package lookup_test

import (
	"encoding/json"
	"log/slog"
	"net/http"
	"net/http/httptest"
	"net/netip"
	"slices"
	"strings"
	"sync"
	"testing"
	"time"

	"sneak.berlin/go/smallwebwaf/internal/lookup"
)

const (
	// germany is where the stand-in for GeoJS places every address but
	// unplaced.
	germany = "DE"
	// unplaced is the address it cannot place.
	unplaced = "192.0.2.1"
	// leftOut is the address it leaves out of its answer when
	// answeringWithoutLeftOut.
	leftOut = "203.0.113.7"
	// timeout is how long a new client waits for its answer.
	timeout = time.Second
	// waitLimit bounds how long a test waits for what should happen.
	waitLimit = 10 * time.Second
	// pollInterval is how often a test looks again.
	pollInterval = 10 * time.Millisecond
	// week is how long an answer is kept.
	week = 7 * 24 * time.Hour
)

func TestKeptAnswerIsUsedFor7DaysThenAskedAgain(t *testing.T) {
	t.Parallel()

	geojs, clock, g := start(t)
	placed := netip.MustParsePrefix("203.0.113.9/32")
	notPlaced := netip.MustParsePrefix(unplaced + "/32")

	wantCountry(t, g, placed, germany)
	wantCountry(t, g, notPlaced, "")
	wantRequests(t, geojs, 2)

	// An answer without a country is kept too.
	clock.advance(week - time.Second)
	wantCountry(t, g, placed, germany)
	wantCountry(t, g, notPlaced, "")
	wantRequests(t, geojs, 2)

	clock.advance(time.Second)
	wantCountry(t, g, placed, germany)
	wantRequests(t, geojs, 3)
	wantAsked(t, geojs, 2, "203.0.113.9")
}

func TestNewClientWaitsAtMostOneSecondThenCountsAsNotFound(t *testing.T) {
	t.Parallel()

	geojs, clock, g := start(t)
	client := netip.MustParsePrefix("203.0.113.9/32")

	// The client comes while GeoJS is asked about an earlier client, which
	// it answers most of a second later. It is then asked about the client
	// and does not answer: that request is abandoned a second after it
	// began, well after the client's wait is over.
	geojs.set(answeringSlowly)

	var earlier sync.WaitGroup

	earlier.Go(func() { g.Country(t.Context(), netip.MustParsePrefix("203.0.113.1/32")) })
	defer earlier.Wait()

	waitForRequests(t, geojs, 1)
	geojs.set(hanging)

	began := time.Now()

	wantCountry(t, g, client, "")

	took := time.Since(began)
	if took < timeout || took > timeout+timeout/2 {
		t.Errorf("waited %s for the answer, want %s", took, timeout)
	}

	// Its next request does not wait.
	began = time.Now()

	wantCountry(t, g, client, "")

	took = time.Since(began)
	if took > timeout/2 {
		t.Errorf("waited %s again, want no wait", took)
	}

	// Once GeoJS answers, the client is asked about again in the
	// background, and has its country.
	geojs.set(answering)
	waitForCountry(t, g, clock, client, germany)
}

func TestAddressLeftOutOfAnAnswerIsAskedAboutAgain(t *testing.T) {
	t.Parallel()

	for _, tc := range []struct {
		name    string
		answers int
		// named is whether the answer names the other client asked about.
		named bool
	}{
		{"null", answeringNull, false},
		{"empty list", answeringEmptyList, false},
		{"list without " + leftOut, answeringWithoutLeftOut, true},
	} {
		t.Run(tc.name, func(t *testing.T) {
			t.Parallel()

			geojs, clock, g := start(t)
			other := netip.MustParsePrefix("203.0.113.1/32")
			client := netip.MustParsePrefix(leftOut + "/32")

			// GeoJS fails, and is left alone for a second while the client
			// comes too, so that the next request asks about both.
			geojs.set(failing)
			wantCountry(t, g, other, "")
			wantCountry(t, g, client, "")

			geojs.set(tc.answers)
			clock.advance(time.Second)
			wantCountry(t, g, other, "")
			waitForRequests(t, geojs, 2)

			// The answer counts as a failure, and the client is asked about
			// again, with the other client only if the answer left it out too.
			geojs.set(answering)
			waitForCountry(t, g, clock, client, germany)
			wantCountry(t, g, other, germany)
			wantRequests(t, geojs, 3)

			if tc.named {
				wantAsked(t, geojs, 2, leftOut)
			} else {
				wantAsked(t, geojs, 2, leftOut, "203.0.113.1")
			}
		})
	}
}

func TestRedirectCountsAsFailure(t *testing.T) {
	t.Parallel()

	geojs, _, g := start(t)
	geojs.set(redirecting)

	wantCountry(t, g, netip.MustParsePrefix("203.0.113.9/32"), "")
	wantRequests(t, geojs, 1)
}

func TestCountryIsKeptInCapitals(t *testing.T) {
	t.Parallel()

	geojs, _, g := start(t)
	geojs.set(answeringInLowerCase)

	wantCountry(t, g, netip.MustParsePrefix("203.0.113.9/32"), germany)
}

func TestFailureIsLoggedWithoutTheAddressesAskedAbout(t *testing.T) {
	t.Parallel()

	var log strings.Builder

	// Nothing listens on port 1, so asking GeoJS fails.
	g := lookup.New(lookup.Params{
		URL:        "http://127.0.0.1:1",
		Now:        time.Now,
		ProcessLog: slog.New(slog.NewTextHandler(&log, nil)),
	})

	wantCountry(t, g, netip.MustParsePrefix("203.0.113.9/32"), "")

	logged := log.String()
	if !strings.Contains(logged, "asking GeoJS failed") ||
		strings.Contains(logged, "203.0.113.9") {
		t.Errorf("logged %q, want the failure without the address asked about", logged)
	}
}

func TestWaitingClientsAreAskedAboutInOneRequest(t *testing.T) {
	t.Parallel()

	geojs, clock, g := start(t)

	// GeoJS fails, and is then left alone for a second, while three more
	// clients come. An IPv6 client is a /64, and GeoJS is asked about its
	// first address.
	geojs.set(failing)
	wantCountry(t, g, netip.MustParsePrefix("203.0.113.1/32"), "")
	wantCountry(t, g, netip.MustParsePrefix("203.0.113.2/32"), "")
	wantCountry(t, g, netip.MustParsePrefix("2001:db8:1:2::/64"), "")
	wantRequests(t, geojs, 1)

	geojs.set(answering)
	clock.advance(time.Second)
	wantCountry(t, g, netip.MustParsePrefix("203.0.113.3/32"), germany)
	wantRequests(t, geojs, 2)
	wantAsked(t, geojs, 1, "203.0.113.1", "203.0.113.2", "2001:db8:1:2::", "203.0.113.3")
}

func TestKeptAnswersUnaffectedWhileGeoJSFailsAndAskedAgainWithBackoff(t *testing.T) {
	t.Parallel()

	geojs, clock, g := start(t)
	clients := newClients()
	kept := clients()

	wantCountry(t, g, kept, germany)

	geojs.set(failing)
	wantCountry(t, g, kept, germany)
	wantRequests(t, geojs, 1)

	// Each failure leaves GeoJS alone twice as long as the one before, up
	// to five minutes. New clients meanwhile count as not found, and the
	// client with a kept answer still gets its country, without GeoJS being
	// asked.
	requests := 1

	for _, delay := range []time.Duration{
		time.Second, 2 * time.Second, 4 * time.Second, 8 * time.Second,
		16 * time.Second, 32 * time.Second, 64 * time.Second, 128 * time.Second,
		256 * time.Second, 5 * time.Minute, 5 * time.Minute,
	} {
		wantCountry(t, g, clients(), "")

		requests++
		wantRequests(t, geojs, requests)

		clock.advance(delay - time.Millisecond)
		wantCountry(t, g, clients(), "")
		wantCountry(t, g, kept, germany)
		wantRequests(t, geojs, requests)

		clock.advance(time.Millisecond)
	}

	// Once GeoJS answers again, it is asked about every client waiting.
	geojs.set(answering)
	wantCountry(t, g, clients(), germany)
	wantRequests(t, geojs, requests+1)

	asked := waitForRequests(t, geojs, requests+1)
	if len(asked[requests]) != 23 {
		t.Errorf("GeoJS was asked about %d clients, want 23", len(asked[requests]))
	}
}

func TestAtMost200AddressesInOneRequest(t *testing.T) {
	t.Parallel()

	geojs, clock, g := start(t)
	clients := newClients()
	first := clients()

	// 201 clients wait while GeoJS is left alone after a failure.
	geojs.set(failing)
	wantCountry(t, g, first, "")

	for range 200 {
		wantCountry(t, g, clients(), "")
	}

	// The first one's next request has GeoJS asked again.
	geojs.set(answering)
	clock.advance(time.Second)
	wantCountry(t, g, first, "")

	asked := waitForRequests(t, geojs, 3)
	if len(asked[1]) != 200 || len(asked[2]) != 1 {
		t.Errorf("GeoJS was asked about %d and then %d clients, want 200 and 1",
			len(asked[1]), len(asked[2]))
	}
}

func TestAtMost10000ClientsWait(t *testing.T) {
	t.Parallel()

	geojs, clock, g := start(t)
	clients := newClients()
	first := clients()

	// 10,000 clients wait while GeoJS is left alone after a failure, and
	// one more cannot join them.
	geojs.set(failing)
	wantCountry(t, g, first, "")

	for range 9999 {
		wantCountry(t, g, clients(), "")
	}

	extra := clients()
	wantCountry(t, g, extra, "")

	// The first one's next request has GeoJS asked about the 10,000, 200
	// at a time, and not about the one more.
	geojs.set(answering)
	clock.advance(time.Second)
	wantCountry(t, g, first, "")

	asked := waitForRequests(t, geojs, 51)
	for i, request := range asked {
		if slices.Contains(request, extra.Addr().String()) {
			t.Errorf("request %d asked about %s", i, extra.Addr())
		}
	}

	// With room among those waiting, it is asked about.
	wantCountry(t, g, extra, germany)
}

// How the stand-in for GeoJS answers.
const (
	answering               = iota
	answeringSlowly         // most of a second later
	answeringInLowerCase    // with each country in lower case
	answeringWithoutLeftOut // with a list that leaves leftOut out
	answeringEmptyList      // with []
	answeringNull           // with null
	failing                 // with 503
	hanging                 // not at all, until the request is abandoned
	redirecting             // with a redirect to itself
)

// standIn is a stand-in for GeoJS. It notes the addresses each request
// asks about.
type standIn struct {
	server *httptest.Server

	mu       sync.Mutex
	answers  int
	requests [][]string
}

// ServeHTTP answers a request about the addresses in its ip parameter.
func (s *standIn) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	addrs := strings.Split(r.URL.Query().Get("ip"), ",")

	s.mu.Lock()
	s.requests = append(s.requests, addrs)
	answers := s.answers
	s.mu.Unlock()

	switch answers {
	case failing:
		w.WriteHeader(http.StatusServiceUnavailable)

		return
	case hanging:
		<-r.Context().Done()

		return
	case redirecting:
		http.Redirect(w, r, "/", http.StatusFound)

		return
	case answeringSlowly:
		select {
		case <-time.After(timeout * 4 / 5):
		case <-r.Context().Done():
			return
		}
	}

	list := make([]map[string]string, 0, len(addrs))

	for _, addr := range addrs {
		country := germany

		switch {
		case addr == unplaced:
			country = ""
		case addr == leftOut && answers == answeringWithoutLeftOut:
			continue
		case answers == answeringInLowerCase:
			country = strings.ToLower(germany)
		}

		list = append(list, map[string]string{"ip": addr, "country": country})
	}

	var answer any = list

	switch answers {
	case answeringEmptyList:
		answer = []string{}
	case answeringNull:
		answer = nil
	}

	err := json.NewEncoder(w).Encode(answer)
	if err != nil {
		http.Error(w, err.Error(), http.StatusInternalServerError)
	}
}

// set sets how the stand-in answers.
func (s *standIn) set(answers int) {
	s.mu.Lock()
	defer s.mu.Unlock()

	s.answers = answers
}

// asked returns the addresses each request has asked about so far.
func (s *standIn) asked() [][]string {
	s.mu.Lock()
	defer s.mu.Unlock()

	return slices.Clone(s.requests)
}

// testClock is a clock the test sets.
type testClock struct {
	mu  sync.Mutex
	now time.Time
}

// Now tells the time.
func (c *testClock) Now() time.Time {
	c.mu.Lock()
	defer c.mu.Unlock()

	return c.now
}

// advance moves the clock on by d.
func (c *testClock) advance(d time.Duration) {
	c.mu.Lock()
	defer c.mu.Unlock()

	c.now = c.now.Add(d)
}

// start starts a stand-in for GeoJS that answers, and returns it, a
// clock, and a GeoJS asking it by that clock.
func start(t *testing.T) (*standIn, *testClock, *lookup.GeoJS) {
	t.Helper()

	geojs := &standIn{}
	geojs.server = httptest.NewServer(geojs)
	t.Cleanup(geojs.server.Close)

	clock := &testClock{now: time.Date(2026, 10, 4, 0, 0, 0, 0, time.UTC)}
	g := lookup.New(lookup.Params{
		URL:        geojs.server.URL,
		Now:        clock.Now,
		ProcessLog: slog.New(slog.DiscardHandler),
	})

	return geojs, clock, g
}

// newClients returns what returns a new IPv4 client each time it is
// called.
func newClients() func() netip.Prefix {
	addr := netip.MustParseAddr("10.0.0.0")

	return func() netip.Prefix {
		addr = addr.Next()

		return netip.PrefixFrom(addr, addr.BitLen())
	}
}

// wantCountry checks the country g gives client.
func wantCountry(t *testing.T, g *lookup.GeoJS, client netip.Prefix, want string) {
	t.Helper()

	got := g.Country(t.Context(), client)
	if got != want {
		t.Errorf("%s is in %q, want %q", client, got, want)
	}
}

// wantRequests checks how many requests GeoJS has had.
func wantRequests(t *testing.T, geojs *standIn, want int) {
	t.Helper()

	got := len(geojs.asked())
	if got != want {
		t.Errorf("GeoJS had %d requests, want %d", got, want)
	}
}

// wantAsked checks the addresses request i asked about, in any order.
func wantAsked(t *testing.T, geojs *standIn, i int, want ...string) {
	t.Helper()

	asked := geojs.asked()
	if len(asked) <= i {
		t.Fatalf("GeoJS had %d requests, want more than %d", len(asked), i)
	}

	got := slices.Sorted(slices.Values(asked[i]))

	slices.Sort(want)

	if !slices.Equal(got, want) {
		t.Errorf("request %d asked about %v, want %v", i, got, want)
	}
}

// waitForRequests waits for GeoJS to have had count requests, and returns
// the addresses each asked about.
func waitForRequests(t *testing.T, geojs *standIn, count int) [][]string {
	t.Helper()

	deadline := time.Now().Add(waitLimit)
	for time.Now().Before(deadline) {
		asked := geojs.asked()
		if len(asked) >= count {
			return asked
		}

		time.Sleep(pollInterval)
	}

	t.Fatalf("fewer than %d requests to GeoJS after %s", count, waitLimit)

	return nil
}

// waitForCountry waits for g to give client the country want, moving the
// clock on a minute at a time, so that GeoJS is asked again after a
// failure.
func waitForCountry(
	t *testing.T, g *lookup.GeoJS, clock *testClock, client netip.Prefix, want string,
) {
	t.Helper()

	deadline := time.Now().Add(waitLimit)
	for g.Country(t.Context(), client) != want {
		if time.Now().After(deadline) {
			t.Fatalf("%s is not in %q after %s", client, want, waitLimit)
		}

		clock.advance(time.Minute)
		time.Sleep(pollInterval)
	}
}