package blocklist

import (
	"context"
	"fmt"
	"log/slog"
	"net/http"
	"net/http/httptest"
	"os"
	"path/filepath"
	"sync/atomic"
	"testing"
	"time"

	"git.k8s-git-k6n.net/mats/fancy-dns/internal/config"
)

type listFixture struct {
	t      *testing.T
	srv    *httptest.Server
	hits   atomic.Int32
	fail   atomic.Bool
	body   atomic.Value // string
	path   string
	mgr    *Manager
	cfgSrc *config.Store
}

func newListFixture(t *testing.T, refresh time.Duration) *listFixture {
	t.Helper()
	f := &listFixture{t: t, path: filepath.Join(t.TempDir(), "lists", "ads")}
	f.body.Store("0.0.0.0 first.example\n")
	f.srv = httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		f.hits.Add(1)
		if f.fail.Load() {
			http.Error(w, "down", http.StatusServiceUnavailable)
			return
		}
		fmt.Fprint(w, f.body.Load().(string))
	}))
	t.Cleanup(f.srv.Close)

	cfg := config.Default()
	cfg.Block.Enabled = true
	cfg.Block.Lists = []config.ListSource{{
		Name: "ads", Format: "hosts", URL: f.srv.URL, Path: f.path, Enabled: true,
		Refresh: config.Duration(refresh), MaxBytes: 1 << 20, Timeout: config.Duration(2 * time.Second),
	}}
	f.cfgSrc = config.NewStore(cfg, "")
	f.mgr = NewManager(ManagerOptions{Config: f.cfgSrc, Logger: slog.New(slog.NewTextHandler(os.Stderr, &slog.HandlerOptions{Level: slog.LevelError}))})
	return f
}

func (f *listFixture) blocks(name string) bool {
	set := f.mgr.Holder().Get()
	return set != nil && set.Match(name) != nil
}

func (f *listFixture) age(d time.Duration) {
	f.t.Helper()
	old := time.Now().Add(-d)
	if err := os.Chtimes(f.path, old, old); err != nil {
		f.t.Fatal(err)
	}
}

// A restart should come up with the list from disk, not wait for the network:
// the network may be this resolver's own cluster DNS, which is not up yet.
func TestFreshCopyStartsWithoutTheNetwork(t *testing.T) {
	f := newListFixture(t, 24*time.Hour)
	if _, err := f.mgr.RefreshAll(context.Background()); err != nil { // first start: downloads and keeps a copy
		t.Fatal(err)
	}
	if f.hits.Load() != 1 || !f.blocks("first.example") {
		t.Fatalf("setup: hits=%d", f.hits.Load())
	}
	f.fail.Store(true)
	again := NewManager(ManagerOptions{Config: f.cfgSrc, Logger: slog.Default()})
	if _, err := again.RefreshAll(context.Background()); err != nil {
		t.Fatal(err)
	}
	if f.hits.Load() != 1 {
		t.Errorf("a fresh copy still went to the network (%d requests)", f.hits.Load())
	}
	if set := again.Holder().Get(); set == nil || set.Match("first.example") == nil {
		t.Error("the restarted manager did not load the copy from disk")
	}
}

// A copy past its refresh interval must be replaced; treating any copy as
// current froze a list at its first download for good.
func TestStaleCopyIsDownloadedAgain(t *testing.T) {
	f := newListFixture(t, time.Hour)
	if _, err := f.mgr.RefreshAll(context.Background()); err != nil {
		t.Fatal(err)
	}
	f.body.Store("0.0.0.0 second.example\n")
	f.age(2 * time.Hour)
	if _, err := f.mgr.RefreshAll(context.Background()); err != nil {
		t.Fatal(err)
	}
	if f.hits.Load() != 2 || !f.blocks("second.example") || f.blocks("first.example") {
		t.Errorf("hits=%d second=%v first=%v: the stale copy was not replaced", f.hits.Load(), f.blocks("second.example"), f.blocks("first.example"))
	}
	if b, _ := os.ReadFile(f.path); string(b) != "0.0.0.0 second.example\n" {
		t.Errorf("the copy on disk was not updated: %q", b)
	}
}

// And when the download fails, the stale copy still stands in: a stale list
// beats no list.
func TestStaleCopyStandsInWhenTheDownloadFails(t *testing.T) {
	f := newListFixture(t, time.Hour)
	if _, err := f.mgr.RefreshAll(context.Background()); err != nil {
		t.Fatal(err)
	}
	f.age(2 * time.Hour)
	f.fail.Store(true)
	again := NewManager(ManagerOptions{Config: f.cfgSrc, Logger: slog.Default()})
	if _, err := again.RefreshAll(context.Background()); err != nil {
		t.Fatalf("refresh with a stale copy and a dead server: %v", err)
	}
	if set := again.Holder().Get(); set == nil || set.Match("first.example") == nil {
		t.Error("the stale copy was not used")
	}
}

func TestForceRefreshDownloadsAFreshCopy(t *testing.T) {
	f := newListFixture(t, 24*time.Hour)
	if _, err := f.mgr.RefreshAll(context.Background()); err != nil {
		t.Fatal(err)
	}
	f.body.Store("0.0.0.0 second.example\n")
	if _, err := f.mgr.RefreshAll(context.Background()); err != nil || f.hits.Load() != 1 {
		t.Fatalf("a plain refresh of a fresh copy should not download: hits=%d err=%v", f.hits.Load(), err)
	}
	if _, err := f.mgr.ForceRefresh(context.Background()); err != nil {
		t.Fatal(err)
	}
	if f.hits.Load() != 2 || !f.blocks("second.example") {
		t.Errorf("a forced refresh did not download: hits=%d", f.hits.Load())
	}
}

func TestNoCopyAndNoNetworkIsAnError(t *testing.T) {
	f := newListFixture(t, time.Hour)
	f.fail.Store(true)
	if _, err := f.mgr.RefreshAll(context.Background()); err == nil && f.blocks("first.example") {
		t.Fatal("blocked a name with no list data")
	}
}

// The source ages from its file, so the scheduled refresh is due when the copy
// is, not a whole interval after a restart.
func TestSourceAgeFollowsTheCopy(t *testing.T) {
	f := newListFixture(t, 10*time.Hour)
	if _, err := f.mgr.RefreshAll(context.Background()); err != nil {
		t.Fatal(err)
	}
	f.age(9 * time.Hour)
	again := NewManager(ManagerOptions{Config: f.cfgSrc, Logger: slog.Default()})
	if _, err := again.RefreshAll(context.Background()); err != nil {
		t.Fatal(err)
	}
	src, ok := again.previous("ads")
	if !ok {
		t.Fatal("no source")
	}
	if age := time.Since(src.Meta.UpdatedAt); age < 8*time.Hour || age > 10*time.Hour {
		t.Errorf("source age = %v, want about 9h (the copy's)", age)
	}
}

// Startup must not wait for the network: the offline pass serves what is on
// disk, however old, and skips what was never downloaded; a normal pass then
// updates it.
func TestOfflinePassNeverTouchesTheNetwork(t *testing.T) {
	f := newListFixture(t, time.Hour)
	st, _ := f.mgr.RefreshOffline(context.Background())
	if st.Errors["ads"] == "" {
		t.Errorf("a list with no copy should be reported as not downloaded yet: %+v", st.Errors)
	}
	if f.hits.Load() != 0 || f.blocks("first.example") {
		t.Fatalf("hits=%d: an offline pass reached for the network", f.hits.Load())
	}

	if _, err := f.mgr.RefreshAll(context.Background()); err != nil { // the background pass
		t.Fatal(err)
	}
	f.body.Store("0.0.0.0 second.example\n")
	f.age(5 * time.Hour) // stale
	again := NewManager(ManagerOptions{Config: f.cfgSrc, Logger: slog.Default()})
	if _, err := again.RefreshOffline(context.Background()); err != nil {
		t.Fatal(err)
	}
	if f.hits.Load() != 1 {
		t.Errorf("hits=%d: the offline pass downloaded a stale copy", f.hits.Load())
	}
	if set := again.Holder().Get(); set == nil || set.Match("first.example") == nil {
		t.Error("the stale copy was not served while offline")
	}
	// ...and the pass that follows brings it up to date.
	if _, err := again.RefreshAll(context.Background()); err != nil {
		t.Fatal(err)
	}
	if f.hits.Load() != 2 || again.Holder().Get().Match("second.example") == nil {
		t.Errorf("hits=%d: the follow-up pass did not refresh the stale copy", f.hits.Load())
	}
}