package lanresolver

import (
	"context"
	"io"
	"log/slog"
	"os"
	"path/filepath"
	"strings"
	"sync"
	"testing"
)

// recRunner records every privileged command EnsureDnsmasq would run and succeeds — nothing reaches
// apt, systemctl or the root checker.
type recRunner struct {
	mu    sync.Mutex
	calls []string
}

func (r *recRunner) Run(_ context.Context, name string, args ...string) ([]byte, []byte, error) {
	r.mu.Lock()
	defer r.mu.Unlock()
	r.calls = append(r.calls, strings.Join(append([]string{name}, args...), " "))
	return nil, nil, nil
}

func (r *recRunner) RunStdin(ctx context.Context, _ io.Reader, name string, args ...string) ([]byte, []byte, error) {
	return r.Run(ctx, name, args...)
}

func (r *recRunner) installed() bool {
	for _, c := range r.calls {
		if strings.HasPrefix(c, "apt-get install") && strings.HasSuffix(c, " dnsmasq") {
			return true
		}
	}
	return false
}

// fixtureRoot builds a fake host root holding exactly the given relative files and points the REAL
// probe at it for the test's duration.
func fixtureRoot(t *testing.T, files ...string) {
	t.Helper()
	root := t.TempDir()
	for _, f := range files {
		p := filepath.Join(root, f)
		if err := os.MkdirAll(filepath.Dir(p), 0o755); err != nil {
			t.Fatal(err)
		}
		if err := os.WriteFile(p, nil, 0o644); err != nil {
			t.Fatal(err)
		}
	}
	prev := hostRoot
	hostRoot = root
	t.Cleanup(func() { hostRoot = prev })
}

func ensure(t *testing.T) *recRunner {
	t.Helper()
	r := &recRunner{}
	m := NewManager(r, "192.0.2.10", []string{"1.1.1.1"}, slog.New(slog.NewTextHandler(io.Discard, nil)))
	if err := m.EnsureDnsmasq(context.Background()); err != nil {
		t.Fatalf("EnsureDnsmasq: %v", err)
	}
	return r
}

// R-317: a host with `dnsmasq-base` (the /usr/sbin/dnsmasq binary) but WITHOUT the `dnsmasq` package
// (the service unit) must get the package installed — else the following `systemctl enable --now
// dnsmasq` hits a unit that does not exist and LAN name resolution silently never comes up.
//
// RED-PROOF: probe "usr/sbin/dnsmasq" instead of the unit paths in dnsmasqUnitInstalled → this fails
// with "install was skipped".
func TestEnsureDnsmasq_BinaryWithoutUnitInstalls(t *testing.T) {
	fixtureRoot(t, "usr/sbin/dnsmasq")
	r := ensure(t)
	if !r.installed() {
		t.Fatalf("install was skipped on a dnsmasq-base-only host (binary present, unit absent) — "+
			"the enable that follows targets a missing unit (R-317). calls: %q", r.calls)
	}
}

func TestEnsureDnsmasq_UnitPresentSkipsInstall(t *testing.T) {
	for _, unit := range []string{"usr/lib/systemd/system/dnsmasq.service", "lib/systemd/system/dnsmasq.service"} {
		t.Run(unit, func(t *testing.T) {
			fixtureRoot(t, "usr/sbin/dnsmasq", unit)
			if r := ensure(t); r.installed() {
				t.Fatalf("apt-get install ran although the dnsmasq unit is present at %s: %q", unit, r.calls)
			}
		})
	}
}

func TestEnsureDnsmasq_NothingPresentInstalls(t *testing.T) {
	fixtureRoot(t)
	if r := ensure(t); !r.installed() {
		t.Fatalf("install skipped on a host with no dnsmasq at all: %q", r.calls)
	}
}

// Production wiring for the hostRoot seam: the shipped probe resolves against the real root and asks
// about the unit the `dnsmasq` package owns — never the dnsmasq-base binary.
func TestEnsureDnsmasq_ProductionProbeIsTheUnit(t *testing.T) {
	if hostRoot != "/" {
		t.Fatalf("hostRoot default = %q, want \"/\" — the production probe would look in the wrong tree", hostRoot)
	}
	var sawUsrLib bool
	for _, p := range dnsmasqUnitPaths {
		full := filepath.Join(hostRoot, p)
		if strings.HasSuffix(full, "/sbin/dnsmasq") || strings.HasSuffix(full, "/bin/dnsmasq") {
			t.Errorf("probe path %s is the dnsmasq-base binary, not the dnsmasq unit (R-317)", full)
		}
		if full == "/usr/lib/systemd/system/dnsmasq.service" {
			sawUsrLib = true
		}
	}
	if !sawUsrLib {
		t.Errorf("probe paths %q miss /usr/lib/systemd/system/dnsmasq.service (dpkg -S: owned by dnsmasq)", dnsmasqUnitPaths)
	}
}