package resolv

import (
	"errors"
	"os"
	"path/filepath"
	"reflect"
	"sync"
	"testing"
)

func newTestManager(t *testing.T, initial string) (*Manager, string) {
	t.Helper()
	dir := t.TempDir()
	path := filepath.Join(dir, "resolv.conf")
	if initial != "" {
		if err := os.WriteFile(path, []byte(initial), 0o644); err != nil {
			t.Fatalf("seed: %v", err)
		}
	}
	return New(path), path
}

func readFile(t *testing.T, path string) string {
	t.Helper()
	b, err := os.ReadFile(path)
	if err != nil {
		t.Fatalf("read: %v", err)
	}
	return string(b)
}

func TestList_EmptyMissingFile(t *testing.T) {
	m, _ := newTestManager(t, "")
	got, err := m.List()
	if err != nil {
		t.Fatalf("List: %v", err)
	}
	if len(got) != 0 {
		t.Fatalf("want empty, got %v", got)
	}
}

func TestList_ParsesNameserversIgnoresOther(t *testing.T) {
	const initial = `# comment
; another comment
search example.com
nameserver 1.1.1.1
options rotate
nameserver 8.8.8.8
nameserver 2001:4860:4860::8888
`
	m, _ := newTestManager(t, initial)
	got, err := m.List()
	if err != nil {
		t.Fatalf("List: %v", err)
	}
	want := []string{"1.1.1.1", "8.8.8.8", "2001:4860:4860::8888"}
	if !reflect.DeepEqual(got, want) {
		t.Fatalf("want %v, got %v", want, got)
	}
}

func TestAdd_AppendsAndPersists(t *testing.T) {
	m, path := newTestManager(t, "search example.com\nnameserver 1.1.1.1\n")
	if err := m.Add("8.8.8.8"); err != nil {
		t.Fatalf("Add: %v", err)
	}
	got, _ := m.List()
	want := []string{"1.1.1.1", "8.8.8.8"}
	if !reflect.DeepEqual(got, want) {
		t.Fatalf("list want %v, got %v", want, got)
	}
	content := readFile(t, path)
	if want := "search example.com\nnameserver 1.1.1.1\nnameserver 8.8.8.8\n"; content != want {
		t.Fatalf("file mismatch:\nwant: %q\ngot:  %q", want, content)
	}
}

func TestAdd_RejectsInvalid(t *testing.T) {
	m, _ := newTestManager(t, "")
	for _, addr := range []string{"", "not-an-ip", "999.999.999.999", "1.1.1"} {
		if err := m.Add(addr); !errors.Is(err, ErrInvalidAddress) {
			t.Fatalf("Add(%q): want ErrInvalidAddress, got %v", addr, err)
		}
	}
}

func TestAdd_DuplicateRejected(t *testing.T) {
	m, _ := newTestManager(t, "nameserver 1.1.1.1\n")
	if err := m.Add("1.1.1.1"); !errors.Is(err, ErrAlreadyExists) {
		t.Fatalf("want ErrAlreadyExists, got %v", err)
	}
}

func TestRemove_DeletesEntry(t *testing.T) {
	const initial = "search example.com\nnameserver 1.1.1.1\nnameserver 8.8.8.8\n"
	m, path := newTestManager(t, initial)
	if err := m.Remove("1.1.1.1"); err != nil {
		t.Fatalf("Remove: %v", err)
	}
	got, _ := m.List()
	if want := []string{"8.8.8.8"}; !reflect.DeepEqual(got, want) {
		t.Fatalf("want %v, got %v", want, got)
	}
	content := readFile(t, path)
	if want := "search example.com\nnameserver 8.8.8.8\n"; content != want {
		t.Fatalf("file mismatch:\nwant: %q\ngot:  %q", want, content)
	}
}

func TestRemove_NotFound(t *testing.T) {
	m, _ := newTestManager(t, "nameserver 1.1.1.1\n")
	if err := m.Remove("8.8.8.8"); !errors.Is(err, ErrNotFound) {
		t.Fatalf("want ErrNotFound, got %v", err)
	}
}

func TestRemove_InvalidAddress(t *testing.T) {
	m, _ := newTestManager(t, "")
	if err := m.Remove("nope"); !errors.Is(err, ErrInvalidAddress) {
		t.Fatalf("want ErrInvalidAddress, got %v", err)
	}
}

func TestConcurrentAddsConsistent(t *testing.T) {
	m, _ := newTestManager(t, "")
	addrs := []string{
		"1.1.1.1", "8.8.8.8", "9.9.9.9", "8.8.4.4",
		"1.0.0.1", "208.67.222.222", "208.67.220.220", "64.6.64.6",
	}
	var wg sync.WaitGroup
	for _, a := range addrs {
		wg.Add(1)
		go func(a string) {
			defer wg.Done()
			if err := m.Add(a); err != nil {
				t.Errorf("Add(%s): %v", a, err)
			}
		}(a)
	}
	wg.Wait()

	got, err := m.List()
	if err != nil {
		t.Fatalf("List: %v", err)
	}
	if len(got) != len(addrs) {
		t.Fatalf("want %d entries, got %d (%v)", len(addrs), len(got), got)
	}
	seen := make(map[string]bool, len(got))
	for _, s := range got {
		if seen[s] {
			t.Fatalf("duplicate %s in %v", s, got)
		}
		seen[s] = true
	}
}