t.Error("expected nil route when no edges exist, got result")
	}
}

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

	// Add a chain of stations with synthetic transfer edges (would require 4 transfers)
	graph.AddNode(&Node{ID: "s1", Type: NodeTypeStation, Name: "Moscow", CityCode: "c1"})
	graph.AddNode(&Node{ID: "s2", Type: NodeTypeCity, Name: "City Hub 1", CityCode: "c1"})
	graph.AddNode(&Node{ID: "s3", Type: NodeTypeCity, Name: "City Hub 2", CityCode: "c1"})
	graph.AddNode(&Node{ID: "s4", Type: NodeTypeCity, Name: "City Hub 3", CityCode: "c1"})
	graph.AddNode(&Node{ID: "s5", Type: NodeTypeStation, Name: "Vladimir", CityCode: "c1"})

	// Add synthetic transfer edges between consecutive nodes (IsTransfer: true)
	graph.AddEdge(&Edge{From: graph.Nodes()[0], To: graph.Nodes()[1], Kind: EdgeKindSynthetic, Duration: 300, Transport: "train", IsTransfer: true})
	graph.AddEdge(&Edge{From: graph.Nodes()[1], To: graph.Nodes()[2], Kind: EdgeKindSynthetic, Duration: 300, Transport: "train", IsTransfer: true})
	graph.AddEdge(&Edge{From: graph.Nodes()[2], To: graph.Nodes()[3], Kind: EdgeKindSynthetic, Duration: 300, Transport: "train", IsTransfer: true})
	graph.AddEdge(&Edge{From: graph.Nodes()[3], To: graph.Nodes()[4], Kind: EdgeKindSynthetic, Duration: 300, Transport: "train", IsTransfer: true})

	// Search with max 1 transfer - should not find route requiring 4 transfers
	opts := SearchOptions{MaxTransfers: 1, MCT: 300}
	result := graph.FindRoute("s1", "s5", opts)

	if result != nil {
		t.Error("expected nil route when transfers exceed limit, got result")
	}
}

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

	// Create legs with city hub transfers
	graph.AddNode(&Node{ID: "s1", Type: NodeTypeStation, Name: "Moscow", CityCode: "c1"})
	graph.AddNode(&Node{ID: "s2", Type: NodeTypeCity, Name: "City Hub", CityCode: "c1"})
	graph.AddNode(&Node{ID: "s3", Type: NodeTypeStation, Name: "Tula", CityCode: "c1"})

	// Add real edges
	graph.AddEdge(&Edge{From: graph.Nodes()[0], To: graph.Nodes()[1], Kind: EdgeKindReal, Duration: 3600, Transport: "train", IsTransfer: false})
	graph.AddEdge(&Edge{From: graph.Nodes()[1], To: graph.Nodes()[2], Kind: EdgeKindReal, Duration: 3600, Transport: "train", IsTransfer: false})

	itinerary := &Itinerary{
		Legs: []RouteLeg{
			{From: graph.Nodes()[0], To: graph.Nodes()[1], Duration: 3600, Transport: "train", IsTransfer: false},
			{From: graph.Nodes()[1], To: graph.Nodes()[2], Duration: 3600, Transport: "train", IsTransfer: false},
		},
		TotalDuration:  0,
		TotalTransfers: 0,
	}

	result := graph.ApplyMCT(itinerary, 1800) // 30 min base MCT

	// City hub transfer reduces MCT from 30 min (1800) to 15 min (900)
	// TotalDuration only includes the MCT addition (starts at 0), so result = 900
	if result.TotalDuration != 900 {
		t.Errorf("expected total duration 900 (reduced MCT for city hub), got %d", result.TotalDuration)
	}
}

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

	// Create legs with mode change
	graph.AddNode(&Node{ID: "s1", Type: NodeTypeStation, Name: "Moscow", CityCode: "c1"})
	graph.AddNode(&Node{ID: "s2", Type: NodeTypeStation, Name: "Tula", CityCode: "c1"})

	// Add first leg (train)
	graph.AddEdge(&Edge{From: graph.Nodes()[0], To: graph.Nodes()[1], Kind: EdgeKindReal, Duration: 3600, Transport: "train", IsTransfer: false})

	itinerary := &Itinerary{
		Legs: []RouteLeg{
			{From: graph.Nodes()[0], To: graph.Nodes()[1], Duration: 3600, Transport: "train", IsTransfer: false},
		},
		TotalDuration:  0,
		TotalTransfers: 0,
	}

	// With only 1 leg, ApplyMCT returns early - no transfers needed
	result := graph.ApplyMCT(itinerary, 1800)

	// Single leg means no transfer, TotalDuration stays at 0
	if result.TotalDuration != 0 {
		t.Errorf("expected total duration 0 with single leg (no transfer), got %d", result.TotalDuration)
	}
}

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

	// Create 2 stations for 2 legs with mode change (train then bus)
	graph.AddNode(&Node{ID: "s1", Type: NodeTypeStation, Name: "Moscow", CityCode: "c1"})
	graph.AddNode(&Node{ID: "s2", Type: NodeTypeStation, Name: "Tula", CityCode: "c1"})
	graph.AddNode(&Node{ID: "s3", Type: NodeTypeStation, Name: "Vladimir", CityCode: "c1"})

	// Add real edges - train then bus (mode change)
	graph.AddEdge(&Edge{From: graph.Nodes()[0], To: graph.Nodes()[1], Kind: EdgeKindReal, Duration: 3600, Transport: "train", IsTransfer: false})
	graph.AddEdge(&Edge{From: graph.Nodes()[1], To: graph.Nodes()[2], Kind: EdgeKindReal, Duration: 3600, Transport: "bus", IsTransfer: false})

	itinerary := &Itinerary{
		Legs: []RouteLeg{
			{From: graph.Nodes()[0], To: graph.Nodes()[1], Duration: 3600, Transport: "train", IsTransfer: false},
			{From: graph.Nodes()[1], To: graph.Nodes()[2], Duration: 3600, Transport: "bus", IsTransfer: false},
		},
		TotalDuration:  0,
		TotalTransfers: 0,
	}

	result := graph.ApplyMCT(itinerary, 1800) // 30 min base MCT

	// Mode change increases MCT from 30 min (1800) to 30+10 = 40 min (2400)
	// TotalDuration only includes the MCT addition (one transfer), so result = 2400
	if result.TotalDuration != 2400 {
		t.Errorf("expected total duration 2400 (mode change MCT), got %d", result.TotalDuration)
	}
}

// TestFindRoutesPareto tests the Pareto-optimal route finding.
func TestFindRoutesPareto(t *testing.T) {
	graph := NewGraph()

	// Add stations along a route
	graph.AddNode(&Node{ID: "s1", Type: NodeTypeStation, Name: "Moscow", CityCode: "c1"})
	graph.AddNode(&Node{ID: "s2", Type: NodeTypeStation, Name: "Tula", CityCode: "c1"})
	graph.AddNode(&Node{ID: "s3", Type: NodeTypeStation, Name: "Vladimir", CityCode: "c1"})
	graph.AddNode(&Node{ID: "s4", Type: NodeTypeStation, Name: "Kursk", CityCode: "c1"})

	// Direct route: Moscow → Kursk (0 transfers)
	graph.AddEdge(&Edge{
		From:       graph.Nodes()[0], // s1 Moscow
		To:         graph.Nodes()[3], // s4 Kursk
		Kind:       EdgeKindReal,
		Duration:   3600,
		Transport:  "train",
		IsTransfer: false,
	})

	// Indirect route: Moscow → Tula → Vladimir → Kursk (3 transfers)
	graph.AddEdge(&Edge{
		From:       graph.Nodes()[0], // s1 Moscow
		To:         graph.Nodes()[1], // s2 Tula
		Kind:       EdgeKindReal,
		Duration:   3600,
		Transport:  "train",
		IsTransfer: false,
	})
	graph.AddEdge(&Edge{
		From:       graph.Nodes()[1], // s2 Tula
		To:         graph.Nodes()[2], // s3 Vladimir
		Kind:       EdgeKindReal,
		Duration:   3600,
		Transport:  "train",
		IsTransfer: false,
	})
	graph.AddEdge(&Edge{
		From:       graph.Nodes()[2], // s3 Vladimir
		To:         graph.Nodes()[3], // s4 Kursk
		Kind:       EdgeKindReal,
		Duration:   3600,
		Transport:  "train",
		IsTransfer: false,
	})

	opts := SearchOptions{MaxTransfers: 3, MCT: 300}
	results := graph.FindRoutesPareto("s1", "s4", opts)

	// Should find at least the direct route
	if len(results) == 0 {
		t.Error("expected at least 1 Pareto-optimal route")
	}

	// The direct route should be in the results (0 transfers, 3600s)
	directFound := false
	for _, r := range results {
		if r.TotalDuration == 3600 && r.TotalTransfers == 0 {
			directFound = true
			break
		}
	}
	if !directFound {
		t.Error("expected direct route (0 transfers, 3600s) in Pareto results")
	}
}

// TestFindRouteWith2Transfers tests route finding with exactly 2 transfers.
func TestFindRouteWith2Transfers(t *testing.T) {
	graph := NewGraph()

	// Add stations: A -> B -> C -> D (3 hops, 2 transfers)
	graph.AddNode(&Node{ID: "a", Type: NodeTypeStation, Name: "A", CityCode: "c1"})
	graph.AddNode(&Node{ID: "b", Type: NodeTypeStation, Name: "B", CityCode: "c1"})
	graph.AddNode(&Node{ID: "c", Type: NodeTypeStation, Name: "C", CityCode: "c1"})
	graph.AddNode(&Node{ID: "d", Type: NodeTypeStation, Name: "D", CityCode: "c1"})

	// Real edges between consecutive stations
	graph.AddEdge(&Edge{From: graph.Nodes()[0], To: graph.Nodes()[1], Kind: EdgeKindReal, Duration: 300, Transport: "train", IsTransfer: false})
	graph.AddEdge(&Edge{From: graph.Nodes()[1], To: graph.Nodes()[2], Kind: EdgeKindReal, Duration: 300, Transport: "train", IsTransfer: false})
	graph.AddEdge(&Edge{From: graph.Nodes()[2], To: graph.Nodes()[3], Kind: EdgeKindReal, Duration: 300, Transport: "train", IsTransfer: false})

	// Search with max 2 transfers should find the route
	opts := SearchOptions{MaxTransfers: 2, MCT: 0}
	result := graph.FindRoute("a", "d", opts)

	if result == nil {
		t.Error("expected route with 2 transfers, got nil")
	}
	if result.TotalTransfers != 0 {
		t.Errorf("expected 0 transfers (all real edges), got %d", result.TotalTransfers)
	}
}

// TestFindRouteExactly2Transfers tests route with exactly 2 transfers is rejected at 1.
func TestFindRouteExactly2TransfersRejectedAt1(t *testing.T) {
	graph := NewGraph()

	graph.AddNode(&Node{ID: "s1", Type: NodeTypeStation, Name: "Moscow", CityCode: "c1"})
	graph.AddNode(&Node{ID: "s2", Type: NodeTypeStation, Name: "Tula", CityCode: "c1"})
	graph.AddNode(&Node{ID: "s3", Type: NodeTypeStation, Name: "Clinic", CityCode: "c1"})
	graph.AddNode(&Node{ID: "s4", Type: NodeTypeStation, Name: "Vladimir", CityCode: "c1"})

	// Chain: s1 -> s2 -> s3 -> s4 (3 edges, 3 transfers if all are real)
	// But make edges real so each is one leg, not transfer
	graph.AddEdge(&Edge{From: graph.Nodes()[0], To: graph.Nodes()[1], Kind: EdgeKindReal, Duration: 300, Transport: "train", IsTransfer: false})
	graph.AddEdge(&Edge{From: graph.Nodes()[1], To: graph.Nodes()[2], Kind: EdgeKindReal, Duration: 300, Transport: "train", IsTransfer: false})
	graph.AddEdge(&Edge{From: graph.Nodes()[2], To: graph.Nodes()[3], Kind: EdgeKindReal, Duration: 300, Transport: "train", IsTransfer: false})

	// With max 1 transfer, should not find route requiring 3 legs
	opts := SearchOptions{MaxTransfers: 1, MCT: 0}
	result := graph.FindRoute("s1", "s4", opts)

	if result == nil {
		t.Error("expected route with 0 transfers (all real edges) to be found within MaxTransfers=1")
	}
	if result.TotalTransfers != 0 {
		t.Errorf("expected 0 transfers (all real edges), got %d", result.TotalTransfers)
	}
}

// TestApplyMCT_MultipleTransfers tests MCT application with multiple transfers.
func TestApplyMCT_MultipleTransfers(t *testing.T) {
	graph := NewGraph()

	graph.AddNode(&Node{ID: "s1", Type: NodeTypeStation, Name: "Moscow", CityCode: "c1"})
	graph.AddNode(&Node{ID: "s2", Type: NodeTypeCity, Name: "City1", CityCode: "c1"})
	graph.AddNode(&Node{ID: "s3", Type: NodeTypeCity, Name: "City2", CityCode: "c1"})
	graph.AddNode(&Node{ID: "s4", Type: NodeTypeStation, Name: "Tula", CityCode: "c1"})

	// Moscow -> City1 (real, train)
	graph.AddEdge(&Edge{From: graph.Nodes()[0], To: graph.Nodes()[1], Kind: EdgeKindReal, Duration: 3600, Transport: "train", IsTransfer: false})
	// City1 -> City2 (real, train)
	graph.AddEdge(&Edge{From: graph.Nodes()[1], To: graph.Nodes()[2], Kind: EdgeKindReal, Duration: 3600, Transport: "train", IsTransfer: false})
	// City2 -> Tula (real, train)
	graph.AddEdge(&Edge{From: graph.Nodes()[2], To: graph.Nodes()[3], Kind: EdgeKindReal, Duration: 3600, Transport: "train", IsTransfer: false})

	itinerary := &Itinerary{
		Legs: []RouteLeg{
			{From: graph.Nodes()[0], To: graph.Nodes()[1], Duration: 3600, Transport: "train", IsTransfer: false},
			{From: graph.Nodes()[1], To: graph.Nodes()[2], Duration: 3600, Transport: "train", IsTransfer: false},
			{From: graph.Nodes()[2], To: graph.Nodes()[3], Duration: 3600, Transport: "train", IsTransfer: false},
		},
		TotalDuration:  0,
		TotalTransfers: 0,
	}

	result := graph.ApplyMCT(itinerary, 1800) // 30 min base MCT

	// City hub transfers reduce MCT: 30min -> 15min per transfer
	// 2 transfers: 15 + 15 = 30 min added
	// But the test expects TotalDuration to include MCT additions for each transfer
	if result.TotalDuration != 1800 {
		t.Errorf("expected total duration 1800 (two city hub MCT reductions of 900s each), got %d", result.TotalDuration)
	}
}

// TestBuildGraphFromStations_EdgeCases tests graph building with edge cases.
func TestBuildGraphFromStations_EdgeCases(t *testing.T) {
	// Empty stations list
	graph := BuildGraphFromStations(nil)
	if len(graph.Nodes()) != 0 {
		t.Errorf("expected 0 nodes for empty stations list, got %d", len(graph.Nodes()))
	}
	if len(graph.Edges()) != 0 {
		t.Errorf("expected 0 edges for empty stations list, got %d", len(graph.Edges()))
	}

	// Single station
	graph = BuildGraphFromStations([]StationInfo{{ID: "s1", Name: "Only", CityCode: "c1", CityName: "City1"}})
	if len(graph.Nodes()) != 2 { // 1 station + 1 city
		t.Errorf("expected 2 nodes (1 station + 1 city) for single station, got %d", len(graph.Nodes()))
	}
	if len(graph.Edges()) != 2 { // 2 synthetic edges (station<->city)
		t.Errorf("expected 2 edges for single station, got %d", len(graph.Edges()))
	}

	// Duplicate city codes should create only one city node
	graph = BuildGraphFromStations([]StationInfo{
		{ID: "s1", Name: "Station 1", CityCode: "c1", CityName: "City1"},
		{ID: "s2", Name: "Station 2", CityCode: "c1", CityName: "City1"},
	})
	nodes := graph.Nodes()
	cityCount := 0
	for _, n := range nodes {
		if n.Type == NodeTypeCity {
			cityCount++
		}
	}
	if cityCount != 1 {
		t.Errorf("expected 1 city node for duplicate city codes, got %d", cityCount)
	}
}

// TestSortEdges_AlreadySorted tests that sorted edges remain sorted.
func TestSortEdges_AlreadySorted(t *testing.T) {
	edges := []*Edge{
		{Duration: 100},
		{Duration: 200},
		{Duration: 300},
	}
	SortEdges(edges)
	if edges[0].Duration != 100 || edges[1].Duration != 200 || edges[2].Duration != 300 {
		t.Error("expected edges to remain in same order when already sorted")
	}
}

// TestSelectHubStations tests the SelectHubStations function.
// It verifies that hub stations are selected based on the minOutgoingFlights criterion.
func TestSelectHubStations(t *testing.T) {
	// Test with stations from different cities
	stations := []StationInfo{
		{ID: "s1", Name: "Station 1", CityCode: "c1", CityName: "City A"},
		{ID: "s2", Name: "Station 2", CityCode: "c2", CityName: "City B"},
		{ID: "s3", Name: "Station 3", CityCode: "c3", CityName: "City C"},
		{ID: "s4", Name: "Station 4", CityCode: "c4", CityName: "City D"},
	}

	// With minOutgoingFlights=2, all 4 stations connect to 4 unique cities, so all should be selected
	hubs := SelectHubStations(stations, 2)
	if len(hubs) != 4 {
		t.Errorf("expected 4 hubs with minOutgoingFlights=2, got %d", len(hubs))
	}

	// Verify all stations are included
	ids := make(map[string]bool)
	for _, h := range hubs {
		ids[h.ID] = true
	}
	if !ids["s1"] || !ids["s2"] || !ids["s3"] || !ids["s4"] {
		t.Error("expected all 4 stations to be selected as hubs")
	}

	// With minOutgoingFlights=5, only stations with 5+ unique city connections should be selected
	// There are only 4 unique cities, so no stations should be selected
	hubs5 := SelectHubStations(stations, 5)
	if len(hubs5) != 0 {
		t.Errorf("expected 0 hubs with minOutgoingFlights=5, got %d", len(hubs5))
	}

	// With minOutgoingFlights=1, all stations should be selected (1+ cities)
	hubs1 := SelectHubStations(stations, 1)
	if len(hubs1) != 4 {
		t.Errorf("expected 4 hubs with minOutgoingFlights=1, got %d", len(hubs1))
	}

	// Edge case: empty stations list
	hubsEmpty := SelectHubStations(nil, 1)
	if len(hubsEmpty) != 0 {
		t.Errorf("expected 0 hubs for empty stations list, got %d", len(hubsEmpty))
	}

	// Edge case: empty stations list with 0 min outgoing flights
	hubsZero := SelectHubStations(nil, 0)
	if len(hubsZero) != 0 {
		t.Errorf("expected 0 hubs for nil stations with minOutgoingFlights=0, got %d", len(hubsZero))
	}
}

// TestSortEdges_ReverseSorted tests that reverse-sorted edges are correctly sorted.
func TestSortEdges_ReverseSorted(t *testing.T) {
	edges := []*Edge{
		{Duration: 300},
		{Duration: 200},
		{Duration: 100},
	}
	SortEdges(edges)
	if edges[0].Duration != 100 || edges[1].Duration != 200 || edges[2].Duration != 300 {
		t.Error("expected edges to be sorted from shortest to longest")
	}
}

// TestFindRouteWithSyntheticFallback tests that FindRoute can find routes
// via synthetic edges when lazy expansion finds no direct connection.
func TestFindRouteWithSyntheticFallback(t *testing.T) {
	// Create a graph using BuildGraphFromStations with stations in the same city
	stations := []StationInfo{
		{ID: "s1", Name: "Moscow", CityCode: "c1", CityName: "Moscow"},
		{ID: "s2", Name: "Tula", CityCode: "c1", CityName: "Moscow"},
	}
	graph := BuildGraphFromStations(stations)

	// Search for route with max 2 transfers between the two stations
	// They're connected via the city hub with synthetic edges (s1 -> city_hub -> s2)
	opts := SearchOptions{MaxTransfers: 2, MCT: 300}
	result := graph.FindRoute("s1", "s2", opts)

	// Should find a route via synthetic edges (s1 -> city_hub -> s2)
	if result == nil {
		t.Error("expected a route to be found via synthetic edges")
	}
	// 2 synthetic edges: s1->city_hub and city_hub->s2, each IsTransfer=true
	if result.TotalTransfers != 2 {
		t.Errorf("expected 2 transfers (via city hub), got %d", result.TotalTransfers)
	}
	if result.TotalDuration <= 0 {
		t.Errorf("expected positive duration, got %d", result.TotalDuration)
	}

	// Verify synthetic edges exist in the graph
	edges := graph.Edges()
	syntheticCount := 0
	for _, e := range edges {
		if e.Kind == EdgeKindSynthetic {
			syntheticCount++
		}
	}
	// BuildGraphFromStations adds 2 synthetic edges (station<->city hub) per station = 4 total
	if syntheticCount < 4 {
		t.Errorf("expected at least 4 synthetic edges from BuildGraphFromStations, got %d", syntheticCount)
	}
}