package link

import (
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"log"
	"strings"
	"testing"
	"time"

	"github.com/nats-io/nats.go"
	"github.com/nats-io/nats.go/jetstream"

	"github.com/novox/mesh-controller/internal/broker"
)

// A module's consumer as the controller makes it, on a bus whose streams the controller asserted.
func aModuleConsumer(t *testing.T, js *broker.JetStream, node, module string, consumes ...string) jetstream.Consumer {
	t.Helper()
	c, ok := broker.ConsumerFor(broker.Principal{Kind: broker.KindModule, Node: node, Module: module,
		Consumes: consumes, PasswordHash: "x"})
	if !ok {
		t.Fatal("a module that consumes got no consumer")
	}
	if err := js.EnsureConsumer(c); err != nil {
		t.Fatal(err)
	}
	api, err := jetstream.New(js.Conn())
	if err != nil {
		t.Fatal(err)
	}
	reading, err := api.Consumer(t.Context(), broker.EventsStream, c.Name)
	if err != nil {
		t.Fatal(err)
	}
	return reading
}

// next is the one message a consumer hands over within a second, or nil.
func next(t *testing.T, c jetstream.Consumer) jetstream.Msg {
	t.Helper()
	batch, err := c.Fetch(1, jetstream.FetchMaxWait(time.Second))
	if err != nil {
		t.Fatal(err)
	}
	for msg := range batch.Messages() {
		return msg
	}
	return nil
}

// keeping takes the notices as the serving controller does, until the test ends.
func keeping(t *testing.T, js *broker.JetStream) {
	t.Helper()
	if err := broker.AssertMeshConsumers(js); err != nil {
		t.Fatal(err)
	}
	sub, err := keepGivenUp(js.Context(), log.New(io.Discard, "", 0))
	if err != nil {
		t.Fatal(err)
	}
	t.Cleanup(func() { _ = sub.Unsubscribe() })
}

// givenUp hands one event to a consumer as often as it may, failing each time, and waits for it kept.
func givenUp(t *testing.T, js *broker.JetStream, c jetstream.Consumer) DeadLetter {
	t.Helper()
	for {
		msg := next(t, c)
		if msg == nil {
			break
		}
		_ = msg.Nak()
	}
	var kept []DeadLetter
	eventually(t, "the event kept", func() bool {
		kept, _, _ = DeadLetters(js.Context(), c.CachedInfo().Name, 0)
		return len(kept) == 1
	})
	return kept[0]
}

// **Delivered again to the consumer that gave it up, and nobody else**: another module consuming the
// same event handled it the first time and must not handle it twice.
func TestADeadLetterIsDeliveredAgainToItsConsumerAlone(t *testing.T) {
	js := aBus(t)
	keeping(t, js)
	failing := aModuleConsumer(t, js, "media", "sonarr", "gitea.pull.merged")
	handling := aModuleConsumer(t, js, "media", "radarr", "gitea.pull.merged")

	const subject = "mesh.mod.gitea.event.pull.merged"
	msg := &nats.Msg{Subject: subject, Data: []byte(`{"n":1}`), Header: nats.Header{}}
	msg.Header.Set("x-node", "forge")
	msg.Header.Set(nats.MsgIdHdr, "event-1")
	if _, err := js.Context().PublishMsg(msg); err != nil {
		t.Fatal(err)
	}
	if m := next(t, handling); m == nil {
		t.Fatal("the other module was not handed the event")
	} else {
		_ = m.Ack()
	}
	d := givenUp(t, js, failing)
	if d.Consumer != "media_sonarr" || d.Stream != "EVENTS" || d.Subject != subject || d.Deliveries != 5 ||
		d.GaveUp.IsZero() || d.Published.IsZero() || d.Lost != "" {
		t.Fatalf("kept as %+v", d)
	}
	held, err := HeldDeadLetters(js.Context())
	if err != nil || held["EVENTS.media_sonarr"] != 1 {
		t.Fatalf("held %v (%v)", held, err)
	}

	whole, err := DeadLetterNamed(js.Context(), d.ID)
	if err != nil || whole.Body != `{"n":1}` || len(whole.Headers["x-node"]) != 1 || whole.Headers["x-node"][0] != "forge" {
		t.Fatalf("one asked whole is %+v (%v)", whole, err)
	}

	_, to, err := DeliverAgain(js.Context(), d.ID)
	if err != nil {
		t.Fatal(err)
	}
	if to != "mesh.again.media_sonarr.mod.gitea.event.pull.merged" {
		t.Fatalf("delivered again on %s", to)
	}
	again := next(t, failing)
	if again == nil {
		t.Fatal("the consumer that gave it up was not handed it again")
	}
	if string(again.Data()) != `{"n":1}` || again.Headers().Get("x-node") != "forge" ||
		again.Headers().Get(AgainHeader) == "" {
		t.Fatalf("handed again as %s %v", again.Data(), again.Headers())
	}
	if original, ok := broker.OriginalOfAgain(again.Subject()); !ok || original != subject {
		t.Fatalf("delivered again on %s, which does not say the event's own subject", again.Subject())
	}
	_ = again.Ack()
	if m := next(t, handling); m != nil {
		t.Fatalf("the module that handled it was handed it twice: %s", m.Subject())
	}
	if _, err := DeadLetterNamed(js.Context(), d.ID); !errors.Is(err, ErrNoDeadLetter) {
		t.Fatalf("still kept after it was delivered again: %v", err)
	}
	held, _ = HeldDeadLetters(js.Context())
	if held["EVENTS.media_sonarr"] != 0 {
		t.Fatalf("still held: %v", held)
	}
	// Asked twice, delivered once: the second finds nothing kept.
	if _, _, err := DeliverAgain(js.Context(), d.ID); !errors.Is(err, ErrNoDeadLetter) {
		t.Fatalf("a second delivery answered %v", err)
	}
}

func TestADeadLetterDroppedIsGone(t *testing.T) {
	js := aBus(t)
	keeping(t, js)
	failing := aModuleConsumer(t, js, "media", "sonarr", "gitea.pull.merged")
	if _, err := js.Context().Publish("mesh.mod.gitea.event.pull.merged", []byte(`{}`)); err != nil {
		t.Fatal(err)
	}
	d := givenUp(t, js, failing)
	if _, err := DropDeadLetter(js.Context(), d.ID); err != nil {
		t.Fatal(err)
	}
	if left, total, err := DeadLetters(js.Context(), "", 0); err != nil || total != 0 || len(left) != 0 {
		t.Fatalf("after the drop: %v %d %v", left, total, err)
	}
	if m := next(t, failing); m != nil {
		t.Fatalf("a dropped event was handed over: %s", m.Subject())
	}
}

// A notice whose message its stream no longer holds is kept as a record that says so — said, and
// dropped by a person, never silently missing — and cannot be delivered again.
func TestANoticeWhoseMessageIsGoneIsKeptAndSaysSo(t *testing.T) {
	js := aBus(t)
	d, err := KeepDeadLetter(js.Context(), []byte(`{"stream":"EVENTS","consumer":"media_sonarr","stream_seq":42,`+
		`"deliveries":5,"timestamp":"2026-10-06T15:51:00Z"}`))
	if err != nil {
		t.Fatal(err)
	}
	if !strings.Contains(d.Lost, "no longer held message 42") || d.Consumer != "media_sonarr" {
		t.Fatalf("kept as %+v", d)
	}
	if _, _, err := DeliverAgain(js.Context(), d.ID); err == nil || !strings.Contains(err.Error(), "Drop it") {
		t.Fatalf("a record without its message was delivered again: %v", err)
	}
	// The same notice taken twice is kept once.
	if _, err := KeepDeadLetter(js.Context(), []byte(`{"stream":"EVENTS","consumer":"media_sonarr","stream_seq":42,`+
		`"deliveries":5}`)); err != nil {
		t.Fatal(err)
	}
	if _, total, _ := DeadLetters(js.Context(), "media_sonarr", 0); total != 1 {
		t.Fatalf("one notice taken twice is kept %d times", total)
	}
}

// What only the giving-up consumer filters is its own: a subject delivered again reads back as the
// event's, and a module's runtime reads the same key from it (the tokens around `.event.`).
func TestASubjectDeliveredAgainSaysTheEventsOwn(t *testing.T) {
	for _, original := range []string{"mesh.mod.gitea.event.pull.merged", "mesh.seat.node-build-agent.event.built"} {
		again := broker.AgainSubject("ace_sonarr", original)
		if back, ok := broker.OriginalOfAgain(again); !ok || back != original {
			t.Errorf("%s reads back as %s", again, back)
		}
		key := func(subject string) string {
			before, event, _ := strings.Cut(subject, ".event.")
			parts := strings.Split(before, ".")
			return parts[len(parts)-1] + "." + event
		}
		if key(again) != key(original) {
			t.Errorf("%s reads as key %s, the event as %s", again, key(again), key(original))
		}
	}
	if _, ok := broker.OriginalOfAgain("mesh.mod.gitea.event.pull.merged"); ok {
		t.Error("an event's own subject reads as delivered again")
	}
}

// Only an event is delivered again, and only to a consumer that is on the bus and filters its again
// subject: a dead letter is never let go as delivered while nobody receives it.
func TestADeadLetterIsDeliveredAgainOnlyWhereItIsReceived(t *testing.T) {
	js := aBus(t)
	keeping(t, js)
	failing := aModuleConsumer(t, js, "media", "sonarr", "gitea.pull.merged")
	if _, err := js.Context().Publish("mesh.mod.gitea.event.pull.merged", []byte(`{}`)); err != nil {
		t.Fatal(err)
	}
	d := givenUp(t, js, failing)

	// A consumer as it was before this fix: its filters do not take what is delivered again.
	c, _ := broker.ConsumerFor(broker.Principal{Kind: broker.KindModule, Node: "media", Module: "sonarr",
		Consumes: []string{"gitea.pull.merged"}, PasswordHash: "x"})
	c.Filters = c.Filters[:len(c.Filters)-1]
	if err := js.EnsureConsumer(c); err != nil {
		t.Fatal(err)
	}
	if _, _, err := DeliverAgain(js.Context(), d.ID); err == nil || !strings.Contains(err.Error(), "does not yet take") {
		t.Fatalf("delivered to a consumer that does not filter its again subject: %v", err)
	}
	if _, err := DeadLetterNamed(js.Context(), d.ID); err != nil {
		t.Fatalf("a refused delivery let the dead letter go: %v", err)
	}

	// The consumer gone: nothing would receive it.
	if err := js.Context().DeleteConsumer(broker.EventsStream, c.Name); err != nil {
		t.Fatal(err)
	}
	if _, _, err := DeliverAgain(js.Context(), d.ID); err == nil || !strings.Contains(err.Error(), "no longer on the bus") {
		t.Fatalf("delivered to a consumer that is gone: %v", err)
	}
	if _, err := DeadLetterNamed(js.Context(), d.ID); err != nil {
		t.Fatalf("a refused delivery let the dead letter go: %v", err)
	}

	// Not an event: refused, whatever stream it is from.
	for _, other := range []DeadLetter{
		{ID: 2, Stream: "SEAT_TELEGRAM_SENDER", Consumer: "SEAT_TELEGRAM_SENDER_worker", Subject: "mesh.seat.telegram-sender.accept.send"},
		{ID: 3, Stream: "KV_x", Consumer: "y", Subject: "$KV.x.k"},
	} {
		if _, err := AgainTo(js.Context(), other); err == nil {
			t.Errorf("%s was given a subject to be delivered again on", other.Stream)
		}
	}
}

// A total says how many are held, however few the list carries.
func TestTheListSaysTheTotalAndStopsAtItsLimit(t *testing.T) {
	js := aBus(t)
	for seq := 1; seq <= 5; seq++ {
		if _, err := KeepDeadLetter(js.Context(), []byte(fmt.Sprintf(`{"stream":"EVENTS","consumer":"media_sonarr",`+
			`"stream_seq":%d,"deliveries":5}`, seq))); err != nil {
			t.Fatal(err)
		}
	}
	list, total, err := DeadLetters(js.Context(), "media_sonarr", 2)
	if err != nil || total != 5 || len(list) != 2 || list[0].Sequence != 5 {
		t.Fatalf("%d of %d (%v): %+v", len(list), total, err, list)
	}
	if _, total, _ := DeadLetters(js.Context(), "another_one", 2); total != 0 {
		t.Fatalf("another consumer's total is %d", total)
	}
}

// An event the controller itself gave up on, delivered again by a person, is acted on as the event it
// was: it arrives under the controller's again subject, which its consumer filters.
func TestTheControllerActsOnAnEventDeliveredAgain(t *testing.T) {
	js := aBus(t)
	told := &toldAbout{}
	s := &Server{inbound: Nats(js), bus: OverNATS{Conn: js.Conn(), JS: js.Context()}, log: quiet()}
	if err := s.Follows(told); err != nil {
		t.Fatal(err)
	}
	if err := s.Answers(replaysWith{}); err != nil {
		t.Fatal(err)
	}
	ctx, stop := context.WithCancel(context.Background())
	defer stop()
	go func() { _ = s.Serve(ctx) }()
	eventually(t, "the controller's event consumer being made", func() bool {
		_, err := js.Context().ConsumerInfo("EVENTS", broker.ControllerName)
		return err == nil
	})
	moved, _ := json.Marshal(Upgraded{Module: "gitea", Commit: "abcdef0123"})
	if _, err := js.Context().Publish(broker.AgainSubject(broker.ControllerName, broker.ControllerFollows[0]), moved); err != nil {
		t.Fatal(err)
	}
	eventually(t, "the upgrade delivered again reaching the controller", func() bool { return told.count() == 1 })
}

// The notices cannot be taken (their stream is gone): said as a condition, and the controller serves on.
func TestNoticesThatCannotBeTakenAreSaidAndServingGoesOn(t *testing.T) {
	js := aBus(t)
	if err := js.Context().DeleteStream(broker.DeadLetterNoticesStream); err != nil {
		t.Fatal(err)
	}
	stop := keepingGivenUp(context.Background(), js, quiet())
	defer stop()
	eventually(t, "the failure said", func() bool {
		for _, a := range Advisories.Since(time.Now().Add(-time.Minute)) {
			if a.Token == AdvisoryNotKept && a.Stream == broker.DeadLetterNoticesStream {
				return true
			}
		}
		return false
	})
	held := &counted{}
	_, stopServing := servingOn(t, js, held)
	defer stopServing()
	if _, err := js.Context().Publish("mesh.control.anchor.report", []byte(`{"node":"anchor"}`)); err != nil {
		t.Fatal(err)
	}
	eventually(t, "a report heard while the notices cannot be taken", func() bool { return held.count() == 1 })
}