package peer

import (
	"net/netip"
	"os"
	"path/filepath"
	"sort"
	"strings"
	"testing"
)

// writeTempHosts creates a temp hosts file with the given content and returns
// its path.
func writeTempHosts(t *testing.T, content string) string {
	t.Helper()
	path := filepath.Join(t.TempDir(), "hosts")
	if err := os.WriteFile(path, []byte(content), 0600); err != nil {
		t.Fatal(err)
	}
	return path
}

// readManagedSection returns the lines between the begin/end markers for the
// given localDomain, plus everything outside the section ("outside").
func readManagedSection(t *testing.T, path, localDomain string) (inside, outside []string) {
	t.Helper()
	raw, err := os.ReadFile(path)
	if err != nil {
		t.Fatal(err)
	}
	begin, end := hostMarkers(localDomain)

	inSection := false
	for _, line := range strings.Split(string(raw), "\n") {
		switch {
		case strings.HasPrefix(line, begin):
			inSection = true
		case strings.HasPrefix(line, end):
			inSection = false
		case inSection:
			if f := strings.Join(strings.Fields(line), " "); f != "" {
				inside = append(inside, f)
			}
		default:
			if f := strings.Join(strings.Fields(line), " "); f != "" {
				outside = append(outside, f)
			}
		}
	}
	return inside, outside
}

func peer(name string) *Peer {
	return &Peer{Name: name}
}

func TestUpdateHosts_AddsSection(t *testing.T) {
	path := writeTempHosts(t, "127.0.0.1 localhost\n")

	peers := map[netip.Addr]*Peer{
		netip.MustParseAddr("10.11.12.1"):  peer("hub"),
		netip.MustParseAddr("10.11.12.10"): peer("laptop"),
	}

	if err := updateHosts(path, "mynet.local", peers); err != nil {
		t.Fatal(err)
	}

	inside, outside := readManagedSection(t, path, "mynet.local")

	sort.Strings(inside)
	want := []string{
		"10.11.12.1 hub.mynet.local",
		"10.11.12.10 laptop.mynet.local",
	}
	if strings.Join(inside, "\n") != strings.Join(want, "\n") {
		t.Errorf("managed section = %v, want %v", inside, want)
	}

	if !contains(outside, "127.0.0.1 localhost") {
		t.Errorf("original content lost; outside = %v", outside)
	}
}

func TestUpdateHosts_ReplacesExistingSection(t *testing.T) {
	path := writeTempHosts(t, "127.0.0.1 localhost\n")

	// First write.
	first := map[netip.Addr]*Peer{
		netip.MustParseAddr("10.11.12.1"): peer("hub"),
	}
	if err := updateHosts(path, "mynet.local", first); err != nil {
		t.Fatal(err)
	}

	// Second write with a different set of peers.
	second := map[netip.Addr]*Peer{
		netip.MustParseAddr("10.11.12.20"): peer("phone"),
	}
	if err := updateHosts(path, "mynet.local", second); err != nil {
		t.Fatal(err)
	}

	inside, outside := readManagedSection(t, path, "mynet.local")

	if len(inside) != 1 || inside[0] != "10.11.12.20 phone.mynet.local" {
		t.Errorf("section not replaced; inside = %v", inside)
	}
	if contains(inside, "10.11.12.1 hub.mynet.local") {
		t.Errorf("stale entry remained; inside = %v", inside)
	}
	if !contains(outside, "127.0.0.1 localhost") {
		t.Errorf("original content lost; outside = %v", outside)
	}
}

func TestUpdateHosts_SkipsEmptyNames(t *testing.T) {
	path := writeTempHosts(t, "127.0.0.1 localhost\n")

	peers := map[netip.Addr]*Peer{
		netip.MustParseAddr("10.11.12.1"):  peer("hub"),
		netip.MustParseAddr("10.11.12.99"): peer(""), // no name
	}
	if err := updateHosts(path, "mynet.local", peers); err != nil {
		t.Fatal(err)
	}

	inside, _ := readManagedSection(t, path, "mynet.local")
	if len(inside) != 1 || inside[0] != "10.11.12.1 hub.mynet.local" {
		t.Errorf("expected only named peer; inside = %v", inside)
	}
}

func TestUpdateHosts_Idempotent(t *testing.T) {
	path := writeTempHosts(t, "127.0.0.1 localhost\n")

	peers := map[netip.Addr]*Peer{
		netip.MustParseAddr("10.11.12.1"): peer("hub"),
	}
	if err := updateHosts(path, "mynet.local", peers); err != nil {
		t.Fatal(err)
	}
	first, err := os.ReadFile(path)
	if err != nil {
		t.Fatal(err)
	}
	if err := updateHosts(path, "mynet.local", peers); err != nil {
		t.Fatal(err)
	}
	second, err := os.ReadFile(path)
	if err != nil {
		t.Fatal(err)
	}
	if string(first) != string(second) {
		t.Errorf("repeated update changed file:\nfirst:\n%s\nsecond:\n%s", first, second)
	}
}

// TestUpdateHosts_PrefixDomainsCoexist guards finding 4.4: two domains where
// one label is a prefix of the other ("net" vs "net2") must each manage their
// own section without clobbering the other's, even sharing one hosts file.
func TestUpdateHosts_PrefixDomainsCoexist(t *testing.T) {
	path := writeTempHosts(t, "127.0.0.1 localhost\n")

	if err := updateHosts(path, "net2.local", map[netip.Addr]*Peer{
		netip.MustParseAddr("10.0.2.1"): peer("a"),
	}); err != nil {
		t.Fatal(err)
	}
	if err := updateHosts(path, "net.local", map[netip.Addr]*Peer{
		netip.MustParseAddr("10.0.1.1"): peer("b"),
	}); err != nil {
		t.Fatal(err)
	}

	// Both sections coexist after writing the prefix domain.
	if in, _ := readManagedSection(t, path, "net2.local"); len(in) != 1 || in[0] != "10.0.2.1 a.net2.local" {
		t.Errorf("net2 section clobbered: %v", in)
	}
	if in, _ := readManagedSection(t, path, "net.local"); len(in) != 1 || in[0] != "10.0.1.1 b.net.local" {
		t.Errorf("net section wrong: %v", in)
	}

	// Re-updating net2 must not disturb the net section.
	if err := updateHosts(path, "net2.local", map[netip.Addr]*Peer{
		netip.MustParseAddr("10.0.2.2"): peer("c"),
	}); err != nil {
		t.Fatal(err)
	}
	if in, _ := readManagedSection(t, path, "net.local"); len(in) != 1 || in[0] != "10.0.1.1 b.net.local" {
		t.Errorf("net section disturbed by net2 update: %v", in)
	}
	if in, _ := readManagedSection(t, path, "net2.local"); len(in) != 1 || in[0] != "10.0.2.2 c.net2.local" {
		t.Errorf("net2 section not updated: %v", in)
	}
}

func contains(ss []string, s string) bool {
	for _, x := range ss {
		if x == s {
			return true
		}
	}
	return false
}